FIELD OF THE INVENTION The present invention relates to a novel platform of vaccines or immunogenic compositions comprising two different serotypes of recombinant vesicular stomatitis viruses and to the use of the novel platform in compositions and methods for prophylactic and therapeutic vaccination regimens against human pathogens.

BACKGROUND OF THE INVENTION Throughout this application, various references are cited in square brackets to describe more fully the state of the art to which this invention pertains. The disclosure of these references is hereby incorporated by reference into the present disclosure.

The best way to prime CD8+ CTL is to synthesize the target antigens by DNA transfection or infection using viral or bacterial vectors. The requirements as viral vaccine vectors are a broad range of hosts and good expression of gene of interests. Vesicular stomatitis virus (VSV) infects most mammalian cells and expresses viral proteins up to 60% of total proteins in infected cells [Kim, G. N., and C. Y. Kang. Virology 357:41, 2007]. In nature VSV infects pigs, cattle, and horses, and causes vesicular disease around the mouth and foot. Although human infection by VSV has been reported, VSV does not cause any serious symptoms [Fields, B. N., and K. Hawkins. N Engl J Med 277:989, 1967; Johnson, K. M. et al. Am J Trop Med Hyg 15:244, 1966].

VSV is a negative stranded RNA virus which encodes five proteins, nucleocapsid protein (N), phosphoprotein (P), matrix protein (M), surface glycoprotein (G), and RNA dependent RNA polymerase (L). The N, P, and L proteins of VSV are required for synthesis of positive sense and negative sense genomic RNAs and mRNA, which are necessary for the synthesis of VSV proteins, as well as gene of interest such as Human Hepatitis C virus (HCV) proteins.

Since the development of VSV reverse genetics system [Lawson, N. D., et al. Proc Natl Acad Sci U S A 92:4477, 1995; Whelan, S. P. et al. Proc Natl Acad Sci U S A 92:8388, 1995] to generate recombinant VSVs from cDNA, VSV has been studied as a viral vaccine vector for the immunization of various pathogens [Brandsma, J. L., et al. J Virol 81:5749, 2007; Daddario-DiCaprio, K. M., et al. J Virol 80:9659, 2006; Kohl, W., et al. J Gen Virol 88:157, 2007; Kuate, S., et al. Virology 362:26, 2007; Palin, A., et al. Vaccine 25:741, 2007; Schwartz, J. A., et al. Virology 366:166, 2007].

Although VSV is a rapidly replicating virus, eventually humoral and cellular immune responses against VSV will be elicited in the animal host, like any other viral vectors [Yewdell, J. W. et al. J Exp Med 163:1529-1938, 1986; Puddington, L. et al. J Virol 60:708- 717, 1986; Kalinke, U. et al Immunity 5:639-652, 1996]. Animals infected with VSV develop immune responses in one or two weeks including a neutralizing antibody [Kalinke, U. et al Immunity 5:639-652, 1996], which hinders the efficacy of boost immunizations for vaccination with the same vector. VSV is neutralized by serotype specific antibodies against viral surface glycoprotein G. Two different serotypes of VSV, VSV-Indiana (VSV] _nd ) and VSV-New Jersey (VSV _N j) show 50% amino acid identity in the glycoprotein [Gallione, C. J., and Rose, J. K. J. Virol. 46:162-169, 1983]. Antibodies raised against one serotype of VSV do not neutralize the other serotype of VSV [Cartwright, B., and Brown, F. J. Gen. Virol. 16:391-398, 1972], Therefore, others have used VSVi _nd as a vaccine vector in which the glycoprotein was replaced with that of VSV _NJ to minimize the problems arising from this immune response against the viral vectors [Rose, N. F. et al. J. Virol. 74:10903-10910, 2000; Rose, N. F. et al. Cell 106:539-549, 2001].

Although the VSVi _nd with G protein of VSV _N J serotype is useful in evading the humoral immune response, it will not prevent the cellular immune response which can be triggered by other VSV proteins including N, P, M, and L proteins. The cellular immune responses against VSV proteins other than the G protein may result in incomplete immune responses against the antigen of interest. Therefore, generation of additional recombinant VSV from another serotype can increase the efficacy of using VSV as a live viral vaccine vector.

Interestingly, it has been previously suggested that generation of a complete ΓVSV _NJ serotype vector was not attempted due to the potential for cross-reactive cytotoxic T-lymphocyte responses between the Indiana and New Jersey serotypes [Clarke et al., Springer Semin Immun 28:239, 2006].

In view of the above background, it would be advantageous to provide an approach for immunoprophylaxis and immunotherapy utilizing both humoral and cellular immune systems. As such, the Applicant has developed a system comprising a combination of vaccines that elicits a response against infectious agents. SUMMARY OF THE INVENTION

In one aspect the present invention provides for an immunization platform for use in a prime boost immunization strategy characterized in that said immunization platform comprises: (a) one vaccine or immunogenic composition comprising a recombinant vesicular stomatitis virus (rVSV) of one serotype, and (b) another vaccine or immunogenic composition comprising a rVSV of another serotype.

In one aspect of the present invention the immunization platform is characterized in that one serotype is Indiana and the other serotype is New Jersey.

In another aspect of the present invention the immunization platform is characterized in that each one of the two rVSV serotypes include a mutant matrix protein (M) gene.

In another aspect of the present invention the immunization platform is characterized in that one serotype includes a surface glycoprotein (G) gene of the other serotype.

In another aspect of the present invention the immunization platform is characterized in that the two rVSV serotypes are capable of expressing one or more proteins of interest. In another aspect of the present invention the immunization platform is characterized in that the two rVSV serotypes are capable of expressing one or more Hepatitis C virus (HCV) proteins.

In a further aspect the present invention provides for an immunization regimen characterized in that said immunization regimen comprises administering to a subject a prime dose of a vaccine or immunogenic composition comprising a rVSV of a first serotype followed by a boost dose of a vaccine or immunogenic composition comprising a rVSV of second serotype.

In one aspect, the immunization regimen is characterized in that the boost dose is followed by at least one more dose of the vaccine or immunogenic composition comprising the rVSV of the first serotype. In another aspect the immunization regimen is characterized in that first serotype is Indiana and the second serotype is New Jersey.

In another aspect the immunization regimen is characterized in that first serotype is New Jersey and the second serotype is Indiana.

In another aspect the immunization regimen is characterized in that the first and the second rVSV serotypes include a mutant M gene. In another aspect the immunization regimen is characterized in that the second rVSV serotype includes the G gene of the first rVSV serotype.

In another aspect the immunization regimen is characterized in that the first and second rVSV serotypes are capable of expressing one or more proteins of interest. In another aspect the immunization regimen is characterized in that said one or more proteins of interest are one or more proteins of an exogenous virus selected from the group comprising of: HCV, Human Immunodeficiency Virus (HIV), West Nile virus, Hantaviruses, Influenza virus, Ebola virus, Dengue hemorrhagic fever virus, Japanese encephalitis virus, SARS Coronavirus. In another aspect the immunization regimen is characterized in that the first and second rVSV serotypes are capable of expressing one or more HCV proteins.

In another aspect the immunization regimen is characterized in that the first serotype is Indiana and the second serotype is New Jersey, wherein both the rVSV Indiana and the rVSV New Jersey include a mutant M gene, and wherein the rVSV Indiana and the rVSV New Jersey are capable of expressing one or more proteins of an exogenous virus.

In a further aspect yet, the present invention provides for a method for inducing an immune response in a mammal to a VSV characterized in that said method comprises the following steps: (a) administering to the mammal an effective amount of a first vaccine or immunogenic composition, wherein said first vaccine or immunogenic composition comprises a rVSV of a first serotype, and (b) administering to the subject an effective amount of a second vaccine or immunogenic composition, wherein said second vaccine or immunogenic composition comprises a rVSV of a second serotype.

In one aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that said method further comprises: (c) administering to the subject an effective amount of the first vaccine or immunogenic composition.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first serotype is Indiana and the second serotype is New Jersey.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first serotype is New Jersey and the second serotype is Indiana. In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first and the second rVSV serotypes include a mutant M gene.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the second rVSV serotype includes the G gene of the first rVSV serotype.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that characterized in that the immune response includes a humoral and/or a cellular immune response. In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first and second rVSV serotypes are capable of producing virus-like particles having the ability to elicit a cell-mediated and/or humoral immune response.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first and the second rVSV serotypes are capable of expressing one or more proteins of an exogenous virus, and said immune response further comprises an immune response to the one or more exogenous virus proteins, wherein said exogenous virus is selected from the group comprising of: Human HCV, HIV, West Nile virus, Hantaviruses, Influenza virus, Ebola virus, Dengue hemorrhagic fever virus, Japanese encephalitis virus, SARS Coronavirus.

In another aspect the method of the present invention for inducing an immune response in a mammal to a VSV is characterized in that the first and second rVSV serotypes are capable of expressing one or more HCV proteins, and said immune response further comprises an immune response to the one or more HCV proteins. In yet a further aspect the present invention provides for a combined medicament useful for inducing an immune response against a pathogen, characterized in that said combined medicament comprises: (a) one vaccine or immunogenic composition comprising a rVSV of one serotype that is capable of expressing one or more proteins of the pathogen, and (b) another vaccine or immunogenic composition comprising a rVSV of another serotype that is capable of expressing the one or more proteins of the pathogen. In one aspect the combined medicament is characterized in that one serotype is a rVSV Indiana and the other serotype is a rVSV New Jersey, wherein the rVSV Indiana and rVSV New Jersey include a mutant M gene.

In a farther aspect of the present invention a method is provided for preventing or treating an infection caused by a pathogen, characterized in that said method comprises: (a) administering to a subject an effective amount of a first vaccine or immunogenic composition comprising a rVSV of a first serotype that is capable of expressing one or more proteins of the pathogen, and (b) administering to the subject an effective amount of a second vaccine or immunogenic composition comprising a rVS V of a second serotype that is capable of expressing the one or more proteins of the pathogen.

In one aspect the method of the present invention for preventing or treating an infection caused by a pathogen is characterized in that said method further comprises: (c) administering to the subject an effective amount of the first vaccine or immunogenic composition.

In another aspect the method of the present invention for preventing or treating an infection caused by a pathogen is characterized in that the first serotype is a rVSV Indiana and the second serotype is a rVSV New Jersey.

In another aspect the method of the present invention for preventing or treating an infection caused by a pathogen is characterized in that the first serotype is a rVSV New Jersey and the second serotype is a rVSV Indiana. In a further aspect yet the present invention provides for a kit comprising: (a) at least one dose of an effective amount of a vaccine comprising a rVSV of one serotype, and (b) at least one dose of an effective amount of a vaccine comprising a rVSV of another serotype.

In one aspect the kit of the present invention is characterized in that (a) and (b) are formulated in a pharmaceutically acceptable carrier. Advantages of using VSV and two serotypes of VSV as a vaccine vectors include:

(1) Utilization of two serotypes of VSV makes the VSV a more effective vaccine vector, because one serotype of VSV (first vaccine) will not neutralize the other serotype of VSV (second vaccine) or easily kill the cells infected with the other serotype of VSV.

(2) VSV does not cause serious disease in humans and most people infected are veterinarians dealing with the sick animals or scientists working with the VSV. Therefore, the seropositive rate in a general human population is very low, which makes the VSV an attractive vaccine vector.

(3) VSV replicates in a self-limiting manner in an infected individual, but it still induces strong cellular and humoral immune responses. (4) VSV replicates well in most of the mammalian cells in culture and yields high viral titer. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein and from the accompanying drawings, which are given by way of illustration only and do not limit the intended scope of the invention. Figure 1 illustrates gene organization of vesicular stomatitis virus (VSV), Indiana (Ind) serotype Heat resistant (HR) strain and New Jersey (NJ) serotype Hazlehurst strain (Haz).

Figure 2 illustrates a reverse genetics system for the recovery of VSV from cDNA. Figure 3 illustrates growth kinetics of recombinant VSVs without gene of interests.

Figure 4 illustrates expression of VSV proteins in the baby hamster kidney cells infected with recombinant VSVs.

Figure 5 depicts VSV peptide specific CD8+ T cell responses in Balb/c mice receiving a single virus, 3 dose schedule VSV vaccines.

Figure 6 depicts VSV peptide specific CD8+ T cell responses in Balb/c mice receiving in a successive dosing schedule of VSV vaccines in the order of New Jersey-Indiana-New Jersey. Figure 7 depicts VSV peptide specific CD8+ T cell responses in Balb/c mice receiving in a successive dosing schedule of VSV vaccines in the order of Indiana-New Jersey-Indiana.

Figure 8 A depicts the comparisons of VSV peptide specific CD8+ T cell responses in Balb/c mice receiving one or two serotypes of VSV vaccines.

Figure 8 B depicts the comparison of re-activation of CD8+ T cells following ex vivo stimulation with HCV MHC class I peptides in a cohort of mice (n=2) vaccinated with VSV _Ind -M(M51R) + HCV-CoreΔER, then VSV _NJ -M(M48/51R) + HCV-CoreΔER, followed 3 weeks later by an additional dose of VSVi _nd -M(M51R) + HCV-CoreΔER (set of bars on right of panel).

Figure 9 illustrates the cloning of HCV Core genes with or without deletion mutations into the cDNA clone of VSV _N j. Figure 10 illustrates the cloning of HCV Core genes with or without deletion mutations into the cDNA clone of VS V _Ind .

Figure 11 depicts the expression of HCV Core proteins from the recombinant VSV _NJ M wild type and M mutant (A). The expression of the VSV proteins from the same cells was detected as well (B). The expression was determined by Western blot analysis using Core antibody or VSVNJ antibody.

Figure 12 depicts the expression of HCV Core proteins from the recombinant VSVin _d M wild type and M mutant (A). The expression of the VSV proteins from the same cells was detected as well (B). The expression was determined by Western blot analysis using Core antibody or VSV _NJ antibody.

Figure 13 depicts the expression of HCV Core from the ΓVSVNJ and rVSVind with HCV core genes. HCV core proteins were detected by labelling the infected cell for an hour with 3H- Leu and immunoprecipitating the core protein with antibody against HCV core.

Figure 14 illustrates the cloning of HCV NS3 genes into the cDNA clone of rVSV _NJ (Mwτ), rVSV _NJ (MM48R-M5if0, rVSV _Ind (M _WT ), and rVSV _]nd (M _M5 iR).

Figure 15 depicts the recovery of rVSV _N j(Mwτ), ΓVSV _N J(M _M 48R-MSIR) ₅ rVSVi _nd (Mwr) ₅ and rVSVi _n d(M _M5 i _R ) expressing NS3. Expression of NS3, serotypes and M phenotypes of the recovered rVSV was confirmed by Western blot analysis using the HCV NS3 antibody and serotype specific VSV antibodies. Figure 16 illustrates the cloning of HCV NS5A and NS5B genes into the cDNA clone of rVSV _N j(Mwτ), rVSV _N j(M _M 48R-MsiR), rVSV _Ind (Mwr), and rVSV _Ind (M _M si _R ).

Figure 17 depicts the recovered ΓVSVNJ(MW _T ), ΓVSV _N J(MM ₄ 8 _R -MSIR), expressing NS5A. Expression of NS5A, serotypes and M phenotypes of the recovered rVSV was confirmed by Western blot analysis using the HCV NS5A antibody and serotype specific VSV _N j antibodies. Figure 18 depicts the recovered rVSVi _nd (Mwτ), and rVSVj _n d(MM5iR) expressing NS5A. Expression of NS5 A, serotypes and M phenotypes of the recovered rVSV was confirmed by Western blot analysis using the HCV NS5A antibody and serotype specific VSVi _nd antibodies.

Figure 19 depicts the recovered TVSVNj(MwT), ΓVSV _NJ (M _M48R -MS _IR ) _> expressing NS5B.

Expression of NS5B, serotypes and M phenotypes of the recovered rVSV was confirmed by Western blot analysis using the HCV NS5B antibody and serotype specific VSV _N j antibodies. Figure 20 depicts the recovered rVSVi _nd (Mwτ), and rVSVi _n d(M _M siR) expressing NS5B. Expression of NS5B, serotypes and M phenotypes of the recovered rVSV was confirmed by Western blot analysis using the HCV NS5B antibody and serotype specific VSVi _nd antibodies.

DETAILED DESCRIPTION OF THE INVENTION 1. Definitions

For convenience, the meaning of certain terms and phrases employed in the specification, examples, and appended claims are provided below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The articles "a" and "an" are used herein to refer to one or more than one (i.e., to at least one) of the grammatical object of the article.

The terms "animal" and "subject" as used herein includes all members of the animal kingdom including mammals, preferably humans.

The term "effective amount" as used herein means an amount effective and at dosages and for periods of time necessary to achieve the desired result.

The term "Indiana", and "IND" are used to refer to the VSV serotype Indiana (VSVm _d ).

"MW _T " "M(WT)" are used to refer to VSV having a wild type M gene. "M51R" is used to refer to an M gene in the VSVi,,d having a methionine changed to an arginine at position 51. M48R-M51R" is used to refer to an M gene in VSV _NJ having a methionine changed to an arginine at positions 48 and 51.

The term "New Jersey", and "NJ" are used to refer to the VSV serotype New Jersey (VSV _NJ ).

"Ind-M(M51 R)/NJ G" is used to refer to VSVi _nd having a mutant M gene and expressing VSV serotype New Jersey (VSV _NJ ) G protein. "Ind-M(WT)/NJ G" is used to refer to VSVi _nd having a wild type M protein and expressing a VSV _NJ G protein. "NJ-M (M48R-M51R)/Ind G" is used to refer to VSV _N j having a mutant M gene and expressing a VSVmd G protein. "NJ-M(WT)/ϊnd G" is used to refer to VSV _N j having a wild type M gene and expressing a VSV _lnd G protein.

The term "protein" as used herein is defined as a chain of amino acid residues, usually having a defined sequence. As used herein the term protein is inclusive of the terms "peptides" and "proteins". The terms also encompass an amino acid polymer that has been modified. "rVSV" is used to refer to a recombinant vesicular stomatitis virus. 2, Overview

The present invention features immunization platforms, immunization regimens and medicaments useful for inducing an immune response in a subject and preventing or treating a pathogenic infection in a subject, wherein said platforms, regimens and medicaments comprise a recombinant VSV of one serotype, and a recombinant VSV of another serotype.

Prior to the present invention, other research groups used the surface glycoprotein (G) gene switched VSVs for the second immunization to prevent the neutralization of the booster virus by the antibodies elicited by the prime viruses. Prior to the present invention, however, no other research groups have used two different serotypes of rVSV in a prime and boost immunization scheme or strategy.

Thus, in one aspect, the present invention provides for an immunization platform for use in a prime boost immunization strategy characterized in that said immunization platform comprises: (a) one vaccine or immunogenic composition comprising a recombinant vesicular stomatitis virus (rVSV) of a one serotype, and

(b) another vaccine or immunogenic composition comprising a rVSV of another serotype.

In another aspect, the present invention provides for a combined medicament useful for inducing an immune response against a pathogen, characterized in that said combined medicament comprises:

(a) one vaccine or immunogenic composition comprising a rVSV of one serotype that is capable of expressing one or more proteins of the pathogen, and

(b) another vaccine or immunogenic composition comprising a rVSV of another serotype that is capable of expressing the one or more proteins of the pathogen. The Applicant developed a reverse genetics system to recover VSV _NJ from cDNA for the first time [see Figures 1 and 2; Kim, G. N. and Kang, C. Y., Virology, 357:41-53, 2007]. The recombinant VSV _NJ is an effective viral vector together with VSVi _n d for the expression of foreign genes (i.e. genes of exogenous viruses), which can be used to minimize problems associated with preexisting immune responses against VSV itself. In addition to the VSV _NJ vector system, the Applicant also generated a full length clone of VSVin _d (Figure 1) that can used as an expression vector to avoid neutralization of VSV vectors after the boost immunization.

The characteristics of Applicant's rVSV immunization platform include, in one aspect, the usage of two different serotypes of VSV, and, in another aspect, the usage of VSVs with wild type M gene and mutant M gene. In aspects of the invention the two different VSV serotypes are VSVi _nd and VSV _NJ .

VSV M protein inhibits cellular protein synthesis very efficiently, but when a methionine is changed to arginine at position 51 in the VSVmaM and at positions 48 and 51 in the VSV _NJ M, M proteins lose their inhibitory effect on the host cellular protein expression [Kim, G. N., and C. Y. Kang. Virology 357:41, 2007; Petersen, J. M., et al. MoI Cell Biol 20:8590, 2000; von Kobbe, C, et al. MoI Cell 6:1243, 2000]. The rVSV with the mutant M gene can, therefore, be a better expression vectors than rVSV with wild type M, because they will not block the expression of immune related proteins such as chemokines in the antigen presenting cells.

3. Vaccines or Immunogenic Compositions of the Invention The present invention further features vaccines or immunogenic compositions comprising an rVSV of a first serotype and vaccines or immunogenic compositons comprising an rVSV of a second serotype, as described above. The vaccine or immunogenic compositions of the invention are suitable for administration to subjects in a biologically compatible form in vivo. The expression "biologically compatible form suitable for administration in vivo" as used herein means a form of the substance to be administered in which any toxic effects are outweighed by the therapeutic effects. The substances maybe administered to any animal or subject, preferably humans. The vaccines of the present invention may be provided as a lyophilized preparation. The vaccines of the present invention may also be provided as a solution that can be frozen for transportation. Additionally, the vaccines may contain suitable preservatives such as glycerol or may be formulated without preservatives. If appropriate (i.e. no damage to the VSV in the vaccine), the vaccines may also contain suitable diluents, adjuvants and/or carriers.

The dose of the vaccine may vary according to factors such as the disease state, age, sex, and weight of the individual, and the ability of antibody to elicit a desired response in the individual. Dosage regime may be adjusted to provide the optimum therapeutic response. The dose of the vaccine may also be varied to provide optimum preventative dose response depending upon the circumstances. 4. Methods of Use

The present invention also features methods of inducing an immune response in a subject and preventing or treating a pathogenic infection in a subject comprising administering to the subject an effective amount of a combination of vaccines or immunogenic compositions. As such, in one aspect, the present invention provides for a method for inducing an immune response in a mammal to a VSV characterized in that said method comprises the following steps:

(a) administering to the mammal an effective amount of a first vaccine or immunogenic composition, wherein said first vaccine or immunogenic composition comprises a rVSV of a first serotype, and

(b) administering to the subject an effective amount of a second vaccine or immunogenic composition, wherein said second vaccine or immunogenic composition comprises a rVSV of a second serotype.

In another aspect, the present invention also provides for a method for preventing or treating an infection caused by a pathogen, characterized in that said method comprises: (a) administering to a subject an effective amount of a first vaccine or immunogenic composition comprising a rVSV of a first serotype that is capable of expressing one or more proteins of the pathogen, and (b) administering to the subject an effective amount of a second vaccine or immunogenic composition comprising a rVSV of a second serotype that is capable of expressing the one or more proteins of the pathogen.

In aspects of the invention the methods for inducing an immune response in a mammal to a VSV and the methods for preventing or treating an infection caused by a pathogen may further comprise step (c) administering to the subject an effective amount of the first vaccine or immunogenic composition. Step (c) may be administered to the subject more than one time over the course of inducing an immune response, preventing or treating.

The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific Examples. These Examples are described solely for purposes of illustration and are not intended to limit the scope of the invention. Changes in form and substitution of equivalents are contemplated as circumstances may suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for purposes of limitation. EXAMPLES

The examples are described for the purposes of illustration and are not intended to limit the scope of the invention.

Example 1 - Recovery of VSV by Reverse Genetics The Applicant generated recombinant VSVs from cDNA by reverse genetics system, which was established before by Rose and Wertz, separately [Lawson, N. D., et al. Proc Natl Acad. Sci U S A 92:4477, 1995; Whelan, S. P. et al. Proc Natl Acad Sci U S A 92:8388, 1995]. Baby hamster kidney cells expressing bacteriophage T7 RNA polymerase, namely BHK-T7 cells [Buchholz, U. J. et al. J Virol 73:251, 1999], were transfected with a DNA plasmid encoding full length genome of VSV, Indiana serotype or New Jersey serotype, and plasmids encoding VSV N, P, and L genes. Cell culture medium containing newly generated virus was harvested 48-72 hours after transfection depending on the degree of cytopathic effects by the recombinant VSV. Figure 2 illustrates the reverse genetics system for the recovery of VSV

Figure 1 illustrates the cDNA clones of VSVmd and VSVN _J generated by the Applicant. The diagram of Figure 1 describes the gene order (N, P, M, G, and L) and restriction enzyme sites (Pac I, Not I, Kpn I, and Spe I) in the full- length DNA clone of VSV genome, which can be used to clone gene of interests (foreign genes) into the VSV genome. The mutations introduced into the M gene (M51R in the VSVi _nd and M48R-M51R in the VSV _NJ ) of VSV are shown as well.

With reference to Figure 3, the recombinant VSV were purified by 3 consecutive plaque picking and amplified in baby hamster kidney cells. In order to determine the replication kinetics of the recombinant VSVs, we infected BHK cells with a multiplicity of infection (MOI) of 3 and harvested the cell culture medium from the infected cells every 2 hrs until 10 hrs after infection. Viral titre in the harvested culture medium was determined by plaque assay.

Example 2 - Expression of VSV Proteins in Baby Hamster Kidney Cells Infected with Recombinant VSVs

Expression of proteins from the recombinant VSVs (two serotypes, VSV[ _n d and VSVN _J , VSVS of M wild type and M mutant, and VSVs with G gene switched) was examined by Western blot analysis using antibodies against VSVm _d and VSV _NJ . Our antibodies against VSVj _n d or VSV _N j detect four proteins of VSV (N, P, M, and G). Figure 4 shows 3 protein bands, because N protein and P protein migrate as the same size proteins on the SDS-PAGE gel. Antibody against VSVi _nd or VSV _NJ could detect all four proteins of VSV, N, P ₅ M, and G that were expressed from a single serotype. Exchange of G gene in the VSVi _n( j NJG was confirmed by the lack of G protein detection by VSVi _n d antibody because VSVi _nd antibody does not cross-react with the G protein of VSV _N/ (lanes 2 and 4). Exchange of G gene in the VSV _N j IG was confirmed by the size differences in VSV _Ind G and VSV _NJ G. VSV _Ind G migrates slightly slower than the G of VSV _N J, which is shown on the lane 6 and 8. Mutation in the M gene (M51R in the VSV _Ind M protein and M48R-M51R in the VSV _N j M protein) makes M proteins migrate slightly faster than the wild type M proteins of both serotypes, which are demonstrated in lanes 3, 4, 7, and 8. The migration pattern of the M proteins confirms the mutation in the mutant VSVs.

Example 3 - Vaccinations Regimens or Schemes to Find Best Combination of Viral Inoculation

With reference to Figures 5-8 and Table 1, since an objective of the Applicant is to utilize a prime and boost regimen for immunizing animals, the Applicant determined the best order of recombinant VSV serotypes for the prime and boost immunization scheme. The Applicant studied whether vaccination with 1) vectors based on two different serotypes (VSVi _nd or VSV _NJ ), 2) VSV vectors expressing the G protein of the alternate serotype or 3) cytotoxic wild type or non-cytopathic mutant VSV M protein provided any advantage to the generation of VSV specific CD8+ T cells. Table 1 illustrates all possible serotype combinations. Mice groups were vaccinated with rVSVs in three doses vaccination schedule. In this vaccination study consisting of 13 groups of mice, the objective was to determine the recombinant VSV vaccine construct(s) that generated the highest percentage of VSV nucleocapsid specific CD8+ T cells, based on interferon gamma (IFNγ) production following stimulation with VSV N peptide, VSV N275 (MHC I H2d specific peptide targeted to amino acid sequence in VSV N). In particular, we studied whether vaccination with (1) vectors based 2 different strains (VSVi _nd or VSV _N j), (2) vectors expressing the G protein of the alternate serotype or (3) cytotoxic wild type or non-cytopathic mutant VSV M protein provided any advantage to the generation of VSV N specific CD8+ T cells.

Six 6-week-oId female Balb/c mice (MHC type H2d) per group received 1 x 10 ⁶ pfii (plaque forming unit) rVSV for dose 1, administered by intramuscular injection into the posterior thigh muscle and diluted in a total volume of 50 μl PBS. Mice received IXlO ⁶ pfu rVSV for the dose 2 and 5 X 10 ⁶ rVSV for the dose 3. A time period of 4 weeks separated doses 1 and 2, and an additional 10 weeks separated doses 2 and 3. Mice were euthanized 7 days following the 3 ^rd dose and splenocytes harvested for detection of CD8+ T cells specific to a VSV nucleocapsid peptide (VSV N275).

A single cell suspension of splenocytes was prepared in complete RPMI and then IxIO ⁶ cells were transferred to appropriate wells in a U-bottom 96 well plate. VSV N specific peptide VSV N275, NH2-MPYLIDFGL-COOH (GenScript Corporation, Piscataway NJ) and co- stimulant anti-CD28 (clone 37.51, BD Biosciences, San Jose CA) mixtures were added and mixtures incubated for 2 hours. Brefeldin A (BD Biosciences) was added according to the manufacturer's instructions to block cytokine secretion and cells incubated for an additional 3 hours. Cells were stained with antibodies recognizing murine CD8 (FITC-CD8a, BD Biosciences clone 53-6.7), or appropriate isotype control antibodies. Cells were washed and then permeabilized with Cytofix/cytoperm kit reagents (BD Biosciences) according to the manufacturer's instructions and then stained for IFNγ (APC-IF ¹ N γ, BD Biosciences, clone XMG 1.2). The stained cells were identified using a FACS Calibur flow cytometer (BD Biosciences) and FlowJo software (Tree Star Inc., Ashland OR). The data is expressed as the average % CD8+IFNγ+ splenocytes in 4-6 mice per group (+/- standard error of the mean, SEM) for each vaccine. Statistical significant was determined using a one-way ANOVA with a Bonferroni correction (Prism 4.0 software, GraphPad Software Inc., San Diego, CA).

Results

The results clearly show that alternating the VSV serotypes for the second dose is better than providing three doses of a single VSV serotype for the generation of VSV N specific CD8+ T cells. In view of the results presented herein, a strategy for inducing VSV N specific CD8+ T cells is a first dose of VSVi _n( (-mutant M, followed by a dose of VSVNj-mutant M, and finally a dose of VSVi _nd -mutant M (Figure 8A).

Example 4: Immunization Studies with Recombinant VSV expressing HCV Proteins Background

Hepatitis C virus (HCV) is causative agent of Hepatitis C in humans. The number of cases of hepatisis C is estimated to be around 170 million worldwide. Approximately 3% of the world's population is chronically infected by the virus. It is estimated that approximately 3 million people in the United States are chronically infected with HCV, with the majority of infections occurring among people 30 to 50 years of age.

Infection with HCV can be extremely serious. The initial infection may cause no disease or may result in hepatitis accompanied by jaundice; fulminant liver failure is rare. However, most HCV infections become chronic. This chronic infection, although tolerated by some, leads to liver disease, cirrhosis and hepatocellular carcinoma. These chronically infected patients are the source of almost all new infections.

Although the HCV genome has been isolated and sequenced more than a decade ago, no effective vaccine to prevent HCV infection or treat acute or chronic HCV, has been developed.

The ideal HCV vaccine or vaccination strategy will be the one that induces both humoral and cellular immune responses. Accordingly, the novel recombinant VSV immunization strategy developed by the Applicant utilizing two different VSV serotypes, provides for a platform for obtaining an HCV vaccine system. Generation of Recombinant VSV Expressing HCV Proteins

With reference to Figures 9 to 20, HCV core, NS3, NS5A, and NS5B genes were first cloned into pBluescript II KS vector (Stratagen) in order to introduce VSV intergenic junction sequences, which are involved in the transcriptional termination at the upstream gene and transcriptional reinitiation at the downstream gene of VSV. Full length core and four HCV core genes with deletions at the regions involved in the nuclear localization and anchoring into ER membrane were cloned into pBluscript II KS vector. Full length NS3 gene was cloned into pBluescript II vector without modifications. Full NS5A and NS5B, and NS5A and NS5B with deletions at the ER membrane anchoring region were cloned into pBluescript II KS vector. After confirmation of the correct sequences in each clone, the HCV genes with VSV intergenic junction sequences, except full NS5B, were cut with restriction enzyme, Kpn I and cloned into pVSV _NJ -M(WT) and pVSV _N j-M(M48R-M51R) between G gene and L gene. Pac I cut of HCV genes with VSV intergenic junction sequences were cloned into Pac I site between G and L genes in the pVSVi _nd -M(WT) and pVSVm _d -M(M51R). Full NS5B were cut with Spe I from the pBluescript II vector and blunt ended with klenow fragment and ligated to pVSV _NJ , which was cut with Kpn I and blunt ended with klenow fragment. The insertion of NS5B into PVSVNJ was confirmed by digesting the plasmid with Pac I, which site was introduced to both ends of NS5B clone. HCV Core genes were partially digested with Kpn I because of the presence of one additional Kpn I site in the core gene. The same clones in the pBluescript II vector were cut with restriction enzyme, Pac I in order to clone HCV genes, Core, NS3, NS5A, and NS5B into pVSV _tnd -M(WT) and pVSV, _nd -M(M51R). Insertion of HCV genes into the pVSVs were confirmed by digesting the plasmids with Kpn I or Pac I and by DNA sequencing. Recombinant VSVmd and VSV _N j expressing HCV Core (Figures 11, 12 and 13), NS3 (Figure 15), NS5A (Figures 17 and 18), and NS5B (Figures 19 and 20) were recovered from cDNA clones by VSV reverse genetics. The recombinant viruses were purified by three consecutive plaque picking and amplified by infecting BHK cells with a multiplicity of infection (MOI) of 0.1. The expression of HCV proteins from the viruses were determined by Western blot analysis using virus infected cell lysates and antisera against each HCV proteins. Western blot analysis of the same cell lysates using antisera against VSVi _nd and VSV _NJ determined the serotype and M gene phenotype of the VSV vector expressing each HCV protein. Mutated M proteins of VSVi _nd (M _M siR) and VSVNJ(MM ₄ 8 _R -MSIR) migrate slightly faster than wild type M proteins on the SDS-PAGE gel.

Results

With reference to Figure 8B, vigorous re-activation of CD8+ T cells was observed following ex vivo stimulation with HCV MHC class I peptides in a cohort of mice (n=2) vaccinated with VSV Ind-M _M5 i _R + HCV-CoreΔER, then VSV NJ-M _M48 /5iR+ HCV-CoreΔER, followed 3 weeks later by an additional dose of VSV Ind-M _M sm + HCV-CoreΔER. This reactivation was shown to be specific for HCV peptides since a control mouse immunized with the VSV vector alone did not exhibit CD8+ T cells specific for HCV peptides (set of bars on left of panel). The reactivation of CD8+ T cells specific for 2 VSV nucleocapsid epitopes was used as positive control in all mice.

Table 1: Vaccinations to find best combinations of viral inoculation to induce strongest immune responses in mice

IM: intramuscularly; Pfu: Plaque forming unit; wks: weeks.