Nucleic acid vaccines against rickettsial diseases and methods of use

Abstract

Described are nucleic acid vaccines containing genes to protect animals or humans against rickettsial diseases. Also described are polypeptides and methods of using these polypeptides to detect antibodies to pathogens.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of Ser. No. 10/062,994, filed Jan. 31, 2002, now U.S. Pat. No.6,653,128 (which claims the benefit of U.S. Provisional Application 60/269/944, filed Feb. 20, 2001); which is a divisional of Ser. No.09/553,662, filed Apr. 21, 2000; which is a continuation-in-part of Ser. No. 09/337,827, filed Jun. 22, 1999 (which claims the benefit of 60/130,725, filed Apr. 11, 1999); which is a divisional of Ser. No. 08/953,326, filed Oct. 17, 1997, now U.S. Pat. No. 6,251,872; which is a continuation-in-part of application Ser. No. 08/733,230, filed Oct. 17, 1996, now U.S. Pat. No. 6,025,338. Each of these patent applications is herein incorporated by reference in its entirety, including all figures, nucleic acid sequences, amino acid sequences, drawings, and tables.

TECHNICAL FIELD

[0003] This invention relates to nucleic acid vaccines for rickettsial diseases of animals, including humans.

BACKGROUND OF THE INVENTION

[0004] The rickettsias are a group of small bacteria commonly transmitted by arthropod vectors to man and animals, in which they may cause serious disease. The pathogens causing human rickettsial diseases include the agent of epidemic typhus, Rickettsia prowazekii, which has resulted in the deaths of millions of people during wartime and natural disasters. The causative agents of spotted fever, e.g., Rickettsia rickettsii and Rickettsia conorii, are also included within this group. Recently, new types of human rickettsial disease caused by members of the tribe Ehrlichiae have been described. Ehrlichiae infect leukocytes and endothelial cells of many different mammalian species, some of them causing serious human and veterinary diseases. Over 400 cases of human ehrlichiosis, including some fatalities, caused by Ehrlichia chaffeensis have now been reported. Clinical signs of human ehrlichiosis are similar to those of Rocky Mountain spotted fever, including fever, nausea, vomiting, headache, and rash.

[0005] Heartwater is another infectious disease caused by a rickettsial pathogen, namely Cowdria ruminantium, and is transmitted by ticks of the genus Amblyomma. The disease occurs throughout most of Africa and has an estimated endemic area of about 5 million square miles. In endemic areas, heartwater is a latent infection in indigenous breeds of cattle that have been subjected to centuries of natural selection. The problems occur where the disease contacts susceptible or naive cattle and other ruminants. Heartwater has been confirmed to be on the island of Guadeloupe in the Caribbean and is spreading through the Caribbean Islands. The tick vectors responsible for spreading this disease are already present on the American mainland and threaten the livestock industry in North and South America.

[0006] In acute cases of heartwater, animals exhibit a sudden rise in temperature, signs of anorexia, cessation of rumination, and nervous symptoms including staggering, muscle twitching, and convulsions. Death usually occurs during these convulsions. Peracute cases of the disease occur where the animal collapses and dies in convulsions having shown no preliminary symptoms. Mortality is high in susceptible animals. Angora sheep infected with the disease have a 90% mortality rate while susceptible cattle strains have up to a 60% mortality rate.

[0007] If detected early, tetracycline or chloramphenicol treatment are effective against rickettsial infections, but symptoms are similar to numerous other infections and there are no satisfactory diagnostic tests (Helmick, C., K. Bernard, L. D'Angelo [1984] J. Infect. Dis. 150:480).

[0008] Animals which have recovered from heartwater are resistant to further homologous, and in some cases heterologous, strain challenge. It has similarly been found that persons recovering from a rickettsial infection may develop a solid and lasting immunity. Individuals recovered from natural infections are often immune to multiple isolates and even species. For example, guinea pigs immunized with a recombinant R. conorii protein were partially protected even against R. rickettsii (Vishwanath, S., G. McDonald, N. Watkins [1990] Infect. Immun. 58:646). It is known that there is structural variation in rickettsial antigens between different geographical isolates. Thus, a functional recombinant vaccine against multiple isolates would need to contain multiple epitopes, e.g., protective T and B cell epitopes, shared between isolates. It is believed that serum antibodies do not play a significant role in the mechanism of immunity against rickettsia (Uilenberg, G. [1983] Advances in Vet. Sci. and Comp. Med. 27:427-480; Du Plessis, Plessis, J. L. [1970] Onderstepoort J. Vet. Res. 37(3):147-150).

[0009] Vaccines based on inactivated or attenuated rickettsiae have been developed against certain rickettsial diseases, for example against R. prowazekii and R. rickettsii. However, these vaccines have major problems or disadvantages, including undesirable toxic reactions, difficulty in standardization, and expense (Woodward, T. [1981] “Rickettsial diseases: certain unsettled problems in their historical perspective,” In Rickettsia and Rickettsial Diseases, W. Burgdorfer and R. Anacker, eds., Academic Press, New York, pp. 17-40).

[0010] A vaccine currently used in the control of heartwater is composed of live infected sheep blood. This vaccine also has several disadvantages. First, expertise is required for the intravenous inoculation techniques required to administer this vaccine. Second, vaccinated animals may experience shock and so require daily monitoring for a period after vaccination. There is a possibility of death due to shock throughout this monitoring period, and the drugs needed to treat any shock induced by vaccination are costly. Third, blood-borne parasites maybe present in the blood vaccine and be transmitted to the vaccinates. Finally, the blood vaccine requires a cold chain to preserve the vaccine.

[0011] Clearly, a safer, more effective vaccine that is easily administered would be particularly advantageous. For these reasons, and with the advent of new methods in biotechnology, investigators have concentrated recently on the development of new types of vaccines, including recombinant vaccines. However, recombinant vaccine antigens must be carefully selected and presented to the immune system such that shared epitopes are recognized. These factors have contributed to the search for effective vaccines.

[0012] A protective vaccine against rickettsiae that elicits a complete immune response can be advantageous. A few antigens which potentially can be useful as vaccines have now been identified and sequenced for various pathogenic rickettsia. The genes encoding the antigens and that can be employed to recombinantly produce those antigen have also been identified and sequenced. Certain protective antigens identified for R. rickettsii, R. conorii, and R. prowazekii (e.g., rOmpA and rOmpB) are large (>100 kDa), dependent on retention of native conformation for protective efficacy, but are often degraded when produced in recombinant systems. This presents technical and quality-control problems if purified recombinant proteins are to be included in a vaccine. The mode of presentation of a recombinant antigen to the immune system can also be an important factor in the immune response.

[0013] Nucleic acid vaccination has been shown to induce protective immune responses in non-viral systems and in diverse animal species (Special Conference Issue, WHO meeting on nucleic acid vaccines [1994] Vaccine 12:1491). Nucleic acid vaccination has induced cytotoxic lymphocyte (CTL), T-helper 1, and antibody responses, and has been shown to be protective against disease (Ulmer, J., J. Donelly, S. Parker et al. [1993] Science 259:1745). For example, direct intramuscular injection of mice with DNA encoding the influenza nucleoprotein caused the production of high titer antibodies, nucleoprotein-specific CTLs, and protection against viral challenge. Immunization of mice with plasmid DNA encoding the Plasmodium yoelii circumsporozoite protein induced high antibody titers against malaria sporozoites and CTLs, and protection against challenge infection (Sedegah, M., R. Hedstrom, P. Hobart, S. Hoffman [1994] Proc. Natl. Acad. Sci. USA 91:9866). Cattle immunized with plasmids encoding bovine herpesvirus 1 (BHV-1) glycoprotein IV developed neutralizing antibody and were partially protected (Cox, G., T. Zamb, L. Babiuk [1993] J. Virol. 67:5664). However, it has been a question in the field of immunization whether the recently discovered technology of nucleic acid vaccines can provide improved protection against an antigenic drift variant. Moreover, it has not heretofore been recognized or suggested that nucleic acid vaccines may be successful to protect against rickettsial disease or that a major surface protein conserved in rickettsia was protective against disease.

BRIEF SUMMARY OF THE INVENTION

[0014] Disclosed and claimed here are novel vaccines for conferring immunity to rickettsia infection, including Cowdria ruminantium causing heartwater. Also disclosed are novel nucleic acid compositions and methods of using those compositions, including to confer immunity in a susceptible host. Also disclosed are novel materials and methods for diagnosing infections by Ehrlichia in humans or animals.

[0015] One aspect of the subject invention concerns a nucleic acid, e.g., DNA or mRNA, vaccine containing the major antigenic protein 1 gene (MAP1) or the major antigenic protein 2 gene (MAP2) of rickettsial pathogens. In one embodiment, the nucleic acid vaccines can be driven by the human cytomegalovirus (HCMV) enhancer-promoter. In studies immunizing mice by intramuscular injection of a DNA vaccine composition according to the subject invention, immunized mice seroconverted and reacted with MAP1 in antigen blots. Splenocytes from immunized mice, but not from control mice immunized with vector only, proliferated in response to recombinant MAP1 and rickettsial antigens in in vitro lymphocyte proliferation tests. In experiments testing different DNA vaccine dose regimens, increased survival rates as compared to controls were observed on challenge with rickettsia. Accordingly, the subject invention concerns the discovery that DNA vaccines can induce protective immunity against rickettsial disease or death resulting therefrom.

[0016] The subject invention further concerns the genes designated Cowdria ruminantium map 2, Cowdria ruminantium 1hworj3, Cowdria ruminantium 4hworf1, Cowdria ruminantium 18hworf1, and Cowdria ruminantium 3gdorf3 and the use of these genes in diagnostic and therapeutic applications. The subject invention further concerns the proteins encoded by the exemplified genes, antibodies to these proteins, and the use of such antibodies and proteins in diagnostic and therapeutic applications.

[0017] In one embodiment of the subject invention, the polynucleotide vaccines are administered in conjunction with an antigen. In a preferred embodiment, the antigen is the polypeptide which is encoded by the polynucleotide administered as the polynucleotide vaccine. As a particularly preferred embodiment, the antigen is administered as a booster subsequent to the initial administration of the polynucleotide vaccine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1A-1C show a comparison of the amino acid sequences from alignment of the three rickettsial proteins, namely, Cowdria ruminantium (C. r.), Ehrlichia chaffeensis (E. c.), and Anaplasma marginale (A.m.).

[0019] FIGS. 2A-2C shows the DNA sequence of the 28 kDa gene locus cloned from E. chaffeensis (FIGS. 2A-2B) and E. canis (FIG. 2C). One letter amino acid codes for the deduced protein sequences are presented below the nucleotide sequence. The proposed sigma-70-like promoter sequences (38) are presented in bold and underlined text as -10 and -35 (consensus -35 and -10 sequences are TTGACA and TATAAT, respectively). Similarly, consensus ribosomal binding sites and transcription terminator sequences (bold letter sequence) are identified. G-rich regions identified in the E. chaffeensis sequence are underlined. The conserved sequences from within the coding regions selected for RT-PCR assay are identified with italics and underlined text.

[0020] FIG. 3A shows the complete sequence of the MAP2 homolog of Ehrlichia canis. The arrow (→) represents the predicted start of the mature protein. The asterisk (*) represents the stop codon. Underlined nucleotides 5′ to the open reading frame with -35 and -10 below represent predicted promoter sequences. Double underlined nucleotides represent the predicted ribosomal binding site. Underlined nucleotides 3′ to the open reading frame represent possible transcription termination sequences.

[0021] FIG. 3B shows the complete sequence of the MAP2 homolog of Ehrlichia chaffeensis. The arrow (→) represents the predicted start of the mature protein. The asterisk (*) represents the stop codon. Underlined nucleotides 5′ to the open reading frame with -35 and -10 below represent predicted promoter sequences. Double underlined nucleotides represent the predicted ribosomal binding site. Underlined nucleotides 3′ to the open reading frame represent possible transcription termination sequences.

BRIEF DESCRIPTION OF THE SEQUENCES

[0022] SEQ ID NO.1 is the coding sequence of the MAP1 gene from Cowdria ruminantium (Highway isolate).

[0023] SEQ ID NO.2 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 1.

[0024] SEQ ID NO.3 is the coding sequence of the MAP1 gene from Ehrlichia chaffeensis.

[0025] SEQ ID NO.4 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 3.

[0026] SEQ ID NO.5 is the Anaplasma marginale MSP4 gene coding sequence.

[0027] SEQ ID NO.6 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 5.

[0028] SEQ ID NO. 7 is a partial coding sequence of the VSA1 gene from Ehrlichia chaffeensis, also shown in FIGS. 2A-2B.

[0029] SEQ ID NO.8 is the coding sequence of the VSA2 gene from Ehrlichia chaffeensis, also shown in FIGS. 2A-2B.

[0030] SEQ ID NO.9 is the coding sequence of the VSA3 gene from Ehrlichia chaffeensis, also shown in FIGS. 2A-2B.

[0031] SEQ ID NO.10 is the coding sequence of the VSA4 gene from Ehrlichia chaffeensis, also shown in FIGS. 2A-2B.

[0032] SEQ ID NO. 11 is a partial coding sequence of the VSA5 gene from Ehrlichia chaffeensis, also shown in FIGS. 2A-2B.

[0033] SEQ ID NO.12 is the coding sequence of the VSA1 gene from Ehrlichia canis, also shown in FIG. 2C.

[0034] SEQ ID NO.13 is a partial coding sequence of the VSA2 gene from Ehrlichia canis, also shown in FIG. 2C.

[0035] SEQ ID NO.14 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 7, also shown in FIGS. 2A-2B.

[0036] SEQ ID NO.15 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 8, also shown in FIGS. 2A-2B.

[0037] SEQ ID NO.16 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 9, also shown in FIGS. 2A-2B.

[0038] SEQ ID NO.17 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 10, also shown in FIGS. 2A-2B.

[0039] SEQ ID NO.18 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 11, also shown in FIGS. 2A-2B.

[0040] SEQ ID NO.19 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 12, also shown in FIG. 2C.

[0041] SEQ ID NO.20 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 13, also shown in FIG. 2C.

[0042] SEQ ID NO.21 is the coding sequence of the MAP2 gene from Ehrlichia canis, also shown in FIG. 3A.

[0043] SEQ ID NO.22 is the coding sequence of the MAP2 gene from Ehrlichia chaffeensis, also shown in FIG. 3B.

[0044] SEQ ID NO.23 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 21, also shown in FIG. 3A.

[0045] SEQ ID NO.24 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 22, also shown in FIG. 3B.

[0046] SEQ ID NO.25 is the coding sequence of the map2 gene from Cowdria ruminantium.

[0047] SEQ ID NO.26 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 25.

[0048] SEQ ID NO.27 is the coding sequence of the 1hworf3 gene from Cowdria ruminantium.

[0049] SEQ ID NO.28 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 27.

[0050] SEQ ID NO.29 is the coding sequence of the 4hworf1 gene from Cowdria ruminantium.

[0051] SEQ ID NO.30 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 29.

[0052] SEQ ID NO. 31 is the coding sequence of the 18hworf1 gene from Cowdria ruminantium.

[0053] SEQ ID NO.32 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 31.

[0054] SEQ ID NO.33 is the coding sequence of the 3gdorf3 gene from Cowdria ruminantium.

[0055] SEQ ID NO.34 is the polypeptide encoded by the polynucleotide of SEQ ID NO. 33.

DETAILED DISCLOSURE OF THE INVENTION

[0056] In one embodiment, the subject invention concerns a novel strategy, termed nucleic acid vaccination, for eliciting an immune response protective against rickettsial disease. The subject invention also concerns novel compositions that can be employed according to this novel strategy for eliciting a protective immune response.

[0057] According to the subject invention, recombinant DNA or mRNA encoding an antigen of interest is inoculated directly into the human or animal host where an immune response is induced. Prokaryotic signal sequences may be deleted from the nucleic acid encoding an antigen of interest. Advantageously, problems of protein purification, as can be encountered with antigen delivery using live vectors, can be virtually eliminated by employing the compositions or methods according to the subject invention. Unlike live vector delivery, the subject invention can provide a further advantage in that the DNA or RNA does not replicate in the host, but remains episomal. See, for example, Wolff, J. A., J. J. Ludike, G. Acsadi, P. Williams, A. Jani (1992) Hum. Mol. Genet. 1:363. A complete immune response can be obtained as recombinant antigen is synthesized intracellularly and presented to the host immune system in the context of autologous class I and class II NMC molecules.

[0058] In one embodiment, the subject invention concerns nucleic acids and compositions comprising those nucleic acids that can be effective in protecting an animal from disease or death caused by rickettsia. For example, a nucleic acid vaccine of the subject invention has been shown to be protective against Cowdria ruminantium, the causative agent of heartwater in domestic ruminants. Accordingly, nucleotide sequences of rickettsial genes, as described herein, can be used as nucleic acid vaccines against human and animal rickettsial diseases.

[0059] In one embodiment of the subject invention, the polynucleotide vaccines are administered in conjunction with an antigen. In a preferred embodiment, the antigen is the polypeptide which is encoded by the polynucleotide administered as the polynucleotide vaccine. As a particularly preferred embodiment, the antigen is administered as a booster subsequent to the initial administration of the polynucleotide vaccine. In another embodiment of the invention, the polynucleotide vaccine is administered in the form of a “cocktail” which contains at least two of the nucleic acid vaccines of the subject invention. The “cocktail” may be administered in conjunction with an antigen or an antigen booster as described above.

[0060] The MAP1 gene, which can be used to obtain this protection, is also present in other rickettsiae including Anaplasma marginale, Ehrlichia canis, and in a causative agent of human ehrlichiosis, Ehrlichia chaffeensis (van Vliet, A., F. Jongejan, M. van Kleef, B. van der Zeijst [1994] Infect. Immun. 62:1451). The MAP1 gene or a MAP1-like gene can also be found in certain Rickettsia spp. MAP1-like genes from Ehrlichia chaffeensis and Ehrlichia canis have now been cloned and sequenced. These MAP-1 homologs are also referred to herein as Variable Surface Antigen (VSA) genes.

[0061] The present invention also concerns polynucleotides encoding MAP2 or MAP2 homologs from Ehrlichia canis and Ehrlichia chaffeensis. MAP2 polynucleotide sequences of the invention can be used as vaccine compositions and in diagnostic assays. The polynucleotides can also be used to produce the MAP2 polypeptides encoded thereby.

[0062] The subject invention further concerns the genes designated Cowdria ruminantium map 2, Cowdria ruminantium 1hworf3, Cowdria ruminantium 4hworf1, Cowdria ruminantium 18hworf1, and Cowdria ruminantium 3gdorf3 and the use of these genes in diagnostic and therapeutic applications. The subject invention further concerns the proteins encoded by the exemplified genes, antibodies to these proteins, and the use of such antibodies and proteins in diagnostic and therapeutic applications.

[0063] Compositions comprising the subject polynucleotides can include appropriate nucleic acid vaccine vectors (plasmids), which are commercially available (e.g., Vical, San Diego, Calif.). In addition, the compositions can include a pharmaceutically acceptable carrier, e.g., saline. The pharmaceutically acceptable carriers are well known in the art and also are commercially available. For example, such acceptable carriers are described in E. W. Martin's Remington's Pharmaceutical Science, Mack Publishing Company, Easton, Pa.

[0064] The subject invention also concerns polypeptides encoded by the subject polynucleotides. Specifically exemplified are the polypeptides encoded by the MAP-1 and VSA genes of C. rumimontium, E. chaffeensis, E. canis and the MP4 gene of Anaplasma marginale. Polypeptides uncoded by E. chaffeensis and E. canis MAP2 genes are also exemplified herein.

[0065] Also encompassed within the scope of the present invention are fragments and variants of the exemplified polynucleotides and polypeptides. Fragments would include, for example, portions of the exemplified sequences wherein procaryotic signal sequences have been removed. Examples of the removal of such sequences are given in Example 3. Variants include polynucleotides and/or polypeptides having base or amino acid additions, deletions and substitutions in the sequence of the subject molecule so long as those variants have substantially the same activity or serologic reactivity as the native molecules. Also included are allelic variants of the subject polynucleotides. The polypeptides of the present invention can be used to raise antibodies that are reactive with the polypeptides disclosed herein. The polypeptides and polynucleotides can also be used as molecular weight markers.

[0066] Another aspect of the subject invention concerns antibodies reactive with MAP-1 and MAP2 polypeptides disclosed herein. Antibodies can be monoclonal or polyclonal and can be produced using standard techniques known in the art. Antibodies of the invention can be used in diagnostic and therapeutic applications.

[0067] In a specific embodiment, the subject invention concerns a DNA vaccine (e.g., VCL1010/MAP1) containing the major antigenic protein 1 gene (MAP1) driven by the human cytomegalovirus (HCMV) enhancer-promoter. In a specific example, this vaccine was injected intramuscularly into 8-10 week-old female DBA/2 mice after treating them with 50 &mgr;l/muscle of 0.5% bupivacaine 3 days previously. Up to 75% of the VCL1010/MAP1-immunized mice seroconverted and reacted with MAP1 in antigen blots. Splenocytes from immunized mice, but not from control mice immunized with VCL1010 DNA (plasmid vector, Vical, San Diego) proliferated in response to recombinant MAP1 and C. ruminantium antigens in in vitro lymphocyte proliferation tests. These proliferating cells from mice immunized with VCL1010/MAP1 DNA secreted IFN-gamma and IL-2 at concentrations ranging from 610 pg/ml and 152 pg/ml to 1290 pg/ml and 310 pg/ml, respectively. In experiments testing different VCL1010/MAP 1 DNA vaccine dose regimens (25 -100 &mgr;g/dose, 2 or 4 immunizations), survival rates of 23% to 88% (35/92 survivors/total in all VCL1010/MAP1 immunized groups) were observed on challenge with 30LD50 of C. ruminantium. Survival rates of 0% to 3% (1/144 survivors/total in all control groups) were recorded for control mice immunized similarly with VCL1010 DNA or saline. Accordingly, in a specific embodiment, the subject invention concerns the discovery that the gene encoding the MAP1 protein induces protective immunity as a DNA vaccine against rickettsial disease.

[0068] The nucleic acid sequences described herein have other uses as well. For example, the nucleic acids of the subject invention can be useful as probes to identify complementary sequences within other nucleic acid molecules or genomes. Such use of probes can be applied to identify or distinguish infectious strains of organisms in diagnostic procedures or in rickettsial research where identification of particular organisms or strains is needed. As is well known in the art, probes can be made by labeling the nucleic acid sequences of interest according to accepted nucleic acid labeling procedures and techniques. A person of ordinary skill in the art would recognize that variations or fragments of the disclosed sequences which can specifically and selectively hybridize to the DNA of rickettsia can also function as a probe. It is within the ordinary skill of persons in the art, and does not require undue experimentation in view of the description provided herein, to determine whether a segment of the claimed DNA sequences is a fragment or variant which has characteristics of the full sequence, e.g., whether it specifically and selectively hybridizes or can confer protection against rickettsial infection in accordance with the subject invention. In addition, with the benefit of the subject disclosure describing the specific sequences, it is within the ordinary skill of those persons in the art to label hybridizing sequences to produce a probe.

[0069] Various degrees of stringency of hybridization can be employed. The more severe the conditions, the greater the complementarity that is required for duplex formation. Severity of conditions can be controlled by temperature, probe concentration, probe length, ionic strength, time, and the like. Preferably, hybridization is conducted under moderate to high stringency conditions by techniques well known in the art, as described, for example, in Keller, G. H., M. M. Manak (1987) DNA Probes, Stockton Press, New York, N.Y., pp. 169-170.

[0070] Examples of various stringency conditions are provided herein. Hybridization of immobilized DNA on Southern blots with 32P-labeled gene-specific probes can be performed by standard methods ( Maniatis et al. (1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York.). In general, hybridization and subsequent washes can be carried out under moderate to high stringency conditions that allow for detection of target sequences with homology to the exemplified polynucleotide sequence. For double-stranded DNA gene probes, hybridization can be carried out overnight at 20-25° C. below the melting temperature (Tm) of the DNA hybrid in 6×SSPE, 5×Denhardt's solution, 0.1% SDS, 0.1 mg/ml denatured DNA. The melting temperature is described by the following formula (Beltz et al. et al. [1983] Methods of Enzymology, R. Wu, L. Grossman and K. Moldave [eds.] Academic Press, New York 100:266-285).

[0071] Tm=81.5° C.+16.6 Log[Na+]+0.41 (% G+C)−0.61 (% formamide)−600/length of duplex in base pairs.

[0072] Washes are typically carried out as follows:

[0073] (1) twice at room temperature for 15 minutes in 1×SSPE, 0.1% SDS (low stringency wash);

[0074] (2) once at Tm-20° C. for 15 minutes in 0.2×SSPE, 0.1 % SDS (moderate stringency wash).

[0075] For oligonucleotide probes, hybridization can be carried out overnight at 10-20° C. below the melting temperature (Tm) of the hybrid in 6×SSPE, 5×Denhardt's solution, 0.1% SDS, 0.1 mg/ml denatured DNA. Tm for oligonucleotide probes can be determined by the following formula:

[0076] Tm (° C.)=2(number T/A base pairs)+4(number G/C base pairs) (Suggs et al. [1981] ICN-UCLA Symp. Dev. Biol. Using Purified Genes, D. D. Brown [ed.], Academic Press, New York, 23:683-693).

[0077] Washes can be carried out as follows:

[0078] (1) twice at room temperature for 15 minutes 1×SSPE, 0.1% SDS (low stringency wash;

[0079] (2) once at the hybridization temperature for 15 minutes in 1×SSPE, 0.1% SDS (moderate stringency wash).

[0080] In general, salt and/or temperature can be altered to change stringency. With a labeled DNA fragment >70 or so bases in length, the following conditions can be used: 1 Low: 1 or 2X SSPE, room temperature Low: 1 or 2X SSPE, 42° C. Moderate: 0.2X or 1X SSPE, 65° C. High: 0.1X SSPE, 65° C.

[0081] Duplex formation and stability depend on substantial complementarity between the two strands of a hybrid and, as noted above, a certain degree of mismatch can be tolerated. Therefore, the probe sequences of the subject invention include mutations (both single and multiple), deletions, insertions of the described sequences, and combinations thereof, wherein said mutations, insertions and deletions permit formation of stable hybrids with the target polynucleotide of interest. Mutations, insertions and deletions can be produced in a given polynucleotide sequence in many ways, and these methods are known to an ordinarily skilled artisan. Other methods may become known in the future.

[0082] It is also well known in the art that restriction enzymes can be used to obtain functional fragments of the subject DNA sequences. For example, Bal31 exonuclease can be conveniently used for time-controlled limited digestion of DNA (commonly referred to as “erase-a-base” procedures). See, for example, Maniatis et al. (1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York; Wei et al. (1983) J. Biol. Chem. 258:13006-13512.

[0083] In addition, the nucleic acid sequences of the subject invention can be used as molecular weight markers in nucleic acid analysis procedures.

[0084] Following are examples which illustrate procedures for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.

EXAMPLE 1

[0085] A nucleic acid vaccine construct was tested in animals for its ability to protect against death caused by infection with the rickettsia Cowdria ruminantium. The vaccine construct tested was the MAP1 gene of C. ruminantium inserted into plasmid VCL1010 (Vical, San Diego) under control of the human cytomegalovirus promoter-enhancer and intron A. In this study, seven groups containing 10 mice each were injected twice at 2-week intervals with either 100, 75, 50, or 25 &mgr;g VCL1010/MAP1 DNA (V/M in Table 1 below), or 100, 50 &mgr;g VCL1010 DNA (V in Table 1) or saline (Sal.), respectively. Two weeks after the last injections, 8 mice/group were challenged with 30LD50 of C. ruminantium and clinical symptoms and survival monitored. The remaining 2 mice/group were not challenged and were used for lymphocyte proliferation tests and cytokine measurements. The results of the study are summarized in Table 1, below: 2 TABLE 1 100 &mgr;g 75 &mgr;g 50 &mgr;g 25 &mgr;g V/M V/M V/M V/M 100 &mgr;g V 50 &mgr;g V Sal. Survived 5 7 5 3 0 0 0 Died 3 1 3 5 8 8 8

[0086] The VCL1010/MAP1 nucleic acid vaccine increased survival on challenge in all groups, with a total of 20/30 mice surviving compared to 0/24 in the control groups.

[0087] This study was repeated with another 6 groups, each containing 33 mice (a total of 198 mice). Three groups received 75 &mgr;g VCL1010/MAP1 DNA or VCL1010 DNA or saline (4 injections in all cases). Two weeks after the last injection, 30 mice/group were challenged with 30LD50 of C. ruminantium and 3 mice/group were sacrificed for lymphocyte proliferation tests and cytokine measurements. The results of this study are summarized in Table 2, below: 3 TABLE 2 V/M 2 inj. V 2 inj. Sal. 2 inj. V/M 4 inj. V 4 inj. Sal. 4 inj. Survived 7 0 0 8 0 1 Died* 23 30 30 22 30 29 *In mice that died in both V/M groups, there was an increase in mean survival time of approximately 4 days compared to the controls (p < 0.05).

[0088] Again, as summarized in Table 2, the VCL1010/MAP1 DNA vaccine increased the numbers of mice surviving in both immunized groups, although there was no apparent benefit of 2 additional injections. In these two experiments, there were a cumulative total of 35/92 (38%) surviving mice in groups receiving the VCL1010/MAP1 DNA vaccine compared to 1/144 (0.7%) surviving mice in the control groups. In both immunization and challenge trials described above, splenocytes from VCL1010/MAP1 immunized mice, but not from control mice, specifically proliferated to recombinant MAP1 protein and to C. ruminantium in lymphocyte proliferation tests. These proliferating splenocytes secreted IL-2 and gamma-interferon at concentrations up to 310 and 1290 pg/ml respectively. These data show that protection against rickettsial infections can be achieved with a DNA vaccine. In addition, these experiments show MAP1-related proteins as vaccine targets.

EXAMPLE 2

Cloning and Sequence Analysis of MAP1 Homologue Genes of E. chaffeensis and E. canis

[0089] Genes homologous to the major surface protein of C. ruminantium MAP1 were cloned from E. chaffeensis and E. canis by using PCR cloning strategies. The cloned segments represent a 4.6 kb genomic locus of E. chaffeensis and a 1.6 kb locus of E. canis. DNA sequence generated from these clones was assembled and is presented along with the deduced amino acid sequence in FIGS. 2A-2B (SEQ ID NOs. 7-11 and 14-18) and FIG. 2C (SEQ ID NOs. 12-13 and 19-20). Significant features of the DNA include five very similar but nonidentical open reading frames (ORFs) for E. chaffeensis and two very similar, nonidentical ORFs for the E. canis cloned locus. The ORFs for both Ehrlichia spp. are separated by noncoding sequences ranging from 264 to 310 base pairs. The noncoding sequences have a higher A+T content (71.6% for E. chaffeensis and 76.1 % for E. canis) than do the coding sequences (63.5% for E. chaffeensis and 68.0% for E. canis). A G-rich region -200 bases upstream from the initiation codon, sigma-70-like promoter sequences, putative ribosome binding sites (RBS), termination codons, and palindromic sequences near the termination codons are found in each of the E. chaffeensis noncoding sequences. The E. canis noncoding sequence has the same feature except for the G-rich region (FIG. 2C; SEQ ID NOs. 12-13 and 19-20).

[0090] Sequence comparisons of the ORFs at the nucleotide and translated amino acid levels revealed a high degree of similarity between them. The similarity spanned the entire coding sequences, except in three regions where notable sequence variations were observed including some deletions/insertions (Variable Regions I, II and III). Despite the similarities, no two ORFs are identical. The cloned ORF 2, 3 and 4 of E. chaffeensis have complete coding sequences. The ORF1 is a partial gene having only 143 amino acids at the C-terminus whereas the ORF5 is nearly complete but lacks 5-7 amino acids and a termination codon. The cloned ORF2 of E. canis also is a partial gene lacking a part of the C-terminal sequence. The overall similarity between different ORFs at the amino acid level is 56.0% to 85.4% for E. chaffeensis, whereas for E. canis it is 53.3%. The similarity of E. chaffeensis ORFs to the MAP1 coding sequences reported for C. ruminantium isolates ranged from 55.5% to 66.7%, while for E. canis to C. ruminantium it is 48.5% to 54.2%. Due to their high degree of similarity to MAP1 surface antigen genes of C. ruminantium and since they are nonidentical to each other, the E. chaffeensis and E. canis ORFs are referred to herein as putative Variable Surface Antigen (VSA) genes. The apparent molecular masses of the predicted mature proteins of E. chaffeensis were 28.75 kDa for VSA2, 27.78 for VSA3, and 27.95 for VSA4, while E. canis VSA1 was slightly higher at 29.03 kDa. The first 25 amino acids in each VSA coding sequence were eliminated when calculating the protein size since they markedly resembled the signal sequence of C. ruminantium MAP1 and presumably would be absent from the mature protein.

[0091] The amino acid sequence derived from the cloned E. chaffeensis MAP1-like gene, and alignment with the corresponding genes of C. ruminantium and A. marginale is shown in FIG. 1.

EXAMPLE 3

[0092] A further aspect of the subject invention are five additional genes which give protection when formatted as DNA vaccines. These genes are Cowdria ruminantium map 2, Cowdria ruminantium 1hworf3, Cowdria ruminantium 4hworf1, Cowdria ruminantium 8hworf1, and Cowdria ruminantium 3gdorf3. The DNA and translated amino acid sequences of these five genes are shown in SEQ ID NOS. 25-34.

[0093] There is published information showing that gene homologs of all five genes are present in other bacteria. For example, a homolog of map2 is present in Anaplasma marginale, a homolog of 1hworf3 is present in Brucella abortus, homologs of 4hworf1 are present in Pseudomonas aeruginosa and Coxiella burnetii, and homologs of 18hworf1 are present in Coxiella burnetii and Rickettsia prowazekii. This can be revealed by a search of DNA and protein databases with standard search algorithms such as “Blast”. Based on the protective ability of these genes against Cowdria ruminantium and their presence in other bacterial pathogens, the subject invention further concerns the use of these genes, their gene products, and the genes and gene products of the homologs as vaccines against bacteria. This includes their use as DNA or nucleic acid vaccines or when formulated in vaccines employing other methods of delivery, e.g., recombinant proteins or synthetic peptides in adjuvants, recombinant live vector delivery systems such as vaccinia (or other live viruses) or Salmonella (or other live bacteria). These methods of delivery are standard to those familiar with the field. This also includes vaccines against heartwater disease, vaccines against rickettsial diseases in general and vaccines against other bacteria containing homologs of these genes.

[0094] Table 3 shows the protective ability of the 5 genes against death from Cowdria ruminantium challenge in mice. Genes were inserted into VR1012 according to the manufacturers instructions (Vical, San Diego) and challenge studies were conducted as described in Example 1. N-terminal sequences which putatively encoded prokaryotic signal peptides were deleted because of the potential for their affects on expression and immune responses in eukaryotic expression systems or challenged animals. The inserts were as follows: map2, SEQ ID NO. 25, beginning at base 46; 18hworf1, SEQ ID NO. 31, beginning at base 67; 3gdorf3, SEQ ID NO. 33, beginning at base 79; 1hworf3, SEQ ID NO. 27, beginning at base 76; and 4hworf1, SEQ ID NO. 29, beginning at base 58. 4 TABLE 3 MWT Survival Rate DNA Construct Size Vaccinated Control P value TMMAP 2 21 kd 9/28* 32%  0/29  0% 0.004 MB18HWORF1 28 kd 10/30* 33% 1/27 4% 0.021 AM3GDORF3 16 kd  7/26  27% 1/27 4% 0.060 TM1HWORF3 36 kd  8/29  28% 2/30 7% 0.093 TM4HWORF1 19 kd 10/30* 33% 2/30 7% 0.054 Control - VR1012 DNA vector plasmid only *Statistically significant difference (Fisher's Exact test)

[0095] It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.

Claims

1. A composition comprising a polynucleotide which encodes a polypeptide having the characteristic of eliciting an immune response protective against disease or death caused by a rickettsial pathogen, wherein said polypeptide comprises the amino acid sequence of SEQ ID NO: 32 or an immunogenic fragment thereof.

2. The composition, according to claim 1, wherein said rickettsial pathogen is selected from the group consisting of Rickettsia spp., Ehrlichia spp., Anaplasma spp., and Cowdria spp.

3. The composition, according to claim 1, wherein said polynucleotide comprises the nucleic acid sequence of SEQ ID NO: 31 and fragments thereof which encode immunogenic polypeptides.

4. The composition, according to claim 1, wherein said polynucleotide further comprises a nucleic acid vaccine vector.

5. The composition, according to claim 1, further comprising a pharmaceutically acceptable carrier.

6. A polynucleotide encoding a polypeptide comprising SEQ ID NO. 32 and fragments thereof.

7. The polynucleotide according to claim 6, wherein said polynucleotide comprises the nucleic acid sequence of SEQ ID NO: 31 and fragments thereof.

8. A method for protecting a susceptible host against disease or death caused by a rickettsial pathogen, said method comprising administering an effective amount of a polynucleotide encoding polypeptide according to claim 1.

9. The method, according to claim 8, wherein said rickettsial pathogen is selected from the group consisting of Rickettsia spp., Ehrlichia spp., Anaplasma spp., and Cowdria spp.

10. The method, according to claim 10, wherein said polynucleotide comprises SEQ ID NO. 31, and fragments thereof.

11. The method, according to claim 10, wherein said nucleic acid further comprises an appropriate nucleic acid vector.

12. The method, according to claim 10, wherein said composition further comprises a pharmaceutically acceptable carrier.

13. The method, according to claim 10, which further comprises administration to said host a polypeptide comprising SEQ ID NO: 32, or immunogenic fragments thereof.

14. The method according to claim 10, wherein said polynucleotide comprises a sequence encoding a polypeptide that begins at base 67 of SEQ ID NO:31.