# Patent

## Title
Polyvalent chimeric OspC vaccinogen and diagnostic antigen

## Abstract

A chimeric polyvalent recombinant protein for use as a vaccine and diagnostic for Lyme disease is provided. The chimeric protein comprises epitopes of the loop 5 region and/or the alpha helix 5 region of outer surface protein C (OspC) types. The OspC types may be associated with mammalian Borrelia infections.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims benefit of U.S. provisional patent application 60/740,272, filed Nov. 29, 2005; 60/789,588, filed Apr. 6, 2006; and 60/790,530, filed Apr. 10, 2006; the complete contents of each of which is hereby incorporated by reference.


STATEMENT OF GOVERNMENT INTEREST
This invention was made with government support under Contract Number R01 1I067746 awarded by the National Institutes of Health. The Government has certain rights in the invention.
This invention was made using funds from grants from the National Institute of Allergy and Infectious Disease having grant number 1RO1AI067746-01A1. The United States government may have certain rights in this invention.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to a vaccine and diagnostic for Lyme's disease. In particular, the invention provides a chimeric polyvalent recombinant protein comprising immunodominant epitopes of loop 5 and/or alpha helix 5 regions/domains of outer surface protein C (OspC) types associated with mammalian infections.
2. Background of the Invention
Lyme disease is the most common arthropod-borne disease in North America and Europe. It is caused by the spirochetes Borrelia burgdorferi, B. garinii and B. afzelii. Transmission to mammals occurs through the bite of infected Ixodes ticks [Burgdorfer et al, 1982, Benach et al., 1983]. Considerable morbidity is associated with Lyme disease and there are areas in the United States and Europe where up to 3% of the population is infected annually [Fahrer et al., 1991]. Infection results in a multi-systemic inflammatory disease with early stage symptoms that may include erythema migrans, low-grade fever, arthralgia, myalgia, and headache [Steere et al., 1977a]. Late stage clinical manifestations can be severe and may include in part, arthritis [Steere et al., 1977a; Eiffert et al., 1998; Steere et al., 2004], carditis [Asch et al., 1994; Nagi et al., 1996 Barthold et al., 1991] and neurological complications [Nachman and Pontrelli, 2003; Coyle and Schutzer 2002]. In addition, Lyme disease has significant socio-economic costs, manifested by reductions in outdoor recreational and social activities due to concerns about tick exposure.
Pharmacoeconomic studies indicate that a clear need exists for a Lyme disease vaccine, particularly in populations where the annual disease risk exceeds 1% [Meltzer et al., 1999; Shadick et al., 2001]. However, at the present time a vaccine is not commercially available. The first human Lyme disease vaccine was the OspA-based LYMErix (GlaxoSmithKline); however, its tenure was short and, citing a drop in sales, it was voluntarily pulled from the market in 2002. The decline in sales can be traced to concerns, real or perceived, of possible adverse effects including a chronic inflammatory arthritis that could theoretically develop in HLA-DR4-positive recipients [Kalish et al., 1993]. While new OspA-based vaccinogens are being developed to mitigate this potential complication [Koide et al., 2005; Willett et al., 2004], questions remain about the viability of an OspA-based vaccine. One concern is the frequency of boosts required to maintain long term protection. OspA is expressed in the tick midgut, is rapidly down-regulated upon tick feeding, and is not expressed in mammals [Gilmore et al., 2001; Schwan et al., 1995]. The mechanism of action of OspA-based vaccines is to target spirochetes within the tick and prevent their transmission [de Silva et al., 1999]. Since transmission occurs within 48 hours of tick feeding, effective protection is dependent on high circulating titers of anti-OspA antibodies, necessitating frequent boosts. The inherent problems associated with OspA-based vaccines can be avoided by the use of antigens that are expressed at high levels during early infection and that elicit bactericidal antibody.
OspC has received considerable attention in Lyme disease vaccine development. It is a 22 kDa, surface exposed lipoprotein [Fuchs et al., 1992] encoded on a 26 kb circular plasmid that is universal among isolates of the B. burgdorferi sensu lato complex [Marconi et al., 1993; Sadziene etg al., 1993]. Its expression is induced upon tick feeding and is maintained during early mammalian infection [Schwan, 2004], and it is genetically stable during infection [Hodzic et al., 2000; Stevenson et al., 1994]. Anti-OspC antibodies have been demonstrated to protect against infection, but only against strains expressing OspC that is closely related in sequence to the vaccinogen [Gilmore et al., 1996; Bockenstedt et al., 1997; Gilmore and Mbow, 1999; Mathiesen et al., 1998; Scheiblhofer et al., 2003; Jobe et al., 2003; Rousselle et al., 1998; Wallich et al., 2001; Mbow et al., 1999; Probert et al., 1997; Brown et al., 2005; Probert and LeFebvre 1994]. Analyses of OspC sequences have delineated  ̃21 OspC phyletic clusters or types that are differentiated by letter designation (A through U) [Seinost et al., 1999; Wang et al., 1999]. While sequence variation within a cluster is generally less than 2%, between OspC types it can be as high as 22% [Wang et al., 1999; Theisen et al., 1995; Brisson and Dykhuizen, 2004]. Such inter-type variation of epitopes most likely explains the limited range of protection afforded by vaccination with a single OspC type.
U.S. Pat. No. 6,248,562 (Jun. 19, 2001) to Dunn and Luft describes chimeric Borrelia proteins that consist of at least two polypeptides from corresponding and/or non-corresponding proteins from the same and/or different species or Borrelia. The chimeric polypeptides incorporated in the chimeric proteins are derived from any Borrelia protein from any strain of Borrelia and include OspA, OspB, OspC, OspD, p12, p39, p41, p66, and p93. The chimeric proteins can be used as immunodiagnostic reagents and as vaccine immunogens against Borrelia infection. However, there is no reference to loop 5 and alpha 5 epitopes present in OspC proteins.
U.S. Pat. Nos. 6,872,550 and 6,486,130 (Mar. 29, 2005, and Nov. 26, 2002, respectively) both to Livey, describe constructs for use a vaccines against Lyme disease which contain OspC antigens. However, there is no mention of the characterization of loop 5 and alpha 5 epitopes in these patents.
U.S. Pat. No. 7,008,625 (Mar. 7, 2006) to Dattwyler et al. discloses antigenic polypeptides of a variety of Borrelia strains and/or proteins within a single protein. The chimeric Borrelia proteins are made up of polypeptide fragments of the outer surface protein OspA and the outer surface protein OspC. These proteins can be effective against Lyme borreliosis as well as for immunodiagnostic reagents. However, there is no mention of the characterization of loop 5 and alpha 5 epitopes.
The publication “Recombinant Chimeric Borrelia Proteins for Diagnosis of Lyme Disease” (Maria J. C. Gomes-Solecki et al. 2000. J. Clin. Microbiol., 38: 2530-2535) is related to the two above-identified patents. The authors engineered recombinant chimeras, each containing portions of the key antigenic proteins of Borrelia burgdorferi, OspA, OspB, OspC, flagellin (Fla or p41), and a protein p93. The paper is directed to diagnosis, but describes applications to vaccinogens in the closing paragraph. The authors mention that better chimeras can be created with further study of the genetic variability of the important epitopes but do not mention the loop 5 and alpha 5 epitopes of OspC.
The prior art has thus-far failed to provide a vaccine that affords broad protection against multiple OspC types for use in the prevention and/or treatment of Lyme disease.
SUMMARY OF THE INVENTION
The invention provides a chimeric polyvalent recombinant protein for use as a vaccine and diagnostic for Lyme disease. The invention is based in part on the discovery and characterization of novel protective, epitopes from several different OspC phyletic groups (types), each of which is associated with mammalian (e.g. human) Lyme disease infection. Identification of these epitopes made possible the construction of a chimeric protein or proteins that comprises a plurality of epitopes from different OspC infective types. Thus, when used as a vaccine, the chimeric recombinant protein elicits broad protection against a plurality of Borrelia strains that express those OspC types, and are associated with mammalian Lyme disease. In addition, the chimeric protein is useful as a diagnostic tool to identify individuals that have antibodies to the epitopes, and to thus determine if an individual has been exposed to or infected by the causative agent of Lyme disease. In some embodiments of the invention, the epitopes are B-cell epitopes and/or immunodominant epitopes.
It is an object of this invention to provide a chimeric recombinant protein comprising epitopes from loop 5 region or alpha helix 5 region, or both, of two or more outer surface protein C (OspC) types. In one embodiment, the OspC types are selected from the group consisting of Smar, PLi, H13, PFiM, SL10, PMit, PKi, Pbes, HT22, Pko, PLj7, VS461, DK15, HT25, A, 72a, F, E, M, D, U, I, L, H, Szid, PHez, PWa, B, K, N, and C. In one embodiment, the chimeric recombinant protein comprises epitopes from OspC types A, B, K and D. In another embodiment, the chimeric recombinant protein comprises epitopes from OspC types E, N, I, C, A, B, K and D. In yet another embodiment, the chimeric recombinant protein has a primary amino acid sequence as represented in SEQ ID NO: 75 or SEQ ID NO: 249. In some embodiments, the OspC types are associated with invasive Borrelia infection
The invention further provides a method for eliciting an immune response against Borrelia in an individual in need thereof. The method comprises the step of administering to the individual a chimeric recombinant protein comprising epitopes from loop 5 region or alpha helix 5 region, or both, of two or more outer surface protein C (OspC) types. In one embodiment of the invention, the OspC types are selected from the group consisting of Smar, PLi, H13, PFiM, SL10, PMit, PKi, Pbes, HT22, Pko, PLj7, VS461, DK15, HT25, A, 72a, F, E, M, D, U, I, L, H, Szid, PHez, PWa, B, K, N, C. In one embodiment of the invention, the chimeric recombinant protein comprises epitopes from OspC types A, B, K and D. In another embodiment, the chimeric recombinant protein comprises epitopes from OspC types E, N, I, C, A, B, K and D. In yet another embodiment, the chimeric recombinant protein has a primary amino acid sequence as represented in SEQ ID NO: 75 or SEQ ID NO: 249. In some embodiments, the OspC types are associated with invasive Borrelia infection
The invention further provides a method for ascertaining whether an individual has been exposed to or infected with Borrelia. The method comprises the steps of 1) obtaining a biological sample from the individual; 2) exposing the biological sample to at least one recombinant chimeric protein, wherein the at least one chimeric protein comprises epitopes from loop 5 region or alpha helix 5 region, or both, of two or more outer surface protein C (OspC) types; and 3) determining whether antibodies in said biological sample bind to the at least one chimeric protein, wherein detection of antibody binding is indicative of prior exposure to or infection with Borrelia. In one embodiment of the invention, the OspC types are selected from the group consisting of Smar, PLi, H13, PFiM, SL10, PMit, PKi, Pbes, HT22, Pko, PLj7, VS461, DK15, HT25, A, 72a, F, E, M, D, U, I, L, H, Szid, PHez, PWa, B, K, N, and C. In one embodiment of the invention, the chimeric recombinant protein comprises epitopes from OspC types A, B, K and D. In another embodiment of the invention, the chimeric recombinant protein comprises epitopes from OspC types E, N, I, C, A, B, K and D. In yet another embodiment of the invention, the chimeric recombinant protein has a primary amino acid sequences as represented in SEQ ID NO: 75 or SEQ ID NO: 249. In some embodiments of the invention, the OspC types are associated with invasive Borrelia infection
The invention further provides antibodies to a chimeric recombinant protein comprising epitopes from loop 5 region or alpha helix 5 region, or both, of two or more outer surface protein C (OspC) types. In one embodiment of the invention, the OspC types are selected from the group consisting of Smar, PLi, H13, PFiM, SL10, PMit, PKi, Pbes, HT22, Pko, PLj7, VS461, DK15, HT25, A, 72a, F, E, M, D, U, I, L, H, Szid, PHez, PWa, B, K, N, and C. In one embodiment, the chimeric recombinant protein comprises epitopes from OspC types A, B, K and D. In another embodiment, the chimeric recombinant protein comprises epitopes from OspC types E, N, I, C, A, B, K and D. In yet another embodiment, the chimeric recombinant protein has a primary amino acid sequences as represented in SEQ ID NO: 75 or SEQ ID NO: 249. In some embodiments, the OspC types are associated with invasive Borrelia infection. The antibodies may be either polyclonal or monoclonal. In one embodiment, the antibody is bactericidal for Borrelia spirochetes.
The invention further provides an immunogenic cocktail of chimeric recombinant proteins. Each chimeric recombinant protein in the cocktail comprises epitopes from loop 5 region or alpha helix 5 region, or both, of two or more outer surface protein C (OspC) types.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1. Evolutionary relationships of OspC sequences derived from human patients in Maryland: OspC type identification. OspC genes were PCR amplified, sequenced, and a phylogram was constructed. Database sequences representative of the 22 ospC types were included in the analysis (accession numbers are indicated). The type designation (capital letters) assigned to each phyletic group is indicated by the capital letters on each branch. Bootstrap values (1000 trials) are displayed at each node critical for group differentiation.
FIG. 2. Demonstration that the antibody response to OspC during infection is predominantly OspC type specific. Recombinant OspC proteins of several OspC types (indicated in the figure) were generated, separated by SDS-PAGE, immunoblotted and screened with HRP conjugated S-Protein or serum collected from mice infected with clonal isolates of known OspC type as indicated.
FIG. 3. Localization of the immunodominant epitopes of type A OspC. Truncations of type A OspC were generated as S-Tag fusion proteins and expressed in E. coli. Panel A presents a schematic of the OspC truncations. The numbering reflects the residue numbering of B. burgdorferi B31MI OspC. In panel A, the ability of each truncated protein to bind infection antibody is indicated to the right by a (+) or (−). The numbers to the left indicate the amino acid residues that comprise each truncation. In panels B and C immunoblots of the recombinant proteins were screened with HRP-conjugated S-Protein to verify expression and loading or with serum from a mouse infected with B. burgdorferi B31 MI (α-B31 MI infection serum), a type A OspC producing strain. For reference, the arrows in panels b and c indicate the migration position of recombinants that were not immunoreactive with the α-B31MI infection serum are indicated. Molecular mass markers are indicate to the right of each immunoblot.
FIG. 4. Comparative analysis of segments of the loop 5 and alpha 5 epitopes at the inter- and intratype levels, shown in tabular form.
FIG. 5. Demonstration of a loop 5 antibody response in multiple animals infected with different type A OspC producing strains. Immunoblots of either 1) full length typeA OspC or 2) a fragment containing amino acids 130-150 (which includes loop 5) were screened with infection sera. The strain used to generate the infection sera and the specific mouse (m) from which the sera were collected is indicated above each panel. The timepoint during infection when the sera were collected is also indicated. An equal amount of protein was immunoblotted for each and all were exposed to film for the same amount of time.
FIG. 6. ELISAs: identification of serum samples harboring type A OspC targeting antibody. r-type A full-length OspC, r-type A loop 5, and bovine serum albumin were used to coat the wells of ELISA plates. The wells were screened with serum from human Lyme disease patients. All assays were performed in triplicate, and the mean is presented along with the standard deviation. All methods were as described in the text. Serum from patient 15 which was determined to be IgG negative for antibody to B. burgdorferi B31MI served as a negative control.
FIG. 7A an B. Identification of the specific residues that comprise the type A OspC loop 5 epitopes through PepSpot analysis. Overlapping peptides that span the loop 5 domain were generated and spotted onto nitrocellulose. The immobilized peptides were then screened with serum from mice infected with a clonal population of a type A OspC-producing strain (B31 MI) or with serum from human Lyme disease patients (as indicated). (A) Immunoblotting results for loop 5 domain; (B) peptide sequences.
FIG. 8. Demonstration that loop 5 is surface exposed and that antibody to loop 5 is bactericidal. The IFAs and bactericidal assays were conducted with antiserum generated against type A loop 5. (A) The results demonstrate the specificity of the anti-loop 5 antiserum. Whole-cell lysates of B. burgdorferi B31 MI, B. parkeri, and r-type A loop 5 fragment were separated by sodium dodecyl sulfatepolyacrylamide gel electrophoresis, immunoblotted, and screened with anti-type A loop 5 antiserum (1:1,000). Molecular masses of the protein markers are to the right of the figure.
FIGS. 9A and B. Generation of a tetravalent chimeric OspC test construct. A, A flow chart for the generation of the tetravalent ABKD chimeric vaccinogen constructs is shown in panel A. The type-specific OspC epitopes used in the ABKD chimeric vaccinogen are represented by different bar shading. The loop 5 epitope of OspC type A and the alpha helix 5 epitope of types B, K and D were amplified in PCR round 1 and gel purified. These initial amplicons were then joined in subsequent rounds of PCR to produce the full chimeric construct. Since the termini (linker sequences) of the amplicons are complementary, after denaturation they can anneal to allow overlap extension followed by PCR amplification. The final amplicon was annealed into the pET46 Ek/LIC vector. B, In panel B, the final protein sequence of the ABKD chimeric vaccinogen construct is shown with constituent epitope-containing regions and linker sequences noted.
FIG. 10. Western blot demonstrating immunoreactivity of anti-ABKD antiserum with the ABKD chimeric vaccinogen and full length OspC. Immunogenicity was evaluated by immunoblotting the ABKD chimeric vaccinogen, full length r-OspC proteins of types A, B, K and D (as indicated), and rBBN39 (negative control). The blots were screened with anti-His tag mAb to demonstrate approximately equal loading, or with representative anti-ABKD antisera (indicated below). Molecular mass is shown on the right. A strong IgG response to A, B and K (but not D) was observed.
FIGS. 11A and B. ELISA titration of the reactivity of sera from mice immunized with the ABKD chimeric vaccinogen. A, Sera from mice vaccinated with the ABKD chimeric vaccinogen (n=12) or sham immunized with PBS/adjuvant (n=3) were titrated for reactivity with the ABKD chimeric vaccinogen or rOspC protein of types A, B, K, and D. Panel A demonstrates the titration of immunoreactivity of all sera to the ABKD chimeric vaccinogen construct (solid lines with a different symbol for each mouse). No Ab response was observed in the sham vaccinated mice (dashed lines). B, Titrations of the specific response to each OspC type were also completed (curves not shown), and the titers determined at 1⁄2 max OD405 are shown in panel B (one point per mouse, horizontal line at the mean titer). Control mice had no titer, and were not plotted.
FIG. 12. Immunoglobulin isotype profile of anti-ABKD antiserum. ELISA wells were coated with the ABKD chimeric vaccinogen construct (100 ng/well) and probed with anti-ABKD antisera in duplicate (1:10000; n=12). Bound Ig was detected by biotinylated isotype-specific secondary Ab (Mouse Isotyping Kit; Zymed Laboratories) and HRP-conjugated streptavidin. Reactivity was quantified by measurement of the colored product created by the HRP-mediated conversion of ABTS substrate.
FIG. 13A-E Schematic representation of the construction of the ABKD vaccine variants. ABKDppa (Panel A) was constructed by amplification of the original construct using a reverse primer with a 5′ overhang to add the C-terminal amino acids. ABKDgg (not shown) was made in an identical manner, but using the OCDH5ggLIC primer. ABKDD (Panel B), ADBK (Panel C), and ADBKD (Panel D) were all made by PCR amplification of constituent sequences using primers that added tails encoding linker sequences. The resultant PCR products were gel purified, and joined by overlap annealing and extension. The final products were cloned into the pET-46 Ek/LIC vector. OspC type-specific epitope containing regions are denoted by letter, and linker sequences by number (see inset for encoded amino acid sequences). Arrows denote primers, and 5′ overhanging LIC tails or linker sequences are noted on the tail of each primer arrow.
FIG. 14. Coomassie stained SDS-PAGE gel of the chimeric vaccinogen test constructs. Vaccinogen r-proteins were expressed in E. coli, affinity purified by nickel chromatography, and quantified by the BCA method. Two μg of the purified proteins were electrophoesed on a 15% SDS-PAGE gel (Criterion; Biorad) and stained with Coomassie G-250. No contaminating proteins were noted, and there was minimal or no degradation of the recombinant proteins.
FIGS. 15 A and B. Assessment of mouse vaccine serum recognition of full length r-OspC. In panel A, r-OspC of types A, B, K, and D were electrophoresed and blotted to PVDF (type indicated at top; 500 ng/lane), and were probed with a 1:2500 dilution of representative sera from mice vaccinated with each of the variant constructs (indicated at left). Secondary detection was by peroxidase-conjugated goat-anti-mouse IgG (1:40000) and chemiluminescence. Molecular masses are indicted at the right. In panel B are the results of a quantitative ELISA titration of mouse vaccine serum reactivity with full length r-OspC. Sera generated against each vaccine construct (noted at bottom) were titrated against immobilized, full length, r-OspC of types A, B, K, and D. Also included are the titers from the ABKD construct dialyzed against PBS (ABKD*) [17]. Bars denote the mean titer against OspC types A (black), B (grey), K (open), and D (hatched). Titers from individual mice are denoted by open triangles. Listed below are the mean numerical titers, as well as the titers indexed either to the corresponding titer of the ABKD construct dialyzed against PBS (ABKD*) or against Arg/Glu buffer (ABKD).
FIG. 16 A-C. Epitope-specific isotype responses to three vaccine constructs. OspC types A, B, K, and D were immobilized on ELISA plates and probed with immune sera from mice vaccinated with the ABKD, ABKDD, or ADBKD constructs in duplicate. Bound Ig isotypes were detected with biotinylated isotype-specific secondary antibodies and peroxidase-conjugated streptavidin.
FIG. 17. IFN-γ response of splenocytes from immunized mice to in vitro restimulation with the immunizing antigen. Erythrocyte-free splenocytes from three mice immunized with each of the six vaccine constructs were collected, pooled, and restimulated in triplicate with the original immunizing antigen (107 cells mL−1 in 24 well plates, antigen at 10 or 5 μg mL−1). Triplicate control wells were administered 10 mg mL−1 BSA or no protein. After incubation (37° C., 5% CO2) for 96 hours, cell free supernatants were collected, and IFN-γ concentrations were determined by ELISA. In all cases, the concentration of IFN-γ in the BSA and no protein wells was below the detection limit of the assay.
FIGS. 18A and B. Assessment of the antibody response to the ABKD vaccinogen administered in Freund's adjuvants or alum. In panel A are the results of a quantitative ELISA titration of IgG in mouse sera generated against the ABKD vaccine emulsified in Freund's adjuvants (solid bars) or adsorbed to alum (hatched bars). The sera were titrated against immobilized ABKD vaccinogen or full length, r-OspC of types A, B, K, and D. In panel B is shown the isotype profile of the sera bound to immobilized ABKD vaccinogen. The bound Ig isotypes were detected with biotinylated isotype-specific secondary antibodies and peroxidase-conjugated streptavidin.
FIG. 19. Distribution of pairwise comparisons of OspC protein sequence identity. OspC protein sequences from 280 Borrelia isolates were Clustal aligned using a PAM40 scoring matrix, and pairwise percent identities were calculated. The histogram interval is 1% and there were no percent identities <50%.
FIGS. 20A-20C. Species, geographical and biological isolation data for assigned OspC types.
FIG. 21A-C. Consensus phylogenetic trees of representative OspC protein sequences. OspC sequences including amino acids 20-200 (A), 20-130 (B), and 131-200 (C) were bootstrapped (n=1000), distances calculated, and neighbor joining trees created and reconciled to a consensus tree. The Vmp33 sequence of B. hermsii was used as an outgroup. Labels indicate the species as B. burgdorferi (Bb), B. garinii (Bg), or B. afzelii (Ba), the isolate strain designation, the assigned OspC type (bold), and the number of identical OspC sequences from other strains represented by this single sequence (in parentheses). Bootstrap support is shown at all nodes that differentiate between OspC types.
FIG. 22. Bootscan analysis of the OspC type PLj7 (B. afzelii) ospC sequence in comparison with OspC types Pki (B. garinii; solid black line), F (B. burgdorferi; solid grey line), and M (B. burgdorferi; dashed black line). The bootscan window was 40 bases, with a 10 base step. Comparison was by strict consensus with 100 bootstrap replicates. The graph has been simplified by showing only those peaks where the % permuted trees exceeds 50%, and the 70% level considered to represent possible recombination is indicated.
FIG. 23. Alignment of the epitope-containing region of OspC protein sequences from all OspC types defined in this study. All sequences within OspC types that differ by more than one amino acid are indicated by a representative sequence. Identity threshold for shading is 80%. Secondary structural alpha helices and loops (corresponding to the B31 structure) are shown below the alignment (Kumaran et al, 2001).
FIG. 24. Clustal X alignment of the parental OspC sequences used in the construction of the ABKD chimeric vaccinogen and physical location of epitope-containing regions included in the vaccinogen. The locations of the epitope-containing region of OspC type A (loop 5 region, light grey box) and types B, K, and D (alpha helix 5 region) dark grey box) are highlighted within a ClustalX alignment of the parent sequences.
FIG. 25A-J. Exemplary chimeric vaccinogens of the invention. The construct title indicates the OspC type-specific loop 5 and helix 5 epitopes incorporated in the construct, as well their order. The bold X represents the position of optional linker sequences.
FIG. 26. Protein and DNA accession numbers of OspC from several Borrelia strains.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention is based on the identification and characterization of novel protective, type-specific epitopes of OspC types that are associated with human Lyme disease infection. The novel epitopes are located within two domains (regions) in the carboxyl-terminal half of OspC. Neither domain was previously identified as highly immunogenic. The first domain (referred to as “alpha helix 5 region/domain” or “alpha 5 region/domain” or “helix 5 region/domain” herein) is located between residues 160 and 200, and contains secondary structural elements including a portion of loop 6, alpha helix 5, and the unstructured C-terminal domain (Kumaran et al., 2001). The second domain (“loop 5 region/domain” herein) is located between residues 131 and 159 and contains secondary structural elements including a portion of alpha helix 3, loop 5 and alpha helix 4 (Kumaran et al., 2001). Each of these regions contains at least one epitope that may be used in the practice of the present invention. Epitopes from these two domains, or antigenic peptides or polypeptides from within these two regions, may be used in the practice of the present invention, either alone or preferably in combination with other epitopes in a chimeric immunogen. In some embodiments of the invention, the epitopes are immunodominant epitopes. Typically, the epitopes are B-cell epitopes, although T-cell epitopes are not excluded.
Discovery of the novel epitopes, and mapping of the epitopes to different OspC types, has made possible the construction of multivalent chimeric proteins that contain a plurality of linear, type-specific immunodominant epitopes from multiple OspC types. When used as a vaccine, the multivalent (polyvalent) recombinant chimeric protein elicits broad protection against infection with Borrelia spirochetes expressing the OspC types that correspond to those in the chimeric protein, i.e. those Borrelia that are highly infective. In addition, the chimeric protein is useful as a diagnostic tool to identify individuals that have antibodies to the epitopes contained in the chimeric protein, and to thus determine if an individual has been exposed to and/or infected by a causative agent of Lyme disease.
In order to facilitate the understanding of the present invention, the following definitions are provided:
Antigen: term used historically to designate an entity that is bound by an antibody, and also to designate the entity that induces the production of the antibody. More current usage limits the meaning of antigen to that entity bound by an antibody, while the word “immunogen” is used for the entity that induces antibody production. Where an entity discussed herein is both immunogenic and antigenic, reference to it as either an immunogen or antigen will typically be made according to its intended utility. The terms “antigen”, “immunogen” and “epitope” may be used interchangeably herein.

B-cell Epitope: a specific chemical domain on an antigen that is recognized by a B-cell receptor, and which can be bound by secreted antibody. The term is interchangeable with “antigenic determinant”.

Immunodominant epitope: The epitope on a molecule that induces the dominant, or most intense, immune response.

Linear epitope: An epitope comprising a single, non-interrupted, contiguous chain of amino acids joined together by peptide bonds to form a peptide or polypeptide. Such an epitope can be described by its primary structure, i.e. the linear sequence of amino acids in the chain.

Conformational epitope: an epitope comprised of at least some amino acids that are not part of an uninterrupted, linear sequence of amino acids, but which are brought into proximity to other residues in the epitope by secondary, tertiary and/or quaternary interactions of the protein. Such residues may be located far from other resides in the epitope with respect to primary sequence, but may be spatially located near other residues in the conformational epitope due to protein folding.

Loop 5 region/domain: The region of OspC that includes residues that align with residues 131 to 159 of the type A OspC sequences as denoted in FIG. 23. Strain B31 OspC secondary structural elements included in the region are a portion of alpha helix 3, loop 5, and alpha helix 4, as defined by Kumaran et al. (2001).

Alpha helix 5 region/domain: The region of OspC that includes residues that align with amino acids 160 to 200 of the strain B31 (OspC type A) sequence as shown in FIG. 23, as well as the C-terminal portion of the protein (amino acids 201-210 of the B31 sequence) not shown in FIG. 23. Strain B31 OspC secondary structural elements included in this region are a portion of loop 6, alpha helix 5, and the unstructured C-terminal domain, as defined by Kumaran et al. (2001).

Protein: A linear sequence of from about 100 or more amino acids covalently joined by peptide bonds.

Polypeptide: A linear sequence of from about 20 to about 100 amino acids covalently joined by peptide bonds.

Peptide: A linear sequence of about 20 or fewer amino acids covalently joined by peptide bonds.

The terms “protein”, “polypeptide” and “peptide” may be used interchangeably herein.

Chimeric protein: a recombinant protein whose primary sequence comprises multiple peptide, polypeptide, and/or protein sequences which do not occur together in a single molecule in nature.

Valency of a chimeric protein (e.g. “multivalent” or “polyvalent”) refers to the number of OspC type-specific epitope-bearing polypeptides included in the chimeric vaccinogen. For example, a divalent chimera may be composed of alpha helix 5 of type A and alpha helix 5 of type B, or, alpha helix 5 of type A and loop 5 of type A. There may be multiple distinct epitopes in each polypeptide epitope-bearing region.

Original or native or wild type sequence: The sequence of a peptide, polypeptide, protein or nucleic acid as found in nature.

Recombinant peptide, polypeptide, protein or nucleic acid: peptide, polypeptide, protein or nucleic acid that has been produced and/or manipulated using molecular biology techniques such as cloning, polymerase chain reaction (PCR), etc.

Type-specific: associated primarily with a single phyletic group.

Invasive infection: An OspC protein is said to be “associated with invasive infection” if Borrelia bearing the OspC type have been isolated during human infection from locations other than the skin surrounding the initial inoculation by tick bite (e.g. from plasma, cerebrospinal fluid, etc.).

The invention thus provides recombinant chimeric proteins that comprise multiple linear epitopes from the loop 5 and/or alpha helix 5 regions, at least two of which are from different OspC types that are associated with invasive infection. Preferably, antigenic epitopes representing from about 2 to about 20, and preferably from about 6 to about 10, different OspC types are included in a single chimeric protein. While typically at least two of the epitopes are different from one another in primary sequence and originate from different OspC types, it is also possible to include multiple copies of a single type of epitope in a chimera, or to include several sequences that are based on or derived from the original sequence of the same OspC type. While the total number of linear epitopes in a chimera may vary somewhat, in general, the range will be from about 10 to 20. In one embodiment of the invention, the immunodominant epitopes are selected from two or more of OspC types Smar, PLi, H13, PFiM, SL10, PMit, PKi, Pbes, HT22, Pko, PLj7, VS461, DK15, HT25, A, 72a, F, E, M, D, U, I, L, H, Szid, PHez, PWa, B, K, N, C. In one embodiment, the chimeric protein is tetravalent and contains epitopes from types A, B, K and D. In another, embodiment, the chimeric protein is octavalent and contains epitopes from OspC types E, N, I, C, A, B, K and D. However, those of skill in the art will recognize that epitopes from other combinations of OspC types may also be used, so long as the resulting chimera produces a suitable immune response and/or is effective as a vaccine in preventing Lyme disease. Examples of other suitable combinations include but are not limited to: 1) E, N, I, C, A, B, K, D; 2) A, B, K, D, E, N, C; 3) I, C, A, B, K, D; and 4) C, A, B, K, D.
In some embodiments, both the loop 5 and alpha helix 5 regions will be included. For example, an “E, N, I, C, A, B, K, D” construct may contain both the loop 5 and helix 5 regions of each of OspC types E, N, I, C, A, B, K, and D. However, this need not be the case. For example, the loop 5 region of type A and the alpha helix 5 regions of E, N, I, C, B, K, and D may be included; or only the loop 5 region for each OspC type may be included; or only the alpha helix 5 region; or other combinations may be included (e.g. loop 5 region of types E, N, I, and C and the alpha helix 5 region of types A, B, K, and D. Many such combinations will occur to those of skill in the art, and all such variations are intended to be encompassed herein.
Further, the linear order of the epitopes within a chimera may vary. In general, the order, from amino to carboxyl terminus, will be “loop 5 region, alpha helix 5 region, loop 5 region, alpha helix 5 region . . . ” etc. For example, in the case of the E, N, I, C, A, B, K, D construct, a preferred order is “E-type loop 5 region, E-type alpha helix 5 region; N-type loop 5 region, N-type alpha helix 5 region; 1-type loop 5 region, 1-type alpha helix 5 region . . . ”., etc. along the length of the chimera, with the different OspC types and/or the different domains optionally separated by neutral linker sequences. However, this order may vary, depending, for example, on the elements that are chosen for inclusion in the chimera. Any order of OspC types and domains may be used, so long as the resulting chimera produces a suitable immune response and/or is effective as a vaccine in preventing Lyme disease, or can be effectively used in a diagnostic. Examples of exemplary chimera sequences are given in FIG. 25A-J. A key to the protein and DNA accession numbers for OspC from several strains of Borrelia is presented in tabular form in FIG. 26.
The amino acid sequences that are included in the chimeric protein may comprise the alpha helix 5 and/or the loop 5 regions, or antigenic fragments thereof. By “antigenic fragment” we mean a segment of the primary OspC sequence that contains at least one linear epitope recognized during infection. Such an epitope, when expressed in a recombinant protein subunit of OspC, retains the ability to bind infection-induced antibodies in a manner similar to the binding of wild-type protein expressed at the cell surface. An individual antigenic fragment may contain more than one distinct epitope. Those of skill in the art will recognize that measurement of the affinity or avidity of antibodies for an epitope is somewhat imprecise, and that the affinity/avidity can change significantly during the immune response, e.g. by affinity maturations/somatic hypermutataiton. In general, however, the affinity/avidity of binding of antibodies to the chimeric protein is in the range of at least about 50%, preferably about 60%, more preferably about 70%, even more preferably about 80%, and most preferably about 90-100% or even greater, than the affinity exhibited by native, intact alpha 5 or loop 5. In general, the antigenic sequences that are included in the chimeric proteins will contain from about 20 to about 100 amino acids, and preferably from about 30 to about 70 amino acids, and the chimeric proteins themselves will contain a total of from about 160 to about 800 amino acids, and preferably from about 240 to about 560 amino acids. Further, the antigenic sequences may be referred to herein as “epitopes”, whether or not they include an entire “natural” epitope, so long as they possess the antibody binding characteristics described herein.
Alternatively, appropriate antigen fragments or antigenic sequences or epitopes may be identified by their ability, when included in a chimeric protein, to elicit suitable antibody production to the epitope in a host to which the chimeric protein is administered. Those of skill in the art will recognize that definitions of antibody titer may vary. Herein, “titer” is taken to be the inverse dilution of antiserum that will bind one half of the available binding sites on an ELISA well coated with 100 ng of test protein. In general, suitable antibody production is characterized by an antibody titer in the range of from about 100 to about 100,000, and preferably in the range of from about 10,000 to about 10,000,000. Alternatively, and particularly in diagnostic assays, the “titer” should be about three times the background level of binding. For example, to be considered “positive”, reactivity in a test should be at least three times greater than reactivity detected in serum from uninfected individuals. Preferably, the antibody response is protective, i.e. prevents or lessens the development of symptoms of disease in a vaccinated host that is later exposed to Borrelia, compared to an unvaccinated host.
The amino acid sequence of one exemplary chimeric protein according to the invention is presented in FIG. 9B. In this illustrative embodiment, the chimera contains loop 5 region amino acid sequences from Type A OspC, and alpha helix 5 regions sequences from OspC types B, K and D. In this case, the Type A OspC sequence is from strain LDP56, with nucleotide accession number EF053513 and protein accession number ABK41054; the Type B OspC is from strain LDP73, with nucleotide accession number EF053525 and protein accession number ABK41066; the Type K OspC is from strain LDP89, with nucleotide accession number EF053523 and protein accession number ABK41064; and the Type D OspC is from strain LDP116, with nucleotide accession number EF053527 and protein accession number ABK41068. Those of skill in the art will recognize that OspC from many strains of Borrelia are known or may be discovered, and may be used in the practice of the present invention.
Those of skill in the art will recognize that, while in some embodiments of the invention, the amino acid sequences that are chosen for inclusion in the chimeric protein of the invention correspond directly to the primary amino acid sequence of the original or native sequence of the OspC protein, this need not be the case. The amino acid sequence of an epitope that is included in the chimeric protein of the invention may be altered somewhat and still be suitable for use in the present invention. For example, certain conservative amino acid substitutions may be made without having a deleterious effect on the ability of the epitope to elicit an immune response. Those of skill in the art will recognize the nature of such conservative substitutions, for example, substitution of a positively charged amino acid for another positively charged amino acid; substitution of a negatively charged amino acid for another negatively charged amino acid; substitution of a hydrophobic amino acid for another hydrophobic amino acid; etc. All such substitutions or alterations of the sequence of an epitope that is contained in the chimeric protein of the invention are intended to be encompassed by the present invention, so long as the resulting epitope still functions to elicit a suitable immune response. In addition, the amino acid sequences that are included in the chimeric proteins of the invention need not encompass a full length native epitope or epitope-containing domain. Those of skill in the art will recognize that truncated versions of amino acid sequences that are known to be or to contain epitopes may, for a variety or reasons, be preferable for use in the present invention, so long as the criteria set forth for an epitope is fulfilled by the sequence. Amino acid sequences that are so substituted or otherwise altered may be referred to herein as “based on” or “derived from” the original wild type or native sequence. In general, the OspC proteins from which the linear epitopes are “derived” or on which the linear epitopes are “based” are the OspC proteins as they occur in nature. These natural OspC proteins may alternatively be referred to as native or wildtype proteins.
Such changes to the primary sequence may be introduced for any of a variety of reasons, for example, to eliminate or introduce a protease cleavage site, to increase or decrease solubility, to promote or discourage intra- or inter-molecular interactions such a folding, ionic interactions, salt bridges, etc, which might otherwise interfere with the presentation and accessibility of the individual epitopes along the length of the chimera. All such changes are intended to be encompassed by the present invention, so long as the resulting amino acid sequence functions to elicit a protective antibody reaction to the OspC type from which the epitope originates. In general, such substituted sequences will be at least about 50% identical to the corresponding sequence in the native protein, preferably about 60 to 70, or even 70 to 80, or 80 to 90% identical to the wild type sequence, and preferably about 95 to about 100% identical.
In some embodiments of the invention, the individual linear epitopes in the chimeric vaccinogen are separated from one another by intervening sequences that are more or less neutral in character, i.e. they do not in and of themselves elicit an immune response to Borrelia. Such sequences may or may not be present between the epitopes of a chimera. If present, they may, for example, serve to separate the epitopes and contribute to the steric isolation of the epitopes from each other. Alternatively, such sequences may be simply artifacts of recombinant processing procedures, e.g. cloning procedures. Such sequences are typically known as linker or space peptides, many examples of which are known to those of skill in the art. See, for example, Crasto, C. J. and J. A. Feng. 2000. LINKER: a program to generate linker sequences for fusion proteins. Protein Engineering 13(5): 309-312, which is a reference that describes unstructured linkers. Structured (e.g. helical) sequence linkers may also be designed using, for example, existing sequences that are known to have that secondary structure, or using basic known biochemical principles to design the linkers. In addition, other elements may be present in the chimeric proteins, for example leader sequences or sequences that “tag” the protein to facilitate purification or detection of the protein, examples of which include but are not limited to histidine tags, detection tags (e.g. S-tag, or Flag-tag), other antigenic amino acid sequences such as known T-cell epitope containing sequences and protein stabilizing motifs, etc. In addition, the chimeric proteins may be chemically modified, e.g. by amidation, sulfonylation, lipidation, or other techniques that are known to those of skill in the art.
The invention further provides nucleic acid sequences that encode the chimeric proteins of the invention. Such nucleic acids include DNA, RNA, and hybrids thereof, and the like. Further, the invention comprehends vectors which contain or house such coding sequences. Examples of suitable vectors include but are not limited to plasmids, cosmids, viral based vectors, expression vectors, etc. In a preferred embodiment, the vector will be a plasmid expression vector.
The chimeric proteins of the invention may be produced by any suitable method, many of which are known to those of skill in the art. For example, the proteins may be chemically synthesized, or produced using recombinant DNA technology (e.g. in bacterial cells, in cell culture (mammalian, yeast or insect cells), in plants or plant cells, or by cell-free prokaryotic or eukaryotic-based expression systems, by other in vitro systems, etc.).
The present invention also provides compositions for use in eliciting an immune response which may be utilized as a vaccine to prevent or treat Borrelia infection, particularly when manifested as Lyme disease (Lyme borreliosis). By eliciting an immune response, we mean that administration of the antigen causes the synthesis of specific antibodies (at a titer as described above) and/or cellular proliferation, as measured, e.g. by 3H thymidine incorporation. By “vaccine” we mean a chimeric protein that elicits an immune response which results protection against challenge with Borrelia, either wholly or partially preventing or arresting the development of symptoms related to Borrelia infection (i.e. the symptoms of Lyme disease), in comparison to a non-vaccinated (e.g. adjunct alone) control organisms. The compositions include one or more substantially purified recombinant chimeric proteins as described herein, and a pharmacologically suitable carrier. The plurality of chimeric proteins in the composition may be the same or different, i.e. the composition may be a “cocktail” of different chimeras, or a composition containing only a single type of chimera. The preparation of such compositions for use as vaccines is well known to those of skill in the art. Typically, such compositions are prepared either as liquid solutions or suspensions, however solid forms such as tablets, pills, powders and the like are also contemplated. Solid forms suitable for solution in, or suspension in, liquids prior to administration may also be prepared. The preparation may also be emulsified. The active ingredients may be mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredients. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol and the like, or combinations thereof. In addition, the composition may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents, and the like. The vaccine preparations of the present invention may further comprise an adjuvant, suitable examples of which include but are not limited to Seppic, Quil A, Alhydrogel, etc. If it is desired to administer an oral form of the composition, various thickeners, flavorings, diluents, emulsifiers, dispersing aids or binders and the like may be added. The composition of the present invention may contain any such additional ingredients so as to provide the composition in a form suitable for administration. The final amount of chimeric protein in the formulations may vary. However, in general, the amount in the formulations will be from about 0.01-99%, weight/volume.
The methods involve administering a composition comprising a chimeric recombinant protein in a pharmacologically acceptable carrier to a mammal. The vaccine preparations of the present invention may be administered by any of the many suitable means which are well known to those of skill in the art, including but not limited to by injection, inhalation, orally, intranasally, by ingestion of a food product containing the chimeric protein, etc. In preferred embodiments, the mode of administration is subcutaneous or intramuscular. In addition, the compositions may be administered in conjunction with other treatment modalities such as substances that boost the immune system, chemotherapeutic agents, and the like.
The present invention provides methods to elicit an immune response to Borrelia and to vaccinate against Borrelia infection in mammals. In one embodiment, the mammal is a human. However, those of skill in the art will recognize that other mammals exist for which such vaccinations would also be desirable, e.g. the preparations may also be used for veterinary purposes. Examples include but are not limited to companion “pets” such as dogs, cats, etc.; food source, work and recreational animals such as cattle, horses, oxen, sheep, pigs, goats, and the like; or even wild animals that serve as a reservoir of Borrelia (e.g. mice, deer). The invention also provides a diagnostic and a method for using the diagnostic to identify individuals who have antibodies to the epitopes contained within the chimeric proteins of the invention. A biological sample from an individual (e.g. a human, a deer, or other mammals susceptible to infection by Borrelia spirochetes) suspected of having been exposed to Borrelia, or at risk for being exposed to Borrelia, is contacted with the chimeric proteins of the invention. Using known methodology, the presence or absence of a binding reaction between the chimeric protein and antibodies in the biological sample is detected. A positive result (binding occurs, thus antibodies are present) indicates that the individual has been exposed to and/or is infected with Borrelia. In this connection, depending on the goal of the analysis, chimeras specific for any subset of interest of OspC types may be constructed, i.e. all possible OspC types may or may not be included in the diagnostic chimera.
Further, the diagnostic aspects of the invention are not confined to clinical use or home use, but may also be valuable for use in the laboratory as a research tool, e.g. to identify Borrelia spirochetes isolated from ticks, to investigate the geographical distribution of OspC types, etc.
The present invention also encompasses antibodies to the epitopes and/or to the chimeric proteins disclosed herein. Such antibodies may be polyclonal, monoclonal or chimeric, and may be generated in any manner known to those of skill in the art. In a preferred embodiment of the invention, the antibodies are bactericidal (borreliacidal), i.e. exposure of Borrelia spirochetes to the antibodies causes death of the spirochetes. Such antibodies may be used in a variety of ways, e.g. as detection reagents to diagnose prior exposure to Borrelia, as a reagent in a kit for the investigation of Borrelia, to treat Borrelia infections, etc.
The following Examples are provided to illustrate various embodiments of the invention, but should not be considered as limiting in any way.
EXAMPLES
Example 1
Demonstration of OspC type Diversity in Invasive Human Lyme Disease Isolates and Identification of Previously Uncharacterized Epitopes that Define the Specificity of the OspC Antibody Response
Introduction
Lyme disease is transmitted to humans through the bite of Ixodes ticks infected with Borrelia burgdorferi, B. garinii or B. afzelii. Outer surface protein C (OspC) is thought to be an important virulence factor involved in the transmission process and possibly in the establishment of early infection in mammals (Grimm et al, 2004; Parl et al, 2004; Schwan et al., 1995). OspC is a variable,  ̃22 kDa, surface exposed, plasmid-encoded lipoprotein (Fuchs et al., 1992; Marconi et al., 1993; Sadziene et al., 1993). Crystal structures have been determined for three OspC proteins (Eicken et al, 2001; Kumaran et al, 2001). The protein is largely helical with 5 alpha helices connected by variable loops. The loops have been postulated to form ligand binding domains (Eicken et al, 2001; Kumaran et al, 2001). Evidence suggests that OspC may facilitate translocation of spirochetes from the tick midgut by serving as an adhesin that binds to unidentified receptors in the salivary gland (Pal et al, 2004). Orthologs of OspC have been identified in several species of the relapsing fever group raising the possibility that the OspC related proteins carry out a similar role in other Borrelia species (Marconi et al, 1993; Margolis et al, 1994). OspC expression is environmentally regulated, induced by tick feeding, and OspC is a dominant antigen during early infection in mammals (Alverson et al, 2003; Schwan et al, 1998; Stevenson et al, 1995). Transcription is regulated, at least in part, by the RpoN/S regulatory network (Hubner et al, 2001). It should be noted that there are conflicting reports regarding the precise details of the temporal nature of OspC expression during transmission and during early infection (Ohnishi et al., 2001; Schwan et al, 1995).
OspC exhibits significant genetic and antigenic diversity (Theisen et al, 1995; Theisen et al, 1993). Twenty one OspC phyletic groups (henceforth referred to as OspC types) have been delineated (Seinost et al., 1999; Wang et al, 1999). OspC types are differentiated by letter designations (A through U). Analysis of several hundred OspC amino acid sequences that are in the databases indicates that divergence between OspC types can be as high as 30% while within a type it is generally less than 6%. Seinost et al. have hypothesized a correlation between OspC types A, B, I and K and invasive infections in humans (Seinost et al., 1999). Lagal et al. also reported that specific ospC variants, as defined by single-strand conformation polymorphism analysis, correlate with invasive human infections (Lagal et al, 2003). However, a recent study by Alghaferi and colleagues has called into question the strength of this correlation (Alghaferi et al., 2005). The influence of OspC type or sequence on function and the host-pathogen interaction represents an important and fertile area of investigation. OspC has been investigated for use in Lyme disease vaccine development (Bockenstedt et al. 1997; Gilmore et al., 2003; Gilmore et al., 1999a; Probert et al., 1994; Theisen et al, 1993; Wilske et al, 1996). However, OspC variation and limited knowledge of the antigenic structure of OspC have complicated these efforts. OspC has protective capability, but only against the same strain (Bockenstedt et al. 1997; Gilmore et al., 1999; Gilmore et al., 1999b; Probert and LeFebvre, 1994; Wilske et al, 1996). This suggests that the protective epitopes reside within regions of the protein that are highly variable in sequence.
The goals of this study were several fold. First, further assessment of the putative correlation between OspC type and invasive infections was sought by determining the OspC type of invasive and non-invasive isolates recovered from a defined patient population in Maryland. Second, in an attempt to better understand the antibody response to OspC, determination of whether or not that response is type specific was sought. Finally, definition of the antigenic structure of OspC was sought by identifying epitopes that elicit an antibody response during infection in mice. The data presented here indicate that the number of OspC types associated with invasive infection is greater than previously postulated (Seinost et al., 1999). In addition, we have identified two previously uncharacterized epitopes and have demonstrated that the antibody response to OspC appears to be type specific. These analyses provide important information that enhance our understanding of the role of OspC in Lyme disease pathogenesis and that will facilitate the construction of an OspC based vaccine.
Experimental Procedures
Bacterial isolates, cultivation and generation of infection serum. Lyme disease isolates recovered from human patients in Maryland were employed in these analyses (Table 1). Patients provided informed consent prior to the study as approved by the John Hopkins Medicine Institutional Review Board. The spirochetes were cultivated in BSK-H complete media (Sigma) at 33° C., monitored by dark-field microscopy and harvested by centrifugation. Clonal populations were generated for some isolates by sub-surface plating as previously described (Sung et al., 2000). To determine the ospC type of individual colonies, the ospC gene was PCR amplified, sequenced and comparative sequence analyses were performed (as described below). To generate antisera against a series of clonal populations expressing OspC proteins of known type, 103 spirochetes were washed in phosphate buffered saline (PBS) and needle inoculated into C3H-HeJ mice (sub-cutaneous, between the shoulder blades; Jackson Labs). Infection of the mice was confirmed by real time PCR of ear punch biopsies at wk 2 or 4 post-inoculation using primers targeting the flaB gene as previously described (Zhang et al., 2005). Blood was collected from each mouse at 0, 2, 4 and 8 wks by tail snip and the infection serum was harvested. Additional antisera and infection serum used in these analyses have been described previously (McDowell et 1., 2002).







TABLE 1







Bacterial isolates, source information and OspC type.











B. burgdorferi

OspC



Isolate
Source
type







B31MI
Tick
A



5A4
Clone derived from B31MI
A



LDP56
Human blood
A



LDP61
Human blood
A



LDP60
Human blood
A



LDP80
Human blood
A



LDP76
Human blood
A



LDS106
Human skin
A



LDP73
Human blood
B



LDS79
Human skin
H



LDS101
Human skin
H



LDP84
Human blood
C



LDP63
Human blood
N



LDC83
Human CSF
N



LDP120
Human blood
N



LDP74
Human blood
K



LDS81
Human skin
K



LDS88
Human skin
K



LDP89
Human blood
K



LDP116
Human blood
D










DNA isolation, OspC typing and computer assisted structural analyses. To determine the OspC type, total DNA was isolated from each strain as previously described (Marconi et al., 2003) and used as template for PCR with the OspC20(+)LIC and OspC210(−)LIC primers (Table 2). PCR was performed using Expand High Fidelity polymerase (Roche) with the following cycling conditions: Initial denaturation at 94° C. for 2 minutes; 94° C. for 15 s, 50° C. for 30 s, 68° C. for 60 s for 10 cycles; 94° C. for 15 s, 50° C. for 30 s, 68° C. for 60 s with an additional 5 s added to each of the last 20 cycles; final elongation at 68° C. for 7 minutes. The amplicons were recovered using QiaQuick PCR Purification kit (Qiagen), treated with T4 DNA polymerase to generate single strand overhangs, annealed into the pET-32 Ek/LIC vector (Novagen) and transformed into E. coli NovaBlue (DE3) cells (Novagen). The methods for these procedures were as described by the manufacturer. Colonies were selected for ampicillin resistance (50 μg ml-1) and screened for the ospC insert by PCR. Selected colonies were transferred into LB broth (Fisher), cultivated at 37° C. with shaking (300 rpm) and the plasmids isolated using QiaFilter Midi Plasmid Isolation Kits (Qiagen). The ospC inserts were sequenced on a fee for service basis (MWG Biotech). The determined sequences were translated and aligned using ClustalX (35) with default parameters. To determine OspC type, a neighbor joining tree was created, and bootstrap values calculated (1000 trials). The resultant phylogram was visualized with N-J Plotter. Additional OspC sequences available in the databases were included in the analysis. Structural models for OspC were generated using the NCBI molecular modeling database files 1GGQ, 1F1M, and 1G5Z (4, 15) and CN3D software available at the website at ncbi.nlm.nih.gov/Structure/CN3D/cn3d.shtml.








TABLE 2







Polymerase Chain Reaction Primers employed



in this study.












SEQ





ID



Primer
Sequence a
NO:





ospC 20(+) LIC
GACGACGACAAGATTAATAATTCAGGGAAA
163




GATGGG


 


ospC 40(+) LIC
GACGACGACAAGATTCCTAATCTTACAGAA
164



ATAAGTAAAAAAAT


 


ospC 60(+) LIC
GACGACGACAAGATTAAAGAGGTTGAAGCG
165



TTGCT


 


ospC 80(+) LIC
GACGACGACAAGATTAAAATACACCAAAAT
166



AATGGTTTG


 


ospC 100(+) LIC
GACGACGACAAGATTGGAGCTTATGCAATA
167



TCAACCC


 


ospC 130(+) LIC
GACGACGACAAGATTTGTTCTGAAACATTT
168



ACTAATAAATTAAAAG


 


ospC 136(+) LIC
GACGACGACAAGATTAATAAATTAAAAGAA
169



AAACACACAGATCTTG


 


ospC 142(+) LIC
GACGACGACAAGATTCACACAGATCTTGGT
170



AAAGAAGG


 


ospC 151(+) LIC
GACGACGACAAGATTACTGATGCTGATGCA
171



AAAGAAG


 


ospC 171(+) LIC
GACGACGACAAGATTGAAGAACTTGGAAAA
172



TTATTTGAATC


 


ospC 191(+) LIC
GACGACGACAAGATTCTTGCTAATTCAGTT
173



AAAGAGCTTAC


 


ospC 130(−) LIC
GACGACAAGCCCGGTTTAACATTTCTTAGC
174



CGCATCAATTTTTTC


 


ospC 150(−) LIC
GACGACAAGCCCGGTTTAAACACCTTCTTT
175



ACCAAGATCTGT


 


ospC 170(−) LIC
GACGACAAGCCCGGTTTAAGCACCTTTAGT
176



TTTAGTACCATT


 


ospC 190(−) LIC
GACGACAAGCCCGGTTTACATCTCTTTAGC
177



TGCTTTTGACA


 


ospC 200(−) LIC
GACGACAAGCCCGGTTTAGCTTGTAAGCTC
178



TTTAACTGAATTAGC


 


ospC 210(−) LIC
GACGACAAGCCCGGTTTAAGGTTTTTTTGG
179



ACTTTCTGC





a LIC tail sequences are underlined






Generation of recombinant proteins. To generate full length and truncations of OspC, primers were designed based on the type A ospC sequence of B. burgdorferi B31 MI (Fraser et al., 1997). The primers possess tail sequences that allow for annealing into the pET-32 Ek/LIC vector (Novagen), a ligase independent cloning (LIC) and expression vector. All LIC procedures were as previously described (Hovis et al, 2004). To verify the sequence of all constructs, recombinant plasmids were purified from E. coli NovaBlue (DE3) cells using QiaFilter Midi Plasmid Purification kits (Qiagen), and the inserts were sequenced (MWG Biotech).
SDS-PAGE and immunoblot analyses. Proteins were separated in 12.5% Criterion Precast Gels (Biorad) by SDS-PAGE and immunoblotted onto PVDF membranes (Millipore) as previously described (Roberts et al, 2002). Expression of recombinant proteins was confirmed using S-Protein horseradish peroxidase (HRP) conjugate (Novagen), which detects the N-terminal S-Tag fusion that is carried by all recombinant proteins employed in this study. The HRP conjugated S-Protein was used at a dilution of 1:10,000. For immunoblot analyses, serum collected from infected mice was used at a dilution of 1:1000. HRP conjugated goat anti-mouse IgG served as the secondary (Pierce) and was used at a dilution of 1:10,000. General immunoblot methods were as previously described (Metts et al, 2003).
Results
ospC typing analysis of isolates recovered from human Lyme disease patients in Maryland. ospC was successfully amplified from each of the isolates analyzed that were recovered from the human Lyme disease patients from Maryland. The sequence of each amplicon was determined and comparative sequence analyses were performed to determine OspC type (FIG. 1). Representatives of several different OspC types including A (n=6), B (n=1), C (n=1), D (n=1), H (n=2), K (n=4) and N (n=3) were identified. It had been previously reported that only OspC types A, B, I and K are associated with invasive infections in humans (Seinost et al., 1999). In that study, invasive isolates were defined as those that were recovered from blood, organs or cerebrospinal fluid whereas non-invasive isolates were those that were recovered from the skin but not found at other body sites (Seinost et al, 1999). However, here it is demonstrated that some isolates expressing OspC types C, D, and N were recovered from blood (LDP84, LDP63, LDP116, and LDP120) or cerebrospinal fluid (LDC83) and hence are invasive. This observation suggests that the correlation of specific OspC types with invasive infection may not be a strict one and that the strength of the correlation requires re-evaluation.
Analysis of the type specificity of the antibody response to OspC during infection in mice. To determine if the antibody response elicited to OspC during infection is type specific, type A, B, C, D, H, K and N recombinant OspC proteins were generated for use as test antigens. The recombinant proteins were immunoblotted and screened with serum collected from mice infected with B. burgdorferi isolates of the A, B, or D OspC type (as determined above) (FIG. 2). Expression of the recombinant proteins in E. coli and the equal loading of protein was confirmed by screening one immunoblot with HRP conjugated S-Protein which recognizes the S-Tag in the N-terminal fusion. When screened with anti-B. burgdorferi B31MI antiserum (type A OspC) collected at wk 2 of infection, strong reactivity was detected only with the type A protein. The strong and early IgG response to OspC is consistent with earlier reports (Theisen et al, 1995; Wilske et al, 1993). Sera collected at wk 8 of infection also reacted predominantly with type A OspC but weak cross immunoreactivity with other OspC types was observed. The Ab response to OspC in mice infected with LDP116 and LDP73 (OspC type D and β isolates respectively) was also type specific. It can be concluded that there is a significant degree of type specificity in the antibody response to OspC and that this specificity implies that the in vivo immunodominant epitopes are located within the type specific domains of the protein.
Localization of the OspC linear epitopes that elicit an antibody response during infection in mice. To identify the linear epitopes of type A OspC that elicit an antibody response during infection, several recombinant OspC fragments were generated and screened with α-B. burgdorferi B31MI infection serum (wk 8) (FIG. 3). B31MI is an OspC type A producing strain. The expression of the recombinant proteins was confirmed by immunoblotting with the HRP conjugated S-Protein. To localize the linear epitopes of OspC, immunoblots of the OspC fragments were screened with infection serum. Two domains containing one or more epitopes were localized, one within the C-terminal half of the protein between residues 168 and 203 of alpha helix 5 and the other between residues 136 and 150 of helix 3 and loop 5 (henceforth, referred to as the alpha 5 and loop 5 epitopes, respectively). These epitopes have not been previously characterized in the literature.
ospC sequence analyses and computer modeling of OspC Structure. To determine where the loop 5 and alpha 5 epitopes spatially reside on the OspC protein, the coordinates determined by X-ray crystallographic analyses (Eicken et al., 2001; Kumaran et al, 2001) were accessed and ribbon and space fill models were generated for monomeric and or dimeric forms of type A OspC (data not shown). Monomeric forms of type I and E OspC proteins were also modeled. These analyses revealed that the loop 5 epitope is surface exposed on both the monomeric and dimeric forms of type A, E and I OspC proteins. In the original X-ray crystallographic analyses, portions of both the N- and C-termini were either not part of the recombinant protein or could not be modeled. In any event, the determined structures indicate that both the N- and C-termini reside in close proximity to one another and are proximal to the cell membrane.
To assess sequence variation within the loop 5 and alpha 5 epitopes at the intra-type level, 227 OspC sequences were aligned. These analyses revealed that both the loop 5 and alpha 5 epitopes are highly variable at the inter-type level but remarkably highly conserved within a type. FIG. 4 provides (in tabular form) the loop 5 and alpha 5 domain sequences for each OspC type and indicates the frequency with which each specific sequence was detected in the OspC sequences analyzed. As evidence for the conservation of loop 5 at the intra-type level, comparison of 57 type A loop 5 epitopes sequences revealed that 53 were identical with the outlying sequences differing at only one or two residues. A similar observation was noted for the alpha 5 epitopes. Of 43 type A OspC sequences, 42 were identical between residues 168 and 203. Note that fewer alpha 5 epitope sequences were analyzed since in many cases the sequences available in the databases were partial and lacked varying amounts of the C-terminus.
Demonstration that the antibody response to the loop 5 epitope is not unique to an individual mouse. In view of the intra-type conservation of loop 5 and its relatively short length, the loop 5 epitope might be an excellent candidate for use in the development of a chimeric OspC loop 5 based vaccinogen. To verify that the antibody response to the loop 5 epitope occurs commonly during infection and was not unique to an individual mouse, immunoblots of the loop 5 containing 130-150 fragment were screened with serum from several additional mice infected with the type A OspC producing strains, B31MI, LDP56 and 5A4. In all cases, antibody was detected that recognized this epitope (FIG. 5). While the response to loop 5 was weaker in the infection serum from the LDP56 infected mouse 2, longer exposure clearly revealed that loop 5 was antigenic in this animal. This demonstrates that the immune response mounted to these epitopes is not unique to an individual animal and provides further support for its possible use in vaccine development.
Discussion
OspC is clearly established as an important contributor to Lyme disease pathogenesis (Grimm et al, 2004; Pal et al, 2004; Schwan et al, 1995). There is strong evidence that it plays an important role during the transit of the Lyme disease spirochetes from the midgut to the salivary gland (Pal et al, 2004). In addition, it is selectively expressed during early infection, is an immunodominant antigen (Fingerle et al, 1995; Schwan et al, 1998; Wilske et al, 1993) and has been hypothesized by others to be a key determinant in the dissemination capability of Lyme disease isolates (Seinost et al., 1999). The goals of this study were to test the potential correlation between OspC type and invasive infection, determine if the antibody response to OspC is type specific and further define the antigenic structure of OspC by localizing the linear epitopes that are presented during infection.
Sequence analyses of OspC have delineated 21 distinct OspC types (Seinost et al., 1999) and it has been postulated that only four of these (types A, B, I and K) are associated with invasive infections in humans (Seinost et al., 1999). However, a recent study has called into question this putative correlation (Alghaferi et al., 2005). To address this further, the OspC type of invasive and non-invasive Lyme disease isolates recovered from human patients in Maryland was determined. To accomplish this the full length ospC gene was PCR amplified, sequenced and comparative sequence analyses were performed. These analyses revealed that the OspC types associated with invasive human infections in this patient population also includes types C, D, and N. While type I OspC producing strains have been suggested to be a dominant type associated with invasive human infections (Seinost et al., 1999), none of the invasive isolates identified in the Maryland patient population carried a type I ospC. Similarly, Alghaferi et al. also did not detect type I OspC producing strains (Alghaferi et al., 2005). Collectively, these two studies have identified 18 invasive isolates in the greater Baltimore area with the following breakdown: A, n=5; B, n=2; C, n=1; D, n=1; H, n=1; K, n=3 and N, n=7. Hence, in this geographic area it appears that OspC type A and N producing invasive isolates predominate. These data argue against the hypothesis that only 4 OspC types are associated with invasive infections in humans. Additional analyses of isolates recovered from larger patient populations from different geographic regions will be required to further assess the validity of OspC type-invasive infection correlation and to determine if differences exist in the prevalence of specific OspC types in defined geographic regions.
The variable protection offered by vaccination with OspC in conjunction with the delineation of distinct OspC types (Seinost et al., 1999), raises the possibility that the antibody response could be type specific. This hypothesis is supported by the fact that vaccination with OspC has been found to provide protection only against the same strain (Bockenstadt et al., 1997; Gilmore et al, 1999a; Probert and LeFebvre, 1994). Until this report, the type specificity of the antibody response to OspC during infection had not been directly assessed. To address this, a series of full length recombinant OspC proteins of types A, B, C, D, H, K and N were screened with infection serum generated in mice with clonal populations expressing known OspC types. The use of infection serum is important as it allows for a focused assessment of the antibody response to epitopes that are specifically presented by the bacterium in vivo. These analyses revealed that in spite of strong sequence conservation within the N and C-terminal domains of OspC, the antibody response to the OspC types analyzed was type specific. For example, serum from mice infected with type A or D strains was immunoreactive in a type specific manner with little or no cross-immunoreactivity with other OspC types. Although the antibody response to all 21 OspC types was not analyzed, the data presented above suggest that the conserved domains are not immunodominant and that the linear epitopes of OspC presented by the bacterium during infection are contained within the variable domains (i.e., type specific domains) of the protein.
Only a few studies have been published to date that have sought to localize or identify the epitopes of OspC. Both linear and conformational epitopes have been identified. Gilmore and Mbow demonstrated that independent N terminal deletions beyond the leader peptide as short as 6 residues and C-terminal truncations of 13 residues abolish the binding of the monoclonal antibody B5 (Gilmore et al, 1999a; Gilmore, 1998). From this it was concluded that the B5 monoclonal antibody recognizes a conformationally defined epitope (Gilmore et al, 1999b). The precise residues that comprise the antibody recognition site within this conformationally defined epitope were not identified. In contrast to that observed with monoclonal antibody B5, this analysis of the polyclonal antibody response to cell associated, native OspC revealed that deletion of the last 10 C-terminal residues of OspC or of extended regions of the N-terminus did not abolish recognition of OspC by IgG elicited during infection. This difference in results is presumably a reflection of the focus on polyclonal versus monclonal antibodies. This data, which certainly do not preclude the existence of conformational epitopes, clearly demonstrate that there are linear epitopes in OspC as well. In an earlier study, Mathieson et al. also reported on a linear epitope in OspC (Mathieson et al, 1998). They found that the C-terminal 7 residues of OspC constitute a linear epitope that is recognized by IgM in serum collected from European neuroborreliosis patients. While IgM binding was not assessed in this report, deletion of the C-terminal 10 residues of OspC did not abolish IgG binding. Epitopes that are recognized by infection induced IgG appear to be localized at several sites in the protein. However, this does not suggest that a C-terminal epitope does not exist or is not recognized by antibody elicited during infection but rather that there are additional epitopes located elsewhere in OspC.
Immunoblot analysis of shorter OspC fragments allowed for more precise localization of OspC epitopes. The antigenic regions of OspC were localized to two regions. One spans residues 136-150 and the other spans residues 168 to 210. Structural models generated using coordinates from X-ray diffraction analyses place residues 136-150 largely within a surface exposed loop, termed loop 5 (Kumaran et al., 2001). Loop 5 is surface exposed in both the mono- and dimeric models of OspC and is located within a prominent bend. While it has been demonstrated that recombinant OspC does in fact form dimers, it has not yet been determined if native OspC forms dimer or larger oligomers in vivo. The dimeric model for OspC indicates a significant buried interface that comprises greater than >30% of the protein. A buried interface of this extent suggests a tight interaction between the monomers and is considered to be an indication that the dimeric form of the protein is the biologically active form [Kumaran et al., 2001; Eicken et al., 2001; Zuckert et al., 2001]. In the OspC dimer, residues within loop 5 are predicted to be a part of a putative conformationally defined ligand binding pocket that may be of biological significance. This charged pocket is lined by amino acids containing carbonyl groups such as glutamate and aspartate residues. Crystal structures have been determined for three OspC proteins of types A, I (Kumaran et al., 2001) and E (Eicken et al., 2001). In all of these proteins the solvent structures of this putative binding pocket are remarkably well conserved. The accessibility of loop 5 to antibody in infection serum supports the postulate that this domain may be surface exposed and potentially available for ligand binding. In spite of strong inter-type structural conservation of loop 5 and the putative ligand binding pocket, the sequence of this domain is highly variable at the inter-type level. The sequence of the alpha 5 domain spanning residues 168 to 210 is also variable at the inter-type level with the exception of the last 20 residues which are highly conserved. To determine if sufficient conservation exists at the intra-type level to allow for the construction of a chimeric OspC vaccine consisting of a series of type specific epitopes, OspC sequences were aligned and a dendogram was constructed. Through these analyses the OspC type was determined for 227 sequences (data not shown). Both the loop 5 and alpha 5 epitopes were found to be well conserved at the intra-type level. For example, the loop 5 epitope of type A OspC proteins were identical in 54 of 57 sequences while the alpha 5 epitope was conserved in 42 of 43 type A sequences. Significant conservation of these domains in the other OspC types was noted as well with types C through I, M, N and O exhibiting absolute intra-type conservation within the loop 5 and alpha 5 epitopes.
This study demonstrates that there is greater OspC diversity among invasive isolates than previously recognized. This study also demonstrates that the antibody response to OspC in mice is largely type specific and is defined by previously uncharacterized loop 5 and alpha 5 epitopes. Earlier studies and the data presented here clearly demonstrate that a single OspC protein will not convey protection against diverse strains (Bockenstedt et al., 1997). One possible vaccination approach is to exploit the epitopes identified in this report in the development of a recombinant chimeric OspC vaccinogen. The loop 5 epitope or a combination of loop 5 and alpha 5 epitopes may offer the most promise if they also prove to be consistently antigenic in humans. These epitopes are relatively short in length, linear, and highly conserved at the intra-type level. In light of these features it should prove technically feasible to construct a loop 5-alpha 5 chimeric vaccinogen that can convey protection against highly diverse Lyme disease isolates.
Example 2
Analysis of Antibody Response in Humans to the Type A OspC Loop 5 Domain and Assessment of the Potential Utility of the Loop 5 Epitope in Lyme Disease Vaccine Development
Outer surface protein C (OspC) of the Lyme disease spirochetes is a 22-kDa immunodominant (Fuchs et al, 1992) antigen that is expressed upon tick feeding and during early stages of infection (Schwan et al, 1995). Although a strong antibody response to OspC is mounted during natural infection, the response does not lead to bacterial clearance because OspC production is turned off shortly after the establishment of infection (Schwan et al, 1995). OspC has emerged as an important virulence factor and a potential candidate for Lyme disease vaccine development. However, efforts to develop an OspC-based vaccine have been hampered by its heterogeneity among strains (Theisen et al, 1993; Wilske et al, 1996; Wilske et al, 1993). Although vaccination with OspC elicits a highly protective response, most studies have reported only strain-specific protection (Bockenstedt et al, 1997; Gilmore et al, 1996; Mbow et al, n 1999; Probert et al, 1997; Rousselle et al, 1998; Scheiblhofer et al., 2003). Recent analyses have provided significant insight into our understanding of the antigenic structure of OspC and the basis of strain-specific protection. Twenty-one OspC types, designated A through U, have been defined (Lagal et al, 2003; Seinost et al, 1999; Wang et al, 1999). By infecting mice with clonal populations of Borrelia burgdorferi that produce specific OspC types, is has been demonstrated that the antibody response during early infection is largely OspC type specific (see Example 1). This suggests that the dominant epitopes presented during early infection are likely to reside within the type-specific domains of OspC. While earlier studies suggested that only 4 of the 21 OspC types are associated with invasive infection (Seinost et al, 1999), recent studies have demonstrated that isolates producing additional OspC types can also establish invasive infection (Alghaferi et al, 2005; Example 1). However, type A OspC appears to predominate in strains that cause invasive infections in humans. Epitope-mapping analyses of type A OspC revealed that one of the dominant linear epitopes that elicits a response in mice resides within the loop 5 domain (see Example 1). The loop 5 domain is highly variable at the intertype level but conserved within sequences of a given type (see Example 1). In the present study, we refine the location of the epitope, demonstrate its surface exposure on intact bacteria, and demonstrate that it elicits bactericidal antibody.
Most studies that have sought to define the immunodominant epitopes of OspC have been conducted with mice (Bockenstedt et al, 1997; Gilmore et al, 1996; Mbow et al, 1999; Probert et al, 1994). However, it has been demonstrated that the antibody responses to some epitopes differ for humans versus mice and other mammals (Lovrich et al, 2005). The first objective of the present study was to determine whether the loop 5 domain of OspC is recognized by antibody elicited during infection in humans. Ideally, these analyses would be conducted with serum collected from individuals infected with a clonal population of a type A-producing strain. Since one cannot determine with absolute certainty whether an individual is infected with a heterogenous or a homogenous population, we sought to identify patient sera that exhibit a response to type A-specific sequences. To accomplish this, a panel of serum samples collected from patients with erythema migrans (early-stage Lyme disease) were screened by enzyme-linked immunosorbent assay (ELISA). Recombinant type (r-type) A OspC and an r-type A OspC subfragment containing loop 5 residues 130 to 150 were used to coat 96-well plates (250 ng of r-protein/well; 0.1 M Na2HPO4; 4° C. overnight). The plates were blocked (10% nonfat dry milk in phosphate-buffered saline, 0.5% Tween 20; 37° C. for 2 h) and washed, and human Lyme disease patient serum (diluted 1:400) was added to each well (37° C.; 1 h). Horseradish peroxidase-conjugated goat anti-human immunoglobulin G (IgG; Sigma) (50 l of a 1:40,000 dilution) was added (1 h; 37° C.), followed by TMB substrate (3,3,5,5-tetramethylbenzidine) as instructed by the supplier (Sigma). The optical density values at 450 nm were determined by using a plate reader. Additional wells were coated with bovine serum albumin to serve as negative controls. All assays were performed in triplicate. The mean A450 value is presented with standard deviations. As shown in FIG. 6, several serum samples were found to have a strong IgG response to both the full-length type A OspC and the loop 5 fragment. Serum samples 8 and 44 displayed the strongest immunoreactivity with the loop 5 fragment and hence were selected for further analysis.
To more accurately define the residues within the loop 5 domain that are recognized by infection-induced antibody, PepSpot arrays were screened with the sera from patients 8 and 44 and with serum from mice infected with a clonal population of the type A OspC-producing strain B31MI (see Example 1). The PepSpot arrays consisted of 12- to 13-residue overlapping peptides (two-amino-acid step) spanning the loop 5 domain of type A OspC spotted onto Whatman 50 cellulose membrane (150 nmol/cm2; JPT Peptide Technologies GmbH, Berlin, Germany). The PepSpot membranes were blocked (5% nonfat dry milk in Tris-buffered saline—0.5% Tween 20), washed, and screened with mouse and human serum samples (diluted 1:1,000 and 1:400 in blocking solution, respectively), and antibody binding was detected with species-specific anti-IgG antiserum. Although the specific residues that make up the immunoreactive domain differed slightly in mice and humans, the major epitopes localized within residues 130 to 146 (FIG. 7). In type A OspC sequences, this region encompasses the C-terminal region of alpha helix 3 and the N-terminal portion of loop 5.
The crystal structures of OspC spatially place loop 5 on a prominent bend of the protein (Eicken et al, 2005; Kumaran et al, 2001; FIG. 24). This loop has been postulated to be part of a potential ligand-binding pocket (Kumaran et al, 2001). To determine whether loop 5 is displayed at the cell surface and is accessible to antibody in in vitro grown spirochetes, immunofluorescence assays (IFAs) were performed by using anti-loop 5 antiserum. Immunoblot analyses with whole-cell lysates of B. burgdorferi B31 MI (type A OspC), B. parkeri, and S-tagged r-type A loop 5 demonstrated that the loop 5 antiserum is specific, establishing the suitability of this antiserum for IFAs. The strains analyzed by IFA consisted of B. burgdorferi B31MI (type A OspC) and LDP74 (type K OspC). The spirochetes were grown at 33° C. and transferred to 37° C. for 3 days to stimulate OspC expression. IFAs were conducted with permeabilized cells (acetone fixed), nonpermeabilized cells (air dried), and standard methods as previously described (Roberts et al, 2002). The slides were screened with a 1:1,000 dilution of mouse-loop 5 antiserum, mouse preimmune serum, or rabbit-flagellin antiserum. Detection was achieved by using Alexa Fluor 568-conjugated goat α-mouse IgG or Alexa Fluor 488-conjugated goat α-rabbit IgG (10 μg ml−1 in blocking buffer). Slides were visualized on an Olympus BX51 fluorescence scope using a rhodamine or fluorescein filter set, as appropriate, or by dark-field microscopy, and photographed by using an Olympus MagnaFIRE camera. The labeling observed by IFA was highly specific and consistent with the immunoblot analyses; the type A-producing isolate was surface labeled, while the B. burgdorferi LDP74 type K OspC was not (data not shown). In addition, consistent with the upregulation of OspC at elevated temperature, IFAs revealed markedly greater surface labeling of spirochetes grown at 37° C. than cells grown at 33° C. The α-FlaB antiserum, which recognizes an inner-membrane anchored, periplasmic protein, did not label nonpermeabilized cells but readily labeled cells permeabilized with acetone (data not shown). This control demonstrates that the loop 5 epitope is in fact surface exposed and that the experimental conditions used in the IFA did not disrupt cell integrity and thereby artificially expose epitopes that are not naturally presented on the surface of the bacteria.
The ability of the loop 5 antiserum to efficiently bind to OspC at the cell surface raised the possibility that the interaction could be bactericidal, as has been demonstrated for antibody to full-length OspC (Bockenstedt et al, 1997; Ikushima et al, 2000; Jobe et al, 2003; Lovrich et al, 2005; Rousselle et al, 1998). To determine whether antibody targeting loop 5 also exhibits bactericidal activity, killing assays were conducted with B. burgdorferi isolates B31MI and LDP74 cultivated at 33° C. or temperature shifted to 37° C. The spirochetes were harvested by centrifugation, washed, and adjusted to 5×105 cells per 500 l (in BSK-H medium), and 12.5 μl was transferred into a sterile 0.65-ml microcentrifuge tube. Then, 10 μl of heat-inactivated (56° C.; 30 min) loop 5 serum was added with or without guinea pig complement (7.5 μl; Sigma Chemical, St. Louis, Mo.), the components were mixed and incubated at 33 or 37° C. for 8 h. A total of 70 μl of H2O was added, and spirochetes were stained with the Live/Dead BacLight stain (Molecular Probes, Eugene, Oreg.) according to the manufacturer's instructions. In brief, two stains are added to the cells; SYTO 9 and propidium iodide. These dyes can distinguish live bacteria (i.e., with intact membranes) from bacteria with compromised membranes. Live bacteria fluoresce green due to staining with SYTO 9, whereas dead or damaged bacteria fluoresce red due to staining with propidium iodide. The baseline level of cells with disrupted membranes observed upon treatment with preimmune heat inactivated serum (with or without complement) was 25%. In contrast,  ̃70% of the cells exposed to the α-loop 5 antiserum displayed membrane disruption. The bactericidal activity was determined to be complement dependent. The blebbing effect seen here upon treatment with anti-loop 5 antibody is consistent with that reported with other anti-OspC antibodies (Bockenstedt et al, 1997; Escudero et al, 1997). It is also important to note that, consistent with the upregulation of OspC at elevated temperature, the percentage of dead cells was consistently higher in spirochetes grown at 37° C. than that in bacteria grown at 33° C. (data not shown). It is clear from the data presented that anti-loop 5 antibody is bactericidal.
Several reports have outlined the clear and strong justification for the development of Lyme disease vaccines (reviewed in Hanson and Edelman, 2004). However, at the present time, no vaccine is commercially available. In an effort to develop a broadly protective Lyme disease vaccine, Baxter pursued a strategy of generating a vaccine cocktail of 14 different full-length r-OspC proteins (Hanson and Edelman, 2004). However, the cocktail was deemed unacceptably reactigenic. The reactigenicity may have resulted from the large amount of protein that was required to elicit a sufficient response to the unique protective epitopes of each OspC type protein in the cocktail. A potential problem with cocktail vaccines that use multiple full-length proteins is the potential for misdirection of the antibody response to conserved, irrelevant, nonprotective epitopes. It may be possible to overcome this problem through the development of a chimeric, r-vaccinogen composed of the naturally presented immunodominant linear epitopes of each of the dominant OspC types. This general concept has its origins in efforts to develop malarial vaccines using epitopes from proteins expressed at different stages of infection (Hanson and Edelman, 2004). The same concept has been applied in the development of a hexavalent M protein vaccine for group A streptococci (Dale, 1999) and in the development of vaccines against several other pathogens with excellent success (Apta et al, 2006; Caro-Aguilar et al, 2005; Fan et al, 2005; Horvath et al, 2005; Kotloff et al, 2005; McNeil et al, 2005; Wang et al, 2005). With new insights into the physical and antigenic structure of OspC, it may now be possible to develop an effective, r-polyvalent, chimeric, OspC vaccine. The newly identified loop 5 domain is ideally suited for inclusion in such a vaccine.
Example 3
Development of an OspC-Based Tetravalent, Recombinant, Chimeric Vacinogen
Lyme disease is the most common arthropod-borne disease in North America and Europe. At present, there is no commercially available vaccine for use in humans. Outer surface protein C (OspC) has antigenic and expression characteristics that make it an attractive vaccine candidate; however, sequence heterogeneity has impeded its use as a vaccinogen. Sequence analyses have identified 21 well defined OspC phyletic groups or “types” (designated A through U). This study reports mapping of the linear epitopes presented by OspC types B, K and D during human and murine infection and exploitation of these epitopes (along with the previously identified type A OspC linear epitopes) in the development of a recombinant, tetravalent, chimeric vaccinogen. The construct was found to be highly immunogenic in mice and the induced antibodies surface labeled in vitro cultivated spirochetes. Importantly, vaccination induced complement-dependent bactericidal antibodies against strains expressing each of the OspC types that were incorporated into the construct. These results suggest that an effective and broadly protective polyvalent OspC-based Lyme disease vaccine can be produced as a recombinant, chimeric protein.
Materials and Methods
Borrelia burgdorferi Isolates and Cultivation
Clonal populations of Borrelia burgdorferi isolates B31MI (type A OspC), LDP73 (type B), LDP 116 (type D) and LDP74 (type K) [see Example 1] were obtained by subsurface plating as previously described [Sung et al, 2000]. The OspC type of individual clones was determined by PCR amplification (Taq Polymerase, Promega) and DNA sequencing of ospC, with assignment to type by phylogenetic analysis [see Example 1]. Spirochetes were cultivated at 33 or 37° C., as indicated, in complete BSK-H medium (Sigma).
Ligase Independent Cloning and Production of Recombinant (r-) OspC Proteins
Full length type B, K and D OspC and a series of truncations and fragments were generated by PCR amplification of the corresponding gene from each isolate. The primers were designed with 5′ overhangs to allow ligase-independent cloning (LIC) in the pET-32 Ek/LIC vector (Table 3) [Example 1]. All LIC methods were performed essentially as directed by the manufacturer (Novagen). In brief, after amplification and regeneration of single stranded tails, the amplicons were annealed with the pET-32 Ek/LIC vector, which was transformed into and propagated in NovaBlue (DE3) E. coli cells. The plasmids were recovered and the insert sequences confirmed by DNA sequencing. For protein purification, purified plasmid was used to transform E. coli BL21 (DE3) cells and protein expression was induced by addition of IPTG (1 mM) to the cultures during the logarithmic growth phase followed by a three hour incubation. The N-terminal fusion added by expression from the pET-32 Ek/LIC vector contains a Trx-tag, S-tag, and a hexahistidine (His-tag) motif. The His-tag was exploited to allow purification of the r-proteins by nickel affinity chromatography. Briefly, cells were lysed and nucleic acid and cell wall peptidoglycan were degraded by benzonase nuclease and r-lysozyme, respectively. The soluble proteins were clarified by centrifugation (16000×g for 15 min), passed over an immobilized nickel column, washed, and eluted as per the manufacturer's protocol (Novagen). The eluted proteins were dialyzed extensively against phosphate buffered saline (PBS; pH 7.4) across a 10 kDa molecular weight cut-off membrane (Slid-a-lyzer, Pierce), the final protein concentration was quantified by the BCA assay (Pierce), and the purity of the preparation assessed by SDS-PAGE.








TABLE 3







PCR primers used in the generation of various



OspC type fragments. LIC tails are in bold.










Primer
Sequence
Description
SEQ ID NO:














ospC20(+)LIC
GACGACGACAAGATTAA
Amplifies OspC
180




TAATTCAGGGAAAGATGG
from aa 20 and



G
adds LIC tail


 


ospC210(+)LIC
GACGACAAGCCCGGTTT
Amplifies OspC
181



AAGGTTTTTTTGGACTTTC
up to aa 210 and



TGC
adds LIC tail


 


OCB110LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
182



ATTGTGTTATTAAGGTTGA
up to aa 110 and



TATTG
adds LIC tail


 


OCB131LIC(+)
GACGACGACAAGATCTTC
Amplifies type B
183



TGAAGAGTTTAGTACTAA
from aa 131 and



ACTAAAA
adds LIC tail


 


OCB140LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
184



ATTTTAGTTTAGTACTAAA
up to aa 140 and



CTCTTCAG
adds LIC tail


 


OCB140LIC(+)
GACGACGACAAGATAGA
Amplifies type B
185



TAATCATGCACAGCTTGGT
from aa 140 and



ATACAG
adds LIC tail


 


OCB148LIC(+)
GACGACGACAAGATTAT
Amplifies type B
186



ACAGGGCGTTACTGATGA
from aa 148 and



AAATGC
adds LIC tail


 


OCB153LIC(+)
GACGACGACAAGATTGA
Amplifies type B
187



AAATGCAAAAAAAGCTAT
from aa 153 and



TTTAAAA
adds LIC tail


 


OCB155LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
188



ATGCATTTTCATCAGTAAC
up to aa 155 and



GCCCTG
adds LIC tail


 


OCB164LIC(+)
GACGACGACAAGATTGC
Amplifies type B
189



AGCGGGTAAAGATAAGGG
from aa 164 and



CGTTGAAG
adds LIC tail


 


OCB169LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
190



ACTTATCTTTACCCGCTGC
up to aa 169 and




adds LIC tail


 


OCB175LIC(+)
GACGACGACAAGATTGA
Amplifies type B
191



AAAGTTGTCCGGATCATTA
from aa 175 and



GAAAGC
adds LIC tail


 


OCB180LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
192



ATGATCCGGACAACTTTTC
up to aa 180 and



AAGTTCTTC
adds LIC tail


 


OCB181LIC(+)
GACGACGACAAGATCTTA
Amplifies type B
193



GAAAGCTTATCGAAAGCA
from aa 181 and



GCTAAAGAG
adds LIC tail


 


OCB185LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
194



ATGATTAAGCTTTCTAATG
up to aa 185 and



ATCCGGAC
adds LIC tail


 


OCB190LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
195



ACTCTTTAGCTGCTTTTGA
up to aa 190 and



TAAGCTTC
adds LIC tail


 


OCB200LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
196



ATGTAAGCTCTTTAACTGA
and K up to aa 200



ATTAGCAAG
and adds LIC tail


 


OCB49LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
197



AAATTTTTTTACTTATTTCT
and D up to aa 49



GTAAG
and adds LIC tail


 


OCB80LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type B
198



ATTTTTTACCAATAGCTTT
up to aa 80 and



AGCAAGCTC
adds LIC tail


 


OCD112LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
199



ATAATTTTTCTGTTATTAG
up to aa 112 and



AGCTG
adds LIC tail


 


OCD130LIC(+)
GACGACGACAAGATTAA
Amplifies type D
200



ATGTTCTGAAAGCTTTAC
from aa 130 and




adds LIC tail


 


OCD135LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
201



AAAAGCTTTCAGAAACAT
up to aa 135 and



TTCTTAGC
adds LIC tail


 


OCD135LIC(+)
GACGACGACAAGATTAC
Amplifies type D
202



TAAAAAACTATCAGATAA
from aa 135 and



TCAAGCAG
adds LIC tail


 


OCD144LIC(+)
GACGACGACAAGATTGA
Amplifies type D
203



GCTTGGTATAGAGAATGC
from aa 144 and



TACTGATG
adds LIC tail


 


OCD151LIC(+)
GACGACGACAAGATTGC
Amplifies type D
204



TACTGATGATAATGCAAA
from aa 151 and



AAAGGC
adds LIC tail


 


OCD155LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
205



AATTATCATCAGTAGCATT
up to aa 155 and



CTCTATACC
adds LIC tail


 


OCD166LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
206



AAGCATTATGTGTTTTTAA
up to aa 166 and



AATAGCC
adds LIC tail


 


OCD167LIC(+)
GACGACGACAAGATTAA
Amplifies type D
207



AGACAAGGGTGCTGAAGA
from aa 167 and



ACTTG
adds LIC tail


 


OCD180LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
208



ATGATTCAGATAACTTTAC
up to aa 180 and



AAGTTC
adds LIC tail


 


OCD180LIC(+)
GACGACGACAAGATTTC
Amplifies type D
209



AGTAGCAGGCTTATTAAA
from aa 180 and



AGCAGCTC
adds LIC tail


 


OCD195LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
210



ATGAATTAGCCAGTATGG
up to aa 195 and



CTTGAGCTGC
adds LIC tail


 


OCD195LIC(+)
GACGACGACAAGATTTC
Amplifies type D
211



AGTTAAAGAGCTTACAAG
from aa 195 and



TCCTG
adds LIC tail


 


OCD80LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type D
212



AATCTATTTTTTTACCAAT
up to aa 80 and



A
adds LIC tail


 


OCK110LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
213



ATTGTGTTATTAGTTTTGA
up to aa 110 and



TATTG
adds LIC tail


 


OCK130LIC(+)
GATGACGACGACAAGAT
Amplifies type K
214



TAAATGTTCTGAAGATTTT
from aa 130 and



AC
adds LIC tail


 


OCK135LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
215



AAAAATCTTCAGAACATTT
up to aa 135 and



CTTAGC
adds LIC tail


 


OCK148LIC(+)
GATGACGACGACAAGAT
Amplifies type K
216



AATTGAAAATGTTACTGAT
from aa 148 and



GAGAATGC
adds LIC tail


 


OCK150LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
217



AATTTTCAATTCCAAGTTG
up to aa 150 and



CGCATGTTC
adds LIC tail


 


OCK160LIC(+)
GATGACGACGACAAGAT
Amplifies type K
218



TATTTTAATAACAGATGCA
from aa 160 and



GCTAAAG
adds LIC tail


 


OCK166LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
219



AAGCTGCATCTGTTATTAA
up to aa 166 and



AATAGC
adds LIC tail


 


OCK175LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
220



ATTCAAGCTCTGCAGCGC
up to aa 175 and



CCTTATC
adds LIC tail


 


OCK180LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
221



ATGCTTTAAATAGCTTTTC
up to aa 180 and



AAGCTCTGC
adds LIC tail


 


OCK180LIC(+)
GATGACGACGACAAGAT
Amplifies type K
222



TGCAGTAGAAACTTGGCA
from aa 180 and



AAAGCAGC
adds LIC tail


 


OCK190LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
223



ACTCTTTAGCTGCTTTTGC
up to aa 190 and



CTTGTTTTC
adds LIC tail


 


OCK191LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
224



ACATCTCTTTAGCTGCTTT
up to aa 191 and



TGCCAAG
adds LIC tail


 


OCK80LIC(−)
GAGGAGAAGCCCGGTTT
Amplifies type K
225



ATTTTTTACCAATAGCTTT
up to aa 80 and



AGTAGC
adds LIC tail









Immunoblot Analyses: Epitope Mapping of OspC Types B, D, and K

To allow for the mapping of epitopes relevant during infection, C3H/HeJ mice were infected with 104 spirochetes of clonal populations expressing OspC types B, K, or D and blood was collected at weeks 2, 4, 6, 8 and 12 by tail bleed. These sera were used to screen purified OspC proteins and truncations as described in Example 1. The r-proteins were subjected to SDS-PAGE, transferred to PVDF, and screened with a 1:1000 dilution of the type-specific murine infection sera (collected at wk 6). Similarly, the r-proteins were screened with serum (1:400) from patients known to have been infected with a B. burgdorferi strain expressing OspC types B, K, or D (kindly provided by Dr. Allen Steere). The appropriate IgG-specific, horseradish peroxidase (HRP)-conjugated secondary antibodies were utilized, and the results were visualized by chemiluminescence.
Construction and Expression of a Tetravalent Chimeric Vaccinogen
The loop 5 region (aa 131 to 149) of type A and the alpha helix 5 region of types B (aa 160-201), K (aa 161-201), and D (aa 161-201) were chosen for inclusion in the tetravalent test vaccinogen. Each epitope-containing region was PCR amplified from the r-plasmids described above and primers listed in Table 4. PCR conditions were standard with an initial 2 min 94° C. denaturation step, followed by 35 cycles of denaturation at 94° C. for 15 sec, primer annealing at 50° C. for 30 sec, and extension at 72° C. for 60 sec, with a final 72° C. extension for 7 min. The primers were designed with vector-specific LIC tails or with unstructured, protease-resistant linker sequences as 5′ overhangs (FIG. 9A) [Crasto and Feng, 2000]. All amplicons were analyzed by electrophoresis in agarose gels using TAE buffer and were gel purified (QiaQuick Gel Extraction, Qiagen). The purified products were then used as templates in subsequent rounds of PCR. In the second round, the amplicons of type A loop 5 and type B alpha helix 5 were combined as templates. After denaturation, the amplicons annealed via their complementary linker sequences allowing for overlap extension and subsequent amplification using the forward type A loop 5 and reverse type B alpha helix 5 primers. The types K and D alpha helix 5 sequences were added to the construct in a similar manner, except that the annealing temperature was increased to 60° C. after the first 10 cycles to increase the annealing specificity. The final product was annealed to the pET-46 Ek/LIC expression vector, which encodes an N-terminal hexahistidine tag fusion (Novagen), and NovaBlue (DE3) E. coli cells were transformed. The vaccinogen sequence was confirmed by DNA sequencing of purified plasmid. Protein expression and purification were completed as described above.








TABLE 4







PCR primers used in the generation of the ABKD chimeric



vaccinogen. LIC tails are in bold, and linker sequences


are underlined.










Primer
Sequence
Description
SEQ ID NO:














OCAL5LIC(+)
GACGACGACAAGATTTCTG
Amplifies type A
226




AAACATTTACTAATAAATTA
from aa 131 and



AAAGAAAAAC
adds LIC tail


 


OCAL5L1(−)
TAACATACCCATGCTACCTT
Amplifies type A
227



CTTTACCAAGATCTGTGTG
up to aa 149 and




adds linker 1




(GSMGML;




SEQ ID 76)


 


OCBH5L1(+)
GGTAGCATGGGTATGTTAA
Amplifies type B
228



AAGCAAATGCAGCGGG
from an 160 and




adds linker 1




(GSMGML;




SEQ ID 76)


 


OCBH5L2(−)
TAAGTTACCGTTTGTGCTTG
Amplifies type B
229



TAAGCTCTTTAACTGAATTA
up to aa 201 and



G
adds linker 2




(STNGNL;




SEQ ID 77)


 


OCKH5L2(+)
AGCACAAACGGTAACTTAA
Amplifies type K
230



TAACAGATGCAGCTAAAGA
from aa 161 and



TAAGG
adds linker 2




(STNGNL;




SEQ ID 77)


 


OCKH5L3(−)
TAAAACGCTCATGCTACTTG
Amplifies type K
231



TAAGCTCTTTAACTGAATTA
up to aa 201 and



GC
adds linker 3




(SSMSVL;




SEQ ID 78)


 


OCDH5L3(+)
AGTAGCATGAGCGTTTTAA
Amplifies type D
232



AAACACATAATGCTAAAGA
from aa 161 and



CAAG
adds linker 3




(SSMSVL;




SEQ ID 78)


 


OCDH5LIC(−)
GAGGAGAAGCCCGGTTTA
Amplifies type D
233



ACTTGTAAGCTCTTTAACTG
up to aa 201 and



AATTAG
adds an LIC tail









Immunization of Mice with the Tetravalent ABKD Chimeric Vaccinogen

Twelve six-week-old, male, C3H/HeJ strain mice were immunized with 50 μg of the chimeric vaccinogen emulsified in a 1:1 ratio with complete Freund's adjuvant (CFA). The vaccinogen was administered in a total volume of 200 μL, in divided intraperitoneal and subcutaneous depots. Three control mice were administered sham vaccinations of PBS in CFA. At weeks 2 and 4, mice were boosted with 50 μg protein in Freund's incomplete adjuvant. Sham immunized mice received PBS in adjuvant. All mice were bled by tail nick prior to the first injection, and at week 6.
Assessment of the Immunogenicity of the ABKD Chimeric Vaccinogen
The immunogenicity of the vaccinogen was assessed by immunoblot analyses and ELISA. Immunoblots were generated and screened as described above. One μg of each purified r-protein (OspC types A, B, K, D, and the chimeric vaccinogen) was analyzed by immunoblot. r-BBN39, an unrelated, His-tagged protein, derived from B. burgdorferi (paralogous protein family 163) served as the negative control. To verify equal protein loading, one blot was screened with anti-His tag monoclonal Ab (mAb) (1:2000; Novagen). To assess the response to vaccination, identical blots were screened with a 1:500 dilution of the mouse anti-ABKD antiserum. HRP-conjugated goat-anti-mouse IgG (1:40000 dilution) served as the secondary antibody and binding was visualized by chemiluminescence. ELISA analyses were conducted using 96 well plates (Costar 3590; Corning) coated with 100 ng per well of the vaccine construct or r-OspC (types A, B, K, or D) in carbonate buffer (pH 9.6; 16 hr at 4° C.). The plates were blocked (1% BSA in PBS with 0.2% Tween-20 (PBS-T); 2 hr), washed 3 times with PBS-T, and serially diluted anti-ABKD antiserum (100 μL ; 1:50 to 1:109350) was added to the wells of duplicate plates (1 hr). HP-conjugated goat-anti-mouse IgG (1:20000) served as the secondary antibody and ABTS as the chromogenic substrate. The absorbance was read at 405 nm in an ELISA plate reader (ELx 808; Biotek) while the reaction rate was linear. Titers were calculated by fitting a sigmoidal curve by a four parameter logistic equation (SigmaPlot) to the absorbance curve and calculating the inverse dilution corresponding to 50% of the maximum absorbance plateau.
Immunoglobulin Isotype Profiling of the Anti-ABKD Antibody Response
The isotype profile of the anti-ABKD antibody response was assessed by coating duplicate ELISA plates with 100 ng per well of the chimeric construct. The plates were washed and blocked as described above. Anti-ABKD antiserum collected from the 12 vaccinated mice were analyzed in duplicate (100 μL; 1:10000; 1 hr). Bound vaccinogen-specific Ig was detected by incubation with isotype specific, biotinylated secondary antibodies (1 hr; Mouse isotyping kit; Zymed). Bound biotinylated antibody was detected by HRP-conjugated streptavidin (30 min) and the chromogenic substrate, ABTS. All incubations were completed at room temperature.
Indirect Immunofluorescence Assays (IFA)
To determine if epitopes included in the ABKD chimeric vaccinogen are presented on the surface of in vitro cultivated B. burgdorferi, IFA analyses were conducted. To maximize OspC production, cultures of clonal populations producing type A, B, K, or D OspC were temperature shifted from 33 to 37° C. The spirochetes from 5 mL of dense culture ( ̃107-108 cells mL−1) were collected by centrifugation (7000×g for 15 min), washed 3 times with PBS, resuspended in 5 mL of PBS, and 100 μL spread over a 2 cm2 area on charged slides (Superfrost Plus, Fisher Scientific). One set of slides was air dried and a second was acetone fixed. The slides were blocked (1 hr; 3% BSA in PBS-T) and then screened with a 1:100 dilution of anti-ABKD antiserum, pre-immune serum, or a 1:1000 dilution of rabbit-anti-flagellin antiserum (1 hr). Bound antibody was detected by Alexafluor 568-conjugated goat-anti-mouse IgG or Alexafluor 488-conjugated goat-anti-rabbit IgG (10 μg mL−1 blocking buffer). Slides were washed three times in PBS-T between each step, and all incubations were for one hour at room temperature in a darkened, humidified chamber. Slides were mounted with Fluoromount-G (Electron Microscopy Sciences), visualized on an Olympus BX51 fluorescence scope using a rhodamine or fluorescein filter set, as appropriate, or by darkfield microscopy, and photographed using an Olympus MagnaFire digital camera.
Assessment of Bactericidal Activity
The ability of the anti-ABKD antisera to kill B. burgdorferi was assessed in vitro. Spirochetes that had been temperature shifted from 33 to 37° C., as described above, were washed 3 times with BSK-H medium and the cell density adjusted to  ̃106 cells ml−1. Eight μL of cells were combined with 8 μL of guinea pig complement (Sigma) and 4 μL of each test serum (heat inactivated at 56° C.; 30 min). Controls included heat inactivated anti-ABKD antisera without complement, complement only, and pooled heat-inactivated preimmune sera with complement. The total reaction volume was brought to 20 μL by the addition of BSK-H medium, as needed, and the samples were incubated at 37° C. for 18 hr. Killing was assessed using the BacLight LIVE/DEAD assay (Molecular Probes) and manual counts of live and dead/damaged cells in five high power fields using an Olympus BX51 fluorescence microscope with fluorescein and rhodamine filter sets.
Results
Identification of the Epitopes of OspC Types B, D, and K that are Presented During Infection in Mice and Humans
To date, OspC types A, B, C, D, H, I, K and N have been recovered from patients determined to have invasive infections [Seinost et al, 1999; Example 1; Alghaferi et al, 2005]. Four of these OspC types (A, B, K, and D) were selected to establish proof of principle of the utility of a polyvalent chimeric OspC vaccine. Since the epitopes presented during infection had only been identified for type A OspC, the first step in this study was to identify the infection-relevant epitopes of OspC types B, K and D. To accomplish this, immunoblots of truncations and fragments of each type were screened with sera from mice infected with clonal populations of B. burgdorferi (OspC types B, K or D) or with sera from human Lyme disease patients determined to have been infected, at least in part, with B. burgdorferi strains producing OspC of types B, K, or D (personal communication, Dr. Allen Steere and Kathryn Jones). The antibody response in mice at week 6 was type-specific; however, some of the human sera displayed cross-immunoreactivity between types (data not shown) suggesting that these patients were possibly infected with mixed spirochete populations. For OspC type B, the epitopes localized in alpha helix 5 (between aa 175 and 200) for mouse infection sera. Human infection sera reacted with a similarly located fragment (aa 164-185), indicating that the alpha helix 5 region of type B is antigenic. In type K OspC, epitopes were mapped between aa 148 and 160 in the mouse, and to the alpha helix 5 region (between aa 160 and 175) in the human. OspC type D epitopes were mapped to the alpha helix 5 region (between aa 167 and 180) in the mouse and in the human, though there were multiple additional epitopes recognized by the human serum. These data indicate that the alpha helix 5 region of OspC types B, K, and D are appropriate selections for inclusion in the tetravalent ABKD vaccinogen construct.
Construction, Expression and Purification of a Tetravalent Chimeric OspC Vaccinogen
Using the alpha helix 5 epitopes defined above for types B, K and D and the type A loop 5 epitope defined in an earlier study [Example 1] a polyvalent, chimeric r-vaccinogen was produced that is composed of the four epitope-containing regions. The epitopes were joined by short, unstructured, protease-resistant linker sequences (FIG. 9B). The recombinant vaccinogen is 169 aa in length with a molecular mass of 18.0 kDa and an isoelectric point of 6.49. Its structure is predicted to be predominantly helical [Gasteiger et al, 2005; Kneller et al, 1990] and to have a high stability index [Guruprasad et al, 1990]. Following dialysis with PBS, there was some precipitation of recombinant vaccinogen; however, approximately 500 μg mL−1 remained soluble, and this soluble protein was used for all experiments. Analysis of the purified vaccinogen protein by SDS-PAGE demonstrated a single band of 18 kDa molecular mass and no contaminating proteins.
Immunogenicity of the ABKD Chimeric Vaccinogen in Mice
To assess the antibody response to the ABKD chimeric vaccinogen and its individual component epitopes, C3H/HeJ mice were administered the vaccinogen in Freund's adjuvants. Serum was collected from the vaccinated (n=12) and sham (PBS+adjuvant) immunized mice (n=3) and assessed for reactivity with the ABKD chimeric vaccinogen and full length r-OspC proteins of types A, B, K, and D. Western blot analysis demonstrated that the anti-ABKD antisera reacted strongly with the vaccinogen protein and with r-OspC of types A, B, and K. In contrast, reactivity with the C-terminal OspC type D epitope of the chimeric construct was considerably weaker (FIG. 10). There was no reactivity of any of the sera with the negative control protein (r-BBN39) and sera from sham-vaccinated mice did not react with any of the proteins. Quantitative ELISA-based titration of serum reactivity demonstrated a high-titered IgG response against the ABKD chimeric vaccinogen protein, with a mean titer of 27,800 (FIG. 11A). Titration of reactivity against type-specific epitopes was accomplished by assessing binding with immobilized full length r-OspC proteins. Significant differences in the antibody titer to the individual epitopes were observed (FIG. 11B). It is notable that the epitope-specific titer decreases with its proximity to the C-terminus of the vaccinogen.
Immunoglobulin Isotype Profile of the Anti-ABKD Antisera
The immunoglobulin isotype profile is critical for the assessment of potential effector functions of vaccine-specific antibodies. To assess immunoglobulin heavy chain class switching induced by the ABKD chimeric vaccinogen, the isotype profile was determined by ELISA. The predominant isotype was IgG1, with marginally lower levels of IgG2a and IgG2b. The six-week sera showed only limited levels of IgM, IgG3, or IgA (FIG. 12).
Indirect Immunofluorescence Assays
The ability of antibody elicited to each epitope of the ABKD chimeric vaccinogen to bind OspC on the Borrelia cell surface was assessed by indirect immunofluorescent microscopy. Specific surface labeling was observed with cells producing OspC of types A, B, K, and D (data not shown). The intensity of the fluorescent signal was consistent with the type-specific titer, with the most intense fluorescence seen with cells bearing OspC types A or B. Fluorescence of cells of bearing types K or D was less intense, and the staining was patchy, giving the cells a stippled appearance. No reactivity was noted in cells probed with matched preimmune sera. The lack of surface labeling by anti-flagellin antibody to air fixed cells served to verify that the outer membrane of the cells was intact and that the epitopes detected are naturally presented at the cell surface. As expected, cells permeabilized with acetone were labeled by anti-flagellin antibody (data not shown).
Demonstration that Vaccination with the ABKD Chimeric Vaccinogen Induces Bactericidal Antibody
The bactericidal activity of the anti-ABKD antisera was assessed using the LIVE/DEAD BacLight assay [Tily et al, 2001; Ledin et al, 2005; Elias et al, 2000; Montgomaery et al, 2006; Elias et al, 2002; Shin et al, 2004]. Bactericidal activity was detected against strains bearing OspC of all types included in the chimeric vaccine construct. Incubation with the anti-ABKD antiserum induced significant cell aggregation. Both live and dead cells were present within the aggregates. Due to the inherent difficulty of counting cells within aggregates, the percentage of live and dead cells were determined by counting only non-aggregated, free cells. For all four OspC types, the background level of dead cells in the cultures used for the bactericidal assay was approximately 20-30%. This background level of dead cells has been consistently observed in our laboratory following transfer of the cultures from 33 to 37° C. to upregulate OspC expression. In the bactericidal assay, killing occurred in a complement dependent fashion, with the percentage of dead cells increasing significantly above background to 56 to 90%. The number of dead cells was in all cases at least twice that of the number of dead cells seen in any of the controls. Complement alone did not elicit killing. There was no bactericidal activity elicited by pooled preimmune serum, indicating that the specific immune response to the vaccinogen was necessary for bactericidal activity.
Discussion
Several studies have explored the potential utility of OspC of the Lyme disease spirochetes as a potential vaccinogen. Although vaccination with OspC elicits a protective antibody response, protection has been reported to be largely strain specific [Gilmore et al, 1996; Scheiblhofer et al, 2003; Wallich et al, 2001; Brown et al, 2005; Probert and LeFebvre, 1994; Gilmore 3t al, 2003]. Attempts to elicit broader protection using cocktails of multiple OspC proteins have not proven successful. Baxter tested an OspC cocktail consisting of 14 different full length OspC variants; however, they were not able to elicit sufficient antibody titers directed against the unique domains of each variant—a requirement if broad protection is to be conveyed. In addition, unacceptable reactigenicity was reported [Hanson et al, 2004]. A general concern with cocktail vaccines is the potential misdirection of the antibody response to epitopes that are not naturally presented during infection and that do not elicit protective antibody. The generation of chimeric vaccines offers an alternative approach that can circumvent the problems encountered using simple cocktails of r-proteins. Chimeric vaccines consisting of a series of immunodominant epitopes have been explored in the development of vaccines against malaria [Hanson et al, 2004; Caro-Aguilar et al, 2005;], group A streptococci [McNeil et al, 2005; Dale et al, 2005; Hu et al, 2002; Dale, 1999; Kotloff et al, 2005; Horvath et al, 2005], and several viruses [Apt et al, 2006; Fan and Mei, 2005; Wang et al, 2005; Bouche et al, 2005]. If a polyvalent OspC vaccine is to be broadly protective it will be necessary to incorporate into the vaccinogen a sufficient array of epitopes to elicit a protective response against diverse strains. The ability to move forward with the construction of such a vaccinogen has been greatly facilitated by phylogenetic analyses which have delineated 21 distinct OspC types designated A through U [Seinost et al, 1999], of which only a subset have been correlated with invasive infection in humans [Seinost et al, 1999; Example 1; Alghaferi et al, n 2005].
A detailed understanding of the epitope structure of OspC is required for the development of a chimeric vaccinogen. There have been several previous descriptions of OspC epitope locations [Gilmore et al, 1996; Jobe et al, 2003; Lovrich et al, 2005]. Two studies have reported that the epitope responsible for eliciting bactericidal antibodies resides within the C-terminal domain of OspC [Jobe et al, 2003; Lovrich et al, 2005]; however, since this domain is relatively conserved it is not clear why antibodies against the C-terminus are not broadly protective. Matheisen et al. also suggested that the C-terminus was the predominant target of the antibody response, noting greater reactivity of sera from European neuroborreliosis patients with full length OspC than with a 10 amino acid C-terminal truncated form [Mathiesen et al, 1998]. From this they concluded that there must be a C-terminal epitope; however, since the test antigen consisted of a single OspC variant of unknown type, the more widespread recognition of the C-terminus may be due to the greater conservation of this domain and not necessarily indicate that the C-terminus is immunodominant. Gilmore et al. demonstrated that immunization of mice with a non-denatured, but not with a denatured, r-OspC conferred protection to challenge with the homologous isolate [Gilmore et al, 1996; Gilmore and Mbow, 1999], indicating that protective epitopes may be conformationally defined. In a separate analysis, Gilmore et al. analyzed the immunoreactivity of a limited number of OspC truncations derived from a single OspC type (type A) with an anti-OspC monoclonal antibody that confers passive immunity [Gilmore and Mbow, 1999]. Deletion of either the N- or C-terminus eliminated detection of the r-proteins by the mAb, further suggesting the existence of a conformational or discontinuous epitope. It is not clear if the epitope recognized by the mAb is immunodominant, relevant during natural infection or conserved among the different OspC types. Linear immunodominant epitopes of type A OspC have recently been mapped and found to reside within the loop 5 and alpha helix 5 regions [Example 1]. A r-protein containing the type A loop 5 epitope elicited bactericidal antibodies in mice, raising the possibility that individual type-specific epitopes can be exploited in vaccine development [see Example 2]. In this report, the epitopes of OspC types B, K, and D that are presented during early infection are mapped, and a tetravalent chimeric vaccinogen based on these epitopes has been constructed. This ABKD chimeric vaccinogen was highly immunogenic in mice and elicited antibodies that bind OspC at the cell surface and effectively kill strains producing types A, B, K, and D OspC in a complement-dependent manner.
The first step in our efforts to develop a tetravalent chimeric test vaccinogen was to identify the linear epitopes of OspC types B, K and D presented during infection in mice and humans. These analyses were conducted essentially as described in Example 1 that identified the loop 5 and alpha helix 5 epitopes of type A OspC. In brief, extensive panels of type B, K and D OspC truncations and fragments were screened with serum from mice infected with clonal isolates and from humans infected with, at least in part, a strain expressing the corresponding OspC type. Precise epitope mapping was possible using sera from the experimentally infected mice; however, in naturally infected humans the antibody response was to a broader epitope array. This is not surprising and presumably reflects the expansion of the antibody response to OspC epitopes that are not normally presented at the bacterial cell surface during early infection. New epitopes, some of which may be from conserved domains of OspC (e.g. alpha helix 1), may become accessible upon bacterial cell death and release of OspC from the membrane. This illustrates the caveats that accompany the use of human serum samples in epitope mapping; namely that the exact duration of infection is typically not known and the clonality of the infecting population is doubtful [Wang et al, 1999; Ruzic-Sabljic et al, 2006; Hofmeister et al, 1999; Guttman et al, 1996; Rijpkema et al, 1997]. In any event, it is clear from the analyses of the human serum samples that epitopes within the alpha helix 5 region are recognized during infection by strains producing OspC types A, B, K or D. In addition, the consistency of the response to alpha helix 5 among several different OspC type producing strains may be an indication of functional relevance of this OspC domain.
Although the alpha helix 5 and loop 5 region sequences are variable between OspC types, these regions are highly conserved within each type [see Examples 1]. This suggests that, in the context of a chimeric vaccine, only a limited number of OspC epitopes will be required to effect broad protection. As a first step in the development of a broadly protective vaccinogen, the type A loop 5 epitope and the alpha helix 5 epitopes from OspC types B, K and D were employed in the development of a test vaccinogen. The region containing these epitopes was PCR amplified with primers designed to encode linker sequences. This allowed the use of PCR overlap extension in the creation of the chimeric construct, and provided a means to separate the epitopes with short, unstructured, protease-resistant amino acid sequences [Crasto and Feng, 2000]. The experimental OspC-based, tetravalent, ABKD chimeric vaccinogen developed in this study elicited a consistent, high titered IgG antibody response in all mice tested (n=12). Furthermore, the vaccinogen elicited antibody to each incorporated epitope. Interestingly, the epitope-specific titer appears to be influenced by the epitope position within the construct. There was a progressive decrease in titer from the N-terminal epitope (loop 5 of type A) through the C-terminal epitope (alpha helix 5 of type D). The phenomenon of decreased titer to C-terminal epitopes was also reported in early studies of a streptococcal M-protein based chimeric vaccine [Dale et al, 1993; Dale et al, 1996]. The basis for the location-specific effect on titer is not clear, but may be due to in vivo degradation or alteration of the structure of the C-terminus [Dale et al, 1999].
Although the Th cytokine response and related immunoglobulin isotype pattern necessary for protection against Borrelia infection have not been completely resolved [Kraiczy et al, n 2000; Widhe et al, 2004; Keane-Myers et al, 1995; Keane-Myers et al, 1996; Keane-Myers and Nickell, 1995], determination of this pattern is an important step in vaccinogen development and may provide important information regarding the potential protective capability of different constructions of the vaccinogen. The isotype profile of the response was determined by ELISA, and heavy chain Ig isotypes associated with a mixed Th1 and Th2 cytokine response were observed. The class switching noted in this study implies adequate T-cell help, even in the absence of a defined T-cell epitope incorporated into the vaccinogen. Analysis of the vaccinogen sequence using predictive peptide binding algorithms for a subset of the murine (H2Ak/H2Ek) and human (HLA-DRB 1) type II MHC, revealed potential T-cell epitopes in the vaccinogen predicted to bind all available alleles [Rammensee et al, 1999; Zhang et al, 2005]. One of the predicted binding peptides, LANSVKELT is repeated three times within the construct, and this repetition may be important in eliciting a Th response [Jiang et al, 1999; Ahlborg et al, 1998; Kjerrulf et al, 1997; Theisen et al, 2000]. While the analysis of potential T-cell epitopes was not exhaustive, the predictions support our data that indicate the chimeric vaccinogen can elicit T-lymphocyte help in the mouse. Further, it implies that this construct would likely do so in humans without the need to incorporate a promiscuous T-cell epitope sequence. The importance of Freund's adjuvants in the generation of this isotype profile is not known, but the responses and isotype profiles will need to be assessed in the context of alum or other adjuvants appropriate for use in humans [ten Hagen et al, 1993; Lindblad, 2004; Petrovsky and Aguilar, 2004; Brewer et al, 1999; McNeela and Mills, 2001]. Additionally, alteration of the epitope order or structure of the chimeric vaccinogen may provide a mechanism by which the immune response can be tailored to maximize in vivo protection [Tongren et al, 2005; Cai et al, n 2004].
For the response to the vaccinogen to be productive in terms of vaccine development, the elicited antibody must be able to bind to the surface of intact B. burgdorferi cells and cause bacterial killing. IFA analyses revealed strong labeling of the cell surface of strains producing OspC types A, B, K and D. Even though the antibody titer to the type D epitope was of significantly lower titer than that elicited to the more N-terminal epitopes, surface labeling of type D producing strains was readily apparent. A subset of cells in each of the OspC type cultures were observed not to label with the anti-ABKD antisera, implying that those cells were not expressing OspC. However, in vivo, it has been demonstrated that most if not all cells are expressing OspC during transmission from the tick to mammal and during early mammalian infection [Gilmore et al, 2001; Zhong et al, 1997]. The ability of anti-ABKD antibody to effect cell killing was also assessed. Serum from vaccinated mice efficiently killed spirochetes expressing types A, B, K and D OspC proteins in a complement dependent manner. While there was less than 100% killing for all of the OspC types, this is likely a function of the heterogeneity of in vitro OspC expression among cells of a population, a phenomenon that has been well documented in vivo [Schwan et al., 1995; Schwan and Piesman, 2000; Hu et al., 1996].
This Example describes the construction and proof of principle of a novel r-chimeric polyvalent OspC-based Lyme disease vaccinogen. The use of an epitope-based r-chimeric protein allows coverage of multiple OspC types in the same construct, and circumvents the potential problem of immune responses misdirected against irrelevant protein domains. The mapping of linear epitopes recognized during active infection is a crucial component of chimeric vaccine development, and this has been successfully completed for four OspC types associated with invasive infection in humans. The epitopes included in the vaccinogen have elicited type-specific IgG antibodies capable of binding OspC at the Borrelia cell surface, and effecting complement-mediated bacterial killing.
Example 4
Immune Responses to Variants of a Chimeric Polyvalent Lyme Disease Vaccine Intended to Improve Immunogenicity
In this study, we sought to improve the solubility of the construct and assess the potential impact of epitope placement, epitope reiteration, and the inclusion of putative C-terminal stabilizing tags on the immune response. These analyses provide new insight into design strategies for a broadly protective OspC vaccine, and for construction of chimeric vaccines in general.
Materials and Methods
Expression and Purification of Recombinant OspC
Recombinant full length OspC proteins of types A, B, K and D were generated as previously described [see Examples 1 and 2]. Briefly, the ospC gene from clonal populations of B. burgdorferi isolates B31MI (type A OspC), LDP73 (type B), LDP74 (type K), and LDP116 (type D) were amplified by PCR using primers with 5′ overhangs to allow ligase-independent cloning (LIC) in the pET-32 Ek/LIC vector (Novagen) [Example 1]. After amplification and regeneration of single stranded tails, the amplicons were annealed with the pET-32 Ek/LIC vector, which was transformed into and propagated in NovaBlue (DE3) E. coli cells. Following confirmation of the insert sequence by DNA sequencing (MWG-Biotech), protein expression was induced with IPTG (1 mM). Proteins were purified by nickel affinity chromatography using the pET-32 Ek/LIC expression tag-encoded hexahistidine motif (Novagen). The imidazole-eluted proteins were dialyzed extensively against phosphate buffered saline (PBS; pH 7.4) across a 10 kDa molecular weight cut-off membrane (Slid-a-lyzer, Pierce), the protein concentration was quantified by the BCA assay (Pierce), and the purity of the preparation was assessed by SDS-PAGE.
Construction, Expression, and Purification of ABKD Vaccine Variants
In order to investigate potential mechanisms of, and solutions to, the decreasing IgG titer to specific epitopes across the vaccine construct, multiple variants of the original vaccine were constructed. All vaccine variants were based on the sequence of the ABKD vaccinogen previously described [Example 3] and contain the same epitope-containing sequences. These include the loop 5 region of type A (amino acids (aa) 131 to 149) and the alpha helix 5 regions of types B (aa 160-201), K (aa 161-201), and D (aa 161-201) (FIG. 13 inset). The ABKDppa and ABKDgg added a Pro-Pro-Ala or Gly-Gly motif, respectively, to the C-terminus of the original ABKD construct. Both of these constructs were made by amplifying the original ABKD construct using reverse primers (Table 5) that added the motif via a 5′ overhang encoding the appropriate amino acids (FIG. 13A). The other vaccine variants were made by overlap annealing and extension techniques similar to those used in construction of the original ABKD vaccinogen [Example 3]. The ABKDD construct was made by re-amplifying the ABKD construct using a reverse primer bearing a 3′ tail sequencing encoding an unstructured, protease-resistant linker. This allowed the PCR product to anneal to the type D OspC epitope-containing sequence that had been amplified with the complementary linker-encoding sequence at the 5′ end, with subsequent overlap extension and amplification of the annealed construct (FIG. 13B). The ADBK construct was made by annealing separately amplified type A and D epitope-containing regions with each other and subsequently with the type B and K helix 5 epitope regions amplified from the original ABKD construct (FIG. 13C). The ADBKD construct was made by annealing amplicons from the ABKD and ADBK sequences (FIG. 13D). In all cases, the PCR amplification was completed with GoTaq Green (Promega) using an initial 2 min 94° C. denaturation step, followed by 35 cycles of denaturation at 94° C. for 15 sec, primer annealing at 50° C. for 30 sec, and extension at 72° C. for 60 sec, with a final 72° C. extension for 7 min. All primers use in construction of these vaccinogens are listed in Table 5. All PCR products were gel purified (Qiagen) prior to use as templates in subsequent PCR reactions. Final amplicons were annealed to the pET-46 Ek/LIC vector by ligase independent cloning, and transformed into Novablue (DE3) E. coli cells. Colonies were screened for inserts using T7 primers, and plasmids were recovered (Qiafilter Midi, Qiagen) for confirmation of the insert by DNA sequencing. Recombinant proteins were expressed and purified as described above. Following purification, the vaccine proteins were dialyzed across a 10 kDa molecular weight cutoff membrane (Slide-a-Lyzer, Pierce) against three changes of either PBS (pH 7.4) or a pH 8 buffer containing 100 mM phosphate, 100 mM NaCl, 50 mM arginine, 50 mM glutamic acid (Arg/Glu buffer) [Golovanov et al, 2004]. The purity of the constructs was assessed by SDS-PAGE.








TABLE 5







Primers used in construction of the chimeric vaccinogens.



LIC tails are in bold, and linker sequences are underlined.










Primer
Sequence
Description
SEQ ID NO:














OCAL5LIC(+)
GACGACGACAAGATTTCT
Amplifies type A from
234




GAAACATTTACTAATAA
aa 131 and adds LIC



ATTAAAAGAAAAAC
tail


 


OCAL5L5(−)
TAAAGCTGACATAGCAC
Amplifies type A up
235



CTTCTTTACCAAGATCTG
to aa 149 and adds



TGTG
linker 5 (GAMSAL;




SEQ ID 80)


 


OCBH5L1(+)
GGTAGCATGGGTATGTT
Amplifies type B from
236



AAAAGCAAATGCAGCGG
aa 160 and adds linker



G
1 GSMGML;




SEQ ID 76)


 


OCKH5L3(−)
TAAAACGCTCATGCTAC
Amplifies type K up
237



TTGTAAGCTCTTTAACTG
to aa 201 and adds



AATTAGC
linker 3 (SSMSVL;




SEQ ID 78)


 


OCKH5LIC(−)
GAGGAGAAGCCCGGTT
Amplifies type K up
238



TAACTTGTAAGCTCTTTA
to aa 201 and adds an



ACTGAATTAGC
LIC tail


 


OCDH5LIC(−)
GAGGAGAAGCCCGGTT
Amplifies type D up
239



TAACTTGTAAGCTCTTTA
to aa 201 and adds an



ACTGAATTAG
LIC tail


 


OCDH5ppaLIC
GAGGAGAAGCCCGGTT
Amplifies type D up
240


(−)
TATGCAGGAGGACTTGT
to aa 201 and adds



AAGCTCTTTAACTGAATT
‘PPA’ and an LIC tail



AG


 


OCDH5ggLIC
GAGGAGAAGCCCGGTT
Amplifies type D up
241


(−)
TATCCTCCACTTGTAAGC
to aa 201 and adds



TCTTTAACTGAATTAG
‘GG’ and an LIC tail


 


OCDH5L1(−)
TAACATACCCATGCTAC
Amplifies type D up
242



CACTTGTAAGCTCTTTAA
to aa 201 and adds



CTGAATTAG
linker 1 (GSMGML;




SEQ ID 76)


 


OCDH5L4(+)
AGTTCAAGCCAAGGCTT
Amplifies type D from
243



AAAAACACATAATGCTA
aa 161 and adds linker



AAGACAAG
4 (SSSQGL;




SEQ ID 79)


 


OCDH5L4(−)
TAAGCCTTGGCTTGAACT
Amplifies type D up
244



TGTAAGCTCTTTAACTGA
to aa 201 and adds



ATTAGC
linker 4 (SSSQGL;




SEQ ID 79)


 


OCDH5L5(+)
GGTGCTATGTCAGCTTTA
Amplifies type D from
245



AAAACACATAATGCTAA
aa 161 and adds linker



AGACAAG
5 (GAMSAL;




SEQ ID 80)


 


3′REVLIC(−)
GAGGAGAAGCCCGGT
Amplifies up to the 3′
246




LIC tail


 


pET46 T7(+)
CGAAATTAATACGACTC
Amplifies from
247



ACTATAGGGG
pET46, 123 bases




upstream of cloning




site


 


pET46 T7(−)
GCTAGTTATTGCTCAGCG
Amplifies up to
248



G
pET46, 117 bases




downstream of the




cloning site









Immunization of Mice with Vaccine Variants

Six week old male C3H/HeJ mice were immunized (3 mice per construct) with each of the six vaccinogen variants. Since the immunogenicity of the variants were to be compared with each other, it was desirable to administer the protein on a molar basis, to compensate for differences in the number of epitopes per unit of vaccinogen mass. Each mouse received approximately 2.8 nanomoles of protein per immunization, which is 50 μg of constructs ABKD, ABKDppa, ABKDgg, and ADBK or 62.5 μg of constructs ABKDD and ADBKD. Mice were immunized with vaccine in complete Freund's adjuvant, then boosted with Freund's incomplete adjuvant on weeks 2 and 4. Sera was collected from all mice by tail nick prior to the first immunization and at week 6. To determine the effect of adjuvant on the total and epitope-specific antibody titers, as well as on isotype profiles, mice (6 per adjuvant) were immunized with the ABKD vaccinogen emulsified in Freund's adjuvants as described above, or adsorbed onto alum (Imject Alum, Pierce), and serum was collected by tail nick at week 6.
Assessment of Epitope-Specific IgG Titer Induced by Vaccine Variants
The immunogenicity of each vaccinogen was assessed both by Western blot and ELISA. For the western blots, r-OspC of types A, B, K, D were loaded at 500 ng per lane in reducing sample buffer, electrophoresed in a 12.5% SDS-PAGE gel (Criterion, Biorad), and electroblotted to PVDF (Immobilon-P, Millipore). The blots were blocked with 1% BSA in phosphate buffered saline with 0.2% Tween-20 (PBS-T). The blots were probed with a 1:2500 dilution of each antiserum in PBS-T for one hour, then washed three times. To verify equal protein loading, one blot was screened with anti-His tag monoclonal antibody (1:2000; Novagen). Secondary detection was by a 1:40000 dilution of peroxidase-conjugated goat-a-mouse IgG and chemiluminescence (Super Signal Pico, Pierce). For quantitative analysis, OspC type-specific IgG titers were determined by ELISA analyses. r-OspC of types A, B, K, or D were coated onto 96 well plates (Costar 3590; Corning) at 100 ng well-1 for 16 hr at 4° C. in carbonate buffer (pH 9.6). The plates were blocked (1% BSA in PBS with 0.2% Tween-20 (PBS-T); 2 hr), washed 3 times with PBS-T, and serially diluted anti-vaccinogen antiserum (100 μL) was added to the wells of duplicate plates (1 hr). HRP-conjugated goat-a-mouse IgG (1:20000) served as the secondary antibody and ABTS as the chromogenic substrate. The absorbance was read at 405 nm in an ELISA plate reader (ELx 808; Biotek) while the reaction rate was linear, and titers were calculated by fitting a sigmoidal curve to the absorbance curve by a four parameter logistic equation (SigmaPlot). The titer is reported as the inverse dilution corresponding to 50% of the maximum absorbance plateau.
Determination of Epitope-Specific Immunoglobulin Isotype Profiles
The isotype profiles of the antibody response to the ABKD, ABKDD, and ADBKD vaccine variant constructs were assessed by ELISA. 96 well plates were coated with 100 ng well-1 of r-OspC of type A, B, K, and D. The plates were blocked and washed as described above. Anti-vaccinogen antisera were added to the plate and analyzed in duplicate (100 μL; 1:10000; 1 hr). Bound epitope-specific Ig was detected by incubation with isotype specific, biotinylated secondary antibodies (1 hr; Mouse isotyping kit; Zymed). The secondary antibodies were detected by peroxidase-conjugated streptavidin (30 min) and the chromogenic substrate, ABTS. All incubations were completed at room temperature.
Determination of IFN-γ and IL-4 Production by Vaccine-Specific T-Lymphocytes
The cytokine response of splenocytes from immunized mice was assessed by in vitro restimulation with vaccinogen using modifications of the methods of Abuodeh et al. [1999]. Vaccinated mice were euthanized by CO2 narcosis, and spleens were aseptically removed and placed into RPMI media (Sigma). Spleens from the three mice immunized with each vaccine construct were pooled, and the cells were harvested by repeated injection of RPMI into the splenic capsule using 22 gauge needles. The cell suspensions were transferred to 50 mL centrifuge tubes and the cells harvested at 200×g for 5 minutes. Erythrocytes were lysed by exposure to 3 mL of 8.3 mg/mL ammonium chloride (R-7757, Sigma) for 1 minute. The ammonium chloride was then diluted with 20 mL of RPMI (Sigma), and the cells were centrifuged and washed three times. The cells were resuspended in 10 mL RPMI containing 10% FCS, 100 μg mL−1 streptomycin, 100 U mL−1 penicillin, 2.5 μg mL−1 amphotericin B. The cells were stained with trypan blue to assess viability, enumerated with a hemacytometer, and all cell suspensions adjusted to 107 cells mL−1. Cells were aliquoted into 24 well plates (Costar 3526) at 107 cells per well (12 wells per vaccinogen type). Triplicate wells were stimulated with the immunizing vaccinogen at 5 or 10 μg mL−1. Controls included triplicate wells stimulated with an irrelevant protein, bovine serum albumin at 10 μg mL−1, and unstimulated wells (no protein). All plates were incubated at 37° C., 5% CO2 for 96 hours, then supernatants were harvested and frozen at −80° C. pending ELISA quantification of cytokines.
To quantify the levels of the Th1/Th2 cytokines IFN-γ and IL-4, an ELISA-based assay (ELISA-Max; Biolegend) was used according to the manufacturer's instructions. Briefly, a capture antibody was coated onto 96-well ELISA plates, the plates were blocked, and 100 uL of each culture supernatant, in duplicate, was incubated for 2 hr in the plates. For IL-4 detection, undiluted culture supernatant was used, whereas for IFN-γ, the supernatant was tested undiluted and diluted 1:20 in PBS. A standard curve was generated using samples containing known concentrations of each of the cytokines. Detection of bound cytokines was by a biotinylated secondary antibody followed by HRP-conjugated streptavidin and colorimetric detection using TMB substrate.
Results
Construction, Expression and Purification of Variant Vaccine Constructs
Using primers with 5′ overhangs and overlap annealing and extension PCR techniques, five variants of the original ABKD vaccine were produced (FIG. 13). The DNA sequences of all of the constructs were confirmed. Select physicochemical properties of the vaccinogens are presented in Table 6 [Gasteiger et al, 2005]. Following purification of the recombinant vaccinogens by nickel chromatography, it was noted that a significant proportion of the r-protein precipitated during dialysis against PBS. This was also noted in the initial report of the ABKD vaccinogen [Example 3]. While the higher molecular weight constructs, ABKDD and ADBKD, had higher solubility in PBS, r-protein precipitation was still significant. For that reason, a modified dialysis buffer (Arg/Glu buffer) was developed based on the work of Golovanov et al. [2004]. The pH of the buffer was increased from that of PBS (pH 7.4) to pH 8.0 to increase the difference between the buffer pH and the pI of the r-proteins (pI 6.49 or 6.85). In addition, the salt concentration was decreased from 150 mM to 100 mM and 50 mM arginine and 50 mM glutamic acid was added. Using this buffer, no precipitation of any of the r-proteins was noted, and there was a marked increase in the concentrations of soluble protein. As visualized by SDS-PAGE, the r-proteins were pure and free of degradation products (FIG. 14).







TABLE 6







Physicochemical properties of the vaccinogens.














Amino
Molecular
Isoelectric
Instability



Construct
acids
mass (Da)
point
index

















ABKD
169
18014.4
6.49
10.14



ABKDppa
172
18279.7
6.49
14.93



ABKDgg
171
18128.5
6.49
10.86



ABKDD
214
22632.7
6.85
15.49



ADBK
170
18027.4
6.49
8.51



ADBKD
215
22645.7
6.85
14.18










Immunogenicity of Vaccine Variants

To assess the relative immunogenicity of the ABKD vaccine variants, mice were immunized with each of the variants in Freund's adjuvants. Epitope-specific reactivity of the sera was assessed by western blot, in which the sera were used to probe PVDF-immobilized r-OspC of each of the four types. The proteins were confirmed to be equally loaded on the blot, as assessed by reactivity with the tag-specific mouse-a-His tag monoclonal antibody. The sera from immunized mice demonstrated vaccinogen-dependent differences in the levels of reactivity with each of the r-OspC proteins (FIG. 15A). Notably, there was diminished reactivity with the type D helix 5 epitope in mice vaccinated with the ABKDppa and ABKDgg variants, and most markedly with the ADBK variant. In order to assess these variations in a quantitative way, titration of IgG reactivity with each of the OspC type-specific epitopes included in the constructs was accomplished by ELISA, again by using full length r-OspC of each of the four types as the immobilized antigens. The titers largely mimicked the qualitative western blot findings, demonstrating vaccine-specific differences in the reactivity of immune serum to individual epitopes (FIG. 15B). The most marked differences were seen in reactivity with the type D epitope, with particularly low titers seen for the ABKDppa, ABKDgg and ADBK variants.
Isotype Profiles of Vaccine Variant-Specific Immunoglobulins
To understand in greater detail the immune response induced by the variant vaccinogens, epitope-specific immunoglobulin isotype profiles were completed for the three variants with the best vaccine potential (ABKD, ABKDD, ADBKD), as determined by epitope-specific titers. In general, there was a preponderance of IgG1 in the antigen-specific immunoglobulins, smaller amounts of IgG2a and IgG2b, and very little IgG3 or IgM, a pattern which has been previously noted [Example 3] (FIG. 16). For all epitopes and all vaccine variants, the pattern of Ig isotype was similar, with one exception. There was a greater reactivity of type K and D epitope-specific IgG2a and IgG2b in mice immunized with the ABKDD than with the ABKD or the ADBKD variants.
Th1/Th2 Cytokine Production by Vaccine-Specific T-Lymphocytes
To assess the potential impact of the cytokine environment and Th1/Th2 balance induced by the variations in the ABKD vaccinogen, mouse splenocytes were re-stimulated in vitro with the vaccinogen with which the mice had been immunized. Marked differences in the induced levels of IFN-γ were noted between the differently immunized mice. All vaccine variants were associated with increased levels of IFN-γ in the culture supernatant, though ADBK and ADBKD had levels two to three times higher than that induced by the other vaccinogens (FIG. 17). In all cases, both the 5 μg mL−1 and 10 μg mL−1 concentrations of antigen induced IFN-γ, with levels ranging from 0.5 to 8.6 ng/mL. Cell culture supernatants from unstimulated splenocytes or from splenocytes stimulated with bovine serum albumin all had IFN-γ levels that were below the 15.6 pg/mL detection limit of the assay. In neither the vaccine-stimulated nor the control culture supernatants was IL-4 detected, indicating that the concentration was below the 2.0 pg/mL detection limit of the assay.
Effect of Adjuvant Type on Antibody Titer and Isotype Profile
To determine the effect of adjuvant type on the response to the vaccinogen, mice were immunized with the ABKD protein emulsified in Freund's adjuvants or adsorbed to alum. The IgG titer against the whole vaccinogen, as well as against each component epitope was slightly lower in mice immunized with alum adjuvant, though the general pattern of the response was similar between the two adjuvants (FIG. 18A). Despite similar levels of IgG1, mice immunized with alum had reduced vaccinogen-specific IgG3, IgG2a, and IgG2b (FIG. 18B). The epitope-specific isotype profiles were very similar to the profile seen using the whole vaccinogen (data not shown).
Discussion
The use of chimeric proteins containing multiple B-cell epitopes has potential advantages over whole-protein polyvalent vaccinogens and peptide conjugates in vaccine development. The inclusion of only protective epitope sequences reduces the potential for misdirection of the response against irrelevant epitopes either in the parent molecule or on a peptide carrier. This is important if, as with OspC, there are large conserved domains that are immunodominant in the recombinant vaccinogen, but are not presented by the bacteria during infection [Example 1; Kumaran et al, 2001; Eicken et al, 2001]. Such epitopes are irrelevant to the generation of a protective immune response. The creation of novel proteins, however, requires consideration of inter- and intramolecular interactions that can occlude epitopes or impact protein stability and solubility. In this Example, we have extended the investigation of a recombinant, polyvalent chimeric Lyme disease vaccinogen based on OspC. The original ABKD vaccine was highly immunogenic in mice, and the induced IgG bound native OspC at the bacterial cell surface and elicited complement-dependent killing [Example 3]. Despite this success, the ABKD construct had two factors that required improvement, its poor solubility in PBS, which interfered with production of r-protein and could impact storage stability, and differences in the IgG titer against individual epitopes in the protein. Specifically, titer decreased in relation to the proximity of the epitope to the vaccine C-terminus. The goals of this study were to improve vaccinogen solubility, and use modified vaccinogens that differed in epitope placement, epitope reiteration, and the inclusion of stabilizing motifs to improve the total and the epitope-specific immune response.
In an earlier study, it was noted that there was significant precipitation of recombinant vaccinogen following dialysis against PBS [Example 3]. This poor solubility not only limited vaccinogen production but may also have impacted vaccine immunogenicity. The maximum concentration of the ABKD construct achieved following dialysis against PBS was 0.5 mg/mL, and was frequently much less. The OspC crystal structure suggests that the helix 5 epitope regions participate in intramonomeric 4-helical bundles in the native OspC proteins [Kumaran et al, 2001; Eicken et al, 2001]. This may lead to interactions between exposed hydrophobic helical faces within and between vaccinogen proteins, in turn leading to precipitation. The addition of Arg and Glu to the dialysis buffer was found to increase the solubility of all of the recombinant vaccinogen proteins by 4 to 100-fold (Table 7). The basis for this increased solubility may be an interaction of Arg and Glu with both with exposed residues of opposite charge, and with hydrophobic residues by interaction with the aliphatic portion of the Arg and Glu side chains [Golovanov et al, 2004]. Mice immunized with the ABKD construct dialyzed in the Arg/Glu buffer had markedly higher titers than those immunized with the ABKD vaccinogen dialyzed against PBS [Example 3]. The Arg/Glu buffer may cause a more advantageous folding pattern or fewer inter- or intramolecular interactions, thereby providing better access of epitopes to B-cell receptors. Adsorption of Arg or Glu to the r-protein apparently did not interfere with epitope recognition. The Arg/Glu buffer has been reported to protect against the activity of proteases in vitro [Golovanov et al, 2004]. While there is no apparent proteolytic degradation in either the PBS- or Arg/Glu-dialyzed samples, in vivo protection against proteolytic cleavage cannot be excluded. Dialysis against buffers containing Arg and Glu may be a useful tool that can be applied to other novel chimeric proteins that have significant intermolecular interactions.







TABLE 7







Concentration of soluble protein for vaccinogens


dialyzed against PBS or Arg/Glu buffer.












Protein concentration (mg mL−1)




Construct
PBSArg/Glu buffer















ABKD
0.15
3.04



ABKDppa
0.20
3.78



ABKDgg
0.22
5.99



ABKDD
0.80
4.66



ADBK
0.04
4.37



ADBKD
1.12
4.66










The association of poor immune response with the C-terminal epitope location has been previously reported in a chimeric streptococcal M-protein vaccinogen, potentially due to structural issues associated with the C-terminus, or proteolytic degradation by carboxypeptidases [Dale et al, 1993; Dale et al, 1996; Dale et al, 1999]. Numerous methods have been proposed for protection of peptides and recombinant proteins from protease activity, including amidation or PEGylation of the C-terminus, acetylation of the amino (N)-terminus, and addition of protective amino acid motifs [Brickerhoff et al, 1999; Powell et al, 1992; Lee et al, 2005; Alvarez et al, 2004; Kawarasaki et al, 2003; Walker et al, 2003]. Amino acid motifs have also been reported to stabilize the C-terminus of proteins by inhibiting the action of carboxypeptidases; however, their ability to protect has only been assessed with a few proteins. Two stabilizing motifs were assessed for their ability to enhance antibody responses to the ABKD vaccinogen. The addition of two neutral, hydrophilic Gly residues may reduce the activity of carboxypeptidases C and D, which have specificity for hydrophobic and basic C-terminal amino acids, respectively [Alvarez et al, 2004; Kawarasaki et al, 2003; Remington and bredam, 1994]. Addition of a Pro-Pro-Ala motif may sterically hinder carboxypeptidase progression through the juxtaposed, bulky proline residues [Walker et al, 2003].
To assess the impact of addition of these motifs on the antibody response to the ABKD chimeric vaccinogen, mice were immunized with the ABKDgg or ABKDppa constructs. In both cases, the sera had lower mean IgG titers against one of more epitopes, compared with those immunized with the unmodified ABKD construct. The ABKDppa construct had a reduction in the titer of type D specific IgG, though this was primarily due to a single outlier. The ABKDgg construct had reduced titers against the types K and D epitopes. On the basis of IgG titers, there was no advantage to the use of either of these motifs. The reduction in the titer to the C-terminal epitopes does not appear to be mediated by the action of those carboxypeptidases to which these motifs should confer resistance, though it is possible that any advantage due to protease protection may have been masked by similar protection provided by the Arg/Glu buffer [Golovanov et al, 2004].
To investigate possible structural factors involved in the poor immune response to the C-terminal epitope, several additional constructs were created. In the chimeric streptococcal vaccine, reiterating the N-terminal epitope at the C-terminus ‘protected’ the former C-terminal epitope by an unknown mechanism [Dale et al, 1999; Dale et al, 2005; Hu et al, 2002; McNeil et al, 2005]. Based on that success, similar variants of the ABKD vaccinogen were developed. The ABKDD construct was created to assess whether the response to the type D epitope could be protected by a second C-terminal type D epitope. To assess whether the decreased titer was due primarily to the C-terminal epitope location, the type D epitope was moved to the second-most N-terminal location (ADBK). Finally, the ADBKD construct was used to assess protection by a reiterated C-terminal epitope and, with ABKDD, the effect of a repeated epitope on the specific immune response. Epitope reiteration in the ABKDD vaccinogen doubled the type D-specific IgG titer, but simultaneously caused a decrease in the titer against the adjacent type K epitope. When the type D epitope was placed in a more N-terminal location in the ADBK construct, the type-D specific IgG titer was significantly reduced. Furthermore, the reactivity against the C-terminal type K epitope in the ADBK construct was improved over that in the ABKD. Adding a C-terminal type D epitope (ADBKD) did not improve the type K-specific titer; however, it yielded a significantly improved, though not doubled, titer against the type D epitope. These results indicate that the C-terminal location of the type D epitope is preferable to an internal location, and that there is no apparent protection of a C-terminal epitope by an additional ‘protective’ C-terminal epitope. The primary determinant of epitope-specific titer in this vaccinogen is not its proximity to the C-terminus, but is more likely the tertiary structure of the chimeric protein.
Vaccinogen-induced Ig isotypes may have consequences on in vivo protective efficacy. By altering the epitopes or their order, it may be possible to alter the isotype profile [Tongren et al, 2005], and thus antibody effector functions. To measure epitope-specific isotype profiles, antisera against the most promising vaccinogens (ABKD, ABKDD, ADBKD) were bound to immobilized rOspC of types A, B, K or D, and the bound antibody detected with isotype-specific antisera. As previously reported for the ABKD vaccinogen [Example 3], the predominant isotype was IgG1, with somewhat lower levels of IgG2a and IgG2b, dependent on the construct, and low levels of IgM and IgG3. The epitope specific Ig isotype profiles were similar between the ABKD and ADBKD antisera, with a decrease in the levels of IgG2a and IgG2b from the N- to the C-terminal epitope, mimicking the total IgG titer. The ABKDD had a consistent level of IgG2a and IgG2b across all of the epitopes, despite the lower type K-specific total IgG titer.
The ABKD vaccinogen elicits complement-dependent bactericidal antibodies [Example 3]. In the mouse, IgG1 does not activate complement [Dangl et al, 1988; Miletic and Frank, 1995], indicating that the major induced isotype may not be protective. While it has been reported that OspA-specific IgG1 can be borreliacidal by a complement-independent mechanism [Munson et al, 2000], bacterial killing by ABKD vaccinogen-induced antibodies is complement dependent [Example 3]. The elicited isotype profile may be influenced by the use of C3H/HeJ mice, a standard animal model for Lyme disease research. Humoral immune differences between C3H/HeJ and BALB/c strain mice have been noted during B. burgdorferi infection, especially in the levels of total IgG and especially in the levels of IgG2a, both of which are higher in C3H/HeJ mice [Yang et al, 1992; Keane-Myers and Nickell, 1995]. Additionally, the C3H/HeJ mouse line is deficient in TLR-4, though this is not expected to be critical for protection against Lyme disease by vaccination or during infection, as Borrelia do not make lipopolysaccharide [Takayama et al, 1987; Barthold et al, 1990].
Since it is generally accepted that humoral borreliacidal activity is complement-dependent, the elicitation of a Th1 cytokine response may be advantageous, as it is in many bacterial diseases (reviewed in [Spellberg and Edwards, 2001]). During active infection, Th cytokines have been implicated in the development and resolution of Lyme disease and its sequelae. Several studies have found that IL-4 is not a critical cytokine for the development of a borreliacidal antibody response [Munson et al, 2000; Potter et al, 2000; Christie et al, 2000; Satoskar et al, 2000-64], implying that a Th1-type response may be associated with protection. Additionally, IFN-γ secreting Th1 cells promote the resolution of carditis associated with Lyme disease [Bockenstedt et al, 2001; Kelleher et al, 1998]. Conversely, arthritis severity and the skin spirochete load are reduced by administration of r-IL-4, and increased by administration of an α-IL-4 antibody during infection [Keane-Myers and Nickell, 1995; Keane-Myers et al, 1996]. The production of IFN-γ has been associated with the development of chronic Lyme disease during natural infection [Widhe et al, 2004], as well as with the degree of joint swelling in Lyme arthritis [Gross et al, 1998]. IFN-γ has also been associated with inhibited production of borreliacidal anti-OspA antibodies induced from in vitro lymph node cultures [Munson et al, 2002]. To investigate the Th cytokine environment induced by vaccination, mouse splenocytes were re-stimulated with vaccinogen in vitro, and Th1 (IFN-γ) and Th2 (IL-4) cytokines and were quantified by ELISA. IFN-γwas detected in the supernatants of cells re-stimulated with vaccinogen, though in differing concentrations depending on the construct. In contrast, IL-4 was not detected in any of the splenocyte supernatants. The ABKD, ABKDppa, and ABKDD constructs all had similar concentrations of IFN-γ. The ADBKD had approximately double the concentration of IFN-γ, and the ADBK had an even higher level. There was no apparent correlation between the level of IFN-γ in the supernatant of re-stimulated cells and the total epitope-specific serum IgG titers or isotype profiles.
The cytokine and associated Ig isotype profiles could be altered by the choice of immunological adjuvant. Freund's complete adjuvant has been associated with a Th1 cytokine response [Cribbs et al, 2003; Shibaki and Katz, 2002], which may increase the level of IgG2a. The only adjuvant currently approved for human use is alum, which is known to increase secretion of Th2 cytokines [Cribbs et al, 2003; Brewer et al, 1999; Lindblad, 2004; Petrovsky and Aguilar, 2004]. In mice immunized with alum, the expected moderate decrease in IgG titer to the vaccinogen and its component epitopes was noted, in comparison with Freund's adjuvant. Additionally, there was a proportionally greater decrease in the IgG3, IgG2a, and IgG2b isotypes, as compared with IgG1. This conforms with the expectation of lower Th1 cytokine response with this adjuvant. The vaccinogen does, however, continue to elicit antibodies capable of complement fixation, indicating that significant changes to the construct or modifications of the adjuvant may not be necessary for an effective response.
In this Example, we have investigated alterations to a potential chimeric polyvalent Lyme disease vaccinogen that were intended to optimize the induced humoral immune response. A significant improvement to the immunogenicity of the construct was effected by increasing its solubility by dialysis against Arg/Glu buffer. This may have reduced protein interactions, allowing greater epitope exposure in vivo [Theisen et al, 2000]. Neither the addition of protease-protective C-terminal motifs nor addition of ‘protective’ C-terminal epitopes improved the immune response to the vaccinogen. Reordering of epitopes caused a substantial decline in the immune response to the epitope that was moved. Differences in the immune response toward component epitopes in this vaccine construct appear to be primarily dependent on the structure of the protein, rather than on the resistance of the protein to protease digestion. Furthermore, there is evidence that Th cytokines and IgG isotypes elicited by a vaccinogen can be altered by the structure of the chimeric construct and by the adjuvant formulation. This study provides important information regarding the basis for suboptimal immune responses to chimeric vaccinogens, as well as methods by which those responses can be improved.
Example 5
Analyses of Available OspC Sequences Demonstrate the Feasibility of a Broadly Protective Polyvalent Chimeric Lyme Disease Vaccine
To facilitate the further development of a broadly protective chimeric construct we have conducted phylogenetic analyses of OspC sequences available in the databases. The segment of OspC analyzed spanned residues 20 through 200 (using numbering for the B31MI sequence). Shorter sequences in the databases were excluded from these analyses, leaving sequences from 280 Borrelia strains available for analysis. The OspC type designation of each sequence was determined through alignment (PAM40 scoring matrix) and pairwise identity matrix analysis. Consistent with earlier studies, sequences that exhibited 95% or greater sequence identity were considered to belong to the same OspC type (Attie et al, 2006; Wang et al, 1999) (FIG. 19). A clear bimodal distribution of sequence comparisons, with a mean sequence identity of 65% between differing OspC type sequences, and >97% identity within types was observed. In addition to the 21 types described by Wang et al (1999), 17 additional clusters were defined. We did not assign OspC type designation to clusters that included less than 3 sequences. In naming new OspC types, we chose to maintain the existing OspC type designations A through U (Wang et al, 1999), with additional types named based on a prototype strain contained within each cluster. Of 280 analyzed sequences, 202 were assigned to OspC types, all of which were from Lyme disease-causing species. The 78 sequences not assigned to an OspC type included both Lyme disease-causing spirochetes (51 isolates) and other Borrelia species (27 isolates). The geographic and biological origin of the isolate from which each OspC sequence was obtained is indicated in FIG. 20 in tabular form. The majority of B. burgdorferi isolates were from North America (80%) with lesser numbers from Europe (16%) and Asia (4%). Fifty three percent of the B. burgdorferi, 48% of the B. afzelii and 79% of the B. garinii OspC sequences originated from isolates collected from humans. It is noteworthy that B. garinii OspC sequences from human isolates were predominantly of cerebrospinal fluid (CSF) origin (68%) whereas B. afzelii isolates were predominantly from the skin (83%). In contrast, B. burgdorferi derived OspC sequences were from isolates recovered from human skin (51%), plasma (30%), and CSF (19%). These findings are in agreement with the known patterns of disease caused by these organisms and indicate that the sample of OspC sequences assessed in this report is representative of the true population of Lyme disease spirochetes.
To facilitate further phylogenetic analyses, the set of sequences analyzed was reduced to 74 by eliminating identical sequences. These sequences were then aligned and analyzed using the Phylip (v. 3.66) phylogenetics package with bootstrapping (n=1000). Distances were calculated for the regions spanning 20 to 200, 20 to 130 and 131 to 200 using the Dayhoff PAM matrix, and trees were created by neighbor joining. The B. hermsii OspC ortholog (Vmp33) sequence served as an outgroup (Margolis et al, 1994). A consensus tree was generated by majority rule (50% cutoff for group inclusion). Distances were re-calculated for the consensus tree by the maximum likelihood method under the Dayhoff PAM model (FIG. 21).
The consensus trees generated with the 20-200 aa segment of OspC were well supported at the terminal nodes, with all determined OspC types clustering as expected. While several of the deeper branches were less supported by the bootstrap analyses (FIG. 21A) this is not unexpected since the extended regions of identity among the sequences makes their phylogenetic differentiation subtle. Consensus trees generated using the 20-200 and 20-130 amino acid segments of OspC exhibited similar phylogenetic clustering (FIG. 21A, 21B), based largely on species identity. However, the consensus tree generated using amino acids 131-200 (FIG. 21C) yielded significantly different clustering patterns that were not strongly supported by bootstrap analyses. This observation is consistent with the hypothesis that recombination between short segments of the ospC gene has occurred between strains of differing OspC types. Evidence for recombination of short segments of OspC between OspC types can be seen in specific sequences. For example, sequences of the B. afzelii OspC type, PLj7, have regions within the amino acid 20-130 domain that are identical to that seen in B. garinii OspC sequences that form the Pki cluster. In the 131-200 region of PLj7, the hypervariable loop 5 and loop 6 regions have motifs identical to those seen in B. burgdorferi OspC types F and M, respectively. Further evidence for recombination came from bootscanning using SimPlot (v. 3.5.1) (Lole et al, 1999). In bootscanning, potential recombination is assessed by generation of phlylogenetic trees (Kimura model, Ts/Tv ratio=2.0, Neighbor joining) of sequence segments within a sliding window (40 base window, 10 base step interval). The trees are bootstrapped (n=100) and the number of permuted trees supporting sequence grouping within that window is reported. Evidence of recombination is typically considered to be supported when >70% of permuted trees cluster the sequences together within a window. Evidence was found of possible recombination in the types described above (FIG. 22), as well as in numerous other OspC types (data not shown).
The evidence that OspC variability occurs by exchange between existing OspC types rather than by hypermutation provides evidence that there is a limit to the absolute number of OspC type-specific epitopes required for inclusion in a broadly protective vaccinogen. Since currently mapped linear epitopes are all contained in the C-terminal region of OspC (aa 131-200), it is possible to define a theoretical number of epitopes required for a chimeric vaccinogen. By inspecting this region in the 74 representative sequences described above, the number of unique epitope-containing regions can be reduced to 34 by elimination of sequences that are either identical or have only a single amino acid change (FIG. 22). It is likely that this number can be further restricted by epitope mapping since some epitopes may convey protection against two or more OspC types. Further reduction in the required number of epitopes could also come from consideration of only those OspC types associated with human disease or, more specifically, with invasive human disease (see Example 1). One theoretical concern with vaccination against a subset of OspC epitopes is the potential to drive selection toward types not included in the vaccinogen, thus increasing the fraction of the population bearing those rare alleles. However, as humans are only incidental hosts, it is unlikely that vaccination will significantly alter the population distribution of strains expressing specific OspC types in the tick vector or mammalian reservoirs.
In summary, the extensive nature of the OspC database has allowed thorough analyses to be conducted which have defined new OspC types and provided information regarding their frequency of isolation and association with human disease. The data suggest that the number of OspC epitope-containing sequences required for inclusion in a broadly protective chimeric vaccinogen is limited and that the development of a chimeric vaccinogen is feasible.
Example 6
Construction of an Octavalent Chimera
The ENICABKD octavalent construct is shown below, and several properties of the construct are presented as calculated by the PROTPARAM program. Segments designated a “L#” are linker sequences. “RS” indicates the location of a restriction sited used in making the construct.











<----TAG----->RS<----------------------Type E---------------




1
AHHHHHHVDDDDKITGLKSEHAVLGLDNLTDDNAQRAILKKHANKDKGAAELEKLFKAVE
(SEQ ID NO: 249)


 



<------------<L9>-----------------Type N-----------------><L


61
NLSKAAQDTLKNAPGVGATTDEEAKKAILRTNAIKDKGADELEKLFKSVESLAKAAQDAT


 



6><----------------Type I----------------><L7><-------------


121
QMLKTNNDKTKGADELEKLFESVKNLSKAAKEMLTNSVKELTSTEPSEEFTKKLKEKHTD


 



------Type C---------------------><L8RS<------Type A-----><-


181
LGKKDATDVHAKEAILKTNGTKDKGAAELEKLFESGEDVSETFTNKLKEKHTDLGKEGSM


 



L1><----------------Type B-----------------><L2><-----------


241
GMLKANAAGKDKGVEELEKLSGSLESLSKAAKEMLANSVKELTSTNGNLITDAAKDKGAA


 



----Type K------------------><L3><---------------Type D-----


301
ELEKLFKAVENLAKAAKEMLANSVKELTSSMSVLKTHNAKDKGAEELVKLSESVAGLLKA


 



----------------------->


361
AQAILANSVKELTSPVVAESPKKP






Number of amino acids: 384

Molecular weight: 41263.7

Theoretical isoelectric point: 6.52

Amino acid composition:


















Ala (A) 51
13.3%




Arg (R) 2
0.5%



Asn (N) 20
5.2%



Asp (D) 25
6.5%



Cys (C) 0
0.0%



Gln (Q) 5
1.3%



Glu (E) 42
10.9%



Gly (G) 21
5.5%



His (H) 12
3.1%



Ile (I) 7
1.8%



Leu (L) 46
12.0%



Lys (K) 62
16.1%



Met (M) 7
1.8%



Phe (F) 7
1.8%



Pro (P) 5
1.3%



Ser (S) 27
7.0%



Thr (T) 26
6.8%



Trp (W) 0
0.0%



Tyr (Y) 0
0.0%



Val (V) 19
4.9%







Total number of negatively charged residues (Asp + Glu): 67



Total number of positively charged residues (Arg + Lys): 64






Atomic composition:


















Carbon
C
1787



Hydrogen
H
2983



Nitrogen
N
501



Oxygen
O
597



Sulfur
S
7







Formula: C1787H2983N501O597S7



Total number of atoms: 5875






Estimated half-life:

The N-terminal of the sequence considered is A (Ala).

The estimated half-life is: 4.4 hours (mammalian reticulocytes, in vitro).

    
    
        >20 hours (yeast, in vivo).
        >10 hours (Escherichia coli, in vivo).

Instability index:

The instability index (II) is computed to be 12.58

This classifies the protein as stable.

Aliphatic index: 81.46

Grand average of hydropathicity (GRAVY): −0.668

    
    


When administered to test mammals, this chimeric protein construct is found to elicit a robust immune response, and to provide protection from the development of Lyme disease.
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While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.

## Claims

1. A chimeric recombinant protein comprising the amino acid sequence as set forth in SEQ ID NO: 75 or SEQ ID NO: 249.

2. A method for eliciting an immune response against Borrelia in an individual in need thereof, comprising the step of
administering to said individual a chimeric recombinant protein comprising the amino acid sequence as set forth in SEQ ID NO: 75 or SEQ ID NO: 249.

3. A immunogenic cocktail of chimeric recombinant proteins, wherein each chimeric recombinant protein in said cocktail comprises the amino acid sequence as set forth in SEQ ID NO: 75 or SEQ ID NO: 249.

4. The method of claim 2, wherein said individual is a companion pet.