CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application Serial No.

62/053,443, filed September 22, 2014, which is incorporated by reference herein. GOVERNMENT FUNDING

This invention was made with government support under AI083409 awarded by the National Institutes of Health. The government has certain rights in the invention.

SEQUENCE LISTING

This application contains a Sequence Listing electronically submitted to the United

States Patent and Trademark Office via EFS-Web as an ASCII text file entitled "2015-09-22- SequenceListing_ST25.txt" having a size of 45 KB and created on September 22, 2015. Due to the electronic filing of the Sequence Listing, the electronically submitted Sequence Listing serves as both the paper copy required by 37 CFR § 1.821(c) and the CRF required by

§ 1.821(e). The information contained in the Sequence Listing is incorporated by reference herein

BACKGROUND

Arenavirus family includes a group of bi-segmented enveloped RNA viruses with genomes encoding a total of four genes in opposite orientation (Buchmeier et al, 2007, p. 1791- 1827. In Knipe DM, Howley PM (ed.), Fields Virology, 5th ed. Lippincott Williams & Wilkins, Philadelphia, PA). The Z protein produced from the large (L) genomic segment is a small RING- domain containing matrix protein that mediates virus budding and also regulates viral RNA synthesis. The large L protein (-200 kDa) encoded also on the L segment is the RNA-dependent RNA polymerase (RdRp) protein that is required for viral RNA synthesis. The glycoprotein (GPC) encoded on the small (S) segment is post-translationally processed into a stable signal peptide (SSP), the receptor-binding Gl protein, and the transmembrane G2 protein. The nucleoprotein (NP) of the S segment encapsidates viral genomic RNAs, is required for viral R A synthesis, and also suppresses host innate immune responses.

Arenaviruses are zoonotic RNA viruses with rodents as their primary natural hosts (for a review, see McLay et al, 2014, J Gen Virol 95(Pt 1): 1-15). Humans can be infected with arenaviruses through direct contact of skin lesions with rodent excretions, eating foods contaminated with rodent excretions, or inhalation of tainted aerosols. Only a few arenaviruses can cause diseases in humans (for a review, see McLay et al, 2013, Antiviral Res 97:81-92). For example, lymphocytic choriomeningitis virus (LCMV) can cause central nerve system diseases, whereas Lassa virus (LASV) and several other arenaviruses can cause hemorrhagic fevers that can potentially result in terminal shock and death. Limited therapeutic options are available for treating these viral infections. The only available antiviral drug (ribavirin) shows some beneficial effects but it has many side effects and must be administered soon after the infection when the disease is often mis-diagnosed as the symptoms are only flu- like and insidious.

Due to the high containment requirement (BSL-4) to work with pathogenic arenaviruses and the cost associated with working with non-human primates, only limited vaccine studies have been done. There are currently no vaccines for these pathogenic arenaviruses, except for the Candid #1 that is not FDA-approved but is available only for off-labeled usage against Junin virus, which causes Argentine hemorrhagic fever. Several safe and convenient systems have been developed to study arenavirus replication and pathogenesis in the conventional BSL-2 laboratory, such as the Pichinde virus model system (Lan et al, 2009, J Virol 83:6357-6362, Liang et al, 2009, Ann N Y Acad Sci 1171 Suppl 1 :E65-74, Kumar et al, 2012, Virology 433:97-103, Wang et al, 2012, J Virol 86:9794-9801, McLay et al, 2013, J Virol 87:6635- 6643). Pichinde virus (PICV) was isolated from rice rats in Columbia. It does not cause disease in humans, but can cause hemorrhagic fever-like symptoms in guinea pigs and thus is an ideal surrogate model to study arenavirus-induced hemorrhagic fevers. Serological evidence suggests a very low seroprevalence in humans (2 out of 82 people living or working in close association with habitats of infected rodents and 6 out of 13 laboratory workers have shown anti-PICV serum positivity but no distinct illnesses (Trapido et al, 1971, Am J Trop Med Hyg 20:631-641, Buchmeier et al., 1974, Infect Immun 9:821-823). Therefore, there is little to no preexisting immunity against PICV in the general human population, in contrast to LCMV, a prototypic arenavirus, which shows 2-5% seroprevalence in humans.

SUMMARY OF THE APPLICATION

Provided herein is a genetically engineered Pichinde virus. In one embodiment, the virus includes three ambisense genomic segments. The first genomic segment includes a coding region encoding a Z protein and a coding region encoding a L RdRp protein. The second genomic segment includes a coding region encoding a nucleoprotein (NP) and a first restriction enzyme site. The third genomic segment includes a coding region encoding a glycoprotein and a second restriction enzyme site. In one embodiment, the NP protein includes an amino acid sequence having at least 80% identity to SEQ ID NO:3. In one embodiment, nucleoprotein includes at least one mutation that reduces the exoribonuclease activity of the nucleoprotein, wherein the mutation is selected from an aspartic acid at about amino acid 380, a glutamic acid at about amino acid 382, an aspartic acid at about amino acid 525, a histidine at about amino acid 520, and an aspartic acid at about amino acid 457, wherein the aspartic acid, the glutamic acid, or the histidine is substituted with any other amino acid. In one embodiment, the glycoprotein includes at least one mutation that alters the activity of the glycoprotein, wherein the mutation is selected from an asparagine at about amino acid 20 and an asparagine at about amino acid 404, and wherein the asparagine is substituted with any other amino acid.D, E, or H is substituted with any other amino acid.

In one embodiment, the second genomic segment includes a multiple cloning site, and the first restriction enzyme site is part of the multiple cloning site. The second genomic segment may further include a coding region encoding a first protein inserted at the first restriction site. In one embodiment, the third genomic segment includes a multiple cloning site, and the second restriction enzyme site is part of the multiple cloning site. In one embodiment, the third genomic segment may further include a coding region encoding a second protein inserted at the first restriction site. In one embodiment, the second genomic segment further includes a coding region encoding a first protein inserted at the first restriction site, and the third genomic segment further includes a coding region encoding a second protein inserted at the first restriction site. In one embodiment, the first protein and the second protein are selected from an antigen and a detectable marker. In one embodiment, the antigen is a protein expressed by a viral pathogen, a prokaryotic pathogen, or a eukaryotic pathogen. The first protein and the second protein may be the same or may be different.

Also provided herein is a collection of vectors. In one embodiment, the vectors are plasmids. In one embodiment, the collection includes a first vector encoding a first genomic segment including a coding region encoding a Z protein and a coding region encoding a L RdRp protein, wherein the first genomic segment is antigenomic, a second vector encoding a second genomic segment including a coding region encoding a nucleoprotein (NP) and a first restriction enzyme site, wherein the second genomic segment is antigenomic, and a third vector encoding a third genomic segment includes a coding region encoding a glycoprotein and a second restriction enzyme site, wherein the third genomic segment is antigenomic. In one embodiment, the NP protein includes an amino acid sequence having at least 80% identity to SEQ ID NO:3.

In one embodiment, the second genomic segment includes a multiple cloning site, and the first restriction enzyme site is part of the multiple cloning site. The second genomic segment may further include a coding region encoding a first protein inserted at the first restriction site. In one embodiment, the third genomic segment includes a multiple cloning site, and the second restriction enzyme site is part of the multiple cloning site. In one embodiment, the third genomic segment may further include a coding region encoding a second protein inserted at the first restriction site. In one embodiment, the second genomic segment further includes a coding region encoding a first protein inserted at the first restriction site, and the third genomic segment further includes a coding region encoding a second protein inserted at the first restriction site. In one embodiment, the first protein and the second protein are selected from an antigen and a detectable marker. In one embodiment, the antigen is a protein expressed by a viral pathogen, a prokaryotic pathogen, or a eukaryotic pathogen. The first protein and the second protein may be the same or may be different.

Further provided are methods. In one embodiment, a method includes making a genetically engineered Pichinde virus as described herein. The method includes introducing into a cell the collection of vectors described herein, and incubating the cells in a medium under conditions suitable for expression and packaging of the first, second, and third genomic segments into a virus particle. The method may also include isolating an infectious virus particle from the medium.

Also provided herein is a reverse genetics system for making a genetically engineered Pichinde virus, wherein the system includes three vectors. The first vector encodes a first genomic segment including a coding region encoding a Z protein and a coding region encoding a L RdRp protein, wherein the first genomic segment is antigenomic, the second vector encodes a second genomic segment including a coding region encoding a nucleoprotein (NP) and a first restriction enzyme site, wherein the second genomic segment is antigenomic, and the third vector encodes a third genomic segment includes a coding region encoding a glycoprotein and a second restriction enzyme site, wherein the third genomic segment is antigenomic. In one embodiment, the NP protein includes an amino acid sequence having at least 80% identity to SEQ ID NO:3.

In one embodiment, a method includes using a reverse genetics system, including introducing into a cell three vectors of genomic segments described herein, incubating the cell under conditions suitable for the transcription of the three genomic segments and expression of the coding regions of each genomic segment. In one embodiment, the method also includes isolating infectious virus particles produced by the cell, wherein each infectious virus particle includes the three genomic segments. In one embodiment, the introducing includes transfecting a cell with the three genomic segments. In one embodiment, the introducing includes contacting the cell with an infectious virus particle including the three genomic segments. In one embodiment, the cell is ex vivo, such as a vertebrate cell. In one embodiment, the vertebrate cell may be a mammalian cell, such as a human cell, or the vertebrate cell may be an avian cell, such as a chicken embryonic fibroblast.

In one embodiment, a method includes producing an immune response in a subject. The method includes administering to a subject an infectious virus particle described herein, wherein the second genomic segment includes a coding region encoding a first antigen, and the third genomic segment further includes a coding region encoding a second antigen. In one

embodiment, the cell is ex vivo, such as a vertebrate cell. In one embodiment, the vertebrate cell may be a mammalian cell, such as a human cell, or the vertebrate cell may be an avian cell. The immune response may include a humoral immune response, a cell-mediated immune response, or a combination thereof. In one embodiment, the antigen is a protein expressed by a viral pathogen, a prokaryotic pathogen, or a eukaryotic pathogen, or a fragment thereof. The subject may have been exposed to, or is at risk of exposure to the viral pathogen, the prokaryotic pathogen, or the eukaryotic pathogen. In one embodiment, the administering includes administering at least two populations of infectious virus particles, wherein each population of infectious virus particle encodes a different antigen.

Also provided herein is an infectious virus particle as described herein, and a composition that includes an infectious virus particle described herein.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1. Diagram of the 2-plasmid PICV reverse genetics system (Lan et al., 2009, J Virol 83:6357-6362).

Figure 2. The 3-plasmid system to generate infectious tri-segmented PICV - rP18tri-

GFP.

Figure 3. Characterization of rP18tri-GFP virus. A549 or BHK-21 cells were infected with rP18tri-GFP virus for 24 hours, and GFP expression was detected in the infected cells. Virus supematants were harvested and used to infect a fresh culture of the BHK-21 cells, in which GFP expression was also detected.

Figure 4. Virus growth comparison of rP2, rP18, tri-segmented viruses rP18tri-GFP and rP18tri-RLuc in BHK-21 cell at high (moi=0.5) and low (moi=0.01) moi.

Figure 5. Generation of tri-segmented PICV carrying influenza HA or NP antigen.

Figure 6. Detection of expression of the GFP reporter gene product and the influenza HA or NP proteins that were expressed from the rP18tri-based vaccine vectors.

Figure 7. The rP18tri-based influenza vaccines confer protective immunity in mice. Ie5, lxlO ⁵ ; 2e4, 2xl0 ⁴ ; IP, intraperitoneal.

Figure 8. HAI titers induced by the rP18tri-based influenza vaccines.

Figure 9. HAI titers induced by the rPl 8tri-GFP/HA virus via different routes of vaccination. IN, intranasal; IM, intramuscular; IP, intraperitoneal.

Figure 10. Protection conferred by rP18tri-GFP/HA following different routes of vaccination.

Figure 11. Analysis of the NP-specific CTL responses by NP tetramer analysis.

Figure 12. Kinetics of CD8+ T cell responses elicited following different routes of vaccination. Figure 13. Vaccine conferred long lasting immunity and protection. C57BL6 mice were challenged with 10LD ₅₀ A/PR/8 after 1 or 2 months of boosting with the rP18tri-GFP/HA vaccine vector. A. HI titres at day 14 and day 30 post prime (dpp), day 30 and day 60 post boost (dpb). B. Viral titre in lungs at 6 dpi. C. Percent weight loss. D. H&E stained lung sections.

Figure 14. Protection conferred by priming with the rP18tri-GFP/HA vaccine vector. A.

Neutralizing antibody titres following different dosages of the rP18tri-GFP/HA vaccination. B. Percent weight loss. C. H&E stained lung sections.

Figure 15. Plaque size and expression of HA and NP from the rP18tri-HA/NP and the rP18tri-NP/HA

Figure 16. T cell and humoral responses induced by vector expressing dual antigens (HA and NP). A. Representative FACS plots for NP336 tetramer ⁺ CD44 ⁺ CD8 ⁺ T cells in mouse blood at day 7 post- vaccination. B. Frequencies of NP specific CD8 ⁺ T cells in the peripheral blood tested 7 days post priming and 7 days after boosting by tetramer staining. C. Viral neutralizing antibody titres were determined using HI assay of sera collected at different time points.

Figure 17. Protection conferred by the rP18tri-based vaccine expressing both influenza viral HA and NP. A. Stained lung sections from animals vaccinated with either a prime-boost of rP18tri-GFP/GFP, rP18tri-HA/NP or rP18tri-NP/HA. B. Virus titre in lungs. C. Percent weight loss after PR8 challenge.

Figure 18. Humoral response in C57BL6 mice and Balb/c mice induced by the rP18tri- based vector vaccine expressing HA proteins of both the H1N1 and H3N2 influenza virus subtypes. Mice were inoculated intramuscularly twice at an interval of 2 weeks between prime and boost, either with rP18tri-GFP/GFP or with 10 ⁴ pfu of rP18tri-GFP/HA, rP18tri-GFP/HA3 and rP18tri-HA/HA3. Two weeks after boosting, serum samples were collected and analysed for HI titres against the PR8 (H1N1) and X31 (H3N2) challenged viruses. Δ represents HI titre after 2 wks of priming and · represents HI titre after 2 wks of boosting. Left panel: HI titre in C57BL6 mice. Right panel: HI titre in Balb/c mice.

Figure 19. Protection against dual influenza virus challenge. Mice were vaccinated with 10 ⁴ pfu/ml rP18tri-HA/HA3. Five or six days after virus challenge, virus titres in the lungs were determined. A. Graph shows viral titres when challenged with either the PR8 or X31 influenza virus. B. Weight loss after challenge with 10LD ₅₀ A/PR/8 or 10 ⁵ pfu X31. C. H&E stained sections of lungs harvested 6 days after challenge with 10LD ₅₀ of A/PR/8 virus and 10 ⁵ pfu of X31.

Figure 20. rP18tri vector induces stronger CTL responses after boosting

Figure 21. Recombinant NP RNase mutant viruses induced type-I IFNs production in infected cells. (A) Alanine-substitution mutations at each of the 5 catalytic residues abolished the ability of PICV NP to suppress the Sendai virus-induced IFNP activation (Qi et al, 2010, Nature 468:779-783). 293T cells were transfected with an IFNP promoter directed-LUC plasmid and the β-gal plasmid, together with an empty vector or the respective NP plasmids, followed by Sendai virus infection. LUC activity was measured and normalized for transfection efficiency by β-gal activity. The results shown are the average of three independent experiments. Expression of the WT (rP2 and rP18) and mutant PICV NP proteins was detected by Western blotting using anti- myc antibody. (B) Recombinant PICV RNase mutant viruses produced high levels of type I IFNs upon viral infection. A549 cells were mock infected or infected with the respective recombinant PICV viruses at MOI of 1. Supematants were collected at 12 and 24 hpi, UV-treated to inactivate viral particles, and subjected to the rNDV-GFP-based biological assay to measure the level of IFNs. Representative GFP images (B) and the average GFP values with standard deviations from three independent experiments (C) are shown.

Figure 22. The NP RNase activity is required for PICV replication in the IFN-competent cells in vitro and PICV infection in vivo. (A) Viral growth kinetics in the IFN-defective Vero and IFN-competent A549 cells. Cells were infected with the respective viruses at MOI of 0.01. At different times post infection, virus titers in the supematants were quantified by plaque assay. The results shown are the average of three independent experiments. (B) Survival rate (left panel) and the normalized body weight (right panel) of guinea pigs (n=6) infected with the respective recombinant PICV viruses. Statistical analyses of the survival curves were performed using the Log-rank (Mantel-Cox) χ Test using GraphPad prism 5 software. p < 0.001. **, p < 0.01. Body weight of each animal was monitored daily and normalized to day 0. The results shown are the average of the normalized body weight for each group.

Figure 23. The PICV NP RNase mutants induced strong IFN responses to block the establishment of virus infection. Guinea pigs were infected i.p. with lxlO ⁴ pfu of the respective recombinant viruses (n=3 animals per vims group) for 1 and 3 days. (A) Viral titers in the livers and spleens at 1 and 3 dpi. (B) The levels of type I IFNs and selective interferon-stimulating genes (ISGs) in the peritoneal cavity cells at day 1 were measured by qRT-PCR. Primer sequences will be provided upon request. Each dot represents a single animal. Statistical analyses were conducted by the student's t test.

Figure 24. Generation of rP18tri expressing dual antigens flu HA and NP. (A) Schematic diagram of rP18tri vectors expressing dual antigens HA and NP of influenza A virus (IAV) A/PR8 on S I and S2 segments, rP18tri-P/H, and rP18tri-H/P. IGR, intergenic region. (B) The rP18tri dual antigen vectors express both HA and NP as shown by immunofluorescence assay (IF A). (C) Growth curve analysis of the recombinant viruses expressing the dual antigens in BHK-21 cells.

Figure 25. The HA/NP dual antigen expressing vaccine vectors can induce protective immunity in mice. A group of C57BL6 mice (n =3) were given two doses of respective rP18tri vectors at lxl 0 ⁴ pfu and challenged intranasally (IN) with lOxMLDso (median lethal dose) of the mouse-adapted influenza A/PR8 virus. Body weight (A) and viral lung titers at 3 and 6 dpi (B) are shown.

Figure 26. The H1/H3 dual antigen vector induces balanced HA neutralizing antibodies. (A)

Schematic diagram of rP18tri vectors expressing eGFP and HI HA (rP18tri-G/Hl), eGFP and H3 HA (rP18tri-G/H3), and HI and H3 (rP18tri-H3/Hl). (B) The rP18tri-H3/Hl induces balanced neutralizing antibodies against both HI and H3 HA subtypes. Groups of C57BL6 (top panels) and Balb/c mice (bottom panels) were immunized with the respective rP18tri vectors (n>=3) twice through the IM route. Blood collected at 14 days post prime and post boost were quantified for the levels of neutralizing antibodies against A/PR8 (H1N1) and A/x31 (H3N2) by HAI assay.

Figure 27. Induction of heterosubtypic neutralizing antibodies by a prime-and-boost strategy with different HA subtypes. (A) Schematic diagram of rP18tri vectors expressing A/PR8 NP together with either HI HA from A/PR8 (rP18tri-P/Hl) or H3 HA from A/x31 (rP18tri- P/H3). (B) NP-specific CTLs increased upon a booster dose. C57BL6 mice were primed with rP18tri-P/Hl , boosted with rP18tri-P/H3, and boosted again with rP18tri-P/Hl , at a 14-day interval. NP-specific effector T cells 7 days after prime (dpp), after the 1 ^st boost (dpb), and after the 2 ^nd boost (dpb2) were quantified by the established NP tetramer analysis. (C) Neutralizing antibodies against A/PR8 (HI), A/x31 (H3), and A/WSN (heterosubtypic HI) after prime and boosts were quantified by HAI assay.

Figure 28. The rP18tri vector can induce both humoral and T cell responses through oral route. Groups of BL6 mice were immunized twice with either rP18tri-G (n=3) vector or rP18tri- P/H (n=4) through oral gavage. NP-specific effector T cells (A) and HI -specific neutralizing antibodies (B) at different days after prime or boost are shown, dpp, days post-prime; dpb, days post-boost.

Figure 29. Inactivated rP18tri vector can induce both humoral and T cell responses. Groups of C57BL6 mice were immunized twice with rP18tri-G vector (n=3), hydrogen peroxide - inactivated rP18tri-P/H (n=3), and live rP18tri-P/H (n=l), respectively. NP-specific effector T cells (left panel) and neutralization antibodies (right) at different days after immunization are shown, dpp, days post-prime; dpb, days post-boost.

Figure 30. The rP18tri vector does not show virulence in guinea pigs and can protect the animals from a lethal challenge with the WT rP18 virus. (A) The rP18tri-G does not cause virulent infections in guinea pigs. Groups of Hartley guinea pigs (n=3) were mock infected (PBS) or infected with WT rP18 (lxlO ⁴ pfu) or rP18tri-G (lxl 0 ⁶ pfu) through the IP route. Body weight was monitored daily and normalized to day 0 (left panel). Rectal temperature is shown on the right. (B) The rP18tri-G-immunized guinea pigs were protected from lethal rP18 challenge. Groups of guinea pigs (n=3) were immunized with either PBS or rP18tri-G at lxl 0 ⁴ pfu through the IP route and, 14 days later, challenged with lxl 0 ⁴ pfu of WT rP18 virus. Normalized body weight (left panel) and rectal temperature (right panel) are shown. Temperature above 39.5 °C is considered to be feverish.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Provided herein is a reverse genetics system for producing genetically modified Pichinde virus. The genetically modified Pichinde virus-based reverse genetics system described herein has multiple advantages over other arenavirus systems. Pichinde virus is not known to cause disease in humans, and there is evidence that Pichinde virus can cause asymptomatic human infections in a laboratory setting. For instance, 46% of laboratory personnel working with the virus are serum positive but do not show a distinct illness (Buchmeier et al, 2007, Arenaviridae: the viruses and their replication. In: Knipe and Howley (eds), Fields Virology. 5th ed.

Philadelphia, PA: Lippincott Williams & Wilkins. pp. 1791-1827). The modified Pichinde virus described herein is further attenuated, compared to the parental virus used in the human-infection study reported by Buchmeier et al. The modified Pichinde virus is genetically stable through serial passages in cell cultures. General human populations are not known to have prior exposure to Pichinde virus, which makes it an ideal vector for vaccine development due to the lack of preexisting immunity against this Pichinde virus vector. As used herein, "genetically modified" and "genetically engineered" refers to a Pichinde virus which has been modified and is not found in any natural setting. For example, a genetically modified Pichinde virus is one into which has been introduced an exogenous polynucleotide, such as a restriction endonuclease site. Another example of a genetically modified Pichinde virus is one which has been modified to include three genomic segments.

The reverse genetics system for this modified Pichinde virus includes two to three genomic segments. The first genomic segment includes two coding regions, one that encodes a Z protein and a second that encodes a R A-dependent R A polymerase (L RdRp). The second genomic segment includes a coding region that encodes a nucleoprotein (NP), and may include at least one restriction enzyme site, such as a multiple cloning site. The third genomic segment includes a coding region that encodes a glycoprotein, and may include at least one restriction enzyme site, such as a multiple cloning site. A "coding region" is a nucleotide sequence that encodes a protein and, when placed under the control of appropriate regulatory sequences expresses the encoded protein. As used herein, the term "protein" refers broadly to a polymer of two or more amino acids joined together by peptide bonds. The term "protein" also includes molecules which contain more than one protein joined by disulfide bonds, ionic bonds, or hydrophobic interactions, or complexes of proteins that are joined together, covalently or noncovalently, as multimers (e.g., dimers, tetramers). Thus, the terms peptide, oligopeptide, and polypeptide are all included within the definition of protein and these terms are used

interchangeably. It should be understood that these terms do not connote a specific length of a polymer of amino acids, nor are they intended to imply or distinguish whether the protein is produced using recombinant techniques, chemical or enzymatic synthesis, or is naturally occurring.

The Z protein, L RdRp, NP protein, and glycoprotein are those encoded by a Pichinde virus. The Z protein is a small RING-domain containing matrix protein that mediates virus budding and also regulates viral RNA synthesis. One example of a Z protein from a Pichinde virus is the sequence available at Genbank accession number ABU39910.1 (SEQ ID NO: l). The L RdRp protein is a RNA-dependent RNA polymerase that is required for viral DNA synthesis. One example of a L RdRp protein from a Pichinde virus is the sequence available at Genbank accession number ABU39911.1 (SEQ ID NO:2). The NP protein encapsidates viral genomic RNAs, is required for viral RNA synthesis, and also suppresses host innate immune responses. One example of a NP protein from a Pichinde virus is the sequence available at Genbank accession number ABU39909.1 (SEQ ID NO:3). The glycoprotein is post-translationally processed into a stable signal peptide (SSP), the receptor-binding Gl protein, and the transmembrane G2 protein. One example of a glycoprotein from a Pichinde virus is the sequence available at Genbank accession number ABU39908.1 (SEQ ID NO:4).

Other examples of Z proteins, L RdRp proteins, NP proteins, and glycoprotein include proteins having structural similarity with a protein that is encoded by a Pichinde virus, for instance, SEQ ID NO: l, 2, 3, and/or 4. Structural similarity of two polypeptides can be determined by aligning the residues of the two polypeptides (for example, a candidate polypeptide and a reference polypeptide described herein) to optimize the number of identical amino acids along the lengths of their sequences; gaps in either or both sequences are permitted in making the alignment in order to optimize the number of identical amino acids, although the amino acids in each sequence must nonetheless remain in their proper order. A reference polypeptide may be a polypeptide described herein, such as SEQ ID NO:l, 2, 3, or 4. A candidate polypeptide is the polypeptide being compared to the reference polypeptide. A candidate polypeptide may be isolated, for example, from a cell of an animal, such as a mouse, or can be produced using recombinant techniques, or chemically or enzymatically synthesized. A candidate polypeptide may be inferred from a nucleotide sequence present in the genome of a Pichinde virus.

Unless modified as otherwise described herein, a pair- wise comparison analysis of amino acid sequences can be carried out using the Blastp program of the blastp suite-2sequences search algorithm, as described by Tatiana et al, (FEMS Microbiol Lett, 174, 247-250 (1999)), and available on the National Center for Biotechnology Information (NCBI) website. The default values for all blastp suite-2sequences search parameters may be used, including general parameters: expect threshold=10, word size=3, short queries=on; scoring parameters: matrix = BLOSUM62, gap costs=existence: l l extension: !, compositional adjustments=conditional compositional score matrix adjustment. Alternatively, polypeptides may be compared using the BESTFIT algorithm in the GCG package (version 10.2, Madison WI).

In the comparison of two amino acid sequences, structural similarity may be referred to by percent "identity" or may be referred to by percent "similarity." "Identity" refers to the presence of identical amino acids. "Similarity" refers to the presence of not only identical amino acids but also the presence of conservative substitutions. A conservative substitution for an amino acid in a polypeptide described herein may be selected from other members of the class to which the amino acid belongs. For example, it is known in the art of protein biochemistry that an amino acid belonging to a grouping of amino acids having a particular size or characteristic (such as charge, hydrophobicity and hydrophilicity) can be substituted for another amino acid without altering the activity of a protein, particularly in regions of the protein that are not directly associated with biological activity. For example, nonpolar (hydrophobic) amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan, and tyrosine. Polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids include arginine, lysine and histidine. The negatively charged (acidic) amino acids include aspartic acid and glutamic acid.

Conservative substitutions include, for example, Lys for Arg and vice versa to maintain a positive charge; Glu for Asp and vice versa to maintain a negative charge; Ser for Thr so that a free -OH is maintained; and Gin for Asn to maintain a free -NH2.

The skilled person will recognize that the Z protein depicted at SEQ ID NO: 1 can be compared to Z proteins from other arenaviruses, including Lassa virus (073557.4), LCMV Armstrong (AAX49343.1), and Junin virus (NP_899216.1) using readily available algorithms such as ClustalW to identify conserved regions of Z proteins. ClustalW is a multiple sequence alignment program for nucleic acids or proteins that produces biologically meaningful multiple sequence alignments of different sequences (Larkin et al, 2007, ClustalW and ClustalX version 2, Bioinformatics, 23(21):2947-2948). Using this information the skilled person will be able to readily predict with a reasonable expectation that certain conservative substitutions to an Z protein such as SEQ ID NO: l will not decrease activity of the polypeptide.

The skilled person will recognize that the L RdRp protein depicted at SEQ ID NO:2 can be compared to L RdRp proteins from other arenaviruses, including Lassa virus (AAT49002.1), LCMV Armstrong (AAX49344.1), and Junin virus (NP_899217.1) using readily available algorithms such as ClustalW to identify conserved regions of L RdRp proteins. Using this information the skilled person will be able to readily predict with a reasonable expectation that certain conservative substitutions to an L RdRp protein such as SEQ ID NO:2 will not decrease activity of the polypeptide.

The skilled person will recognize that the NP protein depicted at SEQ ID NO: 3 can be compared to NP proteins from other arenaviruses, including Lassa virus (P13699.1), LCMV Armstrong (AAX49342.1), and Junin virus (NP_899219.1) using readily available algorithms such as ClustalW to identify conserved regions of NP proteins. Using this information the skilled person will be able to readily predict with a reasonable expectation that certain conservative substitutions to a NP protein such as SEQ ID NO: 3 will not decrease activity of the polypeptide.

The skilled person will recognize that the glycoprotein depicted at SEQ ID NO:4 can be compared to glycoproteins from other arenaviruses, including Lassa virus (P08669), LCMV Armstrong (AAX49341.1), and Junin virus (NP_899218.1) using readily available algorithms such as ClustalW to identify conserved regions of glycoproteins. Using this information the skilled person will be able to readily predict with a reasonable expectation that certain conservative substitutions to a glycoprotein such as SEQ ID NO:4 will not decrease activity of the polypeptide.

Thus, as used herein, a Pichinde virus Z protein, L RdRp protein, an NP protein, or a glycoprotein includes those with at least 50%, at least 55%, at least 60%>, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%o, at least 97%, at least 98%>, or at least 99% amino acid sequence similarity to a reference amino acid sequence. Alternatively, as used herein, a Pichinde virus Z protein, L RdRp protein, an NP protein, or a glycoprotein includes those with at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%), at least 96%, at least 97%, at least 98%, or at least 99% amino acid sequence identity to a reference amino acid sequence. Unless noted otherwise, "Pichinde virus Z protein," "Pichinde virus L RdRp protein," "Pichinde virus NP protein," and "Pichinde virus glycoprotein" refer to a protein having at least 80% amino acid identity to SEQ ID NO: l, SEQ ID NO:2, SEQ ID NO:3, and SEQ ID NO:4, respectively.

A Pichinde virus Z protein, L RdRp protein, an NP protein, or a glycoprotein having structural similarity the amino acid sequence of SEQ ID NO: l, 2, 3, or 4, respectively, has biological activity. As used herein, "biological activity" refers to the activity of Z protein, L RdRp protein, an NP protein, or a glycoprotein in producing an infectious virus particle. The biological role each of these proteins play in the biogenesis of an infectious virus particle is knows, as are assays for measuring biological activity of each protein.

In one embodiment, the NP protein may include one or more mutations. A mutation in the NP protein may result in a NP protein that continues to function in the production of infectious viral particles, but has a decreased ability to suppress the production of certain cytokines by a cell infected with a Pichinde virus. A Pichinde virus that has decreased ability to suppress cytokine production is expected to be useful in enhancing an immunological response to an antigen encoded by the virus. Examples of mutations include the aspartic acid at residue 380, the glutamic acid at residue 382, the aspartic acid at residue 457, the aspartic acid at residue 525, and the histidine at residue 520. A person of ordinary skill in the art recognizes that the precise location of these mutations can vary between different NP proteins depending upon the presence of small insertions or deletions in the NP protein, thus the precise location of a mutation is approximate, and can vary by 1, 2, 3, 4, or 5 amino acids.

In one embodiment, the mutation in the NP protein may be the replacement of the aspartic acid, glutamic acid, or histidine at residues 380, 382, 457, 525, and/or 520 with any other amino acid. In one embodiment, the mutation may be the conservative substitution of the aspartic acid, glutamic acid, or histidine at residues 380, 382, 457, 525, and/or 520. In one embodiment, the mutation may be the replacement of the aspartic acid, glutamic acid, or histidine at residues 380, 382, 457, 525, and/or 520 with a glycine or an alanine. In one embodiment, the NP protein may include a mutation at one, two, three, or four of the residues 380, 382, 457, 525, or 520, and in one embodiment the NP protein may include a mutation at all five residues.

In one embodiment, the glycoprotein may include one or more mutations. A mutation in the glycoprotein may result in a glycoprotein that impairs virus spreading in vivo. Examples of mutations include the asparagine at residue 20, and/or the asparagine at residue 404. A person of ordinary skill in the art recognizes that the precise location of these mutations can vary between different glycoproteins depending upon the presence of small insertions or deletions in the glycoprotein, thus the precise location of a mutation is approximate, and can vary by 1, 2, 3, 4, or 5 amino acids.

In one embodiment, the mutation in the glycoprotein may be the replacement of the asparagine residue 20 and/or 404 with any other amino acid. In one embodiment, the mutation may be the conservative substitution of the asparagine residue 20 and/or 404. In one

embodiment, the mutation may be the replacement of the asparagine residue 20 and/or 404 with a glycine or an alanine.

Proteins as described herein also may be identified in terms the polynucleotide that encodes the protein. Thus, this disclosure provides polynucleotides that encode a protein as described herein or hybridize, under standard hybridization conditions, to a polynucleotide that encodes a protein as described herein, and the complements of such polynucleotide sequences. As used herein, the term "polynucleotide" refers to a polymeric form of nucleotides of any length, either ribonucleotides or deoxynucleotides, and includes both double- and single- stranded DNA and R A. A polynucleotide may include nucleotide sequences having different functions, including for instance coding sequences, and non-coding sequences such as regulatory sequences. A polynucleotide can be obtained directly from a natural source, or can be prepared with the aid of recombinant, enzymatic, or chemical techniques. A polynucleotide can be linear or circular in topology. A polynucleotide can be, for example, a portion of a vector, such as an expression or cloning vector, or a fragment. An example of a polynucleotide is a genomic segment.

An example of a polynucleotide encoding a Z protein is the nucleotides 85-372 of the sequence available at Genbank accession number EF529747.1 (SEQ ID NO:5), an example of a polynucleotide encoding an L RdRp protein is the complement of nucleotides 443-7027 of the sequence available at Genbank accession number EF529747.1 (SEQ ID NO:5), an example of a polynucleotide encoding an NP protein is the complement of nucleotides 1653..3338 of the sequence available at Genbank accession number EF529746.1 (SEQ ID NO:6), and an example of a polynucleotide encoding a glycoprotein protein is the nucleotides 52-1578 of the sequence available at Genbank accession number EF529746.1 (SEQ ID NO:6). It should be understood that a polynucleotide encoding a Z protein, an L RdRp protein, an NP protein, or a glycoprotein represented by SEQ ID N0: 1, 2, 3, or 4, respectively, is not limited to the nucleotide sequence disclosed at SEQ ID NO:5 or 6, but also includes the class of polynucleotides encoding such proteins as a result of the degeneracy of the genetic code. For example, the naturally occurring nucleotide sequence SEQ ID NO: 5 is but one member of the class of nucleotide sequences encoding a protein having the amino acid sequence SEQ ID NO: 1 and a protein having the amino acid sequence SEQ ID NO:2. The class of nucleotide sequences encoding a selected protein sequence is large but finite, and the nucleotide sequence of each member of the class can be readily determined by one skilled in the art by reference to the standard genetic code, wherein different nucleotide triplets (codons) are known to encode the same amino acid.

As used herein, reference to a polynucleotide as described herein and/or reference to the nucleic acid sequence of one or more SEQ ID NOs can include polynucleotides having a sequence identity of at least 60%, at least 65%, at least 70%>, at least 75%, at least 80%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to an identified reference polynucleotide sequence.

In this context, "sequence identity" refers to the identity between two polynucleotide sequences. Sequence identity is generally determined by aligning the bases of the two polynucleotides (for example, aligning the nucleotide sequence of the candidate sequence and a nucleotide sequence that includes, for example, a nucleotide sequence that encodes a protein of SEQ ID NO:l, 2, 3, or 4) to optimize the number of identical nucleotides along the lengths of their sequences; gaps in either or both sequences are permitted in making the alignment in order to optimize the number of shared nucleotides, although the nucleotides in each sequence must nonetheless remain in their proper order. A candidate sequence is the sequence being compared to a known sequence— e.g., a nucleotide sequence that includes the appropriate nucleotide sequence selected from, for example, SEQ ID NO:5 or 6. For example, two polynucleotide sequences can be compared using the Blastn program of the BLAST 2 search algorithm, as described by Tatiana et al., FEMS Microbiol Lett., 1999;174: 247-250, and available on the world wide web at ncbi.nlm.nih.gov/BLAST/. The default values for all BLAST 2 search parameters may be used, including reward for match = 1, penalty for mismatch = -2, open gap penalty = 5, extension gap penalty = 2, gap x dropoff = 50, expect = 10, wordsize = 11, and filter on. In one embodiment, the second and/or third genomic segments may each independently include a "multiple cloning site" with one restriction site or more than one restriction site.

In one embodiment, the second and/or third genomic segments may each independently include an additional coding region that encodes a protein, such as an antigen. Thus, the second genomic segment includes the coding region encoding the nucleoprotein and may include a second coding region that encodes an antigen. Likewise, the third genomic segment includes the coding region encoding the glycoprotein and may include a second coding region that encodes an antigen. The second and third genomic segments may encode the same antigen or different antigens. In both the second genomic segment and the third genomic segment this second coding region may be inserted into a restriction site present, such as a restriction site present in a multiple cloning site. The second coding region that may be present on the second genomic segment and/or the third genomic segment is not intended to be limiting.

In one embodiment, the second coding region may encode a protein that is useful as an antigen that can elicit an immune response in a subject. Examples 1, 2, and 3 show the use of influenza nucleoproteins and influenza hemagglutinins as model antigens to demonstrate the effectiveness of the reverse genetics systems and viruses disclosed herein, and accordingly the identity of the antigen is not intended to be limiting. An example of an antigen is a full length protein encoded by a prokaryotic cell, a eukaryotic cell (including, for instance a fungus, yeast, or protozoan) or a virus, or a fragment thereof. In one embodiment, the protein may be one that is naturally expressed by a pathogen, such as a viral pathogen, a prokaryotic pathogen, or a eukaryotic pathogen. Antigenic proteins encoded by a prokaryotic cell, a eukaryotic cell, or a virus are known to the skilled person in the art. Another example of an antigen is a protein engineered to include one or more epitopes. In one embodiment, the protein may be one that is expressed by a tumor cell or is present in a tumor environment.

Examples of prokaryotic pathogens from which an antigen may be obtained include gram negative pathogens and gram positive pathogens. Examples of gram negative pathogens include enteropathogens, such as members of the family Enterobacteriaceae, including members of the family Enterobacteriaceae that are members of the tribe Escherichieae or Salmonelleae.

Examples of enteropathogens include members of the family Enterobacteriaceae, members of the family Vibrionaceae (including, for instance, Vibrio cholerae), and Campylobacter spp.

(including, for instance, C. jejuni). Examples of preferred members of the family Enterobacteriaceae include, for instance, E. coli, Shigella spp., Salmonella spp., Proteus spp., Klebsiella spp. (for instance, K. pneumoniae), Serratia spp., and Yersinia spp. Examples of strains of E. coli include, for example, E. coli serotypes Ola, 02a, 078, and 0157, different 0:H serotypes including 0104, 0111, 026, 0113, 091, hemolytic strains of enterotoxigenic E. coli such as K88+, F4+, F18ab+, and F18ac+, and non-hemolytic strains such as 987P, F41, and K99. As used herein, the term "strain" refers to members of a species of microbe where the members have different genotypes and/or phenotypes. Other examples of E. coli include five categories of diarrheagenic Escherichia coli that cause foodborne and waterborne diseases in humans: the enteropathogenic (EPEC), enterohemorrhagic (EHEC), enterotoxigenic (ETEC), enteroinvasive (EIEC) and enteroaggregative (EAEC) strains. Other gram negative microbes include members of the family Pasteurellaceae, preferably Pasturella spp., such as P. multocida, and Mannheimia haemolytica, and members of the family Pseudomonadaceae, such as Pseudomonas spp., including P. aeruginosa. Yet other gram negative microbes include Bordetella spp.,

Burkholderia spp., Chlamydia spp., Enterobacter spp., Helobacter spp., Histophilus spp., Moraxella spp., Legionella spp., Leptospiria spp., Rickettsia spp., Treponnema spp., Neisseria spp., Actinobacillus spp., Haemophilus spp., Myxcobacteria spp., Sporocytophaga spp.,

Chondrococcus spp., Cytophaga spp., Flexibacter spp., Flavobacterium spp., Aeromonas spp. Examples of Yersinia spp. include Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica.

Examples of Fusobacterium spp. belonging to the family Fusobacteriaceae include F.

necrophorum (including subspecies F. necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme), F. nucleatum, F. canifelinum, F. gonidiaformans, F. mortiferum, F.

naviforme, F. necrogenes, F. russii, F. ulcerans, and F. variu.

Examples of gram-positive pathogens include members of the family Micrococcaceae, including Staphylococcus spp., such as S. aureus. Other gram positive pathogens include members of the family Deinococcaceae, such as Streptococcus agalactiae, Streptococcus uberis, Streptococcus bovis, Streptococcus equi, Streptococcus zooepidemicus, and Streptococcus dysgalatiae. Other gram positive microbes from which an antigen may be obtained include Bacillus spp., Clostridium spp., Corynebacterium spp., Erysipelothrix spp., Listeria spp., Mycobacterium spp., Other gram positive pathogens include members of the

Corynebacteriaceae, Enterococcacae, Micrococcaceae, Mycobacteriaceae, Nocardiaceae, and Peptococcaceae, which include such bacterial species as Actinomyces spp., Bifidobacterium spp., Enterococcus spp., Eubacterium spp., Kytococcus spp., Lactobacillus spp., Micrococcus spp., Mobiluncus spp., Mycobacteria spp., Peptostreptococcus spp., and Propionibacterium spp., Gardnerella spp., Mycoplasma., Norcardia spp., Streptomyces spp., Borrelia spp., and Bacillus spp.

Examples of pathogenic protozoa include intestinal protozoa, urogenital protozoa,

Systemic protozoa, and extraintestinal protozoa. Specific examples include, but are not limited to, e.g. Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum, Cystoisospora belli, Cyclospora cayetanensis, members of the phylum Microsporidia, Trichomonas vaginalis, Plamodium falciparum, Toxoplasma gondii, members of the subclass Coccidiosis such as members of the genus Eimeria, including E. acervulina., E. necatrix and E. tenella, Nematodes, Trematodes, and Cestodes.

Examples of viral pathogens include, but are not limited to members of the family Rhabdoviridae (including Vesicular stomatitis virus VSV), members of the genus Aphthovirus (including Foot-and-mouth disease virus FMDV), members of the genus Pestivirus (including Bovine viral diarrhea virus), members of the family Arterivirus (including porcine reproductive and respiratory syndrome virus PRRSV), Coronaviruses (including Porcine Epidemic Diarrhea virus EPDV, SARS-CoV, MERS-CoV), members of the genus Torovirus (including Equine torovirus), members of the family Orthomyxoviridae (including influenza virus), members of the family Reoviridae (including rotavirus, Bluetongue disease virus, avian reoviruses), members of the family Circovirus, members of the family Herpesviridae, members of the family Retroviridae (including HIV, FIV, SIV, ALV, BLV, RSV), members of the Asfariridae family (including African swine fever virus), members of the genus Flavivirus (including Dengue virus, Yellow fever virus), members of the family Paramyxoviridae (including Newcastle disease virus and Respiratory syncytial virus RSV), as well as members of the genus arenavirus (including members of the LCMV-Lassa virus (Old World) complex and the Tacaribe virus (New World) complex). Specific non-limiting examples of members of the genus arenavirus include

Lymphocytic choriomeningitis virus, Pichinde virus, Lassa virus, Mopeia virus, Junin virus, Guanarito virus, Lujo virus , Machupo virus, Sabia virus, and Whitewater Arroyo virus.

In one embodiment, the protein encoded by the second coding region may be from an influenza virus, such as a nucleoprotein, a hemagglutinin, or a portion thereof. The

nucleoprotein may be of any subtype, including but not limited to, A/PR8 NP (e.g., Genbank accession number NP 040982.1 ). The hemagglutinin may be of any subtype, including but not limited to, HI and H3.

The protein encoded by the second coding region may be one that results in a humoral immune response, a cell-mediated immune response, or a combination thereof. In one embodiment, the protein encoded by the second coding region of the second and third genomic segments is at least 6 amino acids in length. The antigen may be heterologous to the cell in which the coding region is expressed. The nucleotide sequence of a second coding region present on a second and third genomic segment and encoding the antigen can be readily determined by one skilled in the art by reference to the standard genetic code. The nucleotide sequence of a second coding region present on a second and third genomic segment and encoding the antigen may be modified to reflect the codon usage bias of a cell in which the antigen will be expressed. The usage bias of nearly all cells in which a Pichinde virus would be expressed is known to the skilled person.

In one embodiment, the second coding region may encode a protein that is useful as a detectable marker, e.g., a molecule that is easily detected by various methods. Examples include fluorescent polypeptides (e.g., green, yellow, blue, or red fluorescent proteins), luciferase, chloramphenicol acetyl transferase, and other molecules (such as c-myc, flag, 6xhis, HisGln (HQ) metal-binding peptide, and V5 epitope) detectable by their fluorescence, enzymatic activity or immunological properties.

When the second and/or third genomic segments include a coding region that encodes an antigen, the maximum size in nucleotides of the coding region(s) is determined by considering the total size of the second genomic segment and the third genomic segment. The total size of the two genomic segments may be no greater than 3.4 kilobases (kb), no greater than 3.5 kb, no greater than 3.6 kb, no greater than 3.7 kb, no greater than 3.8 kb, no greater than 3.9 kb, no greater than 4.0 kb, no greater than 4.1 kb, no greater than 4.2 kb, no greater than 4.3 kb, no greater than 4.4 kb, or no greater than 4.5 kb.

Pichinde virus is an arenavirus, and one characteristic of an arenavirus is an ambisense genome. As used herein, "ambisense" refers to a genomic segment having both positive sense and negative sense portions. For example, the first genomic segment of a Pichinde virus described herein is ambisense, encoding a Z protein in the positive sense and encoding a L RdRp protein in the negative sense. Thus, one of the two coding regions of the first genomic segment is in a positive-sense orientation and the other is in a negative-sense orientation. When the second and/or the third genomic segment includes a second coding region encoding an antigen, the coding region encoding the antigen is in a negative-sense orientation compared to the NP protein of the second genomic segment and to the glycoprotein of the third genomic segment.

Each genomic segment also includes nucleotides encoding a 5 ' untranslated region

(UTR) and a 3 ' UTR. These UTRs are located at the ends of each genomic segment.

Nucleotides useful as 5 ' UTRs and 3 ' UTRs are those present in Pichinde virus and are readily available to the skilled person (see, for instance, Buchmeier et al., 2007, Arenaviridae: the viruses and their replication. In: Knipe and Howley (eds), Fields Virology. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins. pp. 1791-1827). In one embodiment, a genomic segment that encodes a Z protein and an L RdRp protein includes a 5 ' UTR sequence that is 5 '

CGCACCGGGGAUCCUAGGCAUCUUUGGGUCACGCUUCAAAUUUGUCCAAUUUGAA CCCAGCUCAAGUCCUGGUCAAAACUUGGG (SEQ ID NO:8) and a 3' UTR sequence that is CGCACCGAGGAUCCUAGGCAUUUCUUGAUC (SEQ ID NO:9). In one embodiment, a genomic segment that encodes a NP protein or a glycoprotein includes a 5' UTR sequence that is 5 ' CGCACCGGGGAUCCUAGGCAUACCUUGGACGCGCAUAUUACUUGAUCAAAG (SEQ ID NO: 10) and a 3' UTR sequence that is 5'

CGCACAGUGGAUCCUAGGCGAUUCUAGAUCACGCUGUACGUUCACUUCUUCACUG ACUCGGAGGAAGUGCAAACAACCCCAAA (SEQ ID NO: l 1). Alterations in these sequences are permitted, and the terminal 27-30 nucleotides are highly conserved between the genomic segments.

Each genomic segment also includes an intergenic region located between the coding region encoding a Z protein and the coding region encoding a L RdRp protein, between the coding region encoding a nucleoprotein and the at least one first restriction enzyme site, and between the coding region encoding a glycoprotein and at least one second restriction enzyme site. Nucleotides useful as an intergenic region are those present in Pichinde virus and are readily available to the skilled person. In one embodiment, an IGR sequence of a genomic segment that encodes a Z protein and an L RdRp protein includes 5 '

ACCAGGGCCCCUGGGCGCACCCCCCUCCGGGGGUGCGCCCGGGGGCCCCCGGCCCC AUGGGGCCGGUUGUU (SEQ ID NO: 12). In one embodiment, an IGR sequence of a genomic segment that encodes a NP protein or a glycoprotein includes 5 ' GCCCUAGCCUCGACAUGGGCCUCGACGUCACUCCCCAAUAGGGGAGUGACGUCGA GGCCUCUGAGGACUUGAGCU (SEQ ID NO:13).

In one embodiment, each genomic segment is present in a vector. In one embodiment, the sequence of a genomic segment in the vector is antigenomic, and in one embodiment the sequence of a genomic segment in the vector is genomic. As used herein, "anti-genomic" refers to a genomic segment that encodes a protein in the orientation opposite to the viral genome. For example, Pichinde virus is a negative-sense R A virus. However, each genomic segment is ambisense, encoding proteins in both the positive-sense and negative-sense orientations. "Antigenomic" refers to the positive-sense orientation, while "genomic" refers to the negative-sense orientation.

A vector is a replicating polynucleotide, such as a plasmid, phage, or cosmid, to which another polynucleotide may be attached so as to bring about the replication of the attached polynucleotide. Construction of vectors containing a genomic segment, and construction of genomic segments including insertion of a polynucleotide encoding an antigen, employs standard ligation techniques known in the art. See, e.g., Sambrook et al, Molecular Cloning: A

Laboratory Manual, Cold Spring Harbor Laboratory Press (1989) or Ausubel, R.M., ed. Current Protocols in Molecular Biology (1994). A vector can provide for further cloning (amplification of the polynucleotide), i.e., a cloning vector, or for expression of an RNA encoded by the genomic segment, i.e., an expression vector. The term vector includes, but is not limited to, plasmid vectors, viral vectors, cosmid vectors, or artificial chromosome vectors. Typically, a vector is capable of replication in a prokaryotic cell and/or a eukaryotic cell. In one

embodiment, the vector replicates in prokaryotic cells, and not in eukaryotic cells. In one embodiment, the vector is a plasmid.

Selection of a vector depends upon a variety of desired characteristics in the resulting construct, such as a selection marker, vector replication rate, and the like. Suitable host cells for cloning or expressing the vectors herein are prokaryote or eukaryotic cells.

An expression vector optionally includes regulatory sequences operably linked to the genomic segment. The term "operably linked" refers to a juxtaposition of components such that they are in a relationship permitting them to function in their intended manner. A regulatory sequence is "operably linked" to a genomic segment when it is joined in such a way that expression of the genomic segment is achieved under conditions compatible with the regulatory sequence. One regulatory sequence is a promoter, which acts as a regulatory signal that bind RNA polymerase to initiate transcription of the downstream (3' direction) genomic segment. The promoter used can be a constitutive or an inducible promoter. The invention is not limited by the use of any particular promoter, and a wide variety of promoters are known. In one embodiment, a T7 promoter is used. Another regulatory sequence is a transcription terminator located downstream of the genomic segment. Any transcription terminator that acts to stop transcription of the RNA polymerase that initiates transcription at the promoter may be used. In one embodiment, when the promoter is a T7 promoter, a T7 transcription terminator is also used. In one embodiment, a ribozyme is present to aid in processing an RNA molecule. A ribozyme may be present after the sequences encoding the genomic segment and before a transcription terminator. An example of a ribozyme is a hepatitis delta virus ribozyme. One example of a hepatitis delta virus ribozyme is 5 '

AGCTCTCCCTTAGCCATCCGAGTGGACGACGTCCTCCTTCGGATGCCCAGGTCGGAC CGCGAGGAGGTGGAGATGCCATGCCGACCC (SEQ ID NO: 14).

Transcription of a genomic segment present in a vector results in an RNA molecule.

When each of the three genomic segments is present in a cell the coding regions of the genomic segments are expressed and viral particles that contain one copy of each of the genomic segments are produced. The three genomic segments of the reverse genetics system described herein are based on Pichinde virus, an arenavirus with a segmented genome of two single- stranded ambisense RNAs. While the ability of the reverse genetics system to replicate and produce infectious virus typically requires the presence of the ambisense RNAs in a cell, the genomic segments described herein also include the complement thereof (i.e., complementary RNA), and the corresponding DNA sequences of the two RNA sequences.

The polynucleotide used to transform a host cell optionally includes one or more marker sequences, which typically encode a molecule that inactivates or otherwise detects or is detected by a compound in the growth medium. For example, the inclusion of a marker sequence can render the transformed cell resistant to an antibiotic, or it can confer compound-specific metabolism on the transformed cell. Examples of a marker sequence are sequences that confer resistance to kanamycin, ampicillin, chloramphenicol, tetracycline, and neomycin.

Also provided herein are compositions including a viral particle described herein, or the three genomic segments described herein. Such compositions typically include a pharmaceutically acceptable carrier. As used herein "pharmaceutically acceptable carrier" includes saline, solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Additional active compounds can also be incorporated into the compositions.

A composition described herein may be referred to as a vaccine. The term "vaccine" as used herein refers to a composition that, upon administration to an animal, will increase the likelihood the recipient mounts an immune response to an antigen encoded by one of the genomic segments described herein.

A composition may be prepared by methods well known in the art of pharmaceutics. In general, a composition can be formulated to be compatible with its intended route of

administration. Administration may be systemic or local. Examples of routes of administration include parenteral (e.g., intravenous, intradermal, subcutaneous, intraperitoneal, intramuscular), enteral (e.g., oral), and topical (e.g., epicutaneous, inhalational, transmucosal) administration. Appropriate dosage forms for enteral administration of the compound of the present invention may include tablets, capsules or liquids. Appropriate dosage forms for parenteral administration may include intravenous administration. Appropriate dosage forms for topical administration may include nasal sprays, metered dose inhalers, dry-powder inhalers or by nebulization.

Solutions or suspensions can include the following components: a sterile diluent such as water for administration, saline solution, fixed oils, polyethylene glycols, glycerin, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates; electrolytes, such as sodium ion, chloride ion, potassium ion, calcium ion, and magnesium ion, and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. A composition can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.

Compositions can include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile solutions or dispersions. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, phosphate buffered saline (PBS), and the like. A composition is typically sterile and, when suitable for injectable use, should be fluid to the extent that easy syringability exists. It should be stable under the conditions of manufacture and storage and preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyetheylene glycol, and the like), and suitable mixtures thereof. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, polyalcohols such as mannitol, sorbitol, sodium chloride in the composition. Prolonged absorption of the injectable compositions can be brought about by including in the composition an agent which delays absorption, for example, aluminum monostearate and gelatin.

Sterile solutions can be prepared by incorporating the active compound (e.g., a viral particle described herein) in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the active compound into a sterile vehicle, which contains a basic dispersion medium and any other appropriate ingredients. In the case of sterile powders for the preparation of sterile injectable solutions, preferred methods of preparation include vacuum drying and freeze-drying which yields a powder of the active ingredient plus any additional desired ingredient from a previously sterilized solution thereof.

Oral compositions generally include an inert diluent or an edible carrier. For the purpose of oral therapeutic administration, the active compound can be incorporated with excipients and used in the form of tablets, troches, or capsules, e.g., gelatin capsules. Oral compositions can also be prepared using a fluid carrier for use as a mouthwash. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition. The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as

peppermint, methyl salicylate, or orange flavoring. For administration by inhalation, the active compounds are delivered in the form of an aerosol spray from a pressured container or dispenser which contains a suitable propellant, e.g., a gas such as carbon dioxide, or a nebulizer.

Systemic administration can also be by transmucosal or transdermal means. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, for example, for transmucosal administration, detergents, bile salts, and fusidic acid derivatives. Transmucosal administration can be accomplished through the use of nasal sprays or

suppositories. For transdermal administration, the active compounds are formulated into ointments, salves, gels, or creams as generally known in the art.

The active compounds may be prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Such formulations can be prepared using standard techniques. Liposomal suspensions can also be used as pharmaceutically acceptable carriers. These can be prepared according to methods known to those skilled in the art.

The data obtained from cell culture assays and animal studies can be used in formulating a range of dosage for use in an animal. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED50 (the dose therapeutically effective in 50% of the population) with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized.

The compositions can be administered once to result in an immune response, or one or more additional times as a booster to potentiate the immune response and increase the likelihood immunity to the antigen is long-lasting. The skilled artisan will appreciate that certain factors may influence the dosage and timing required to effectively treat a subject, including but not limited to the severity of the disease or disorder, previous treatments, the general health and/or age of the subject, and other diseases present.

Also provided herein are methods for using the genomic segments. In one embodiment, a method includes making an infectious viral particle. Such a method includes, but is not limited to, providing a cell that includes each of the three genomic segments described herein (a first genomic segment, a second genomic segment, and a third genomic segment) and incubating the cell under conditions suitable for generating full-length genomic R A molecules of each genomic segment. The full-length genomic RNA of each genomic segment is antigenomic. Production of full-length genomic RNA molecules of each genomic segment results in transcription and translation of each viral gene product and amplification of the viral genome to generate infectious progeny virus particles. As used herein, an "infectious virus particle" refers to a virus particle that can interact with a suitable eukaryotic cell, such as a mammalian cell (e.g., a murine cell or a human cell) or an avian cell, to result in the introduction of the three genomic segments into the cell, and the transcription of the three genomic segments in the cell. The method may also include introducing into the cell vectors that encode the three genomic segments. Infectious virus particles are released into supernatants and may be isolated and amplified further by culturing on cells. The method may include isolating a viral particle from a cell or a mixture of cells and cellular debris. The method may include inactivating virus particles using standard methods, such a hydrogen peroxide treatment. Also provided is a viral particle, infectious or inactivated, that contains three genomic segments described herein.

In one embodiment, a method includes expression of an antigen in a cell. Such a method includes, but is not limited to, introducing into a cell the three genomic segments described herein. In one embodiment, the introducing is by introduction of a virus particle that is infectious or inactivated. The second and/or the third genomic segment may include a second coding region that encodes an antigen. The second and third genomic segments may encode the same antigen or they may encode different antigens. More than one type of virus particle may be administered. For instance, two populations of virus particles may be administered where each population encodes different antigens. In this embodiment, a single administration can result in expressing multiple antigens in a cell. The cell is a suitable eukaryotic cell, such as a

mammalian cell (e.g., a murine cell or a human cell) or an avian cell. In one embodiment, the avian cell is a chicken embryonic fibroblast. The cell may be ex vivo or in vivo. The three genomic segments may be introduced by contacting a cell with an infectious virus particle that contains the three genomic segments, or by introducing into the cell vectors that include the genomic segments. The method further includes incubating the cell under conditions suitable for expression of the coding regions present on the three genomic segments, including the one or two second coding regions present on the second and/or third genomic segments. As used herein, "ex vivo" refers to a cell that has been removed from the body of an animal. Ex vivo cells include, for instance, primary cells (e.g., cells that have recently been removed from a subject and are capable of limited growth in tissue culture medium), and cultured cells (e.g., cells that are capable of long term culture in tissue culture medium). "In vivo" refers to cells that are within the body of a subject.

In one embodiment, a method includes immunizing an animal. Such a method includes, but is not limited to, administering to an animal a viral particle that is infectious or inactivated, that contains the three genomic segments described herein. The second and/or the third genomic segment may include a second coding region that encodes an antigen. The second and third genomic segments may encode the same antigen or they may encode different antigens. More than one type of virus particle may be administered. For instance, two populations of virus particles may be administered where each population encodes different antigens. In this embodiment, a single administration can result in vaccinating an animal against multiple pathogens. The animal may be any animal in need of immunization, including a vertebrate, such as a mammal or an avian. The animal can be, for instance, avian (including, for instance, chicken or turkey), bovine (including, for instance, a member of the species Bos taurus), caprine (including, for instance, goat), ovine (including, for instance, sheep), porcine (including, for instance, swine), bison (including, for instance, buffalo), a companion animal (including, for instance, cat, dog, and horse), members of the family Muridae (including, for instance, rat or mouse), Guinea pig, or human. In one embodiment, the animal may be an animal at risk of exposure to an infectious disease, such as a disease caused by or associated with a viral, prokaryotic, or eukaryotic pathogen. In one embodiment, the animal may be an animal in need of immunization against an antigen that is associated with non-infectious disease, such as cancer. For instance, the antigen may be one that helps an animal mount an immune response that targets and eliminates cancer cells. The immune response may be a humoral response (e.g., the immune response includes production of antibody in response to an antigen), a cellular response (e.g. the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of cytokines in response to an antigen), or a combination thereof.

In another embodiment, a method includes treating one or more symptoms of certain conditions in an animal. In one embodiment, a condition is caused by infection by a virus or a microbe. As used herein, the term "infection" refers to the presence of and multiplication of a virus or microbe in the body of a subject. The infection can be clinically inapparent, or result in symptoms associated with disease caused by the virus or microbe. The infection can be at an early stage, or at a late stage. In another embodiment, a condition is caused by a disease, such as cancer. As used herein, the term "disease" refers to any deviation from or interruption of the normal structure or function of a part, organ, or system, or combination thereof, of a subject that is manifested by a characteristic symptom or set of symptoms. The method includes

administering an effective amount of a composition described herein to an animal having or at risk of having a condition, or symptoms of a condition, and determining whether at least one symptom of the condition is changed, preferably, reduced.

Treatment of symptoms associated with a condition can be prophylactic or, alternatively, can be initiated after the development of a condition. As used herein, the term "symptom" refers to objective evidence in a subject of a condition caused by infection by disease. Symptoms associated with conditions referred to herein and the evaluations of such symptoms are routine and known in the art. Treatment that is prophylactic, for instance, initiated before a subject manifests symptoms of a condition, is referred to herein as treatment of a subject that is "at risk" of developing the condition. Accordingly, administration of a composition can be performed before, during, or after the occurrence of the conditions described herein. Treatment initiated after the development of a condition may result in decreasing the severity of the symptoms of one of the conditions, or completely removing the symptoms. In this aspect of the invention, an "effective amount" is an amount effective to prevent the manifestation of symptoms of a condition, decrease the severity of the symptoms of a condition, and/or completely remove the symptoms.

Also provided herein is a kit for immunizing an animal. The kit includes viral particles as described herein, where the second and/or third genomic segments each independently include a coding region that encodes an antigen, in a suitable packaging material in an amount sufficient for at least one immunization. In one embodiment, the kit may include more than one type of viral particle, e.g., the kit may include one viral particle that encodes one or two antigens and a second viral particle that encodes one or two other antigens. Optionally, other reagents such as buffers and solutions needed to practice the invention are also included. Instructions for use of the packaged viral particles are also typically included. As used herein, the phrase "packaging material" refers to one or more physical structures used to house the contents of the kit. The packaging material is constructed by known methods, preferably to provide a sterile, contaminant-free environment. The packaging material has a label which indicates that the viral particles can be used for immunizing an animal. In addition, the packaging material contains instructions indicating how the materials within the kit are employed to immunize an animal. As used herein, the term "package" refers to a solid matrix or material such as glass, plastic, paper, foil, and the like, capable of holding within fixed limits viral particles. Thus, for example, a package can be a glass vial used to contain an appropriate amount of viral particles. "Instructions for use" typically include a tangible expression describing the amount of viral particles, route of administration, and the like.

The term "and/or" means one or all of the listed elements or a combination of any two or more of the listed elements.

The words "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

The terms "comprises" and variations thereof do not have a limiting meaning where these terms appear in the description and claims.

Unless otherwise specified, "a," "an," "the," and "at least one" are used interchangeably and mean one or more than one.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

For any method disclosed herein that includes discrete steps, the steps may be conducted in any feasible order. And, as appropriate, any combination of two or more steps may be conducted simultaneously.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

The present invention is illustrated by the following examples. It is to be understood that the particular examples, materials, amounts, and procedures are to be interpreted broadly in accordance with the scope and spirit of the invention as set forth herein.

Example 1

An arenavirus-based vaccine vector carrying influenza virus antigens confers long-term protection of mice against lethal influenza virus challenge

Pichinde virus (PICV) is a non-pathogenic arenavirus that has been used as a model virus to study viral hemorrhagic fever infection. A reverse genetics system was previously developed to generate infectious PICV viruses from two plasmids that encode the viral large (L) and small (S) R A segments (Lan et al, 2009, J Virol 83:6357-6362). In the current study, a second- generation reverse genetics system was created to produce recombinant infectious PICV viruses from 3 separate plasmids that are referred to as the tri-segmented PICV system. These recombinant viruses carry 3 viral genomic RNA segments that encode for all of the viral gene products as well as two foreign genes. This tri-segmented PICV system can be used as a novel vaccine vector to deliver the hemagglutination (HA) and the nucleoprotein (NP) of the influenza virus A/PR8 strain. Mice immunized with these recombinant viruses are protected against lethal influenza virus challenge as evidenced by the survival of the animals afforded by the high levels of HA neutralizing antibodies and NP-specific cytotoxic T lymphocyte (CTL) responses to viral infection. These tri-segmented recombinant PICV viruses do not induce strong anti-PICV vector immunity, thus making them ideal candidates in a prime-boost vaccination strategy in order to induce cross-reactive immunity. In summary, a novel live vaccine vector has been developed that can express multiple foreign antigens to induce strong humoral and cell-mediated immunity and little anti- vector immunity in vivo. Introduction

We have developed the only available reverse-genetics system to generate infectious PICV viruses from plasmid transfection into appropriate mammalian cells (Lan et al., 2009, J Virol 83:6357-6362). This system consists of 2 plasmids to generate full-length genomic L and S RNAs from an engineered bacteriophage T7 regulatory (promoter/terminator) signals and the hepatitis delta ribozyme sequence located upstream and downstream of the PICV genomic sequences, respectively. When transfected into baby hamster's kidney epithelial cells that constitutively express the bacteriophage T7 RNA polymerase (BSRT7-5, a.k.a. BHK-T7), the L and S RNA segments of PICV are generated, from which all PICV viral gene products, including the L polymerase and NP nucleoprotein are transcribed and translated in order to amplify the viral genome and generate infectious progeny virus particles. Infectious PICV viruses are released into supernatants and are isolated and amplified further by culturing on African green- monkey epithelial (Vera) cells.

As described herein a second-generation reverse genetics system has been developed to produce recombinant infectious PICV viruses from 3 separate plasmids that are referred to as the tri-segmented PICV system. These recombinant viruses carry 3 viral genomic RNA segments that encode for all of the viral gene products as well as two foreign genes. This tri-segmented PICV system can be used as a novel vaccine vector to deliver other viral antigens, such as those of the influenza virus. Briefly summarized, tri-segmented PICV viruses expressing the hemagglutination (HA) or the nucleoprotein (NP) of the influenza virus A/PR8 strain have been produced, and these tri-segmented PICV vaccine vectors can induce strong humoral and cell- mediated immunity, such as a robust production of influenza-specific neutralizing antibodies and a strong influenza-specific cytotoxic T lymphocyte (CTL) response in vaccinated mice with little anti-PICV vector immunity, which makes them ideal candidates for the prime-boost vaccination strategy in order to induce long-lasting and cross-reactive immunity. Therefore, this novel PICV- based vaccine vector system described herein we have developed satisfies all required criteria of an ideal viral vector, such as safety, induction of strong and durable cellular and humoral immune responses, no pre-existing immunity and lack of anti-vector immunity.

Materials and Methods

Construction of plasmids encoding the engineered Pichinde virus PI 8 S RNA segments with multiple-cloning-sites (MCS) replacing either GPC or NP gene.

A reverse genetics system for PICV was previously developed by transfection of 2 plasmids, encoding the L and S RNA segments in anti-genomic (ag) sense, into BHK-T7 cells (Fig. 1) (Lan et al., 2009, J Virol 83:6357-6362). The overlaping polymerase chain reaction (PCR) method was used to replace the open-reading-frame (ORF) of either the viral glycoprotein (GPC) or nucleoprotein (NP) gene with multiple cloning sites (MCS) in the S agRNA encoding plasmid. The resulting plasmids (Fig. 2A), P18S-GPC/MCS and P18S-MCS/NP, contain MCS with the restriction enzyme sequences (Nhe I-Mfe I-Acc65I-Kpn I- EcoR V-Xho I-Sph I) that are introduced into these plasmids for the convenience of cloning foreign genes (e.g., reporter genes and/or viral antigens). Subcloning of GFP reporter gene, influenza HA or NP gene into PI 8S-GPC/MCS vector. PCR was used to subclone the green fluorescence protein (GFP) reporter gene and the influenza HA or NP gene from the A/PR8 (H1N1) strain into the vector P18S-GFP/MCS between Nhe I and Xho I sites, respectively. The amino acid sequence of the A/PR8 hemagglutinin can be found at Genbank Accession number NC 002017.1, and the amino acid sequence of the A/PR8 nucleoprotein can be found at Genbank Accession number NC 002019.1. The recombinant plasmid constructs were confirmed by DNA sequencing. The resulting plasmids (Fig. 5) are called P18S-GPC/GFP, P18S-GPC/H1, and P18S-GPC/NP, respectively.

Recovery of recombinant tri-segmented Pichinde viruses expressing GFP, influenza HA or NP.

Recombinant viruses were recovered from plasmids by transfecting BSRT7-5 (a.k.a.

BHK-T7) cells with 3 plasmids expressing the full-length PI 8 L agRNA segment, a P18S segment with MCS in place of GPC (P18S-MCS/NP), and a P18S segment with GFP, HA, or NP gene in place of NP (P18S-GPC/GFP, P18S-GPC/N1, or P18S-GPC/NP) (Fig. 2B and Fig. 5). The procedures to generate recombinant PICV are essentially the same as previously described (Fig. IB) (Lan et al, 2009, J Virol 83:6357-6362). Briefly, BHK-T7 cells were grown to 80% confluency and 4 hours before transfection the cells were washed and incubated with antibiotic- free media. For transfection, 2 ug of each plasmid was diluted in 250 ul of Opti-MEM and incubated at room temperature for 15 minutes. An equal volume of Opti-MEM with 10 ul of lipofectamine (Invitrogen, Life technologies) was added and the mixture was incubated for 20 mins at room temperature. Following incubation, the cells were transfected with the plasmids and media was again replaced after 4 hours to remove lipofectamine. After 48 hours of transfection, cell supernatants were collected for plaque assay. Virus grown from individual plaques was used to prepare stocks that were grown on BHK-21 cells and was stored at -80C. Detection of influenza antigen expression in cells infected with recombinant tri-segmented PICV vectors. BHK-21 cells grown on coverslips were infected with wild type Pichinde virus (PICV) or recombinant PICV viruses expressing either the influenza HA (rPICV-HA) or NP gene (rPICV- NP). After 24 hours of virus infection, cells were fixed with 4% paraformaldehyde for 15 mins at room temperature followed by 3 washes with phosphate buffer saline (PBS). Cells were then incubated in 0.1% Triton X-100 for 12 minutes followed by 1 hour incubation with primary antibody (mouse anti-NP influenza A). Cells were then washed and incubated with secondary antibody (anti mouse alexa flour-647) for 1 hour at room temperature.

Mouse immunization and challenge.

Six- to eight- week old female C57BL/6 mice were obtained from Charles River

Laboratories and housed for at least 1 week for acclimatization. Mice were housed in

microisolator cages in BSL-2 equipped animal facility. Mice were injected with 100,000 pfu of rPICV virus in 100 ul of total volume through intra-peritoneal route. After 14 days of last booster, mice were challenged intra-nasally with 10 LD ₅₀ (10,000 pfu) of the mouse-adapted influenza A/PR8 strain.

Analysis of virus specific CTL by tetramer staining.

Single-cell splenocytes were obtained and red blood cells (RBCs) were lysed using ACK lysis buffer. The splenocytes were then washed with FACS buffer (PBS+2% FBS) twice. Cells (lxlO ⁵ ) were stained with CD8-PerCP-Cy5.5, CD3-APC and H-2Db-PE tetramer with the NP ₃₆₆ - ₃₇ 4 epitope ASNENMETM (SEQ ID NO: 7) for 1 hr at room temperature. After incubation, cells were washed with FACS buffer three times and the labeled cells were analyzed by flow cytometry. The FACS data was analyzed using FloJo software. Hemagglutination inhibition assay.

Blood was collected after 14 days of each immunization and serum was harvested. Nonspecific inhibitors were removed from the serum by an overnight treatment with 5 volumes of receptor destroying enzyme (Sigma), followed by 45 min incubation at 56°C to inactivate the enzyme and serum. Each serum sample was then serially diluted in 25 ul of PBS and then mixed with an equal volume of PBS containing 4 HA units of A/PR8. After 15 min incubation at room temperature, 50 ul of 0.5% turkey RBC was added and the mixture was incubated for 1 hour at 4C before evaluation of agglutination. The titre was recorded as the inverse of the last dilution that inhibited agglutination.

Determination of virus titers in the lungs.

To evaluate the replication of influenza A/PR8 in mice, lungs were collected on day 6 of post challenge, weighed and homogenized in L15 media. Tissue homogenate was centrifuged at 10,000 rpm for 10 mins and virus was titrated in 12-well plate on monolayers of Madin-Darby canine kidney (MDCK) cells.

Results

1. Generation of recombinant tri-segmented Pichinde virus expressing the GFP reporter gene.

A tri-segmented arenavirus system was first reported for LCMV by de la Torre group (Emonet et al, 2009,Proc Natl Acad Sci U S A 106:3473-3478), which has generated infectious recombinant LCMV that packages 3 RNA segments, one full-length L segment, and two S segments with deletion in either GPC or NP. We have previously developed a reverse genetics system for the Pichinde virus (PICV) (Lan et al, 2009, J Virol 83:6357-6362), which is a prototypic arenavirus that is non-pathogenic in humans. This system consists of 2 plasmids expressing the L and S segments of PICV when they are transfected into the BSRT7-5 (a.k.a. BHKT7) cells (Fig. 1).

In the current study, a second-generation of the PICV reverse genetic system has been generated that consists of 3 plasmids that produce two distinct S RNA segments, one carrying a deletion in GPC and the other S segment contains a deletion of the NP gene (Fig. 2). In place of the deleted viral genes, we have inserted the multiple cloning sites (MCSs) (Fig. 2A). We then subcloned the GFP reporter gene into the PI 8 S2 segment at the deleted GPC position using Nhe I/Kpn I sites within MCS, and generated infectious viruses from the supernatants of BSRT7-5 cells transfected with three plasmids, one encoding the viral Z and L genes on the full-length PI 8 L segment, and the other two SI and S2 plasmids (i.e., PI 8 SI -MCS and PI 8 S2-GFP) expressing either the viral GPC gene alone or both NP and GFP reporter genes (Fig. 2B). Stock viruses were prepared from plaque-purified viruses. All plaques appeared green under fluorescence microscopy, demonstrating the successful recovery of the rP18tri-GFP virus. In addition to Vera cells (data not shown), rP18tri-GFP virus infection expressed GFP in other permissive cells such as BHK-21 and A549 (Fig. 3), and released more infectious progeny viruses that expressed GFP upon infection of a fresh culture of BHK-21 target cells (Fig. 3), demonstrating the stability and integrity of the rP18tri-GFP virus in cell cultures. Time course studies demonstrated that GFP was strongly expressed after 12 h post-infection and that the complete life cycle of rP18tri-GFP was about 16 h as the concentration of the rP18tri-GFP virus in the supernatants sharply increased at ~ 16 hpi (Fig. 4). In a preliminary experiment it was found that the PICV-tri-GFP virus vector can infect chicken embryonic fibroblasts (CEF cell line) in cell culture (data not shown).

Virus growths of the bi- and tri-segmented PICVs was compared by performing the growth curve analysis of the rP2, rP18, and rP18tri-GFP on BHK-21 cells at the multiplicity of infection (moi) of 0.01. As expected, the known virulent rP18 virus grew slightly faster and better than rP2 by ~ 0.5 log in virus titer. The tri-segmented rP18tri-GFP virus grew at a similar kinetic as the rP2 and rP18 viruses albeit at ~1 to 1.5 log lowered virus titers (Fig. 4). In summary, the tri-segmented PICV virus appears to be retarded in growth rate and titers as compared to the bi-segmented rP2 and rP18 PICV viruses.

In order to determine the stability of the rP18tri-GFP virus, that is to test whether in vitro culturing of the rP18tri-GFP virus will select for a bi-segmented wild-type virus revertant that have lost GFP gene due to genome recombination, the rP18tri-GFP was passaged in the BHK-21 cell cultures continuously, and conducted plaque assay at various passages to examine GFP expression in each of the plaques. At any tested passages (up to 23 passages), all plaques still expressed strong GFP reporter gene levels, suggesting that the GFP reporter gene could be stably maintained in the infectious viral particles even after extensive passages in cell culture.

2. Generation of recombinant tri-segmented Pichinde virus expressing influenza virus antigens.

HA and NP genes of the influenza virus A/PR8/H1N1 strain were molecularly cloned into the MSC of the P18 S2 plasmid, respectively (Fig. 5). The resulting P18 S2-HA and P18 S2- NP were separately transfected into BHK-T7 cells along with the full-length P18L and P18S1- GFP in order to generate the rP18tri-GFP/HA and rP18tri-GFP/NP viruses, respectively. All infected cells (i.e., plaques) were green under fluorescence microscopy as the recombinant viruses carried the GFP reporter gene on the P18S2-GFP segment (Fig. 6). In addition, HA and NP protein expressions were detected by immunofluorescence assay using specific anti-HA and anti-NP antibodies in Vera cells at 24 hr post infection (hpi) (Fig. 6). Taken together, we have shown that the tri-segmented viruses can be made to express different foreign genes, including the GFP reporter gene and two different influenza viral antigens (HA and NP) upon cellular infection.

3. The rP18tri-based influenza vaccines induce protective immunity in mice.

Previous work from our laboratory demonstrated that infection of mice with PICV even at high doses via different routes does not cause diseases as PICV is cleared by 4 days post infection (dpi) (data not shown). Here, we have examined whether rP18tri-based vaccine vectors can induce protective immunity in mice. C57BL6 mice were mock infected or infected intra- nasally (i.n.) with a low dose (50 pfu) of A/PR8 or via i.p. route with lxlO ⁵ pfu of rP18tri-GFP, rP18tri-GFP/HA, and rP18tri-GFP/NP viruses, respectively. Mice were boosted twice with the same virus at the same dosage at day 14 and 28. Blood samples were collected at different time points post priming and post boosting for neutralizing antibody titer determination. Mice were challenged at 14 d after the 2 ^nd boost with a known lethal dose of A/PR8 (10xMLD50) and monitored for body weight and disease symptoms for up to 21 days. All challenged animals that have previously received PBS or rP18tri-GFP vaccination reached terminal points by 7 dpi, whereas all mice vaccinated with rP 18tri-GFP/HA were completely protected from lethal influenza virus infection. Two out of three mice vaccinated with rP18tri-GFP/NP survived (Fig. 7). For rP18tri-GFP/HA vaccination, challenged mice maintained body weight, while the two survivors in the rP18tri-GFP/NP group showed a slight body weight loss at the early stage but quickly recovered (data now shown). Consistent with the mortality data, mice vaccinated with HA or NP had minimal pathological changes in the lungs at 3 dpi, compared to those with PBS or vector alone. Similarly, virus titers in the lungs at 3 dpi also correlated with protection. A/PR8 virus replicated to high levels in mouse lungs at 3 dpi when the animals were vaccinated with mock or the rP18tri-GFP vector alone. In contrast, virus titer was not detectable in the rP18tri- GFP/HA vaccination group and was significantly reduced in the rP18tri-GFP/NP group.

Taken together, these results suggest that the rP 18tri-based vaccine vector can induce protective immunity from lethal influenza virus infection in mice. Consistent with previous influenza vaccine studies, HA vaccination can induce a complete protection from influenza virus-induced disease while NP vaccination normally leads to partial protection by reducing disease severity and controlling virus replication in vivo. 4. The rP 18tri-GFP/HA vaccine induces high neutralizing antibody titers in mice.

The hemagglutination inhibition (HAI) titers was measured in peripheral blood collected from vaccinated mice at different time points: 14 d post-prime, 7 d and 14 d post- 1 ^st boost, and 14 d post-2 ^nd -boost (Fig. 8). As expected, HAI titers from the rP18tri-GFP and rP18tri-GFP/NP groups did not surpass the background level, because neither GFP nor NP is expected to induce HA-specific neutralizing antibodies. In contrast, HAI titers from the rP18tri-GFP/HA vaccination group reached the level of 40 at 14 d post-prime, and increased substantially after boosting (Fig. 8), suggesting that the rP18tri-GFP/HA vaccine can induce high levels of neutralizing antibody titers in vivo. As a threshold HAI titer of >=40 is generally used as a measure of success, i.e., in providing 50% reduction in the risk of influenza (seroprotective titer) (Reber et al., 2013, Expert Rev Vaccines 12:519-536), the HAI data suggests that a single dose of rP18tri-GFP/HA may be sufficient to confer protection.

HAI titers generated by different vaccination routes were compared (Fig. 9). Mice were vaccinated with rP18tri-GFP/HA by one prime and one boost via intraperitoneal (i.p.), intramuscular (i.m.), or intranasal (i.n.) route. All three routes of immunization elicited significant levels of humoral response as demonstrated by relatively high HAI titers overall. However, it appears that the HAI titres in sera of the i.m and i.p injected routes were relatively higher than those of the i.n. group. Regardless, these HAI titers were high enough to confer complete protection against a lethal challenge with the PR8 influenza virus. As shown in Fig. 10 there was no significant weight loss observed in the vaccinated animals.

5. The rP18tri-GFP/NP vaccine induces strong CTL responses in mice.

NP is an intracellular viral protein and is known to induce CD8+ T cell response against it. Whether the rP18tri-GFP/NP vaccine can induce CTL responses was examined by conducting NP-specific tetramer analysis of splenic cells and PBMCs at different time points after prime and boost with rP18tri-GFP/NP intraperitoneally. As shown in Fig. 11 (top), NP-specific CD8+ and CD44+ T cells were detected in the rP18tri-GFP/NP vaccinated group even at 7 d post-prime, at comparable (if not higher) level to a low dose of PR8 infection, which increased further at 7 d post-boost, and were still present at 14 d post-boost (Fig. 11 middle). We also explored the effect of different inoculation routes on CTL responses. As shown in Fig. 12 both i.m. and i.p.

inoculation routes induced stronger CTL responses than the i.n. route of infection. Collectively, our data demonstrate that rP18tri-based vector can induce strong CTL responses in vivo and that the intramuscular and intraperitoneal routes are better than intranasal route in inducing strong CTL responses. Since the i.m route elicited optimal humoral and T cell responses, subsequent experiments were conducted following the i.m route of immunization. 6. Can rP 18tri-based vaccine trigger long-lasting immunity?

The potential of the rP18tri-GFP/HA vaccine vector to induce long lasting immunity was evaluated. C57BL6 mice were immunized twice at an interval of 4 wks and were challenged either 4 or 8 wks after second immunization with a lethal dose of the A/PR/8 (H1N1) virus. Serum samples analysed for HAI titres at days 14 and 30 post prime and days 30 and 60 post boost demonstrated a strong neutralizing antibody titer (Fig. 13 A). The challenged virus A/PR/8 replicated well in the lungs of mock-vaccinated mice whereas there was no detectable virus titer in the lungs of vaccinated mice that were challenged after 4 wks of vaccination. However, there were significantly less viral titers in the lungs of immunized mice that were challenged after 8 wks of vaccination (Fig. 13B). As shown in Fig. 13C, complete protection was observed as there was no significant weight loss in the rP18tri-GFP/HA immunized mice challenged after either 4 wks or 8 wks of vaccination. Consistently, there were no significant pathological changes in the lungs of immunized mice (Fig. 13D). Overall, the levels of immunity and protection were comparable with those seen at 2 wks after immunization. Single immunization with rP18tri-GFP/HA induced protection against lethal H1N1 challenge C57BL6 mice were immunized with rP18triGFP-HA through intramuscular route.

Remarkably, a single dose of rP18tri-GFP/HA induced complete protection against lethal infection with the mouse-adapted A/PR/8 (H1N1) virus. As shown in Fig.14B, rPl 8tri-GFP vaccinated control mice continued to lose weight after challenge until they required euthanasia. The results also demonstrated that a single immunization with a minimum dose of 10 ³ pfu of the rP18tri-GFP/HA vector elicited a robust hemagglutination inhibiting (HI) Ab response and was sufficient to confer protection (Fig. 14A). Histological analyses of the lung section conducted 5- 6 days after challenge revealed a significant reduction in inflammation in mice vaccinated with rP18tri-GFP/HA whereas mice vaccinated with rP18tri-GFP showed massive infiltration of inflammatory cells into the lung, lung congestion and intra-alveolar edema (Fig.l4C).

Generation and characterization of rP18tri-based virus expressing dual influenza viral protein antigens

To obtain the rP18tri-based vector expressing influenza HA and NP or HAl and HA3, DNA encoding the respective influenza virus genes was inserted into plasmid vectors P18S- GPC/MCS and P 18S-MCS/NP accordingly. The RT-PCR amplified HAl , NP and HA3 were cloned and each clone was sequence verified. The resulting plasmids were designated as P18S- GPC/HA1, P18S-NP1/NP and P18S-HA3/NP. The recombinant virus expressing dual antigens (influenza HAl and NP1) was then rescued by co-transfecting 3 plasmids expressing the full- length P18 L agRNA segment, P18S-GPC/HA1 and P18S-NP1/NP. Simultaneously, a similar 3- segmented recombinant virus with swapped influenza genes was also generated by co- transfecting the full-length P18 L agRNA segment, P18S-GPC/NP1 and P18S-HA1/NP.

Similarly, recombinant virus expressing dual antigens (influenza HAl and HA3) was rescued by co-transfecting 3 plasmids expressing the full-length PI 8 L agRNA segment, P18S- GPC/HAland P18S-HA3/NP.

Interestingly, rP18tri-HA/NP had lower titres than rP18tri-NP/HA and formed smaller plaques in Vera cells (Fig. 15 A). However, the expression level of the influenza viral protein antigens was higher in the rP18tri-HA/NP as compared to the rP18tri-NP/HA (Fig.l5B). rPl 8tri-based vector encoding multiple influenza viral protein antigens (HA and NP) induced both humoral and T cell responses in immunized mice.

rP18tri-based vector encoding both influenza viral HA and NP successfully induced potent humoral and T cell responses in mice that were immunized with 10 ⁴ pfu/ml of either the rP18tri-HA/NP or rP18tri-NP/HA vector. Peripheral blood and spleen of mice were used to monitor the levels of T cell responses to immunodominant NP336 epitope using an MHC class I tetramer. Anti-NP-specific CD8+ T cells were detected in peripheral blood and splenocytes of immunized mice. On day 7 post-immunization, mice had a significantly greater percentage of NP-specific T cells (Fig. 16A). Tetramer positive CD8+ T cells peaked after 7 days of boost and were maintained at a resting level until 14 days post boost (Fig. l6B). Both of the vaccine candidates also elicited a strong humoral response that was assessed by hemagglutination inhibition titre in sera collected at 14 days post prime and 14 days post boost. The HI titres were increased post boost in mice immunized with rP 18tri-HA/NP whereas no such elevation was observed in mice immunized with the rP18tri-NP/HA (Fig.l6C).

Taken altogether, the rtriP18-HA/NP vaccine elicited a stronger immune response in comparison to the rP18tri-NP/HA vaccine. The better levels of immune response of the rP18tri- HA/NP could be attributed to a higher expression level of the influenza viral antigens (Fig. 15B). Nevertheless, both the vector vaccines rP 18tri-HA/NP and rP 18tri-NP/HA conferred complete protection against a lethal challenge of the A/PR/8 influenza virus. No disease symptoms were observed in the immunized mice. As shown in Fig. 17A, no significant histological changes could be detected in the lungs of mice immunized with either of the vaccine candidates. In contrast, infiltration of inflammatory cells was observed in lungs of mice vaccinated with the rPl 8tri-GFP. Viral titres in lungs were analyzed to determine the replication of the challenged virus at day 3 and 6 post infection. The mock- vaccinated mice showed high viral titres while mice vaccinated with the rP18tri-HA/NP and rP18tri-NP/HA showed no detectable titres at day 6 and one out of three mice in each group showed titres of 3xl0 ³ pfu/ml and 5xl0 ³ pfu/ml respectively at day 3 post infection (Fig. 17B). Mice vaccinated with either of the vaccine candidate showed no weight loss (Fig. 17C). rP18tri-based vector encoding multiple influenza antigens (HA1 and HA3) induced protection against dual challenges

Different groups of C57BL6 female mice were immunized with two dosages of either the rtriP18-based vector vaccine encoding only HA of the Hl-subtyped virus (rP18tri-HAl) or HA of the H3-subtyped (rP18tri-HA3) or both HA of the HI subtype and the H3 subtype (rP18tri- HA1/HA3). The results indicated that the first dose of the rtriP18-based vector encoding HA1 and HA3 induced antibody responses to both the encoded influenza viral antigens as revealed by robust HI titres for PR8 and X31. The second dose of the vaccine further boosted the antibody response. Interestingly, the HI titres induced for PR8 (HI) and X31 (H3) by rP18tri encoding both HA1 and HA3 were comparable to that induced by the rtriP18-based vector encoding only HAl or HA3 (Fig. 18A). Similar results were obtained in Balb/c mice (Fig.l8B). Upon challenge with a lethal dose of the PR8 (H1N1) or X31 (H3N2) virus, mice immunized with the rP18tri- based vector encoding both HAl and HA3 (rP18tri-HAl/HA3) were protected against both viral challenges. The protective efficacy of the rP18tri-HAl/HA3 in preventing the replication of the challenged viruses was evaluated on day 5 following virus challenge. The challenged viruses PR8 (H1N1) and X31 (H3N2) replicated well in the lungs of mock- vaccinated mice with a mean titres of 10 ⁵ and 10 ⁴ pfu/ml respectively. Immunization with the rP18tri-HAl/HA3 protected mice from both of the viral challenges as there was no loss of body weight and none of the immunized mice had any detectable viral titres in the lungs (Fig. 19A and B). rP18tri-based flu vaccines do not induce anti-vector immunity.

A perceived weakness of live viral vector is the anti-vector immunity, which impairs the immune responses induced by the same vector and excludes its usage in a prime-boost vaccination strategy. PICV has little to no pre-existing immunity in general population (Trapido et al., 1971, Am J Trap Med Hyg 20:631-641). We determined the effect of anti-vector immunity against PICV vector by measuring the levels of antibody and CTL responses by prime-boost with the same vector. Surprisingly, we found no evidence for anti-vector immunity against rPICVtri vector. Shown in Fig. 8, boosting with the same vector further substantially increased the HAl titers, suggesting that HA-specific humoral responses increased after the 2 ^nd and even 3 ^rd boosting. Similar finding was observed for the CTL responses. The NP-specific CD8 and CD44 T cells in both spleen and PBMCs increased after boosting (Fig. 20). Taken together, our data suggest that rPICV vector does not induce strong anti-vector immunity and thus can be repeatedly used in the prime-boost vaccine strategy. Summary

A novel PICV reverse genetic system has been developed to generate tri-segmented recombinant PICV viruses that can encode up to two foreign genes of interest. These rP18tri- based recombinant viruses can express the influenza HA and/or NP genes along with the GFP reporter gene in target cells. When tested in mice, the rP18tri-GFP/HA virus can induce high levels of HA-specific neutralizing antibodies, while the rP18tri-GFP/NP virus can induce strong NP-specific CTL responses. In addition, the rP18tri-based vector expressing dual influenza viral antigens HA and NP successfully induced both humoral and T cell responses that conferred complete protection in immunized mice against a lethal challenge with the A/PR8. More importantly, the triP18- based vector expressing HA of two different influenza virus subtypes i.e PR8 (H1N1) and X31 (H3N2) conferred protection against both of the viral challenges, demonstrating the prowess and versatility of these novel vaccine vectors against pathogenic influenza viruses. It is also important to note that there is no pre-existing immunity against PICV vector and that animals immunized with the tri-segmented PICV viruses generate little anti-PICV vector immunity, making this an ideal vector vaccine platform for inducing potent, long-lasting and cross-reactive immunity upon repeated vaccination in the event that a prime- boost vaccination strategy is needed.

Example 2 The biological role of NP exoribonuclease in arenavirus infection in vitro and in vivo

Arenavirus NP RNase activity is important for type I interferon (IFN) suppression but its biological role(s) have not been well characterized. Recombinant Pichinde viruses with RNase catalytic mutations induced high levels of IFNs and grew poorly in IFN-competent cells, and, when infecting guinea pigs, stimulated strong IFN responses, failed to replicate productively, and generated wild-type revertants. Thus, the NP RNase activity is essential for the IFN suppression and establishing productive replication early in arenavirus infection.

Arenaviruses include several hemorrhagic fever (HF)-causing agents (e.g., Lassa virus - LASV), with limited preventative or therapeutic measures (McLay et al., 2013, Antiviral Res 97:81-92, McLay et al, 2014, J Gen Virol 95: 1-15). Arenavirus pathogenesis is associated with high viremia and generalized immune suppression, the mechanism of which is poorly

understood. It has been shown that viral NP can effectively mediate Type-I IFN suppression via its exoribonuclease (RNase) function (Jiang et al, 2013, J Biol Chem 288:16949-16959, Martinez-Sobrido et al, 2007, J Virol 81 : 12696-12703, Martinez-Sobrido et al, 2006, J Virol 80:9192-9199, Qi et al, 2010, Nature 468:779-783, Hastie et al, 2011, Proc Natl Acad Sci U S A 108:2396-2401, Hastie et al, 2012, PLoS ONE 7:e44211). However, the role of the NP RNase activity in mediating host immune suppression in vivo has not been well characterized. In this study, Pichinde virus (PICV) infection of guinea pigs was used as a surrogate model of arenavirus hemorrhagic fevers (HFs) (Aronson et al., 1994, Am J Pathol 145:228-235, Lan et al., 2009, J Virol 83:6357-6362) to characterize the role of the NP RNase in viral infection and host IFN responses. Single alanine substitution at each of the RNase catalytic residues (D380A, E382A, D525A, H520A, and D457A) could abolish the NP ability to suppress Sendai virus- induced ΙΚΝβ activation by a luciferase (LUC) reporter assay (Fig. 21 A), corroborating our previous observations with LASV NP (Qi et al, 2010, Nature 468:779-783). Using our developed rP18 PICV reverse genetics system (Lan et al, 2009, J Virol 83:6357-6362), we successfully generated recombinant viruses carrying individual RNase mutations, which were confirmed by sequencing. The 5 RNase mutants, together with the WT rP18 that causes virulent infection in guinea pigs, and PICV rP2 that causes avirulent infection, were used to infect human airway epithelial A549 cells at MOI=l . Type-I IFN productions at 12 hpi and 24 hpi were quantified by the rNDV-GFP biological assay (Park et al, 2003, J Virol 77:1501-1511). Both rP2 and rP18 produced low levels of IFNs similar to mock infection, as demonstrated by the high levels of GFP expression (Fig. 2 IB). This is not surprising as NP proteins of both strains encode a functional RNase domain and do not seem to differ in their ability to suppress IFN production (Lan et al., 2008, Arch Virol 153: 1241-1250). In contrast, the RNase mutants produced significantly more IFNs, as shown by the greatly reduced GFP expression (Fig. 21B). Thus, the NP RNase activity is required for the efficient inhibition of type I IFNs in virus-infected cells.

Viral growth kinetics was determined in the IFN-deficient Vera cells and IFN-competent A549 cells at moi=0.01. All 5 mutants replicated well in Vera cells, reaching 10 ⁶ pfu/ml at 48 hpi, albeit at ~ 0.5-1 log lower than the WT rP18 (Fig. 22A, left). In sharp contrast, these RNase mutant viruses barely grew in A549 cells (Fig. 22A, right). Our results suggest that the NP

RNase activity is non-essential for the basic virus life cycle but is required for productive viral replication in the IFN-competent cells, consistent with the recently published data on the LASV double-mutant (D389A/G392A) (Carnec et al, 2011, J Virol 85: 12093-12097).

To compare viral virulence in vivo, we infected 6 Hartley outbred guinea pigs intraperitoneally with lxlO ⁴ pfu of each virus as previously described (Lan et al, 2009, J Virol 83:6357-6362, Kumar et al, 2012, Virology 433:97-103, McLay et al, 2013, J Virol 87:6635- 6643). All procedures were approved by the Institutional Animal Care and Use Committee (IACUC) at University of Minnesota. Animals were monitored daily for body weight and disease signs for up to 18 days, and were euthanized when they reached the predetermined terminal points (moribund), such as more than 30% weight loss compared to a nomogram or rectal temperature below 38°C in combination with continuing weight loss. As expected, all rP2- infected animals survived and cleared the virus, while rP18-infected animals developed early onset of fever, showed significantly decreased body weight starting at 7 dpi, and reached terminal points by 13 dpi (Fig. 22B). The R ase mutant viruses caused variable disease outcomes (Fig. 22B and Table 1). All E382A mutant virus-infected animals survived without any evidence of body weight loss, while animals infected with each of 3 other mutant viruses

(D525A, H520A, and D457A) showed various degrees of attenuation (Fig. 22B). Most D380A- infected animals, however, succumbed to the infection albeit at a later time point than the rP18. To determine whether WT revertants occurred, we measured the viremia levels at end point and sequenced the viruses (Table 1). As expected, moribund animals were associated with high viremia while all those who survived had very low to undetectable levels of virus infection.

Without exception, viruses isolated from mutants-infected animals had reverted back to the WT NP sequence (Table 1). This is highly unlikely due to PCR contamination or sequencing error as the viruses isolated from other mutant virus-infected animals conducted at the same time still contain the expected mutations (data not shown). We therefore believe that the disease phenotypes are caused by WT viruses, including the WT revertants, and that the disease severity is determined by how fast the reversion occurs in vivo (a few surviving animals were found to carry low levels of WT virus at day 18). Our results strongly suggest an essential role of the NP RNase activity in arenaviral infection in vivo.

reached terminal points or at day 18 post infection.

² , Sequences of viruses isolated from animals at the time of euthanization when animals reached terminal points or at day 18 post infection.

³ , All 6 animals in the rP2-infected group survived with no detectable viremia at day 18 post infection.

⁴ , ND, not detectable by plaque assay To examine the role(s) of R ase in early viral infection and host innate immune responses in infected animals, we monitored viral spread and quantified innate antiviral genes at 1 dpi and 3 dpi. At day 1, viruses were detected at low levels in the livers and spleens of rP18- infected animals and in the livers of some animals infected with rP2 and the RNase mutant viruses (Fig. 23 A). At day 3, both rP18 and rP2 replicated to relatively high levels in both livers and spleens. In contrast, RNase mutant viruses appeared to be cleared from the livers and only detected in a few spleens at very low levels (Fig. 23 A), Representative innate immune response genes, IFN-al, IFN-βΙ, ISG15, IRF7, RIG-I, and MDA5, in the peritoneal cavity cells at day 1 were quantified by qRT-PCR (Fig. 23B). These genes were highly activated by the RNase mutant viruses but not by the WT viruses (rP2 and rP18), demonstrating that NP RNase is required for arenavirus-induced innate immune suppression in vivo.

In summary, our study with recombinant PICV RNase mutants has not only confirmed the important role of NP RNase in type I IFNs suppression and viral replication in vitro, but also provided unequivocal evidence for its essential role in early innate immune suppression to allow establishment of a productive infection in vivo. Given that the NP RNase-dependent IFN suppression mechanism is conserved among arenaviruses (Jiang et al, 2013, J Biol Chem 288: 16949-16959), our results can be extrapolated to other arenaviral pathogens and implicate NP RNase as an ideal target for antivirals development.

Example 3

The arenavirus-based vaccine vector delivers two antigens and confers immunity to each of the antigens

1. Generation of rP18tri live vaccine vectors expressing dual influenza antigens HA and NP

Example 1 discloses a replication-competent tri-segmented rPICV system (rP18tri) and using this rP18tri vector to express either the influenza HA (abbreviated as H) or NP antigen (P), it was demonstrated that the vector can induce strong antibody and CTL responses in mice. To determine whether a single rP18tri virion particle can be used to deliver both HA and NP genes, S 1 and S2 viral genomic RNA segments were generated to encode the influenza HA and NP genes, respectively. By using different combinations of plasmids in the transfection reactions, we have successfully generated live vaccine vectors, rP18tri-P/H and rP18tri-H/P, which encode HA and NP genes on different S segments as illustrated in Fig. 24A. As a control vector, the rP18tri vector encoding the eGFP reporter gene on both the SI and S2 segments - rP18tri-G/G - was also generated. To examine the antigens expression, Vera cells were infected with rP18tri-G/G, rP18tri-P/H, and rP18tri-H/P respectively. At 24 hpi, cells were examined for the expression of HA and NP by IFA using the mouse anti-HA and anti-NP antibodies, respectively, followed by detection with a PE-conjugated anti-mouse antibody. Expression of both HA and NP proteins was detected in cells infected with rP18tri-P/H and rP18tri-H/P but not in those infected with the vector control rP18tri-G/G. The lower number of cells expressing HA and NP by the rP18tri-H/P infection than by the rP18tri-P/H is due to a lower viral titer used in the infection (Fig. 24B). Subsequent viral growth analysis in BHK-21 cells at moi of 0.01 suggests that rP18tri-P/H and rP18tri-H/P replicate at similar kinetics and are < 0.5 log lower than the vector control rP18tri- G/G (Fig. 24C).

2. The HA/NP dual antigen vaccine vectors can induce protective immunity in mice.

To test the protective immunity of rP18tri-P/H and rP18tri-H/P live vectors in vivo, we immunized a group of mice (n >= 3) with the rP18tri-G/G control vector, rP18tri-P/H, or rP18tri- H/P at lxl 0 ⁴ pfu through the IM route, boosted with the same vectors 14 days later, and challenged with a lethal dose of the mouse-adapted A/PR8 influenza virus (lOxMLDso) 14 days after vaccination. All the control vector-immunized mice succumbed to the infection by day 6, while all mice receiving rP18tri-P/H or rP18tri-H/P survived the challenge without any disease signs or body weight loss (Fig. 25 A). Compared to the control vector-immunized mice that had high viral titers (2-10 xlO ⁵ pfu/g) in the lungs at 3 and 6 dpi, the rP18tri-P/H or rP18tri-H/P- immunized mice (n=3 in each group) had no detectable viruses at 6 dpi and only one of three had a relatively low level of viruses (< 5xl0 ³ pfu/g) at 3 dpi (Fig. 25B). Our data suggest that the dual antigen expressing viral vectors can induce strong protective immunity against influenza virus, which is conferred by HA-specific neutralizing antibody. 3. The H1/H3 dual antigen vector induces balanced HA neutralizing antibodies. Whether two different HA subtypes can be used to induce neutralizing antibodies at equal efficiency was determined. Toward this end, we have cloned the H3 HA gene of the A/x31 (H3N2 subtype of the influenza virus) to the S2 segment and when transfected with the full- length L segment, and the SI segment encoding the HI HA of A/PR8, live rP18tri-H3/Hl vector can be generated (Fig. 26A). As controls, we have also generated the rP18tri vectors encoding eGFP on the S2 segment and either HI or H3 on the SI segment, respectively called rP18tri- G/Hl or rP18tri-G/H3 (Fig. 26A). To test their immunogenicity, groups of C57BL6 mice (n=3 per group) were primed and boosted with the three vectors respectively at a 14-day interval through the IM route. Blood collected 14 days after prime and boost were measured for the levels of neutralizing antibody against A/PR8/H1N1 and A/x31/H3N2 (Fig. 26B top panel). The rP18tri vectors encoding single HA subtypes, rP18tri-G/Hl and rP18tri-G/H3, each induced strong homosubtypic neutralizing antibodies that increase over a boost dose, but did not induce detectable levels of cross-reactive antibodies after prime or boost. The rP18tri-Hl/H3 dual antigen vector induced both HI and H3 neutralizing antibodies that increased upon a booster dose and that the level of each neutralizing antibody was comparable to that induced by the respective single antigen vectors (Fig. 26B top). Similar findings were obtained with Balb/c mice (Fig. 26B bottom). Taken together, our data strongly suggest that the H1/H3 dual antigen vector induces balanced neutralizing antibodies against both antigens in mice. In other words, there is no preference (skewing) of production of neutralizing antibodies against one or the other HA antigen.

4. Induction of heterosubtypic neutralizing antibodies by a prime-and-boost strategy with different HA subtypes

Recent studies have suggested that broadly neutralizing antibodies can be generated by prime-and-boost vaccinations or sequential infections (Wei et al, 2010, Science 329: 1060-1064, Wei et al, 2012, Sci Transl Med 4: 147ral l4, Miller et al, 2013, Sci Transl Med 5: 198ral07, Wrammert et al, 2011, J Exp Med 208: 181-193, Krammer et al, 2012, J Virol 86: 10302-10307, Miller et al, 2013, J Infect Dis 207:98-105, Margine et al, 2013, J Virol 87:4728-4737). As the rP18tri vector enhances immune responses upon a booster dose, whether it can induce cross- reactive immunity using a prime and boost strategy with different HA subtypes was tested.

Toward this end, live rP18tri-P/Hl and rP18tri-P/H3 vectors were generated, each encoding A/PR8 NP, a conserved viral protein (see GenBank Accession number NP 040982.1) that is known to elicit T cell responses, together with either HI (A/PR8) or H3 (x31) HA (Fig. 27A). Mice were primed with rP18tri-P/Hl, boosted with rP18tri-P/H3, and boosted again with rP18tri- P/Hl, each time at a 14-d interval. As expected, NP-specific CTLs were detected after prime (7 dpp), significantly increased upon a booster dose (7 dpb), and still remained at high levels (3- 5%) after a second booster dose (Fig. 27B). Blood were collected 14 days after each

administration and tested for the levels of neutralizing antibodies against A/PR8, A/x31, and A/WSN. Neutralizing antibodies specific to homologous viruses A/PR8 (HI) and A/31 (H3) were highly induced upon the exposure of the same HA antigens and were not generally enhanced by the heterologous HA boosting, whereas neutralizing antibodies against

heterosubtypic virus A/WSN (HI) were steadily increased upon the booster doses (Fig. 27C). These immunized mice showed a significantly improved survival after a lethal challenge with the heterosubtypic virus A/WSN (Fig. 27D). Taken together, our data suggest that prime-and-boost with heterologous HA subtypes using the rP18tri vector can elicit cross-reactive neutralizing antibodies and cause cross protection against heterosubtypic influenza virus challenge.

5. The rP18tri vector can induce both humoral and T cell responses through oral route.

To determine whether the rP18tri vector can be conveniently given through oral route, C57BL6 mice were immunized with lxlO ⁴ pfu of the rP18tri-G vector (n=3) or rP18tri-P/H (n=4) through oral gavage and boosted with the same vector 42 days later. The NP tetramer- positive effector T cells (CD8 ⁺ CD44 ^hlgh ) at 7 days post prime and post boost were measured by the established NP tetramer analysis. At 7 days post prime, two out of three tested mice from the rP18tri-P/H-immunized mice had NP ⁺ CD8 ⁺ CD44 ^high cells (1.24% and 0.55%) that were clearly higher than the background level seen in the vector-immunized mice (0.13% and 0.09%). The NP-specific effector cells increased significantly at 7 days post boost, ranging from 5.7 to 7.1% in all 4 immunized mice (Fig. 28A). Similar patterns were observed for the neutralizing antibodies. Two out of four immunized mice showed a positive HAI titer (HAI = 20) at 14 days post-prime. At 42 days post-prime, all 4 mice showed HAI titers in average of 40. After a boost dose, the HAI titer increased significantly for all 4 mice, ranging from 80 to 160 (Fig. 28B). Taken together, our data strongly suggest that the rP18tri vector can induce high levels of both humoral and T cell responses through oral route after a booster dose. 6. Inactivated rP18tri vector can induce both humoral and T cell responses.

Whether inactivated rP18tri vector can induce vaccine immunity was determined. Live or hydrogen peroxide-treated rP18tri-P/H vaccine vector (i.e., inactivated vaccine vector) was used to immunize mice in 2 doses at a 34-day interval. Neither neutralizing antibodies nor NP- specific T cells were detected immediately after prime (7 days post-prime, 7 dpp). However, high levels of NP-specific effector T cells were detected after a booster dose (7 days post-boost, 7 dpb) with the inactivated vaccine vector (Fig. 29, left). Neutralizing antibodies were detected at a low level (HAI=20) in all three mice 34 days after prime (34 dpp), and increased significantly after a booster dose (14 days post-boost, 14 dpb), ranging from 40 to 80 with the inactivated vaccine vector (Fig. 29, right). It is worth noting that the levels of both T cell and humoral responses induced by the chemically inactivated rP18tri-P/H vaccine vector are significantly lower than those induced by the live vaccine vector. Nevertheless, that the inactivated rP18tri- P/H can still induce both humoral and T cell responses after a booster dose suggests the versatility of this viral vector as a vaccine platform as both a live and inactivated vaccines.

7. The rP18tri vector induces protective immunity against virulent PI 8 virus in a guinea pig model.

WT PI 8 virus was obtained after serial passages of the Pichinde virus (PICV) in guinea pigs and causes a hemorrhagic fever-like disease in the animals, which has been used as a safe surrogate model for studying pathogenesis of Lassa fever virus infection in humans (Jahrling et al, 1981, Infect Immun 32:872-880, Aronson et al., 1994, Am J Pathol 145:228-235, Liang et al, 2009, Ann N Y Acad Sci 1171 Suppl 1 :E65-74). Compared to WT P18 virus, the tri- segmented rP18tri vectors grow at least 1 log lower in vitro. We also determined the virulence potential of the rP18tri-G vector in guinea pigs. Guinea pigs infected with lxl 0 ⁴ pfu of rP18 virus developed early onset fever, rapidly lost weight after 7 days post-infection, and reached terminal points by day 14 (Fig. 30A). In contrast, guinea pigs infected with lxlO ⁶ pfu of rP18tri- G (100-fold higher titer than rP18 control) showed a similar body weight growth as the mock- infected animals and did not experience fever of more than 1 day (Fig. 30A).

Whether this non-pathogenic rPl 8tri vectors could induce protective immunity against a lethal rP18 challenge in guinea pigs was determiend. Guinea pigs were injected with either phosphor buffer saline (PBS) to represent mock infection or with lxlO ⁴ pfu of rP18tri-G through IP route and, 14 days later, challenged with a lethal dose of rP18 virus. PBS-immunized guinea pigs (n=3) soon developed fevers and lost body weight significantly and all animals reached predetermined terminal points by day 11 (Fig. 30B). In contrast, rP18tri-G-immunized guinea pigs (n=3) were completely protected with no appreciable body weight loss (Fig. 30B). The protective immunity against PICV is likely mediated by T cell responses as neutralizing antibodies have yet to develop at the time of challenge. Previous studies have demonstrated the cross-protection among different arenaviruses, such as LCMV and PICV, Lassa and Mopeia virus, Junin and Tacaribe complex viruses, and that apathogenic arenaviruses have been explored as live vaccines (reviewed in Olschlager et al, 2013, PLoS Pathog 9:el003212). We propose that the rP18tri vector incorporating protective T cell epitopes into PICV proteins can induce cross- protective immunity against other arenavirus pathogens. With a capacity of encoding up to two additional antigens, the rP18tri vector can be developed as a dual (or triple) vaccine vector against both arenavirus pathogen and other desired pathogen(s).

In summary, a novel Pichinde virus (PlCV)-based live viral vector rP18tri was developed that packages 3 R A segments and encodes 2 foreign protein antigens. The viral vector was attenuated in vitro and in vivo. Using influenza HA as a model antigen, rP18tri-G/H can induce long-lasting protective immunity in mice. The rP18tri vector can induce strong humoral responses in mice and in guinea pigs and high levels of virus-specific effector T cells. The rPl 8tri-vector-induced antibody and T cell responses were significantly increased by a booster vaccination and were at high levels even after four applications, a unique feature of this live viral vector that is ideal for a prime-and-boost vaccination strategy. The vector can be given via various routes including intramuscular (IM), intraperitoneal (IP), intranasal (IN), and oral.

Priming and boosting with different HA proteins from different influenza virus strains induced heterosubtypic immunity, thus there is potential to develop universal flu vaccines. Chemically inactivated rP18tri-P/H induced both humoral and CTL responses after a boost dose. The rP18tri vector induced protective immunity against virulent rP18 virus, thus there is the potential for developing cross-reactive vaccines against other pathogenic arenaviruses such as Lassa fever virus, and dual (triple) vaccines against combinations of other pathogens. The complete disclosure of all patents, patent applications, and publications, and electronically available material (including, for instance, nucleotide sequence submissions in, e.g., GenBank and RefSeq, and amino acid sequence submissions in, e.g., SwissProt, PIR, PRF, PDB, and translations from annotated coding regions in GenBank and RefSeq) cited herein are incorporated by reference in their entirety. Supplementary materials referenced in publications (such as supplementary tables, supplementary figures, supplementary materials and methods, and/or supplementary experimental data) are likewise incorporated by reference in their entirety. In the event that any inconsistency exists between the disclosure of the present application and the disclosure(s) of any document incorporated herein by reference, the disclosure of the present application shall govern. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for variations obvious to one skilled in the art will be included within the invention defined by the claims.

Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. All numerical values, however, inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.