CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to US Provisional Application No. 61/782,390, filed on March 14, 2013, the content of which is hereby incorporated herein in its entirety.

BACKGROUND

Clostridium difficile (Cd) is an emerging pathogen of opportunistic infection in hospitals worldwide. It is the major cause of antibiotic-associated pseudo- membranous colitis and diarrhea in human.

Cd asserts its effect through two large protein toxins: toxin A (tcdA) and toxin B (tcdB), which disrupt intestinal epithelial cells. tcdA and tcdB are large (250-308 kDa) protein toxins with multiple domains. The binding of the receptor binding domain (RBD) of Cd to carbohydrates on colonic epithelial cells is an initial step in pathogenesis. tcdA and/or tcdB enters the cells through receptor-mediated endocytosis and disrupts normal signaling pathways necessary for maintaining the cells' cytoskeleton, ultimately leading to

inflammation and diarrhea. Various oligosaccharides, including the trisaccharide a-Gal- (l,3)-P-Gal-(l,4)-P-GlcNAc, bind specifically to tcdA, but the native human ligand has not been definitively identified.

Patients in hospitals treated with antibiotics have high risk of Cd infection, especially in children and those over 65 years old. C -associated diseases incurr additional health care costs and extend hospital time. Morbidity and mortality of Ctf-associated diseases have increased significantly, because of changes in the virulence of the causative strains.

Therefore, there is a need for prophylactic and therapeutic agents against Cd infection and C -associated diseases.

SUMMARY

Described herein are novel polypeptides, fusion polypeptides, nucleic acids encoding the polypeptides, immunotherapeutic compositions containing the polypeptides, and methods of using the polypeptides.

Polypeptides and/or lipo-ploypeptides each containing one or more functional domains of Cd tcdA can be used for the preparation of vaccines against diseases caused by CcZ-infection, the diagnosis of Cd infection, and for the generation of immunogenic reagents. Mono- or polyclonal antibodies raised against these polypeptides can be used for the diagnosis of infection by Cd and for immunizing against or treating diseases associated with 5 Cd infection.

Accordingly, described herein is an isolated polypeptide containing one or more functional domains of Cd tcdA, e.g., tai4-RBD. For example, the isolated polypeptide can have the amino acid sequence of any of SEQ ID NOs: 2, 4, 6, and 8-18 or a sequence that is at least 80% (e.g., 85%, 90%, 95%, 98%, or 99%) identical thereto. The polypeptide can o further include a lipidating sequence. Such a polypeptide can be expressed in lipidated form.

Also described herein are an isolated nucleic acid molecule containing a sequence encoding the above-described polypeptide and a vector containing the nucleic acid molecule.

Further, an antibody or an antigenic fragment thereof that binds specifically to the above-described polypeptide is described. A kit for diagnosing Cd infection or a disease 5 associate with the infection can contain one or more such antibodies.

A chimeric molecule containing a tcdA-ΚΒΌ or a fragment thereof described herein can be linked to another molecule, e.g., a polypeptide, a polysaccharide, a nucleic acid molecule, or a small molecular compoound. The linked polypeptide can include an antigenic surface protein or peptide from a pathogenic bacteria or virus, e.g., the evn protein of HIV, o Eprotein of dengue virus, HA protein of influenza virus, F protein from RSV, and HN protein from PIV3. The linked polysaccharide can include different serotypes of oligosaccharide molecules from bacteria such as pneumococcal, meningococcal, H. influenza, A. baumannii, or C. difficile.

In another aspect, describe herein is an immunogenic composition containing the5 polypeptide, chimeric molecule, or nucleic acid molecule described herein. Such

immunogenic composition can be used to protect against or treat Cd infection or diseases associated with the infection, or to induce an immune response.

An immunogenic composition containing an antigen and the above-described polypeptide as an adjuvant is also described.

0 The details of one or more embodiments are set forth in the accompanying drawing and the description below. Other features, objects, and advantages will be apparent from the description and drawing, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

FIG.1 is a set of sequences showing (A) the alignment of C-terminal repetitive sequences of tcdA; and (B) the rationally designed consensus sequence of RBD (SEQ ID NO:26). The putative receptor binding sites are underlined.

5 FIG. 2 is a schematic representation showing the construction of plasmids expressing either rRBD or rlipo-RBD in the E. coli system.

FIG. 3 is a set of SDS-PAGE (Panels A and B) and Western blot (Panel C) showing analysis of recombinant tcdA-RBD (rRBD) purified using Ni-affmity column from E. coli lysate. Molecular weight markers are 35 kDa, 48 kDa, 63 kDa, 75 kDa, lOOkDa, and 135kDa. o FIG. 4 is a set of SDS-PAGE (Panel A) and Western blot (Panels B and C) showing analysis of recombinant tcdA-RBD fragments (rRBD-Fl, -F2 and -F3) purified using Ni- affmity column from E. coli lysate. Molecular weight markers are 31 kDa, 42kDa, 57kDa, 72kDa, 93kDa, 125kDa).

FIG 5 is a set of SDS-PAGE (Panels A and B) and Western blot (Panel C) showing 5 analysis of recombinant lipidated tcdA-RBO (rlipo-RBD) purified using Ni-affmity column from E. coli lysate. Molecular weight markers are 35 kDa, 48 kDa, 63 kDa, 75 kDa, lOOkDa, and 135kDa.

FIG. 6 is a bar graph showing the ELISA results (IgG titer against rRBD) at different time points with antisera obtained from mice immunized with different amounts of rRBD and o rlipo-RBD vaccine candidates.

FIG. 7 is a graph showing that rlipo-RBD elicited dose-dependent immune protection against toxicity of tcdA in a mouse challenge model.

FIG. 8 is a graph showing that rRBD and rlipo-RBD elicited dose-dependent systemic IgA antibody responses and that rlipo-RBD was 10 times more potent than rRBD.

5 FIG. 9 is a set of bar graphs showing that both rRBD and rlipo-RBD had adjuvant function for enhancing both IgG (top panel) and systemic IgA (lower panel) antibody responses against ovalbulin (OVA) in mouse immunogenicity studies.

FIG. 10 is a plot showing the identification of the receptor binding activity of rRBD and its fragments (Fl, F2 and F3) using a flow cytometric analysis of in vitro VERO cell0 binding screening assay.

FIG. 11 is a set of plots shows structural analysis of tcdA-rRBD and its truncated fragments using Circular Dichroism (CD) spectroscopy. FIG. 12 is an image showing hemagglutinin activity (HA) of tcdA and rRBD in a rabbit red blood cell assay.

FIG. 13 is an image showing hemagglutinin activity (HA) of rRBD truncated fragment (rRBD-Fl, -F2 and -F3) in a rabbit red blood cell assay.

FIG. 14 is a Western blot showing the binding affinity of different RBD fragments for the host receptors.

FIG 15 is a set of bar graphs showing the ELISA results of guinea pig sera raised against different synthetic peptides and their mixture. Panel A shows anti-peptide sera IgG titer against rRBD. Panel B shows anti-peptide sera IgG titer against individual peptides. Mixture includes PI, P2 and P3.

FIG 16 is a set of Western blots showing analysis of guinea pig antisera raised against a synthetic peptide mixture. Panels (A) and (B) are rRBD and its fragments blot against mouse anti-rRBD sera and guinea pig anti-peptide mixture, respectively.

FIG 17 is an image showing that anti-peptide guinea pig sera inhibited the hemagglutinin activity (HA) of rRBD in a rabbit red blood cell assay.

FIG. 18 is an image showing the hemagglutinin inhibition (HAI) activity of guinea pig antisera generated from immunization with individual RBD fragments.

FIG. 19 is a set of confocal microscopy images showing that tcdA-RBD and its fragment can quickly bind to the host receptor within a minute, and then internalize and delocalize inside the cell within 10 minutes and start to be degraded in 30 minutes.

FIG. 20 is a plot showing the biological and immunological functions of antisera generated from mice immunized with RBD fragments.

FIG. 21 is a set of plots showing the adjuvant activities of rRBD and its truncated fragments.

FIG. 22 is a set of graphs showing that rRBD and its fragments up-regulated T-cell effector biomarkers in a dendritic cell activation study.

FIG. 23 is a set of graphs showing that rRBD and its fragments up-regulated proinflammatory cytokines in a dendritic cell activation study. DETAILED DESCRIPTION

Described herein are novel polypeptides each containing the receptor-binding domain (RBD) of toxin A (tcdA) of Clostridium difficile (Cd). Unexpectedly, these polypeptides, particularly when expressed in lipidated form, are highly immunogenic and capable of inducing immunity against Cd challenge in animal models.

Desceribed below are polypeptides (and nucleic acids encoding them) each containing one or more functional domains of Cd tcdA.

One exemplary polypeptide contains a C-terminal portion of tcdA, which includes the receptor-binding domain (RBD) of tcdA, i.e., tcdA-RBD or RBD. Shown below are the nucleic acid sequence (SEQ ID NO: l) encoding tcdA-RBD and the amino acid sequence of tcdA-RBD (SEQ ID NO:2). The putative receptor binding sites within the RBD are highlighted in SEQ ID NO:2. tcdA-RBD nucleic acid sequence (SEQ ID ΝΟ: Π

TTTAATAGCGAGAATGAACTGGATCGTGATCATCTGGGCTTCAAAATCATCGATAATAAA ACCTATTATTATGAT GAAGATAGCAAACTGGTGAAAGGCCTGATTAACATTAACAACAGCCTGTTTTACTTCGAT CCGATTGAAAGCAAT CTGGTTACCGGTTGGCAGACCATTAACGGCAAAAAATATTATTTTGATATTAATACCGGT GCAGCCAGCACCAGC TATAAAATTATCAACGGCAAGCATTTCTATTTCAATAATAATGGCGTGATGCAGCTGGGC GTTTTTAAAGGTCCG GATGGTTTTGAATATTTTGCACCGGCAAATACCCAGAACAATAATATTGAAGGTCAGGCC ATTGTGTATCAGAGC AAATTTCTGACCCTGAACGGTAAAAAATACTACTTCGACAACGATAGCAAAGCAGTGACC GGTTGGCGCATTATT AACAACGAGAAATATTATTTCAATCCGAATAACGCCATTGCAGCAGTTGGTCTGCAGGTT ATTGACAACAATAAA TATTACTTTAACCCGGACACCGCCATTATTAGCAAAGGCTGGCAGACCGTTAATGGTAGC CGTTATTATTTCGAT ACCGATACCGCGATTGCCTTTAATGGCTATAAAACCATCGACGGCAAACACTTCTATTTT GATAGCGATTGCGTG GTGAAAATTGGTGTTTTTAGCGGTAGCAACGGCTTTGAATACTTTGCCCCTGCCAATACC TACAACAACAACATC GAAGGCCAGGCAATCGTTTATCAGTCAAAATTCCTGACGCTGAATGGGAAAAAATATTAC TTTGACAATAACAGC AAAGCCGTTACGGGATGGCAGACAATTGATAGCAAAAAATACTACTTCAATACCAATACC GCAGAAGCAGCAACA GGTTGGCAGACGATCGATGGTAAAAAATATTATTTCAACACGAACACAGCCGAAGCAGCC ACCGGCTGGCAAACC ATTGATGGAAAAAAATATTACTTCAATACAAATACGAGCATTGCCAGCACCGGTTATACC ATTATCAACGGCAAA TATTTCTACTTCAACACCGATGGCATTATGCAGATTGGTGTGTTCAAAGTGCCGAATGGC TTTGAGTATTTCGCT CCGGCTAACACCCATAATAACAATATTGAGGGCCAGGCGATCCTGTATCAGAATAAATTC CTGACACTGAACGGC AAAAAATACTATTTCGGCAGCGATTCAAAAGCAATTACAGGTTGGCAAACAATTGACGGG AAAAAGTACTATTTT AATCCGAACAATGCGATCGCAGCAACCCATCTGTGTACCATTAATAACGATAAATACTAC TTTAGCTATGACGGC ATCCTGCAGAATGGCTATATCACCATTGAACGCAACAACTTTTACTTTGATGCCAACAAC GAAAGCAAAATGGTG ACCGGTGTTTTTAAAGGCCCTAATGGCTTCGAATACTTCGCACCAGCGAATACGCATAAC AATAACATCGAGGGT CAAGCGATTGTCTACCAGAATAAATTTCTGACTCTGAATGGTAAAAAATATTACTTCGAT AATGATTCAAAAGCC GTGACCGGATGGCAAACTATCGATTCAAAAAAATACTACTTTAACCTGAACACCGCAGTT GCAGTTACAGGGTGG CAAACCATCGACGGTGAGAAATACTACTTCAATCTGAATACAGCCGAAGCCGCTACTGGA TGGCAGACGATTGAC GGAAAACGCTATTATTTTAATACCAACACCTATATTGCGAGCACAGGCTATACCATCATT AATGGTAAACACTTC TACTTTAACACGGACGGTATCATGCAAATCGGCGTGTTTAAAGGCCCAGACGGTTTCGAG TACTTTGCGCCAGCA AACACCCACAATAATAACATCGAAGGACAAGCCATCCTGTATCAAAACAAATTTCTGACG CTGAATGGCAAAAAA TACTACTTCGGTAGTGATAGCAAAGCTGTTACAGGTCTGCGTACCATCGACGGAAAAAAA TATTACTTTAATACT AACACGGCAGTGGCAGTGACGGGCTGGCAAACGATCAACGGGAAAAAATACTACTTCAAC ACCAACACGTATATT GCCTCAACCGGCTATACAATTATCAGCGGTAAACACTTTTATTTCAATACAGATGGGATC ATGCAGATCGGAGTT TTCAAAGGACCTGATGGATTCGAGTATTTTGCTCCTGCGAATACCGATGCCAATAACATT GAGGGACAGGCAATT CGCTATCAGAATCGTTTTCTGTATCTGCACGATAATATTTATTATTTTGGCAATGATTCC AAAGCGGCAACCGGT TGGGCCACCATTGATGGTAATCGTTATTATTTTGAGCCGAATACCGCAATGGGTGCCAAT GGTTATAAAACGATT GATAACAAAAACTTTTATTTTCGCAACGGCCTGCCGCAGATTGGCGTATTCAAAGGTCCT AACGGTTTTGAGTAC TTCGCTCCAGCCAATACAGATGCAAATAATATCGACGGCCAGGCCATCCGCTACCAGAAC CGCTTCCTGCATCTG CTGGGTAAAATCTATTATTTCGGCAACAACAGCAAAGCGGTAACTGGTTGGCAAACCATC AATAGCAAAGTGTAT TATTTCATGCCGGATACAGCAATGGCAGCAGCCGGTGGTCTGTTTGAAATTGATGGTGTG ATCTATTTCTTTGGT GTGGATGGTGTT AAGCACCGGGTATTTATGGC tcdA-RBD amino acid sequence fSEO ID NO:21

FNSENELDRDHLGFKIIDNKTYYYDEDSKLVKGLININNSLFYFDPIESNLVTGWQTING KKYYFDINTGAASTS YKIINGKHFYFNNNGVMQLGVFKGPDGFEYFAPANTQNNNIEGQAIVYQS FLTLNGKKYYFDNDSKAVTGWRII NNEKYYF PNNAIAAVGLQVIDNNKYYFNPDTAIISKGWQTV GSRYYFDTDTAIAF GYKTIDGKHFYFDSDCV VKIGVFSGSNGFEYFAPANTYNNNIEGQAIVYQSKFLTLNGKKYYFDNNSKAVTG QTIDSKKYYFNTNTAEAAT G OJIDG YYFNT TAEAATGWQTIDGKKYYFNTN SIAS GYTIIN^^^^^^^^^^^^^¾^^g B—PilEGOAILYONKFLTLNGKKYYFGSDSKAITGWOTIDG KYYFNPNNAIAATHLCTINNDKYYFSYDG ILQNGYITIERNNFYFDANNE5K VTGVFKGPNGFEYFAPANTHNNNIEGQAIVYQNKFLTLNGKKYYFDNDSKA VTGWQTli ^" VTGWQTIDGKRYYFNTNTYIASTGYTIINGKHF YFNTDGIMQIGVFKGPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNG KYYFGSDSKAVTGLRTIDGKKYYFNT NTAVAVTGWQTINGKKYYFNTNTYIASTGYTIISGKHFYFNTDGIMQIGVFKGPDGFEYF APANTDANNIEGQAI RYQNRFLYLHDNIYYFGNDSKAATG ATIDGNRYYFEPNTA GANGYKTIDNKNFYFRNGLPQIGVFKGPNGFEY

VDGVKAPGIYG ^"" "

Also described herein are three fragments of tcdA-RBD, i.e., Fl, F2 and F3. The amino acid sequences of these fragments and the nucleic acid sequences encoding them are shown below. The putative receptor binding sites are highlighted. Fl nucleic acid sequence (SEQ ID NO:3

TTTAATAGCGAGAATGAACTGGATCGTGATCATCTGGGCTTCAAAATCATCGATAATAAA ACCTATTATTATGAT GAAGATAGCAAACTGGTGAAAGGCCTGATTAACATTAACAACAGCCTGTTTTACTTCGAT CCGATTGAAAGCAAT CTGGTTACCGGTTGGCAGACCATTAACGGCAAAAAATATTATTTTGATATTAATACCGGT GCAGCCAGCACCAGC TATAAAATTATCAACGGCAAGCATTTCTATTTCAATAATAATGGCGTGATGCAGCTGGGC GTTTTTAAAGGTCCG GATGGTTTTGAATATTTTGCACCGGCAAATACCCAGAACAATAATATTGAAGGTCAGGCC ATTGTGTATCAGAGC AAATTTCTGACCCTGAACGGTAAAAAATACTACTTCGACAACGATAGCAAAGCAGTGACC GGTTGGCGCATTATT AACAACGAGAAATATTATTTCAATCCGAATAACGCCATTGCAGCAGTTGGTCTGCAGGTT ATTGACAACAATAAA TATTACTTTAACCCGGACACCGCCATTATTAGCAAAGGCTGGCAGACCGTTAATGGTAGC CGTTATTATTTCGAT ACCGATACCGCGATTGCCTTTAATGGCTATAAAACCATCGACGGCAAACACTTCTATTTT GATAGCGATTGCGTG GTGAAAATTGGTGTTTTTAGCGGTAGCAACGGGTTTGAATACTTTGCCCCTGCCAATACC TACAACAACAACATC GAAGGCCAGGCAATCGTTTATCAGTCAAAATTCCTGACGCTGAATGGGAAAAAATATTAC TTTGACAATAACAGC AAAGCCGTTACGGGATGGCAGACAATTGATAGCAAAAAATACTACTTCAATACCAATACC GCAGAAGCAGCAACA GGTTGGCAGACGATCGATGGTAAAAAATATTATTTCAACACGAACACAGCCGAAGCAGCC ACCGGCTGGCAAACC ATTGATGGAAAAAAATATTACTTCAATACAAATACGAGCATTGCCAGCACCGGTTATACC ATTATCAACGGCAAA ATTTCTACTTCAACACCGATGGCATTATGCAGATTGGTGTGTTCAAAGTGCCGAATGGCT TTGAGTATTTCGCT CCGGCTAACACCCATAATAACAATATTGAGGGCCAGGCGATCCTGTATCAGAATAAATTC CTGACACTGAACGGC AAAAATACTATTTCGGCAGCGATTCAAAAGCA

Fl amino acid sequence (SEQ ID NO:4)

FNSENELDRDHLGFKIIDNKTYYYDEDSKLVKGLININNSLFYFDPIESNLVTGWQT ING KYYFDINTGAASTS YKIINGKHFYFNNNGVMQLGVFKGPDGFEYFAPANTQNNNIEGQAIVYQSKFLTLNGKKY YFDNDSKAVTGWRII NNEKYYFNPNNAIAAVGLQVIDNNKYYFNPDTAIISKGWQTVNGSRYYFDTDTAIAFNGY KTIDGKHFYFDSDCV VKIGVFSGSNGFEYFAPANTYNNNIEGQAIVYQSKFLTLNGKKYYFDNNS AVTG QTIDSKKYYFNTNTAEAAT GWQTIDGKKYYFNTNTAEAATG QTIDGKKYYFNTNTSIASTGYTIINI

|^¾|gilEGQAILYQNKFLTLNGKKYYFGSDSKA F2 nucleic acid sequence fSEQ ID NO: 5)

GCCGAAGCAGCCACCGGCTGGCAAACCATTGATGGAAAAAAATATTACTTCAATACAAAT ACGAGCATTGCCAGC ACCGGTTATACCATTATCAACGGCAAATATTTCTACTTCAACACCGATGGCATTATGCAG ATTGGTGTGTTCAAA GTGCCGAATGGCTTTGAGTATTTCGCTCCGGCTAACACCCATAATAACAATATTGAGGGC CAGGCGATCCTGTAT CAGAATAAATTCCTGACACTGAACGGCAAAAAATACTATTTCGGCAGCGATTCAAAAGCA ATTACAGGTTGGCAA ACAATTGACGGGAAAAAGTACTATTTTAATCCGAACAATGCGATCGCAGCAACCCATCTG TGTACCATTAATAAC GATAAATACTACTTTAGCTATGACGGCATCCTGCAGAATGGCTATATCACCATTGAACGC AACAACTTTTACTTT GATGCCAACAACGAAAGCAAAATGGTGACCGGTGTTTTTAAAGGCCCTAATGGCTTCGAA TACTTCGCACCAGCG AATACGCATAACAATAACATCGAGGGTCAAGCGATTGTCTACCAGAATAAATTTCTGACT CTGAATGGTAAAAAA TATTACTTCGATAATGATTCAAAAGCCGTGACCGGATGGCAAACTATCGATTCAAAAAAA TACTACTTTAACCTG AACACCGCAGTTGCAGTTACAGGGTGGCAAACCATCGACGGTGAGAAATACTACTTCAAT CTGAATACAGCCGAA GCCGCTACTGGATGGCAGACGATTGACGGAAAACGCTATTATTTTAATACCAACACCTAT ATTGCGAGCACAGGC TATACCATCATTAATGGTAAACACTTCTACTTTAACACGGACGGTATCATGCAAATCGGC GTGTTTAAAGGCCCA GACGGTTTCGAGTACTTTGCGCCAGCAAACACCCACAATAATAACATCGAAGGACAAGCC ATCCTGTATCAAAAC AAATTTCTGACGCTGAATGGCAAAAAATACTACTTCGGTAGTGATAGCAAAGCTGTTACA GGTCTGCGTACCATC GACGGAAAAAAATATTACTTTAATACTAACACGGCAGTGGCAGTGACGGGCTGGCAAACG ATCAACGGGAAAAAA TACTACTTCAACACCAACACGTATATTGCC

F2 amino acid sequence (SEP ID NO:6 ^" )

QNKFLTLNGKKYYFGSDSKAITGWQTIDGKKYYFNPNNAIAATHLCTINNDKYYFSY DGILQNGYITIERNNFYF PANNES!^

DGFEYFAPANTHNNNIEGQAILYQN FLTLNG KYYFGSDS AVTGLRTIDGKKYYF TNTAVAVTGWQTINGKK YYFNTNTYIA

F3 nucleic acid sequence (SEP ID NO:7)

AAAGCCGTGACCGGATGGCAAACTATCGATTCAAAAAAATACTACTTTAACCTGAACACC GCAGTTGCAGTTACA GGGTGGCAAACCATCGACGGTGAGAAATACTACTTCAATCTGAATACAGCCGAAGCCGCT ACTGGATGGCAGACG ATTGACGGAAAACGCTATTATTTTAATACCAACACCTATATTGCGAGCACAGGCTATACC ATCATTAATGGTAAA CACTTCTACTTTAACACGGACGGTATCATGCAAATCGGCGTGTTTAAAGGCCCAGACGGT TTCGAGTACTTTGCG CCAGCAAACACCCACAATAATAACATCGAAGGACAAGCCATCCTGTATCAAAACAAATTT CTGACGCTGAATGGC AAAAAATACTACTTCGGTAGTGATAGCAAAGCTGTTACAGGTCTGCGTACCATCGACGGA AAAAAATATTACTTT AATACTAACACGGCAGTGGCAGTGACGGGCTGGCAAACGATCAACGGGAAAAAATACTAC TTCAACACCAACACG TATATTGCCTCAACCGGCTATACAATTATCAGCGGTAAACACTTTTATTTCAATACAGAT GGGATCATGCAGATC GGAGTTTTCAAAGGACCTGATGGATTCGAGTATTTTGCTCCTGCGAATACCGATGCCAAT AACATTGAGGGACAG GCAATTCGCTATCAGAATCGTTTTCTGTATCTGCACGATAATATTTATTATTTTGGCAAT GATTCCAAAGCGGCA ACCGGTTGGGCCACCATTGATGGTAATCGTTATTATTTTGAGCCGAATACCGCAATGGGT GCCAATGGTTATAAA ACGATTGATAACAAAAACTTTTATTTTCGCAACGGCCTGCCGCAGATTGGCGTATTCAAA GGTCCTAACGGTTTT GAGTACTTCGCTCCAGCCAATACAGATGCAAATAATATCGACGGCCAGGCCATCCGCTAC CAGAACCGCTTCCTG CATCTGCTGGGTAAAATCTATTATTTCGGCAACAACAGCAAAGCGGTAACTGGTTGGCAA ACCATCAATAGCAAA GTGTATTATTTCATGCCGGATACAGCAATGGCAGCAGCCGGTGGTCTGTTTGAAATTGAT GGTGTGATCTATTTC TTTGGTGTGGATGGTGTTAAAGCACCGGGTATTTATGGC F3 amino acid sequence (SEP ID NP:8)

KAVTGWQTljj¾¾S^

HFYFNTDGIMQIGVFKGPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSDSi vAVTGLRTI DGKKYYF NTNTAVAVTGWQTINGKKYYFNTNTYIASTGYTI ISGKHFYFNTDGIMQIGVFKGPDGFEYFAPANTDANNIEGQ AIRYQNRFLYLHDNIYYFGNDSKAATGWATIDGNRYYFEPNTAMGANGYKTIDNKNFYFR NGLPQIGVFKGPNGF EYFAF TDSft¾¾

FGVDGVKAPGIYG ^"* TABLE 1

In addition, polypeptides each containing a potential functional domain of tcdA are described herein. The amino acid sequences of these polypeptides are shown in Table 1.

A fusion protein containing one of the above-mentioned polypeptides and a lipidating sequence at the N-terminus can be produced in an E. coli expression system. The term "lipidating sequence" or "lipid leader sequence" refers to an amino acid sequence that (a) includes a first fragment that is at least 80% (85%, 90%, 95%, or 99%) identical to SP of Ag473 and a second fragment at least 80% (85%, 90%, 95%, or 99%) identical to Domain 1 of Ag473, the first fragment being at the N-terminus of the lipidating sequence, and (b) facilitates lipidation in E. coli of a polypeptide carrying the lipidating sequence at its N- terminus. In the lipidating sequence, the first fragment is linked to the second fragment either directly or via a peptide linker. Preferably, this sequence has a maximum length of 40-100 (e.g., 40-80) amino acids.

Ag473 is a Neisseria Mengitidis lipoprotein consisting of four domains, SP and

Domains 1-3. Shown below is its amino acid sequence (SEQ ID NO: 19) with the four domains identified:

SP: amino acid residues 1-17 (underlined) Domain 1 : amino acid residues 18-40 (highlited)

Domain 2: amino acid residues 41-71 (bold face)

Domain 3: amino acid residues 72-121 (italic)

In one example, the lipidating sequence described herein includes residues 1-40 of 5 SEQ ID NO: 19, i.e., KKLLIAAMMAAALAACSQEAKQEVKEAVQAVESDVKDTA

(SEQ ID NO:20; the Dl domain of Ag473).

The lipidating sequence mentioned above can be linked to a target polypeptide by conventional recombinant technology to form a fusion protein, which is in lipidated form when expressed in E. coli. An example follows. A DNA fragment encoding the lipidating o sequence and a DNA fragment encoding the target polypeptide are inserted into an

expression vector, preferably carrying a strong promoter (e.g., T7, T5, T3, or SP6), to construct an expression plasmid. The strong promoter can be inducible, e.g., by isopropyl β- D-thiogalactoside (IPTG). The expression plasmid is then introduced into an E. coli host strain and positive transformants are cultured under suitable conditions for protein

5 expression. It is preferred that the E. coli host strain be resistant to the toxic effects induced by over-expression of exogenous proteins. Such E. coli strains can be identified/generated by the methods described in US Patent No. 6,361,966. Examples of these E. coli strains include, but are not limited to, C43(DE3) (ECCC B96070445), C41(DE3) (ECCC B96070444), C0214(DE3), DK8(DE3)S (NCIMB 40885), and C2014(DE3) (NCIMB 40884).

o The fusion protein thus expressed can be isolated from the E. coli host cells and its lipidation status can be confirmed via methods known in the art, e.g., immunoblotting with an anti-lipoprotein antibody or mass spectrometry.

Also described is an isolated nucleic acid molecule that contains a sequence encoding the above-described polypeptide or fusion protein or a complementary sequence thereof.5 Examples of the nucleic acid molecule include SEQ ID NO: 1 and its degenerate variants where one or more codons are replaced by other codons encoding the same residues.

The nucleic acid molecule described above can be used to express the polypeptide or fusion protein described herein, or as a DNA vaccine. One can operatively link the nucleic acid molecule to suitable regulatory sequences to generate an expression vector.

o Examples of the vector include a plasmid, cosmid, or viral vector. The vector

includes a nucleic acid in a form suitable for expression of the nucleic acid in a host cell. Preferably the vector includes one or more regulatory sequences operatively linked to the nucleic acid sequence to be expressed. A regulatory sequence includes promoters, enhancers, and other expression control elements (e.g., T7 promoter, cauliflower mosaic virus 35S promoter sequences or polyadenylation signals). Regulatory sequences include those that direct constitutive expression of a nucleotide sequence, as well as tissue-specific regulatory and/or inducible sequences. The design of the expression vector can depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, and the like. The expression vector can be introduced into host cells to produce the polypeptide or fusion protein of this invention. The host cell is, for example, Escherichia coli, B.

pertussis, Bacillus, VERO cell, Haemophilus, fungi, yeast, or CHO cell. The baculovirus expression system can also be used.

A host cell that contains the above-described nucleic acid can be genenerated.

Examples include E. coli cells, insect cells (e.g., using baculovirus expression vectors), plant cells, yeast cells, and mammalian cells. See e.g., Goeddel, (1990) Gene Expression

Technology: Methods in Enzymology 185, Academic Press, San Diego, CA.

A polypeptide, fusion protein, or nucleic acid molecule described herein can be used to prepare an immunogenic composition (e.g., a vaccine) for generating antibodies and/or immune responses against Clostridium difficile in a subject (e.g., a human subject) susceptible to the pathogen or infected with the pathogen. Such compositions can be prepared, e.g., in the manners described below, or by any other methods known in the art.

For example, the composition can contain an effective amount of the polypeptide, fusion protein, or nucleic acid molecule, and a pharmaceutically acceptable carrier such as a phosphate buffered saline, a bicarbonate solution. The composition can also include an adjuvant. The carrier must be "acceptable" in the sense that it is compatible with the active ingredient of the composition and is not deleterious to the subject to be treated. The carrier is selected on the basis of the mode and route of administration and standard pharmaceutical practice. Suitable pharmaceutical carriers and diluents, as well as pharmaceutical necessities for their use, are described in Remington's Pharmaceutical Sciences. An adjuvant, e.g., a cholera toxin, Escherichia coli heat-labile enterotoxin (LT), liposome, immune-stimulating complex (ISCOM), or immunostimulatory sequences oligodeoxynucleotides (ISS-ODN), can also be included in the composition, if necessary. The composition can also include a polymer that facilitates in vivo delivery. See Audran R. et al. Vaccine 21: 1250-5, 2003; and Denis-Mize et al. Cell Immunol, 225: 12-20, 2003. The polypeptide or fusion polypetide described herein can also be used as an adjuvant in an immunogenic composition containing another antigen, or linked to another protein (e.g., an antigen) or polysaccharide to generate a chimeric molecule. For example, the other antigen can be an antigenic protein or fragment thereof from a pathogen such as human papillomavirus (HPV), hepatitis C virus (HCV), Epstein-Barr virus (EBV), herpes simplex virus 1 (HSV-1), herpes simplex virus 2 (HSV-2), cytomegalovirus (CMV), respiratory syncytial virus (RSV), parainfluenza virus type 3 (PIV3), influenza viruses, dengue virus, west Nile virus, Norovirus, and SARS coronavirus.

The immunogenic composition can be formulated as a microparticle preparation, capsule preparation or liposome preparation. In addition, such immunogenic composition can include or be co-administered with a targeting molecule for delivery to specific cells of the immune system or to mucosal surfaces.

In addition, those polypeptides and fusion polypeptides described herein that contain one or more receptor binding sites within the RBD can be used as drug carriers. For example, a drug molecule (e.g., a polypeptide and a small molecule compound) can be conjugated to one of the polypeptides.

Also described herein is a kit for diagnosing Cd infection and associated diseases. The kit contains one or more antibodies that each specifically recongize tcdA. For example, an antibody of the kit can specifically bind to a polypeptide consisting of a sequence selected from the group consisting of SEQ ID NOs: 2, 4, 6, and 8-18. Such an antibody can be generated using methods known in the art. The kit can be used to detect the presence of tcdA in samples (e.g., blood samples) obtained from subjects suspected of being infected with Cd.

Any of the pharmaceutical compositions described above may be administered parenterally, e.g., subcutaneous injection or intramuscular injection. Alternatively, other modes of administration including suppositories and oral formulations may be desirable. For suppositories, binders and carriers may include, for example, polyalkalene glycols or triglycerides. Oral formulations may include normally employed incipients such as pharmaceutical grades of saccharine, cellulose, magnesium carbonate and the like. These compositions take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations or powders.

A "subject" refers to a human and a non-human animal. Examples of a non-human animal include all vertebrates, e.g., mammals, such as non-human primates (particularly higher primates), dog, rodent (e.g., mouse or rat), guinea pig, cat, and non-mammals, such as birds, amphibians, etc. In a preferred embodiment, the subject is a human. In another embodiment, the subject is an experimental animal or animal suitable as a disease model.

The term "treating" as used herein refers to the application or administration of a composition including one or more active agents to a subject, who has a disease, a symptom of the disease, or a predisposition toward the disease, with the purpose to cure, heal, alleviate, relieve, alter, remedy, ameliorate, improve, or affect the disease, the symptoms of the disease, or the predisposition toward the disease. "An effective amount" as used herein refers to the amount of each active agent required to confer therapeutic effect on the subject, either alone or in combination with one or more other active agents. Effective amounts vary, as recognized by those skilled in the art, depending on route of administration, excipient usage, and co-usage with other active agents.

The term "immune response" or "immunogenic response" refers to any reaction of the immune system in response to an antigen in a subject. Examples of an immune response in a vertebrate include, but are not limited to, antibody production, induction of cell-mediated immunity, and complement activation.

An "antigen" refers to a molecule containing one or more epitopes that will stimulate a host's immune system to make an antigen-specific immune response. The term "antigen" is used interchangeably with "immunogen." The term "epitope" as used herein refers to the site on an antigen to which a specific antibody molecule or a T-cell receptor binds. The term is used herein interchangeably with "antigenic determinant" or "antigenic determinant site."

An "antibody" refers to an immunoglobulin molecule or at least one immunologically active portion of an immunoglobulin molecule that has a specific amino acid sequence and binds only to an antigen or a group of antigens that are closely related. Examples of antibodies include IgG, IgM, IgA, IgD and IgE. Examples of immunologically active portions of immunoglobulin molecules include Fab and F(ab)'.sub.2 fragments which can be generated by treating the antibody with an enzyme such as pepsin. An antibody can be a monoclonal antibody or a polyclonal antibody.

An "adjuvant" refers to a substance added to an immunogenic composition, such as a vaccine, that while may or may not having any specific antigenic effect in itself, can stimulate the immune system and increase the immune response to the immunogenic composition. Examples of adjuvants include, but are not limited to, alum-precipitate, Freund's complete adjuvant, Freund's incomplete adjuvant, monophosphoryl-lipid A/trehalose dicorynomycolate adjuvant, water in oil emulsion containing Corynebacterium parvum and tRNA, and other substances that accomplish the task of increasing immune response by mimicking specific sets of evolutionarily conserved molecules including liposomes, lipopolysaccharide (LPS), molecular cages for antigen, components of bacterial cell walls, and endocytosed nucleic acids such as double-stranded RNA, single-stranded DNA, and unmethylated CpG dinucleotide-containing DNA. Other examples include cholera toxin, E. coli heat-labile enterotoxin, liposome, immune-stimulating complex (ISCOM),

immunostimulatory sequences oligodeoxynucleotide, and aluminum hydroxide.

The specific example below is to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. Without further elaboration, it is believed that one skilled in the art can, based on the description herein, utilize the present disclosure to its fullest extent. All publications cited herein are incorporated herein by reference in their entirety.

Materials and Methods

(1) Consensus sequence analysis

We rationally designed a sequence containing the C-terminal binding domain of C. difficile toxin A, a highly conserved and repetitive region, from NCBI database based on strain VPI10463 by a sequence alignment tool, i.e., Vector NTI Advance 11.5. This sequence as shown in FIG 1 was analyzed by an online software for detection and alignment of repetitive protein sequences (found at the world wide web at ebi.ac.uk /Tools/pfa).

(2) Cloning and plasmid construction

The nucleotide sequence of TcdA RBD was optimized with E. coli expression codons and chemically synthesized for cloning, i.e., SEQ ID NO:l . In order to clone three fragments of TcdA RBD (RBD-F1, RBD-F2, and RBD-F3), PCR was used to amplify their coding regions with the following primes: Fl forward primer = TAA CAT ATG GGA TCC TTT AAT AGC GAG AAT GAA (SEQ ID NO:37), Fl reverse primer = ATT CTC GAG TGC TTT TGAATC GCT GCC (SEQ ID NO:38), F2 forward = TAA CAT ATG GGA TCC GCC GAA GCA GCC ACC GGC (SEQ ID NO:39), F2 reverse primer = ATT CTC GAG GGC AAT ATA CGT GTT GGT (SEQ ID NO:40), F3 forward primer = TAA CAT ATG GGA TCC AAA GCC GTG ACC GGA TGG (SEQ ID NO:41), F3 reverse primer = ATT CTC GAG GCC ATAAAT ACC CGG TGC (SEQ ID NO:42). RBD-F1, RBD-F2, RBD-F3, and RBD were inserted into pET-22b vector (Novagen) by Ndel and Xhol restriction enzyme sites. The constructs were transformed into E. coli BL21 (+) RIL (Novagen) and JM109 (DE3) (Agilent technologies), respectively. RBD was fused with a lipid signal sequence at its 5 '-end to obtain another construct, rlipo- RBD. This plasmid was transformed into E. coli C43 (DE3) (Lucigen).

The constructs and the sequences of the cloned inserts are described in more detail below (Underlined - restriction enzyme site; Regular font - RBD, Fl, F2, or F3 sequence; Boldfaced - lipid leader sequence (LLS)).

A plasmid (pET22b_rRBD) was constructed by inserting a BamHI-RBD-XhoI frament into cloning plasmid pET-22b. See Fig. 2.

Ndel-BamHI-RBD-XhoI (SEQ ID NO: 21)

CATATGGGATCCTTTAATAGCGAGAATGAACTGGATCGTGATCATCTGGGCTTCAAAATC ATCGATAATAAAACC TATTATTATGATGAAGATAGCAAACTGGTGAAAGGCCTGATTAACATTAACAACAGCCTG TTTTACTTCGATCCG ATTGAAAGCAATCTGGTTACCGGTTGGCAGACCATTAACGGCAAAAAATATTATTTTGAT ATTAATACCGGTGCA GCCAGCACCAGCTATAAAATTATCAACGGCAAGCATTTCTATTTCAATAATAATGGCGTG ATGCAGCTGGGCGTT TTTAAAGGTCCGGATGGTTTTGAATATTTTGCACCGGCAAATACCCAGAACAATAATATT GAAGGTCAGGCCATT GTGTATCAGAGCAAATTTCTGACCCTGAACGGTAAAAAATACTACTTCGACAACGATAGC AAAGCAGTGACCGGT TGGCGCATTATTAACAACGAGAAATATTATTTCAATCCGAATAACGCCATTGCAGCAGTT GGTCTGCAGGTTATT

GACAACAATAAATATTACTTTAACCCGGACACCGCCATTATTAGCAAAGGCTGGCAG ACCGTTAATGGTAGCCGT TATTATTTCGATACCGATACCGCGATTGCCTTTAATGGCTATAAAACCATCGACGGCAAA CACTTCTATTTTGAT AGCGATTGCGTGGTGAAAATTGGTGTTTTTAGCGGTAGCAACGGCTTTGAATACTTTGCC CCTGCCAATACCTAC AACAACAACATCGAAGGCCAGGCAATCGTTTATCAGTCAAAATTCCTGACGCTGAATGGG AAAAAATATTACTTT GACAATAACAGCAAAGCCGTTACGGGATGGCAGACAATTGATAGCAAAAAATACTACTTC AATACCAATACCGCA GAAGCAGCAACAGGTTGGCAGACGATCGATGGTAAAAAATATTATTTCAACACGAACACA GCCGAAGCAGCCACC GGCTGGCAAACCATTGATGGAAAAAAATATTACTTCAATACAAATACGAGCATTGCCAGC ACCGGTTATACCATT ATCAACGGCAAATATTTCTACTTCAACACCGATGGCATTATGCAGATTGGTGTGTTCAAA GTGCCGAATGGCTTT GAGTATTTCGCTCCGGCTAACACCCATAATAACAATATTGAGGGCCAGGCGATCCTGTAT CAGAATAAATTCCTG ACACTGAACGGCAAAAAATACTATTTCGGCAGCGATTCAAAAGCAATTACAGGTTGGCAA ACAATTGACGGGAAA AAGTACTATTTTAATCCGAACAATGCGATCGCAGCAACCCATCTGTGTACCATTAATAAC GATAAATACTACTTT AGCTATGACGGCATCCTGCAGAATGGCTATATCACCATTGAACGCAACAACTTTTACTTT GATGCCAACAACGAA AGCAAAATGGTGACCGGTGTTTTTAAAGGCCCTAATGGCTTCGAATACTTCGCACCAGCG AATACGCATAACAAT AACATCGAGGGTCAAGCGATTGTCTACCAGAATAAATTTCTGACTCTGAATGGTAAAAAA TATTACTTCGATAAT GATTCAAAAGCCGTGACCGGATGGCAAACTATCGATTCAAAAAAATACTACTTTAACCTG AACACCGCAGTTGCA GTTACAGGGTGGCAAACCATCGACGGTGAGAAATACTACTTCAATCTGAATACAGCCGAA GCCGCTACTGGATGG CAGACGATTGACGGAAAACGCTATTATTTTAATACCAACACCTATATTGCGAGCACAGGC TATACCATCATTAAT GGTAAACACTTCTACTTTAACACGGACGGTATCATGCAAATCGGCGTGTTTAAAGGCCCA GACGGTTTCGAGTAC TTTGCGCCAGCAAACACCCACAATAATAACATCGAAGGACAAGCCATCCTGTATCAAAAC AAATTTCTGACGCTG AATGGCAAAAAATACTACTTCGGTAGTGATAGCAAAGCTGTTACAGGTCTGCGTACCATC GACGGAAAAAAATAT TACTTTAATACTAACACGGCAGTGGCAGTGACGGGCTGGCAAACGATCAACGGGAAAAAA TACTACTTCAACACC AACACGTATATTGCCTCAACCGGCTATACAATTATCAGCGGTAAACACTTTTATTTCAAT ACAGATGGGATCATG CAGATCGGAGTTTTCAAAGGACCTGATGGATTCGAGTATTTTGCTCCTGCGAATACCGAT GCCAATAACATTGAG GGACAGGCAATTCGCTATCAGAATCGTTTTCTGTATCTGCACGATAATATTTATTATTTT GGCAATGATTCCAAA GCGGCAACCGGTTGGGCCACCATTGATGGTAATCGTTATTATTTTGAGCCGAATACCGCA ATGGGTGCCAATGGT TATAAAACGATTGATAACAAAAACTTTTATTTTCGCAACGGCCTGCCGCAGATTGGCGTA TTCAAAGGTCCTAAC GGTTTTGAGTACTTCGCTCCAGCCAATACAGATGCAAATAATATCGACGGCCAGGCCATC CGCTACCAGAACCGC TTCCTGCATCTGCTGGGTAAAATCTATTATTTCGGCAACAACAGCAAAGCGGTAACTGGT TGGCAAACCATCAAT AGCAAAGTGTATTATTTCATGCCGGATACAGCAATGGCAGCAGCCGGTGGTCTGTTTGAA ATTGATGGTGTGATC TATTTCTTTGGTGTGGATGGTGTTAAAGCACCGGGTATTTATGGCCTCGAG

Amino acid sequence encoded by SEQ ID NO: 21 (SEQ ID NO:22)

H GSFNSENELDRDHLGFKIIDN TYYYDEDS LVKGLININNSLFYFDPIESNLVTGWQTINGKKYYFDINTGA ASTSYKIINGKHFYFNNNGVMQLGVFKGPDGFEYFAPANTQNNNIEGQAIVYQSKFLTLN GKKYYFDNDSKAVTG WRIINNEKYYFNPNNAIAAVGLQVIDNNKYYFNPDTAIISKGWQTVNGSRYYFDTDTAIA FNGYKTIDG HFYFD SDCVVKIGVFSGSNGFEYFAPANTYNNNIEGQAIVYQSKFLTLNGKKYYFDNNSKAVTGW QTIDSKKYYFNTNTA EAATG QTIDGKKYYFNTNTAEAATG QTIDGKKYYFNTNTSIASTGYTIINGKYFYFNTDGIMQIGVFKVPNGF EYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSDSKAITGWQTIDGKKYYFNPNNAI AATHLCTINNDKYYF SYDGILQNGYITIERNNFYFDANNESK VTGVFKGPNGFEYFAPANTHNNNIEGQAIVYQNKFLTLNGKKYYFDN DSKAVTGWQTIDSKKYYFNLNTAVAVTGWQTIDGEKYYFNLNTAEAATGWQTIDGKRYYF NTNTYIASTGYTIIN GKHFYFNTDGIMQIGVFKGPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSD S AVTGLRTIDGKKY YFNTNTAVAVTGWQTINGKKYYFNTNTYIASTGYTIISGKHFYFNTDGIMQIGVFKGPDG FEYFAPANTDANNIE GQAIRYQNRFLYLHDNIYYFGNDSKAATG ATIDGNRYYFEPNTAMGANGYKTIDNKNFYFRNGLPQIGVFKGPN GFEYFAPANTDANNIDGQAIRYQNRFLHLLGKIYYFGNNSKAVTG QTINSKVYYFMPDTA AAAGGLFEIDGVI YFFGVDGVKAPGIYGLE

A plasmid (pET22b_rlipo-RBD) was constracted by inserting a Ndel-LLS-BamHI- RBD-XhoI fragment into cloning plasmid pET-22b. See Fig. 2.

Ndel-LLS-BamHI-RBD-XhoI (SEQ ID NO:23)

CJVTATGAAAAAATTATTG-M!TGCCGC-^

GTTAAGGAAGCGGTTCAAGCCGTTGAGTCCGATGTTAAAGACACTGCGGGATCCTTTAAT AGCGAGAATGAACTG

GATCGTGATCATCTGGGCTTCAAAATCATCGATAATAAAACCTATTATTATGATGAA GATAGCAAACTGGTGAAA GGCCTGATTAACATTAACAACAGCCTGTTTTACTTCGATCCGATTGAAAGCAATCTGGTT ACCGGTTGGCAGACC ATTAACGGCAAAAAATATTATTTTGATATTAATACCGGTGCAGCCAGCACCAGCTATAAA ATTATCAACGGCAAG CATTTCTATTTCAATAATAATGGCGTGATGCAGCTGGGCGTTTTTAAAGGTCCGGATGGT TTTGAATATTTTGCA CCGGCAAATACCCAGAACAATAATATTGAAGGTCAGGCCATTGTGTATCAGAGCAAATTT CTGACCCTGAACGGT AAAAAATACTACTTCGACAACGATAGCAAAGCAGTGACCGGTTGGCGCATTATTAACAAC GAGAAATATTATTTC AATCCGAATAACGCCATTGCAGCAGTTGGTCTGCAGGTTATTGACAACAATAAATATTAC TTTAACCCGGACACC GCCATTATTAGCAAAGGCTGGCAGACCGTTAATGGTAGCCGTTATTATTTCGATACCGAT ACCGCGATTGCCTTT AATGGCTATAAAACCATCGACGGCAAACACTTCTATTTTGATAGCGATTGCGTGGTGAAA ATTGGTGTTTTTAGC GGTAGCAACGGCTTTGAATACTTTGCCCCTGCCAATACCTACAACAACAACATCGAAGGC CAGGCAATCGTTTAT CAGTCAAAATTCCTGACGCTGAATGGGAAAAAATATTACTTTGACAATAACAGCAAAGCC GTTACGGGATGGCAG ACAATTGATAGCAAAAAATACTACTTCAATACCAATACCGCAGAAGCAGCAACAGGTTGG CAGACGATCGATGGT AAAAAATATTATTTCAACACGAACACAGCCGAAGCAGCCACCGGCTGGCAAACCATTGAT GGAAAAAAATATTAC TTCAATACAAATACGAGCATTGCCAGCACCGGTTATACCATTATCAACGGCAAATATTTC TACTTCAACACCGAT GGCATTATGCAGATTGGTGTGTTCAAAGTGCCGAATGGCTTTGAGTATTTCGCTCCGGCT AACACCCATAATAAC AATATTGAGGGCCAGGCGATCCTGTATCAGAATAAATTCCTGACACTGAACGGCAAAAAA TACTATTTCGGCAGC GATTCAAAAGCAATTACAGGTTGGCAAACAATTGACGGGAAAAAGTACTATTTTAATCCG AACAATGCGATCGCA GCAACCCATCTGTGTACCATTAATAACGATAAATACTACTTTAGCTATGACGGCATCCTG CAGAATGGCTATATC ACCATTGAACGCAACAACTTTTACTTTGATGCCAACAACGAAAGCAAAATGGTGACCGGT GTTTTTAAAGGCCCT AATGGCTTCGAATACTTCGCACCAGCGAATACGCATAACAATAACATCGAGGGTCAAGCG ATTGTCTACCAGAAT AAATTTCTGACTCTGAATGGTAAAAAATATTACTTCGATAATGATTCAAAAGCCGTGACC GGATGGCAAACTATC GATTCAAAAAAATACTACTTTAACCTGAACACCGCAGTTGCAGTTACAGGGTGGCAAACC ATCGACGGTGAGAAA TACTACTTCAATCTGAATACAGCCGAAGCCGCTACTGGATGGCAGACGATTGACGGAAAA CGCTATTATTTTAAT ACCAACACCTATATTGCGAGCACAGGCTATACCATCATTAATGGTAAACACTTCTACTTT AACACGGACGGTATC ATGCAAATCGGCGTGTTTAAAGGCCCAGACGGTTTCGAGTACTTTGCGCCAGCAAACACC CACAATAATAACATC GAAGGACAAGCCATCCTGTATCAAAACAAATTTCTGACGCTGAATGGCAAAAAATACTAC TTCGGTAGTGATAGC AAAGCTGTTACAGGTCTGCGTACCATCGACGGAAAAAAATATTACTTTAATACTAACACG GCAGTGGCAGTGACG GGCTGGCAAACGATCAACGGGAAAAAATACTACTTCAACACCAACACGTATATTGCCTCA ACCGGCTATACAATT ATCAGCGGTAAACACTTTTATTTCAATACAGATGGGATCATGCAGATCGGAGTTTTCAAA GGACCTGATGGATTC GAGTATTTTGCTCCTGCGAATACCGATGCCAATAACATTGAGGGACAGGCAATTCGCTAT CAGAATCGTTTTCTG TATCTGCACGATAATATTTATTATTTTGGCAATGATTCCAAAGCGGCAACCGGTTGGGCC ACCATTGATGGTAAT CGTTATTATTTTGAGCCGAATACCGCAATGGGTGCCAATGGTTATAAAACGATTGATAAC AAAAACTTTTATTTT CGCAACGGCCTGCCGCAGATTGGCGTATTCAAAGGTCCTAACGGTTTTGAGTACTTCGCT CCAGCCAATACAGAT GCAAATAATATCGACGGCCAGGCCATCCGCTACCAGAACCGCTTCCTGCATCTGCTGGGT AAAATCTATTATTTC GGCAACAACAGCAAAGCGGTAACTGGTTGGCAAACCATCAATAGCAAAGTGTATTATTTC ATGCCGGATACAGCA ATGGCAGCAGCCGGTGGTCTGTTTGAAATTGATGGTGTGATCTATTTCTTTGGTGTGGAT GGTGTTAAAGCACCG GGTATTTATGGCCTCGAG

Amino acid sequence encoded by SEQ ID NO:23 (SEQ ID NO:24)

HMKKI-LIAAMMAAAI-^^

GLININNSLFYFDPIESNLVTGWQTINGK YYFDINTGAASTSYKIINGKHFYFNNNGV QLGVFKGPDGFEYFA PANTQNNNIEGQAIVYQSKFLTLNG YYFDNDS AVTGWRIINNEKYYFNPNNAIAAVGLQVIDNN YYFNPDT AIISKGWQTVNGSRYYFDTDTAIAFNGYKTIDGKHFYFDSDCVVKIGVFSGSNGFEYFAP ANTYNNNIEGQAIVY QSKFLTLNGKKYYFDNNSKAVTG QTIDSKKYYFNTNTAEAATG QTIDGKKYYFNTNTAEAATGWQTIDGKKYY FNTNTSIASTGYTIINGKYFYFNTDGIMQIGVFKVPNGFEYFAPANTHNNNIEGQAILYQ NKFLTLNGKKYYFGS DSKAITGWQTIDGKKYYFNPNNAIAATHLCTINND YYFSYDGILQNGYITIERNNFYFDANNESK VTGVFKGP NGFEYFAPANTHNN IEGQAIVYQNKFLTLNGKKYYFDNDSKAVTG QTIDSiCKYYFNLNTAVAVTGWQTIDGEK YYFNLNTAEAATGWQTIDGKRYYFNTNTYIASTGYTIINGKHFYFNTDGI QIGVFKGPDGFEYFAPANTHNNNI EGQAILYQNKFLTLNGKKYYFGSDSKAVTGLRTIDGKKYYFNTNTAVAVTGWQTINGKKY YFNTNTYIASTGYTI ISGKHFYFNTDGI QIGVFKGPDGFEYFAPANTDANNIEGQAIRYQNRFLYLHDNIYYFGNDSKAATGWATIDG N RYYFEPNTA GANGYKTIDNKNFYFRNGLPQIGVFKGPNGFEYFAPANTDANNIDGQAIRYQNRFLHLLG KIYYF GNNSKAVTGWQTINSKVYYFMPDTAMAAAGGLFEIDGVIYFFGVDGVKAPGIYGLE

A plasmid (pET22b_Fl) was constructed by inserting a Ndel-Fl-Xhol fragment into cloning plasmid pET-22b.

Ndel-BamHI-F 1 -Xhol (SEQ ID NO:25)

CATATGGGATCCTTTAATAGCGAGAATGAACTGGATCGTGATCATCTGGGCTTCAAAATC ATCGATAATAAAACC TATTATTATGATGAAGATAGCAAACTGGTGAAAGGCCTGATTAACATTAACAACAGCCTG TTTTACTTCGATCCG ATTGAAAGCAATCTGGTTACCGGTTGGCAGACCATTAACGGCAAAAAATATTATTTTGAT ATTAATACCGGTGCA GCCAGCACCAGCTATAAAATTATCAACGGCAAGCATTTCTATTTCAATAATAATGGCGTG ATGCAGCTGGGCGTT TTTAAAGGTCCGGATGGTTTTGAATATTTTGCACCGGCAAATACCCAGAACAATAATATT GAAGGTCAGGCCATT GTGTATCAGAGCAAATTTCTGACCCTGAACGGTAAAAAATACTACTTCGACAACGATAGC AAAGCAGTGACCGGT TGGCGCATTATTAACAACGAGAAATATTATTTCAATCCGAATAACGCCATTGCAGCAGTT GGTCTGCAGGTTATT GACAACAATAAATATTACTTTAACCCGGACACCGCCATTATTAGCAAAGGCTGGCAGACC GTTAATGGTAGCCGT TATTATTTCGATACCGATACCGCGATTGCCTTTAATGGCTATAAAACCATCGACGGCAAA CACTTCTATTTTGAT AGCGATTGCGTGGTGAAAATTGGTGTTTTTAGCGGTAGCAACGGCTTTGAATACTTTGCC CCTGCCAATACCTAC AACAACAACATCGAAGGCCAGGCAATCGTTTATCAGTCAAAATTCCTGACGCTGAATGGG AAAAAATATTACTTT GACAATAACAGCAAAGCCGTTACGGGATGGCAGACAATTGATAGCAAAAAATACTACTTC AATACCAATACCGCA GAAGCAGCAACAGGTTGGCAGACGATCGATGGTAAAAAATATTATTTCAACACGAACACA GCCGAAGCAGCCACC GGCTGGCAAACCATTGATGGAAAAAAATATTACTTCAATACAAATACGAGCATTGCCAGC ACCGGTTATACCATT ATCAACGGCAAATATTTCTACTTCAACACCGATGGCATTATGCAGATTGGTGTGTTCAAA GTGCCGAATGGCTTT GAGTATTTCGCTCCGGCTAACACCCATAATAACAATATTGAGGGCCAGGCGATCCTGTAT CAGAATAAATTCCTG ACACTGAACGGCAAAAAATACTATTTCGGCAGCGATTCAAAAGCACTCGAG

Amino acid sequence encoded by SEQ ID NO:25 (SEQ ID NO:26)

HMGSFNSENELDRDHLGFKI IDNKTYYYDEDSKLVKGLININNSLFYFDPIESNLVTGWQTINGKKYYFDINTGA ASTSYKIINGKHFYFNNNGVMQLGVFKGPDGFEYFAPANTQNNNIEGQAIVYQSKFLTLN GKKYYFDNDSKAVTG WRIINNEKYYFNPNNAIAAVGLQVIDNNKYYFNPDTAIISKGWQTVNGSRYYFDTDTAIA FNGYKTIDGKHFYFD SDCVVKIGVFSGSNGFEYFAPANTYNNNIEGQAIVYQSKFLTLNGKKYYFDNNSKAVTGW QTIDSKKYYFNTNTA EAATGWQTIDGKKYYFNTNTAEAATGWQTIDGKKYYFNTNTSIASTGYTIINGKYFYFNT DGIMQIGVFKVPNGF EYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSDSKALE

A plasmid (pET22b_lipo-Fl) was constructed by inserting a Ndel-LLS-BamHI-F l- Xhol fragment into cloning plasmid pET-22b. Ndel-LLS-BamHI-Fl-XhoI (SEQ ID NO:27)

CATATGA¾AAAA.TTATT SATTGCCGCAATGA,TGGCGGCTGCCTTGGCAGCTTGTTCGCAAGAAGCCAAACAGGR,G GTTAAGGAAGCGGTTCAAGCCGTTGAGTCCGATGTTAAA.GACACTGCGGGATCCT T T AATAGCGAGAATGAACT G GATCGTGATCATCTGGGCTTCAAAATCATCGATAATAAAACCTATTATTATGATGAAGAT AGCAAACTGGTGAAA GGCCTGATTAACATTAACAACAGCCTGTTTTACTTCGATCCGATTGAAAGCAATCTGGTT ACCGGTTGGCAGACC ATTAACGGCAAAAAATATTATTTTGATATTAATACCGGTGCAGCCAGCACCAGCTATAAA ATTATCAACGGCAAG CATTTCTATTTCAATAATAATGGCGTGATGCAGCTGGGCGTTTTTAAAGGTCCGGATGGT TTTGAATATTTTGCA CCGGCAAATACCCAGAACAATAATATTGAAGGTCAGGCCATTGTGTATCAGAGCAAATTT CTGACCCTGAACGGT AAAAAATACTACTTCGACAACGATAGCAAAGCAGTGACCGGTTGGCGCATTATTAACAAC GAGAAATATTATTTC AATCCGAATAACGCCATTGCAGCAGTTGGTCTGCAGGTTATTGACAACAATAAATATTAC TTTAACCCGGACACC GCCATTATTAGCAAAGGCTGGCAGACCGTTAATGGTAGCCGTTATTATTTCGATACCGAT ACCGCGATTGCCTTT AATGGCTATAAAACCATCGACGGCAAACACTTCTATTTTGATAGCGATTGCGTGGTGAAA ATTGGTGTTTTTAGC GGTAGCAACGGCTTTGAATACTTTGCCCCTGCCAATACCTACAACAACAACATCGAAGGC CAGGCAATCGTTTAT CAGTCAAAATTCCTGACGCTGAATGGGAAAAAATATTACTTTGACAATAACAGCAAAGCC GTTACGGGATGGCAG ACAATTGATAGCAAAAAATACTACTTCAATACCAATACCGCAGAAGCAGCAACAGGTTGG CAGACGATCGATGGT AAAAAATATTATTTCAACACGAACACAGCCGAAGCAGCCACCGGCTGGCAAACCATTGAT GGAAAAAAATATTAC TTCAATACAAATACGAGCATTGCCAGCACCGGTTATACCATTATCAACGGCAAATATTTC TACTTCAACACCGAT GGCATTATGCAGATTGGTGTGTTCAAAGTGCCGAATGGCTTTGAGTATTTCGCTCCGGCT AACACCCATAATAAC AATATTGAGGGCCAGGCGATCCTGTATCAGAATAAATTCCTGACACTGAACGGCAAAAAA TACTATTTCGGCAGC GATTCAAAAGCACTCGAG

Amino acid sequence encoded by SEQ ID NO:27 (SEQ ID NO:28)

HMiq LLIAA lMftAAIAACSQEAKQEVKEAVC^VESDVKDTAGjFNSENELDRDHLGFKI IDNKTYYYDEDSKLVK

GLININNSLFYFDPIESNLVTGWQTINGKKYYFDINTGAASTSYKI INGKHFYFNNNGVMQLGVFKGPDGFEYFA PANTQNNNIEGQAIVYQSKFLTLNGKKYYFDNDSKAVTG RI INNEKYYFNPNNAIAAVGLQVIDNNKYYFNPDT AIISKGWQTVNGSRYYFDTDTAIAFNGYKTIDGKHFYFDSDCVVKIGVFSGSNGFEYFAP ANTYNNNIEGQAIVY QSKFLTLNGKKYYFDNNSKAVTGWQTIDSKKYYFNTNTAEAATGWQTIDGKKYYFNTNTA EAATGWQTIDG KYY FNTNTSIASTGYTIINGKYFYFNTDGIMQIGVF VPNGFEYFAPANTHNNNIEGQAILYQNKFLTLNGK YYFGS DSKALE

A plasmid (pET22b_F2) was constructed by inserting a NdeI-F2-XhoI fragment into cloning plasmid pET-22b.

NdeI-BamHI-F2-XhoI (SEQ ID NO:29)

CATATGGGATCCGCCGAAGCAGCCACCGGCTGGCAAACCATTGATGGAAAAAAATATTAC TTCAATACAAATACG AGCATTGCCAGCACCGGTTATACCATTATCAACGGCAAATATTTCTACTTCAACACCGAT GGCATTATGCAGATT GGTGTGTTCAAAGTGCCGAATGGCTTTGAGTATTTCGCTCCGGCTAACACCCATAATAAC AATATTGAGGGCCAG GCGATCCTGTATCAGAATAAATTCCTGACACTGAACGGCAAAAAATACTATTTCGGCAGC GATTCAAAAGCAATT ACAGGTTGGCAAACAATTGACGGGAAAAAGTACTATTTTAATCCGAACAATGCGATCGCA GCAACCCATCTGTGT ACCATTAATAACGATAAATACTACTTTAGCTATGACGGCATCCTGCAGAATGGCTATATC ACCATTGAACGCAAC AACTTTTACTTTGATGCCAACAACGAAAGCAAAATGGTGACCGGTGTTTTTAAAGGCCCT AATGGCTTCGAATAC TTCGCACCAGCGAATACGCATAACAATAACATCGAGGGTCAAGCGATTGTCTACCAGAAT AAATTTCTGACTCTG AATGGTAAAAAATATTACTTCGATAATGATTCAAAAGCCGTGACCGGATGGCAAACTATC GATTCAAAAAAATAC TACTTTAACCTGAACACCGCAGTTGCAGTTACAGGGTGGCAAACCATCGACGGTGAGAAA TACTACTTCAATCTG AATACAGCCGAAGCCGCTACTGGATGGCAGACGATTGACGGAAAACGCTATTATTTTAAT ACCAACACCTATATT GCGAGCACAGGCTATACCATCATTAATGGTAAACACTTCTACTTTAACACGGACGGTATC ATGCAAATCGGCGTG TTTAAAGGCCCAGACGGTTTCGAGTACTTTGCGCCAGCAAACACCCACAATAATAACATC GAAGGACAAGCCATC CTGTATCAAAACAAATTTCTGACGCTGAATGGCAAAAAATACTACTTCGGTAGTGATAGC AAAGCTGTTACAGGT CTGCGTACCATCGACGGAAAAAAATATTACTTTAATACTAACACGGCAGTGGCAGTGACG GGCTGGCAAACGATC AACGGGAAAAAATACTACTTCAACACCAACACGTATATTGCCCTCGAG

Amino acid sequence encoded by SEQ ID NO:29 (SEQ ID NO:30)

HMGSAEAATGWQTIDGKKYYFNTNTSIASTGYTI INGKYFYFNTDGIMQIGVFiCVPNGFEYFAPA THNNNIEGQ AILYQNKFLTLNGKKYYFGSDSKAITGWQTIDGKKYYFNPNNAIAATHLCTINNDKYYFS YDGILQNGYITIERN NFYFDANNES VTGVFKGPNGFEYFAPANTHNNNIEGQAIVYQNKFLTLNGKKYYFDNDSKAVTGWQTIDS KKY YFNLNTAVAVTGWQTIDGEKYYFNLNTAEAATGWQTIDGKRYYFNTNTYIASTGYTIING KHFYFNTDGIMQIGV FKGPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSDSKAVTGLRTIDGKKYY FNTNTAVAVTG QTI NGKKYYFNTNTYIALE

A plasmid (pET22b_lipo-F2) was constructed by inserting a NdeI-LLS-BamHI-F2- Xhol fragment into cloning plasmid pET-22b.

NdeI-LLS-BamHI-F2-XhoI (SEQ ID NO:31)

CMMVGAAAAAATTAT^

GTTAAGGAAGCGGTTCAAGCCGTTGAGTCCGATGTTAAAGACACTGCGGGATCCGCC GAAGCAGCCACCGGCTGG

CAAACCATTGATGGAAAAAAATATTACTTCAATACAAATACGAGCATTGCCAGCACC GGTTATACCATTATCAAC GGCAAATATTTCTACTTCAACACCGATGGCATTATGCAGATTGGTGTGTTCAAAGTGCCG AATGGCTTTGAGTAT TTCGCTCCGGCTAACACCCATAATAACAATATTGAGGGCCAGGCGATCCTGTATCAGAAT AAATTCCTGACACTG AACGGCAAAAAATACTATTTCGGCAGCGATTCAAAAGCAATTACAGGTTGGCAAACAATT GACGGGAAAAAGTAC TATTTTAATCCGAACAATGCGATCGCAGCAACCCATCTGTGTACCATTAATAACGATAAA TACTACTTTAGCTAT GACGGCATCCTGCAGAATGGCTATATCACCATTGAACGCAACAACTTTTACTTTGATGCC AACAACGAAAGCAAA ATGGTGACCGGTGTTTTTAAAGGCCCTAATGGCTTCGAATACTTCGCACCAGCGAATACG CATAACAATAACATC GAGGGTCAAGCGATTGTCTACCAGAATAAATTTCTGACTCTGAATGGTAAAAAATATTAC TTCGATAATGATTCA AAAGCCGTGACCGGATGGCAAACTATCGATTCAAAAAAATACTACTTTAACCTGAACACC GCAGTTGCAGTTACA GGGTGGCAAACCATCGACGGTGAGAAATACTACTTCAATCTGAATACAGCCGAAGCCGCT ACTGGATGGCAGACG ATTGACGGAAAACGCTATTATTTTAATACCAACACCTATATTGCGAGCACAGGCTATACC ATCATTAATGGTAAA CACTTCTACTTTAACACGGACGGTATCATGCAAATCGGCGTGTTTAAAGGCCCAGACGGT TTCGAGTACTTTGCG CCAGCAAACACCCACAATAATAACATCGAAGGACAAGCCATCCTGTATCAAAACAAATTT CTGACGCTGAATGGC AAAAAATACTACTTCGGTAGTGATAGCAAAGCTGTTACAGGTCTGCGTACCATCGACGGA AAAAAATATTACTTT AATACTAACACGGCAGTGGCAGTGACGGGCTGGCAAACGATCAACGGGAAAAAATACTAC TTCAACACCAACACG TATATTGCCCTCGAG

Amino acid sequence encoded by SEQ ID NO:31 (SEQ ID NO:32)

H KKLLIAftM AAALAACSQEAKQ

GKYFYFNTDGIMQIGVFKVPNGFEYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYF GSDSKAITGWQTIDGKKY YFNPNNAIAATHLCTINNDKYYFSYDGILQNGYITIERNNFYFDANNES VTGVFKGPNGFEYFAPANTHNNNI EGQAIVYQNKFLTLNGKKYYFDNDSKAVTGWQTIDS KYYFNLNTAVAVTG QTIDGEKYYFNLNTAEAATGWQT IDGKRYYFNTNTYIASTGYTIINGKHFYF TDGIMQIGVF GPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNG KKYYFGSDSKAVTGLRTIDGKKYYFNTNTAVAVTGWQTINGKKYYFNTNTYIALE

A plasmid (pET22b_F3) was constructed by inserting a NdeI-F3-XhoI fragment into a standard cloning plasmid pET-22b.

NdeI-BamHI-F3-XhoI (SEQ ID NO:33)

CATATGGGATCCAAAGCCGTGACCGGATGGCAAACTATCGATTCAAAAAAATACTACTTT AACCTGAACACCGCA GTTGCAGTTACAGGGTGGCAAACCATCGACGGTGAGAAATACTACTTCAATCTGAATACA GCCGAAGCCGCTACT GGATGGCAGACGATTGACGGAAAACGCTATTATTTTAATACCAACACCTATATTGCGAGC ACAGGCTATACCATC ATTAATGGTAAACACTTCTACTTTAACACGGACGGTATCATGCAAATCGGCGTGTTTAAA GGCCCAGACGGTTTC GAGTACTTTGCGCCAGCAAACACCCACAATAATAACATCGAAGGACAAGCCATCCTGTAT CAAAACAAATTTCTG ACGCTGAATGGCAAAAAATACTACTTCGGTAGTGATAGCAAAGCTGTTACAGGTCTGCGT ACCATCGACGGAAAA AAATATTACTTTAATACTAACACGGCAGTGGCAGTGACGGGCTGGCAAACGATCAACGGG AAAAAATACTACTTC AACACCAACACGTATATTGCCTCAACCGGCTATACAATTATCAGCGGTAAACACTTTTAT TTCAATACAGATGGG ATCATGCAGATCGGAGTTTTCAAAGGACCTGATGGATTCGAGTATTTTGCTCCTGCGAAT ACCGATGCCAATAAC ATTGAGGGACAGGCAATTCGCTATCAGAATCGTTTTCTGTATCTGCACGATAATATTTAT TATTTTGGCAATGAT TCCAAAGCGGCAACCGGTTGGGCCACCATTGATGGTAATCGTTATTATTTTGAGCCGAAT ACCGCAATGGGTGCC AATGGTTATAAAACGATTGATAACAAAAACTTTTATTTTCGCAACGGCCTGCCGCAGATT GGCGTATTCAAAGGT CCTAACGGTTTTGAGTACTTCGCTCCAGCCAATACAGATGCAAATAATATCGACGGCCAG GCCATCCGCTACCAG AACCGCTTCCTGCATCTGCTGGGTAAAATCTATTATTTCGGCAACAACAGCAAAGCGGTA ACTGGTTGGCAAACC ATCAATAGCAAAGTGTATTATTTCATGCCGGATACAGCAATGGCAGCAGCCGGTGGTCTG TTTGAAATTGATGGT GTGATCTATTTCTTTGGTGTGGATGGTGTTAAAGCACCGGGTATTTATGGCCTCGAG

Amino acid sequence encoded by SEQ ID NO:33 (SEQ ID NO:34)

HMGSKAVTGWQTIDSKKYYFNLNTAVAVTG QTIDGEKYYFNLNTAEAATGWQTIDGKRYYFNTNTYIASTGYTI ING HFYFNTDGIMQIGVFKGPDGFEYFAPANTHNNNIEGQAILYQNKFLTLNGKKYYFGSDSK AVTGLRTIDGK KYYFNTNTAVAVTGWQTINGKKYYFNTNTYIASTGYTIISGKHFYFNTDGI QIGVFKGPDGFEYFAPANTDANN IEGQAIRYQNRFLYLHDNIYYFGNDSKAATGWATIDGNRYYFEPNTAMGANGYKTIDNKN FYFRNGLPQIGVFKG PNGFEYFAPANTDANNIDGQAIRYQNRFLHLLGKIYYFGNNSKAVTG QTINSKVYYFMPDTAMAAAGGLFEIDG VIYFFGVDGVKAPGIYGLE

A plasmid (pET22b_lipo-F3) was constructed by inserting a NdeI-LLS-BamHI-F3- Xhol fragment into a standard cloning plasmid pET-22b.

NdeI-LLS-BamHI-F3-XhoI (SEQ ID NO:35)

CATATGAAAAAATTATTGATTGCCGCAATGATGGCGGCTGCCTTGGCAGCTTGTTCG CAAGAAGCC^AACAGG^ GTTAAflGAAGCGGTTCAAGCCGTTGAGTCCGATGTTAAAGACACTGCGGGATCCAAAGC CGTGACCGGATGGCAA

ACTATCGATTCAAAAAAATACTACTTTAACCTGAACACCGCAGTTGCAGTTACAGGG TGGCAAACCATCGACGGT GAGAAATACTACTTCAATCTGAATACAGCCGAAGCCGCTACTGGATGGCAGACGATTGAC GGAAAACGCTATTAT TTTAATACCAACACCTATATTGCGAGCACAGGCTATACCATCATTAATGGTAAACACTTC TACTTTAACACGGAC GGTATCATGCAAATCGGCGTGTTTAAAGGCCCAGACGGTTTCGAGTACTTTGCGCCAGCA AACACCCACAATAAT AACATCGAAGGACAAGCCATCCTGTATCAAAACAAATTTCTGACGCTGAATGGCAAAAAA TACTACTTCGGTAGT GATAGCAAAGCTGTTACAGGTCTGCGTACCATCGACGGAAAAAAATATTACTTTAATACT AACACGGCAGTGGCA GTGACGGGCTGGCAAACGATCAACGGGAAAAAATACTACTTCAACACCAACACGTATATT GCCTCAACCGGCTAT ACAATTATCAGCGGTAAACACTTTTATTTCAATACAGATGGGATCATGCAGATCGGAGTT TTCAAAGGACCTGAT GGATTCGAGTATTTTGCTCCTGCGAATACCGATGCCAATAACATTGAGGGACAGGCAATT CGCTATCAGAATCGT TTTCTGTATCTGCACGATAATATTTATTATTTTGGCAATGATTCCAAAGCGGCAACCGGT TGGGCCACCATTGAT GGTAATCGTTATTATTTTGAGCCGAATACCGCAATGGGTGCCAATGGTTATAAAACGATT GATAACAAAAACTTT TATTTTCGCAACGGCCTGCCGCAGATTGGCGTATTCAAAGGTCCTAACGGTTTTGAGTAC TTCGCTCCAGCCAAT ACAGATGCAAATAATATCGACGGCCAGGCCATCCGCTACCAGAACCGCTTCCTGCATCTG CTGGGTAAAATCTAT TATTTCGGCAACAACAGCAAAGCGGTAACTGGTTGGCAAACCATCAATAGCAAAGTGTAT TATTTCATGCCGGAT ACAGCAATGGCAGCAGCCGGTGGTCTGTTTGAAATTGATGGTGTGATCTATTTCTTTGGT GTGGATGGTGTTAAA GCACCGGGTATTTATGGCCTCGAG

Amino acid sequence encoded by SEQ ID NO:35 (SEQ ID NO:36)

IMKKLLIAAMMAAAl-AACSQEAKQEVKE^ DSKKYYFNLNTAVAVTGWQ IDG

EKYYFNLNTAEAATGWQTIDGKRYYFNTNTYIASTGYTIINGKHFYFNTDGIMQIGV FKGPDGFEYFAPANTHNN NIEGQAILYQNKFLTLNGKKYYFGSDSKAVTGLRTIDGKKYYFNTNTAVAVTG QTINGKKYYFNTNTYIASTGY TIISGKHFYFNTDGIMQIGVFKGPDGFEYFAPANTDAN IEGQAIRYQNRFLYLHD I YFGNDSKAATGWATID GNRYYFEPNTAMGANGYKTIDNK FYFRNGLPQIGVFKGPNGFEYFAPANTDANNIDGQAIRYQNRFLHLLGKIY YFGNNSKAVTGWQTINSKVYYFMPDTAMAAAGGLFEIDGVIYFFGVDGVKAPGIYGLE

(3) Recombinant protein expression and purification

rRBD, Fl, F2, and F3 polypeptides (i.e., including SEQ ID NOs:2, 4, 6, 8, respectively) each fused to a C-terminal polyhistidine tag were expressed in E. coli BL21 (+) RIL after 1 mM isopropyl-P-D-thiogalacto- pyranoside (IPTG) induction, and cultured in LB medium with 100 ug/ml ampicillin at 20 C for 16 hours. Cells from 2 liters of cultures were harvested by centrifugation and stored at -20 C before being suspended in 50 mM sodium phosphate buffer, pH 7.2 containing 250 mM NaCl and 5 mM imidazol. The cells were disrupted by French Press and collected supernatant was applied to nickel resin for purification. The RBD-truncated proteins were dialyzed against IX PBS, pH 7.2 containing 50mM Arg and 10% glycerol. rRBD was dialyzed against IX PBS, pH 7.2 containing 10% glycerol. The four proteins were passed through E membranes for endotoxin removal, rlipo- 5 RBD fused to C-terminal polyhistidine tag was purified according to the procedure used for recombinant lipoprotein purification described in Tseng and Leng ( Appl Microbiol

Biotechnol. 2012; 93:1539-1552). Briefly, rlipo-RBD expressed in E. coli C43 (DE3) was extracted from pellet with 50 mM Tris-Cl, pH8.0 containing 0.5% Triton X-100 after cell lysis. The extraction was purified by two steps affinity chromatograph. First, nickel resin o was used for separation. Second, the eluent obtained after dialysis to remove imidazol was applied to immobilized metal affinity chromatography (IMAC) (GE) charged with copper ion for LPS remove.

(4) Peptide synthesis

5 All peptides were purchased from NIIDV peptide synthesis core facility in Taiwan.

(5) SDS-PAGE and Western blot analysis

Protein samples were quantified by BCA Protein Assay Kit (Thermo Pierce) before being loaded onto 10% SDS-PAGE. After a sample was transferred to PVDF (GE), PVDF o membrane was blocked by 5% milk for 1 hour. The membrane was then inoculated with anti- his tag and specific anti-CD toxin A antibodies in PBS containing 1% milk and 0.05% Tween-20 for 1 hour. Finally, the membrane was incubated with HRP-conjugated secondary antibodies (GeneTex) in PBS containing 1% milk and 0.05% Tween-20 for 1 hour. The membrane was developed using Luminata Crescendo substrate (Merck Millipore).

5

(6) In vitro neutralization assay using Vero cells

Vero cells were maintained in 75T flask (Corning) containing Virus production-serum free medium (VP-SFM) (Invitrogen)/ 4mM glutamine at 37 ^° C, 5% C0 ₂ , until the cells were confluent. 2x10 ⁴ cells were seeded into 96-well plates at 37 ^° C, 5% C0 ₂ , overnight and0 replaced with fresh VP-SFM. Serially two fold dilutions of serum samples from mice

immunized with or without rRBD or rlipo-RBD were mixed with Toxin A by equal volume and incubated at room temperature for 1 hour. The mixture was added into 96-well plates to arrive at 16 ng/ml toxin A and incubated at 37 C, 5% C0 ₂ , for 24 hours. Toxin A neutralizing titer was determined by 100% cell rounding and cell image was captured by camera on the microscope.

5 (7) Animal immunization and tcdA challenge model

BALB/c mice and Syrian golden hamsters were purchased from the National Animal Center in Taiwan and held in the Animal Center of the NHRI. BALB/c mice were immunized three times with 0.3, 3.0 and 30 μg rRBD and rlipo-RBD every two weeks and hamsters were immunized three times with 10 μg rRBD and rlipo-RBD every two weeks. o Before immunization, mice and hamsters were bled from facial vein and orbital sinus

sampling, respectively, and then collected serum to calculate antigen-specific IgG and IgA titer by ELISA. Toxin A challenge was administrated as previously described by Sergin SS et al., 2012. Vaccine 30:1492-1501. Briefly, BALB/c mice were immunized with 0.3 and 3 μg rRBD and rlipo-RBD three times via intramuscular injection every two weeks. Toxin A

5 challenge was performed at fifth week via intraperitoneal injection of 150 ng toxin A

(NativeAntigen Inc.). Animal mortality was continuously observed every six hours by lab personal.

(8) Peptides immunization

Guinea pigs purchased from National Animal Center in Taiwan were immunized with o three peptides only and mixture formulated with incomplete Freund's adjuvant (IFA) (Sigma) by three times of subcutaneous injection every month and held in the Animal Center of the NHRI.

(9) Cell staining and flow cytometry

5 Vero cells on 75T flask containing Virus production-serum free medium (VP-SFM)/

4mM glutamine were confluent at 37 C, 5% C0 ₂ . An aliquot of 5xl0 ⁵ cells was performed to inoculate with 1 μg specific monoclonal antibodies (GeneTex) and anti-his tag antibodies (AbD Serotec) on ice for 30 min. After washing twice, FITC -conjugated secondary antibodies (Sigma) were treated on ice for surface staining for 30 min. Before flowcytometry o analysis, propidium iodide (PI) was carried out for a cell viability marker to exclude dead cells. (10) Hemagglutination assay

Hemagglutinin (HA) activity assay was performed as described by Wren et al. (Infect. Immun. 1991, 59:3151-3155.) In brief, 250 pMoles of either rRBD, or rRBD-Fl, or rRBD- F2 or rRBD-F3 in 25μί of PBS were serially two-fold diluted in PBS and placed in the wells 5 of a 96-wells round-bottom plate. 25 μΐ of a suspension of 2% rabbit erythrocyte re-washed with PBS to remove serum contamination were added into the wells at a 1 to 1 ratio. The mixtures were incubated at 4°C overnight. HA activity was calculated by visual scoring.

(11) ELISA

o After antigen coating in ELISA plates (Costar) overnight, 5% BSA (Calbiochem) in

PBS was performed to block plates. The plates with serially diluted sera were incubated at room temperature for 2 hours. HRP-conjugated IgG (KPL) and IgA (Invitrogen) specific antibodies in PBS containing 1% BSA were treated and inoculated at room temperature for 1 hour. The plates were treated with TMB micro well peroxidase substrate (KPL) at room 5 temperature in the dark for 20 min. Spectrophotometer was performed to calculate sera titer by detection of OD45 _0n m absorbance.

(12) Mucosal immunization

Female C57BL/6 mice at age of 6 to 8 weeks were purchased from National Animal Center in Taiwan and held in the Animal Center of the NHRI. All experiments were o performed by following the guidelines of the animal center of NHRI. 6 mice of each group received three intranasal immunizations with 2μg or^g of tcdA-RBD formulated with 10μg of ovalbumin (OVA) every two weeks. 10μg of OVA formulated with l ug of cholera toxin and PBS, respectively, were used as positive and negative controls of the intranasal study. Mice were bled 1 week prior to every immunization via facial vein. Each antigen was 5 prepared in a total volume of 40μί for the intranasal administration. 7 days after the last immunization, mice were bled and sacrificed to collect their broncho-alveolar lavage fluid (BALF) and fecal in the small intestine. The BALF was administrated by washing with 1 mL PBS containing Protease Inhibitor Cooktail Set III (Calbiochem, Darmstadt, Germany). Fecal was resuspended in the same buffer as the BALF wash at lmg/ml. Both the BALF0 wash and fecal solution remained on ice until being stored at -20°C. Levels of IgG and IgA of mouse sera and IgA of BALF and fecal were determined by ELISA. (13) Dendritic cell (DC) maturation surface markers and cytokines analysis

Analysis of DC maturation was performed in vitro as previously described in

Takeuchi et al., (J. Immunol (2002) 169:10-14). C57B/6 mice were purchased from National Animal Center in Taiwan and held in the Animal Center at the NHRI. In brief, bone marrow- derived DCs (BMDCs) were collected from the tibiae of 6 to 8-week old female C57B/6. Bone marrow cells were isolated by vigorously washing with LCM (RPMI 1640 containing 1% antibiotics with penicillin and streptomycin, 10% heat-inactivated FBS, 50μΜ β- mercaptoethanol, and 50mM HEPES) and treated with lysis buffer to remove erythrocytes. BMDCs were re-suspended in LCM at 2x10 ⁶ cells/mL and treated with 20ng/mL

recombinant granulocyte macrophage colony stimulating factor (MoGM-CSF) on days 0 and 3. An aliquot of suspended BMDCs equivalent to 2*10 ⁶ /mL was seeded into 24- wells plates at day 6. Different concentrations of tcclA-RBD combined with or without 10 ng/mL of polymyxin B were added. LPS and toxin A served as positive controls. After 16 to 18 hr inoculation, BMDCs were analyzed by flow cytometer (FACSCalibur, BD Biosciences, Franklin Lakes, NJ, USA) to evaluate up-regulation of cell surface markers. In order to exclude immature DCs, composed of 50% of total cell population, CD1 lc+ cell population was gated for surface marker staining with specific monoclonal antibodies to CD-40, CD-80, CD-86, and MHC-II. In addition, after indicated treatment, cell culture medium was collected to analyze the expression of cytokines including IL-6, IL-12p40, and TNF-a which were typically secreted from activated DCs.

(14) Adjuvant effect of tcdA-RBD

The immunization protocol for measuring the systemic adjuvant effect of tcdA-RBD is described below. Four cohorts of 6 BALB/c mice were each immunized with 2 μg of ovalbumin (OVA) (Sigma, US) formulated with 3μg or lO g of tcdA-RBD, RBD-Fl, RBD- F2, RBD-F3, or aluminum hydroxide via intramuscular injection. Mice receiving 2μg of OVA only were used as immunization controls. The mice were given three immunizations with at 14-day intervals and bled before each injection by facial vein sampling. The blood samples were collected and inactivated at 56°C for 30 minutes, and then stored at -80°C for future analysis. (15) Fluorescence-activated cell sorting (FASC) analysis

Vero cells in 75T flask containing VP-SFM/4mM glutamine was 80% confluent at 37°C, 5% C02. An aliquot of 5xl0 ⁵ cells was mixed with ^g of specific monoclonal antibodies (PCG-4) (GeneTex) and anti-his tag antibodies (AbD Serotec) and incubated on ice for 30 min. After washing twice, FITC -conjugated secondary antibodies (Sigma) were add and the sample was incubated on ice for 30 min for surface staining. Before flow cytometry analysis, propidium iodide (PI) was added as a cell viability marker to exclude dead cells. Results

(1) Rational design of DNA Sequences Coding for tcdA-RBD

A clone encoding the designated tcdA-KBD was generated by linking cDNA fragments generated from several synthetic DNA fragments with sequences derived from consensus sequence analysis as described above. The nucleic acid sequences encoding tcdA- RBD with lipo-box sequences and individual tcdA -RBD fragments were subcloned into pET- 22b to produce pET-22b-rlipo-RBD, pET-22b-rRBD-F 1 , pET-22b-rRBD-F2 and pET-22b- rRBD-F3 and used to transform E. coli BL21(+)RIL and/or JM109(DE3) as described above. Plasmid DNA was prepared for sequence confirmation from two individual colonies of E. coli JM109(DE3) containing individual plasmid. Sequencing was performed on an ABI DNA sequencer model 370A using dye-terminator chemistry and oligonucleotide primers which had been synthesized on an ABI DNA synthesizer model 380B, and purified by

chromatography. Nucleotide sequence analysis of the tcdA-ΚΒΌ and its fragments revealed 1 or 2 mismatched base pairs. The mis-match base pairs were corrected by site-specific mutagenesis.

(2) Expression of rRBD, rlipo-RBD, and its fragments in E. coli expression systems

As described above, three truncated proteins (rRBD-Fl, -F2 and -F3) and rRBD fused to a C-terminal polyhistidine tag were expressed in E. coli BL21 (+) RIL. rlipo-RBD was specifically expressed in E. coli C43 (DE3). If necessary, tcdA-RBD and its fragments can be cloned into CHO cells or baculovirus expression systems as fusion proteins either with Myc-His tag in CHO cells or Vero cells. rRBD-Fl, -F2 and -F3, and rRBD were purified as described above. The LPS contents found in these recombinant antigens were <3 EU/mL, which normally would not have adjuvant effect. The purity of these recombinant antigens were analyzed by SDS-PAGE and Western blot. See FIG. 3 and FIG. 4. This is the first time a full length recombinant tcdA-KBO (911 amino acids) was expressed in E. coli and purified with a small amount of LPS contamination.

rlipo-RBD was purified as described above. The purity was also analyzed by SDS- PAGE and Western blot. See FIG. 5. The LPS contents were <30 EU/mL, which normally would have adjuvant effect.

(3) Guinea pig immunogenicity study of synthetic peptides

Groups of 3 guinea pigs were immunized three times with either RBD-P1, -P2, -P3

(see Table 1 above), or a mixture containing all three peptides in equal amounts. One hundred microgram of individual peptide or the mixture was formulated with completed Fruend's adjuvant and injected at day zero, then boosted with half of the amount of peptide or mixture in Incompleted Fruend's adjuvant at days 14 and 56, then bleed out at day 78.

Before immunization, guinea pigs were bled from ear vein, and serum samples were collected to determine antigen-specific IgG titer by ELISA, and other biological activities as described above. Pre-bleed sera have no reactivity to peptide and rRBD.

All 3 synthetic peptides individually elicited strong anti-peptide IgG antibody responses. See Table 2 below. These anti-peptide sera also reacted with rRBD and tcdA in

ELISA. Also see Table 2 below.

TABLE 2

Reactivity of anti-peptide final bleed sera with synthetic peptides (IgG titer x PI P2 P3 rRBD tcdA

RBD-Pl 6.8 <2 <2 4.6 4.2

RBD-P2 <2 6.1 <2 5.1 4.6

RBD-P3 <2 <2 6.1 4.2 4.1

Mixture 6.1 6.1 6.1 5.3 5.1 (4) Mouse immunogenicity studies with different rRBD and rlipo-RBD antigens

BALB/c mice were purchased from the National Animal Center in Taiwan and held in the Animal Center of the NHRI. Each group of 6 mice (6-8 weeks old) was immunized with PBS, 30 μg of rRBD, or 3 μg of rlipo-RBD at day zero, 14 and 28, and then challenged with 5 a toxin at day 42. Before immunization, mice were bled from facial vein, and serum was collected to determine antigen-specific IgG and IgA titer by ELISA, and other biological activities as described above.

Both rRBD and rlipo-RBD were both highly immunogenic and elicited strong anti- RBD IgG antibodies with titers over 10,000. See FIG 6. The antibodies reacted with rRBD l o and tcdA as determined by Western blot analysis (data not shown). A single dose of rlipo- RBD ^g) alone was at least ten times more potent than rRBD (30μg), as shown in Table 3 below. To our surprise only anti-rlipo-RBD mouse sera could significantly inhibit (100%) tcdA toxicity in the Vero cell assay (p<0.001). See Table 3. The results indicate that rRBD alone elicited antibody responses, but the antibodies were not totally able to block tcdA

15 binding to Vero cells and killing the cells.

TABLE 3

When TCID ₅₀ (50% inhibition) was used as the end point, anti-rRBD mouse sera were found to have significant inhibition against tcdA toxicity in the Vero cell toxicity assay. See 20 Table 4.

TABLE 4

(5) rlipo-RBD elicited protective effect in mouse tcdA challenge model tcdA (toxin A) challenge in a mouse model was performed as described above.

Briefly, BALB/c mice were immunized with 3(^g of rRBD or rlipo-RBD three times via intramuscular injection every two weeks. Toxin A challenge was performed at fifth week via intraperitoneal injection of 150 ng toxin A (NativeAntigen Inc.) and animal mortality was continuously observed every six hours by lab personal. As shown in Table 5 below, 30 μg of either rRBD or rlipo-RBD could protect >90% of mice challenged by Toxin A, while those mice immunized with PBS were killed by Toxin A.

TABLE 5

Further studies showed that 0.3 μg of rlipo-RBD was sufficient to protect mice from Toxin A toxicity. See FIG. 7 and Table 6. rRBD was less effective; a 3 μg dosage only protected 10% of the mice from Toxin A toxicity. These results were consistent with the results of Vero cell inhibition assay discussed above. Namely, rlipo-RBD elicited strong protective immune responses against Toxin A.

TABLE 6

Toxin A challenge dosage: 150 ng (5X LD50) (6) rlipo-RBD elicited a strong systemic IgA antibody response

When mouse antisera raised against either rRBD or rlipo-RBD were tested for systemic IgA reactivity against rRBD, we found that 3 μg of rlipo-RBD elicited a strong systemic IgA titer (>10,000) and was as effective as 30 μg of rRBD. See FIG 8.

5 (7) rRBD functioned as an adjuvant to enhance immune response against non-immunogenic protein

Since rRBD was highly immunogenic at 30 μg dose without an adjuvant, it was of interest to know whether rRBD and/or rlipo-RBD could enhance immune responses against non-immunogenic proteins. Ovalbulin (OVA) is well known as a poor immunogen that could o not elicit good IgG antibody responses without an adjuvant. Therefore, different groups of mice were immunized with OVA alone, or with OVA and either rRBD or rlipo-RBD. To our surprise, both rRBD and rlipo-RBD could effectively enhance both IgG and systemic IgA antibody responses against OVA. See FIG 9. Again, the IgA antibody response at 4 weeks elicited by 2 doses (0.3μg) of rlipo-RBD was significantly (pO.001) better than those5 obtained from 3μg of rRBD. There was not much difference after 3 doses (6 weeks immune responses). See FIG 9.

(8) Receptor-binding fragments of tcdA-KBO

rRBD and its fragments (rRBD-Fl, -F2 and -F3) were tested for their ability to bind to Vero cells using flow-cytometry assay as described above. As shown in FIG 10, rRBD-F3 o was found to be more potent than rRBD, rRBD-Fl, or rRBD-F2 in this binding assay. These results suggest that the repetitive sequences in rRBD-F3 form a higher affinity receptor- binding site than those repetitive sequences in Fl and F2. Circular dichroism (CD) structural analysis showed that significant β-sheet structure can be observed in the Fl and F3 fragments. See FIG. 11. The F2 fragment showed less β-sheet structure signal than the other two 5 fragments.

(9) Hemaggulutinin activity (HA) of the functional domains of tcdA

rRBD and its fragments (rRBD-Fl, -F2 and -F3) were tested for HA activity in rabbit red blood cells (RRBC) as described above. At around 1% of RRBC, rRBD was found to be very effective at hemaggulutinating RRBC and was more potent than tcdA. See FIG 12. The o HA activity test indicated that rRBD can easily agglutinate rabbit erythrocyte at 4 pMoles. In addition, anti-rlipo-RBD mouse sera were found to effectively neutralize the HA activity of rRBD in the RRBC assay.

Further studies showed that rRBD-F3 was more potent than rRBD and rRBD-F2 in the HA assay. See FIG 13. To our surprise, rRBD-Fl did not show any HA activity in the 5 RRBC assay, but was bound strongly to Vero cells as discussed above. These results suggest that there are other non-carbohydrate binding sites located in the Fl fragment. This observation is further supported by the direct Vero cell binding assay. Western blot analysis showed that RBD-Fl exhibited strong binding to Vero cells, while RBD- F2 exhibited less binding than the other two fragments. See FIG. 14. These results taken together indicate l o that, the small differences in the repetitive sequences in the RBD fragments can affect their affinity for the host receptor and their hemagglutination activity.

(10) Guinea pig anti -peptide antibodies inhibited the HA activity of rRBD in RRBC assay Synthetic peptides RBD-P1, -P2, and -P3 elicited anti-rRBD antibody responses in guinea pig immunogenicity studies as described above. See FIG. 15 and FIG. 16. We tested 15 whether these anti-peptide sera could inhibit the HA activity of rRBD in a RRBC assay. As shown in FIG. 17, these sera were effective at inhibiting the HA activity of rRBD in the RRBC assay. The potency of guinea pig anti-peptide sera against the HA of RBD is shown in FIG. 18.

(11) rRBD and its fragments can function as carriers for drug delivery

As shown by the FACS analysis and Vero cell direct binding assay described above, rRBD and its fragments can quickly recognize and bind to the host receptor(s). Using confocal microscopy, we observed that rRBD and its fragments quickly bound to the host receptor within a minute. They were then internalized and delocalized inside the cell within 10 minutes and started to be degraded within 30 minutes. See FIG. 19. These results suggest that rRBD and its fragments can function as carriers for drug delivery.

(12) Comparison of immunogenicity of rRBD and its fragments

RBD-Fl, -F2 and -F3 were designed to have the same number of repetitive sequences 30 derived from the N-terminus, middle region and the C-terminus of RBD, respectively, but each fragment had different level of functions and biophysical characterization as described above. We assess their immunogenicity and the immunological properties of the elicited antibodies. Mouse immunogenicity study was performed with individual RBD fragment at 30 μg dose. RBD-F1 and -F3 fragments were found to be as potent as rRBD in the mouse immunogenicity studies. See FIG. 20. RBD-F2 was less immunogenic as compared to the other RBD fragments (p<0.05). Although RBD fragments could elicit good IgG antibody responses, the biological function of these antibodies as determined by the Toxin A neutralization assay (TCID ₅₀ ) was found to be less effective than that of anti-rRBD antibodies. See Table 7. The best titer obtained from anti-RBD-F3 sera was 16, whereas the titer of 256 was obtained from anti-rRBD antibodies. Nevertheless, these results suggest that RBD fragments can be used individually or in combination as vaccine candidates against Cd infection.

TABLE 7

(13) RBD fragments can act as immuno-stimulators to enhance immune responses against poor immunogenic antigen

We tested whether the RBD fragments could enhance immune responses against non- immunogenic proteins. OVA was again used as model protein for this study. Different groups of mice (6 in each group) were immunized with OVA alone (10 μg), or with OVA formulated either with alum, rRBD (10 μg), or different RBD fragment (30 μg each).

Interestingly, RBD and its fragments could effectively increase IgG antibody responses against OVA. See FIG. 21. We also tested the adjuvant effect of each RDB fragment at 10 μg dose. These results indicate that all RBD fragments can function as adjuvants to enhance the immune responses against poorly immunogenic antigens. (14) Dendritic cell maturation could be triggered either by rRBD or RBD fragments

Cd toxin A has been reported to up-regulate surface effect molecules and expression of chemokine CXCL2 of dendritic cells (DCs). We tested whether rRBD and its fragments could promote maturation of DCs, which are important antigen-presenting cells that modulate the immune system. After BMDCs from C57BL/6 were treated with rRBD, DC maturation markers (CD40, CD80, CD86, and MHC-II) correlated with T-cell activity and

proinflammatory cytokines (IL-6, IL-12, and TNF-a) were analyzed. Indeed, significantly up-regulation of surface T-cell effector molecules and high level of pro-inflammatory cytokines (IL-6, IL-12, and TNF-a) from culture medium could be detected after rRBD treatment. See FIG. 22 and FIG. 23.

In order to preclude LPS contamination, LPS in the rRBD solution was limited to 0.03 EU^g. Additionally, every test received polymyxin B to neutralize LPS function to rule out DC activation by LPS through the Toll-like receptor 4 pathway.

The results also demonstrated that there were no significant differences between polymyxin B-treated and non-treated rRBD. In addition, we also boiled both rRBD solution and LPS to denature and destroy biological functions of rRBD. DC activity was not significantly affected in the LPS only treatment, but impeded to the same extend as the medium control in boiled rRBD. Overall, these data clearly demonstrate that the observed DC activity was attributed to rRBD.

The DC activation studies were also performed with individual RBD fragments. The results were found to be similar to those obtained with rRBD. See FIG. 22 and FIG. 23. RBD-F3 was found to be the most potent as compared with the other fragments.

Taking these results together, we conclude that the activation of DCs at the immunization site could contribute to the immunological potency of rRBD and its truncated fragments.

(15) Immunogenic peptides identified from other regions of tcdA

To prepare an effective diagnostic kit for detecting Cd infection and diseases associated with it, polypeptides (CdTx-CP, CdTx-GTl, CdTx-GT2, CdTx-GT3, CdTx-TMl, CdTx-TM2, and CdTx-TM3) including other functional domains of tcdA (see Table 1 above) were synthesized and tested in guinea pigs to determine whether these peptides can elicit antibody responses recognizing tcdA from patient samples. As shown in Table 8, the peptide mixture from each region (GT, CP and TM) was found to induce regional specific anti- peptide antibody responses with titer >10,000. These antisera were found to specifically react with tcdA and not RBD in a Western blot analysis. The results showed that these peptides have the capability to elicit antibody responses that recognize tcdA from patient samples, and can be used to effectively diagnose Cd infection and diseases caused by the infection.

TABLE 8

Guinea pig anti-peptide ELISA Titer

GT-mixture CP TM-mixture

1 2 1 2 1 2

GT-1 4.41 4.41 2.60 2.60 2.60 2.60

GT-2 3.81 3.81 2.60 2.60 2.60 2.60

GT-3 5.01 5.61 2.60 2.60 2.60 2.60

CP 3.20 3.20 5.01 5.01 3.20 3.20

Coating

TM-1 2.60 2.60 2.60 2.60 5.61 5.01

TM-2 2.60 2.60 2.60 2.60 5.01 5.01

TM-3 2.60 2.60 2.60 2.60 5.61 5.61 tcdA-rRBD 2.60 3.20 3.20 3.20 2.60 2.60

OTHER EMBODIMENTS

All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

From the above description, one skilled in the art can easily ascertain the essential characteristics of the embodiments described herein, and without departing from the spirit and scope thereof, can make various changes and modifications of the described embodiments to adapt them to various usages and conditions. Thus, other embodiments are also within the claims.