CD8 T-cell responses against the immunodominant Theileria parva peptide Tp249-59 are composed of two distinct populations specific for overlapping 11-mer and 10-mer epitopes.

Immunity against Theileria parva is associated with CD8 T-cell responses that exhibit immunodominance, focusing the response against limited numbers of epitopes. As candidates for inclusion in vaccines, characterization of responses against immunodominant epitopes is a key component in novel vaccine development. We have previously demonstrated that the Tp249-59 and Tp1214-224 epitopes dominate CD8 T-cell responses in BoLA-A10 and BoLA-18 MHC I homozygous animals, respectively. In this study, peptide-MHC I tetramers for these epitopes, and a subdominant BoLA-A10-restricted epitope (Tp298-106 ), were generated to facilitate accurate and rapid enumeration of epitope-specific CD8 T cells. During validation of these tetramers a substantial proportion of Tp249-59 -reactive T cells failed to bind the tetramer, suggesting that this population was heterogeneous with respect to the recognized epitope. We demonstrate that Tp250-59 represents a distinct epitope and that tetramers produced with Tp50-59 and Tp49-59 show no cross-reactivity. The Tp249-59 and Tp250-59 epitopes use different serine residues as the N-terminal anchor for binding to the presenting MHC I molecule. Molecular dynamic modelling predicts that the two peptide-MHC I complexes adopt structurally different conformations and Tcell receptor ß sequence analysis showed that Tp249-59 and Tp250-59 are recognized by non-overlapping T-cell receptor repertoires. Together these data demonstrate that although differing by only a single residue, Tp249-59 and Tp250-59 epitopes form distinct ligands for T-cell receptor recognition. Tetramer analysis of T. parva-specific CD8 T-cell lines confirmed the immunodominance of Tp1214-224 in BoLA-A18 animals and showed in BoLA-A10 animals that the Tp249-59 epitope response was generally more dominant than the Tp250-59 response and confirmed that the Tp298-106 response was subdominant.

Analysis of the Cellular Immune Responses to Vaccines.

Flow cytometry, enzyme-linked immunospot (ELISpot), and cellular cytotoxicity assays are powerful tools for studying the cellular immune response toward intracellular pathogens and vaccines in livestock species. Lymphocytes from immunized animals can be purified using Ficoll-Paque density gradient centrifugation and evaluated for their antigen specificity or reactivity toward a vaccine. Here, we describe staining of bovine lymphocytes with peptide (p)-MHC class I tetramers and antibodies specific toward cellular activation markers for evaluation by multiparametric flow cytometry, as well as interferon (IFN)-γ ELISpot and cytotoxicity using chromium (51Cr) release assays. A small component on the use of immunoinformatics for fine-tuning the identification of a minimal CTL epitope is included, and a newly developed and simple assay to measure TCR avidity.

Extensive polymorphism and evidence of immune selection in a highly dominant antigen recognized by bovine CD8 T cells specific for Theileria annulata.

Although parasite strain-restricted CD8 T cell responses have been described for several protozoa, the precise role of antigenic variability in immunity is poorly understood. The tick-borne protozoan parasite Theileria annulata infects leukocytes and causes an acute, often fatal lymphoproliferative disease in cattle. Building on previous evidence of strain-restricted CD8 T cell responses to T. annulata, this study set out to identify and characterize the variability of the target antigens. Three antigens were identified by screening expressed parasite cDNAs with specific CD8 T cell lines. In cattle expressing the A10 class I major histocompatibility complex haplotype, A10-restricted CD8 T cell responses were shown to be focused entirely on a single dominant epitope in one of these antigens (Ta9). Sequencing of the Ta9 gene from field isolates of T. annulata demonstrated extensive sequence divergence, resulting in amino acid polymorphism within the A10-restricted epitope and a second A14-restricted epitope. Statistical analysis of the allelic sequences revealed evidence of positive selection for amino acid substitutions within the region encoding the CD8 T cell epitopes. Sequence differences in the A10-restricted epitope were shown to result in differential recognition by individual CD8 T cell clones, while clones also differed in their ability to recognize different alleles. Moreover, the representation of these clonal specificities within the responding CD8 T cell populations differed between animals. As well as providing an explanation for incomplete protection observed after heterologous parasite challenge of vaccinated cattle, these results have important implications for the choice of antigens for the development of novel subunit vaccines.

Impact of COVID-19 pandemic on African indigenous vegetables value chain in Kenya.

BACKGROUND: African indigenous vegetables are important for food security and nutrition, and income of the poor farm households. In the era of COVID-19, they are critical for boosting people's immunity. Unfortunately, both production of and trade in these vegetables is likely to be severely affected by the pandemic. METHODS: This study examined potential effects of COVID-19 pandemic on production and trade of African indigenous vegetables using a cross-sectional survey of 244 farmers and 246 traders from different regions in Kenya. RESULTS: COVID-19 has a negative impact on production and trading of AIVs in Kenya. Findings indicate that 75% of the farmers are experiencing declining production due to reduced access to input, farm labour and output market. Secondly, about 98% of the traders have recorded a drop in sales volumes due to containment measures implemented by the government and personal safety precautions. In particular, farmers' production and traders' sales volumes declined by 39 and 65%, respectively, during the first phase of the pandemic. CONCLUSION: The findings indicate that the sub-sector requires targeted interventions which may include input support, careful reopening and control of the open-air markets, reduced taxation and facilitated access to urban markets.

CD8+ T-cell responses to Theileria parva are preferentially directed to a single dominant antigen: Implications for parasite strain-specific immunity.

Although immunodominance of CD8(+) T-cell responses is a well-recognised feature of viral infections, its role in responses to more antigenically complex pathogens is less clear. In previous studies we have observed that CD8(+) T-cell responses to Theileria parva exhibit different patterns of parasite strain specificity in cattle of different MHC genotypes. In the current study, we demonstrated that animals homozygous for the A10 and A18 MHC haplotypes have detectable responses to only one of 5 T. parva antigens. Over 60% of the responding T cells from the A18(+) and A10(+) animals recognised defined epitopes in the Tp1 and Tp2 antigens, respectively. Comparison of T-cell receptor beta chain expression profiles of CD8(+) T-cell lines and CD8(+) T cells harvested ex vivo confirmed that the composition of the T-cell lines was representative of the in vivo memory CD8(+) T-cell populations. Analysis of the Tp1 and Tp2 antigens revealed sequence polymorphism, which was reflected by differential recognition by T-cell lines. In conclusion, we have demonstrated a profound immunodominance in the CD8(+) T-cell response to T. parva, which we propose is a major determinant of the parasite strain specificity of the response and hence immune protection.

Characterization of the fine specificity of bovine CD8 T-cell responses to defined antigens from the protozoan parasite Theileria parva.

Immunity against the bovine intracellular protozoan parasite Theileria parva has been shown to be mediated by CD8 T cells. Six antigens targeted by CD8 T cells from T. parva-immune cattle of different major histocompatibility complex (MHC) genotypes have been identified, raising the prospect of developing a subunit vaccine. To facilitate further dissection of the specificity of protective CD8 T-cell responses and to assist in the assessment of responses to vaccination, we set out to identify the epitopes recognized in these T. parva antigens and their MHC restriction elements. Nine epitopes in six T. parva antigens, together with their respective MHC restriction elements, were successfully identified. Five of the cytotoxic-T-lymphocyte epitopes were found to be restricted by products of previously described alleles, and four were restricted by four novel restriction elements. Analyses of CD8 T-cell responses to five of the epitopes in groups of cattle carrying the defined restriction elements and immunized with live parasites demonstrated that, with one exception, the epitopes were consistently recognized by animals of the respective genotypes. The analysis of responses was extended to animals immunized with multiple antigens delivered in separate vaccine constructs. Specific CD8 T-cell responses were detected in 19 of 24 immunized cattle. All responder cattle mounted responses specific for antigens for which they carried an identified restriction element. By contrast, only 8 of 19 responder cattle displayed a response to antigens for which they did not carry an identified restriction element. These data demonstrate that the identified antigens are inherently dominant in animals with the corresponding MHC genotypes.

Evaluation of the recognition of Theileria parva vaccine candidate antigens by cytotoxic T lymphocytes from Zebu cattle.

East Coast fever (ECF) is a highly fatal lymphoproliferative disease of cattle caused by Theileria parva, a tick-borne intracellular apicomplexan parasite. Parasite antigens that are targets of protective cytotoxic T lymphocyte (CTL) responses are required to formulate a sub-unit vaccine against ECF. A number of CTL target antigens have recently been identified and initial evaluation has shown their vaccine potential. This study aimed to evaluate whether these antigens were recognised by CTL obtained from six genetically diverse Zebu cattle immunized with a cocktail of T. parva stocks. T. parva Muguga specific polyclonal CD8(+) CTL lines were generated and confirmed to specifically lyse autologous infected cells. CTL recognition of autologous skin fibroblasts (iSF) transduced with recombinant modified vaccinia virus Ankara strain (MVA) expressing previously identified T. parva Muguga vaccine candidate antigens was evaluated using an IFN-gamma ELISpot assay. CTL lines from one of the four calves, BY120, responded specifically to cells infected with MVA expressing the antigen Tp2 and synthetic peptides were employed to map a new CTL epitope on this antigen. Immunoscreening of the T. parva genome with these CTL lines should identify novel antigens that will constitute valuable additions to the vaccine candidates currently being evaluated.

Assessment of in vitro interferon-gamma responses from peripheral blood mononuclear cells of cattle infected with Mycoplasma mycoides ssp. mycoides small colony type.

Contagious bovine pleuropneumonia (CBPP) is a lung disease caused by the bacterial pathogen Mycoplasma mycoides ssp. mycoides small colony type (MmmSC). It has been spreading due to a number of factors including poor vaccine efficacy and poor sensitivity of current diagnostic tests. The purpose of this study was to assess interferon gamma (IFN-gamma) release after stimulation of peripheral blood mononuclear cells (PBMC) from experimentally infected cattle. PBMC collected from 15 artificially infected animals were incubated with different concentrations of total MmmSC antigen. After 72h of incubation the IFN-gamma release was measured and found to be elevated in 11 animals. We did not observe a correlation between IFN-gamma release of animals with and without pathomorphological gross lesions. Therefore, our data do not confirm a role for CD4 T-lymphocytes in protection, since there is no correlation between IFN-g secretion (supposed to be mainly derived from CD4 T-cells) and disease severity. Additionally, we applied immunocytochemistry on affected lung tissue and detected no build up of T-lymphocytes (CD4 T-cells, CD8 T-cells) but a high presence of myeloid cells.

Immunostimulatory CpG oligodeoxynucleotides enhance the induction of bovine CD4+ cytotoxic T-lymphocyte responses against the polymorphic immunodominant molecule of the protozoan parasite Theileria parva.

Enhancement of the induction of cytotoxic T-cell responses by immunostimulatory CpG oligodeoxynucleotides has been described in humans and mouse models. The present study attempted to address whether CpG has a similar effect in cattle. Immunisation of cattle with a recombinant form of the polymorphic immunodominant molecule from Theileria parva emulsified with immunostimulatory CpG oligodeoxynucleotides in adjuvant had no effect on the induction of antibody responses including the isotype profile, but significantly enhanced the induction of cytolytic responses that were mediated by CD4+CD3+ T cells utilizing the perforin-granzyme pathway.

Analysis of the transcriptome of the protozoan Theileria parva using MPSS reveals that the majority of genes are transcriptionally active in the schizont stage.

Massively parallel signature sequencing (MPSS) was used to analyze the transcriptome of the intracellular protozoan Theileria parva. In total 1,095,000, 20 bp sequences representing 4371 different signatures were generated from T.parva schizonts. Reproducible signatures were identified within 73% of potentially detectable predicted genes and 83% had signatures in at least one MPSS cycle. A predicted leader peptide was detected on 405 expressed genes. The quantitative range of signatures was 4-52,256 transcripts per million (t.p.m.). Rare transcripts (<50 t.p.m.) were detected from 36% of genes. Sequence signatures approximated a lognormal distribution, as in microarray. Transcripts were widely distributed throughout the genome, although only 47% of 138 telomere-associated open reading frames exhibited signatures. Antisense signatures comprised 13.8% of the total, comparable with Plasmodium. Eighty five predicted genes with antisense signatures lacked a sense signature. Antisense transcripts were independently amplified from schizont cDNA and verified by sequencing. The MPSS transcripts per million for seven genes encoding schizont antigens recognized by bovine CD8 T cells varied 1000-fold. There was concordance between transcription and protein expression for heat shock proteins that were very highly expressed according to MPSS and proteomics. The data suggests a low level of baseline transcription from the majority of protein-coding genes.

Enzootic Circulation of Chikungunya Virus in East Africa: Serological Evidence in Non-human Kenyan Primates.

Chikungunya virus (CHIKV) is a globally emerging pathogen causing debilitating arthralgia and fever in humans. First identified in Tanzania (1953), this mosquito-borne alphavirus received little further attention until a 2004 re-emergence in Kenya from an unknown source. This outbreak subsequently spread to the Indian Ocean, with adaptation for transmission by a new urban vector. Under the hypothesis that sylvatic progenitor cycles of CHIKV exist in Kenya (as reported in West Africa, between non-human primates (NHPs) and arboreal Aedes spp. mosquitoes), we pursued evidence of enzootic transmission and human spillover events. We initially screened 252 archived NHP sera from Kenya using plaque reduction neutralization tests. Given an overall CHIKV seroprevalence of 13.1% (marginally higher in western Kenya), we sought more recent NHP samples during 2014 from sites in Kakamega County, sampling wild blue monkeys, olive baboons, and red-tailed monkeys (N = 33). We also sampled 34 yellow baboons near Kwale, coastal Kenya. Overall, CHIKV seropositivity in 2014 was 13.4% (9/67). Antibodies reactive against closely related o'nyong-nyong virus (ONNV) occurred; however, neutralization titers were too low to conclude ONNV exposure. Seroprevalence for the flavivirus dengue was also detected (28%), mostly near Kwale, suggesting possible spillback from humans to baboons. CHIKV antibodies in some juvenile and subadult NHPs suggested recent circulation. We conclude that CHIKV is circulating in western Kenya, despite the 2004 human outbreaks only being reported coastally. Further work to understand the enzootic ecology of CHIKV in east Africa is needed to identify sites of human spillover contact where urban transmission may be initiated.

Using the transcriptome to annotate the genome revisited: application of massively parallel signature sequencing (MPSS).

Transcriptome analysis can provide useful data for refining genome sequence annotation. Application of massively parallel signature sequencing (MPSS) revealed reproducible transcription, in multiple MPSS cycles, from 73% of computationally predicted genes in the Theileria parva schizont lifecycle stage. Signatures spanning consecutive exons confirmed 142 predicted introns. MPSS identified 83 putative genes, >100 codons overlooked by annotation software, and 139 potentially incorrect gene models (with either truncated ORFs or overlooked exons) by interfacing signature locations with stop codon maps. Twenty representative models were confirmed as likely to be incorrect using reverse transcription PCR amplification from independent schizont cDNA preparations. More than 50% of the 60 putative single copy genes in T. parva that were absent from the genome of the closely related T. annulata had MPSS signatures. This study illustrates the utility of MPSS for improving annotation of small, gene-rich microbial eukaryotic genomes.

Post-translational signal peptide cleavage controls differential epitope recognition in the QP-rich domain of recombinant Theileria parva PIM.

The presence of the schizont stage of the obligate intracellular parasites Theileria parva or T. annulata in the cytoplasm of an infected leukocyte results in host cell transformation via a mechanism that has not yet been elucidated. Proteins, secreted by the schizont, or expressed on its surface, are of interest as they can interact with host cell molecules that regulate host cell proliferation and/or survival. The major schizont surface protein is the polymorphic immunodominant molecule, PIM, which contains a large glutamine- and proline-rich domain (QP-rd) that protrudes into the host cell cytoplasm. Analyzing QP-rd generated by in vitro transcription/translation, we found that the signal peptide was efficiently cleaved post-translationally upon addition of T cell lysate or canine pancreatic microsomes, whereas signal peptide cleavage of a control protein only occurred cotranslationally and in the presence of microsomal membranes. The QP-rd of PIM migrated anomalously in SDS-PAGE and removal of the 19 amino acids corresponding to the predicted signal peptide caused a decrease in apparent molecular mass of 24kDa. The molecule was analyzed using monoclonal antibodies that recognize a set of previously defined PIM epitopes. Depending on the presence or the absence of the signal peptide, two conformational states could be demonstrated that are differentially recognized, with N-terminal epitopes becoming readily accessible upon signal peptide removal, and C-terminal epitopes becoming masked. Similar observations were made when the QP-rd of PIM was expressed in bacteria. Our observations could also be of relevance to other schizont proteins. A recent analysis of the proteomes of T. parva and T. annulata revealed the presence of a large family of potentially secreted proteins, characterized by the presence of large stretches of amino acids that are also particularly rich in QP-residues.

Analysis of the Cellular Immune Responses to Vaccines.

Flow cytometry, enzyme-linked immunospot (ELISpot) and cellular cytotoxicity assays are powerful tools for studying the cellular immune response towards intracellular pathogens and vaccines in livestock species. Lymphocytes from immunized animals can be purified using Ficoll-Paque density gradient centrifugation and evaluated for their antigen specificity or reactivity towards a vaccine. Here, we describe staining of bovine lymphocytes with peptide (p)-MHC class I tetramers and antibodies specific towards cellular activation markers for evaluation by multiparametric flow cytometry, as well as interferon (IFN)-γ ELISpot and cytotoxicity using chromium ((51)Cr) release assays. A small component on the use of immunoinformatics for fine-tuning the identification of a minimal CTL epitope is included.

Antibodies against bovine herpesvirus 4 are highly prevalent in wild African buffaloes throughout eastern and southern Africa.

Bovine herpesvirus 4 (BoHV-4) has been isolated from cattle throughout the world. Interestingly, a survey of wild African buffaloes mainly from the Maasai Mara Game Reserve in Kenya revealed that 94% of the animals tested had anti-BoHV-4 antibodies [Rossiter, P.B., Gumm, I.D., Stagg, D.A., Conrad, P.A., Mukolwe, S., Davies, F.G., White, H., 1989. Isolation of bovine herpesvirus-3 from African buffaloes (Syncerus caffer). Res. Vet. Sci. 46, 337-343]. These authors also proposed that the serological antigenic relationship existing between BoHV-4 and alcelaphine herpesvirus 1 (AlHV-1) could confer to BoHV-4 infected buffaloes a protective immune response against lethal AlHV-1 infection. In the present study, we addressed two questions related to Rossiter et al. paper. Firstly, to investigate the role of the African buffalo as a natural host species of BoHV-4, the seroprevalence of anti-BoHV-4 antibodies was analysed in wild African buffaloes throughout eastern and southern Africa. A total of 400 sera was analysed using two complementary immunofluorescent assays. These analyses revealed that independently of their geographical origin, wild African buffaloes exhibit a seroprevalence of anti-BoHV-4 antibodies higher than 68%. This result is by far above the seroprevalence generally observed in cattle. Our data are discussed in the light of our recent phylogenetic study demonstrating that the BoHV-4 Bo17 gene has been acquired from a recent ancestor of the African buffalo. Secondly, we investigated the humoral antigenic relationship existing between BoHV-4 and AlHV-1. Our results demonstrate that among the antigens expressed in AlHV-1 infected cells, epitope(s) recognised by anti-BoHV-4 antibodies are exclusively nuclear, suggesting that the putative property of BoHV-4 to confer an immune protection against AlHV-1 relies on a cellular rather than on a humoral immune response.

Exploring farmer preferences for contagious bovine pleuropneumonia vaccination: a case study of Narok District of Kenya.

Contagious bovine pleuropneumonia (CBPP) is an economically important disease in most of sub-Saharan Africa. A conjoint analysis and ordered probit regression models were used to measure the preferences of farmers for CBPP vaccine and vaccination attributes. This was with regard to inclusion or not of an indicator in the vaccine, vaccine safety, vaccine stability as well as frequency of vaccination, vaccine administration and the nature of vaccination. The analysis was carried out in 190 households in Narok District of Kenya between October and December 2006 using structured questionnaires, 16 attribute profiles and a five-point Likert scale. The factors affecting attribute valuation were shown through a two-way location interaction model. The study also demonstrated the relative importance (RI) of attributes and the compensation value of attribute levels. The attribute coefficient estimates showed that farmers prefer a vaccine that has an indicator, is 100% safe and is administered by the government (p<0.0001). The preferences for the vaccine attributes were consistent with expectations. Preferences for stability, frequency of vaccination and nature of vaccination differed amongst farmers (p>0.05). While inclusion of an indicator in the vaccine was the most important attribute (RI=43.6%), price was the least important (RI=0.5%). Of the 22 household factors considered, 15 affected attribute valuation. The compensation values for a change from non inclusion to inclusion of an indicator, 95-100% safety, 2h to greater than 2h stability and from compulsory to elective vaccination were positive while those for a change from annual to biannual vaccination and from government to private administration were negative. The study concluded that the farmers in Narok District had preferences for specific vaccine and vaccination attributes. These preferences were conditioned by various household characteristics and disease risk factors. On average the farmers would need to be compensated or persuaded to accept biannual and private vaccination against CBPP. There is need for consideration of farmer preferences for vaccine attribute levels during vaccine formulations and farmer preferences for vaccination attribute levels when designing delivery of vaccines.

Leishmania donovani whole cell antigen delivered with adjuvants protects against visceral leishmaniasis in vervet monkeys (Chlorocebus aethiops).

In a previous immunogenicity and efficacy study in mice, montanide ISA 720 (MISA) was indicated to be a better adjuvant than bacillus calmette guerin vaccine (BCG) for a Leishmania vaccine. In the present study, we report the safety, immunogenicity and efficacy of Leishmania donovani (L. donovani) sonicated antigen delivered with alum-BCG (AlBCG), MISA or monophosphoryl lipid A (MPLA) in vervet monkeys following intradermal inoculums. Vaccinated and control animals were challenged with virulent L. donovani parasites and the parasitic burden was determined. Only animals vaccinated with alum-BCG adversely reacted to the inoculum by producing ulcerative erythematous skin indurations. Non-parametric ANOVA followed by a post test showed significantly higher IgG antibodies, and revealed the presence of lymphoproliferative and interferon gamma responses in both AlBCG+Ag and MISA+Ag as compared to the MPLA+Ag or other groups (P < 0.001). We conclude that L. donovani sonicated antigen containing MISA is safe and is associated with protective immune response against Leishmania donovani infection in the vervet monkey model.

Safety and skin delayed-type hypersensitivity response in vervet monkeys immunized with Leishmania donovani sonicate antigen delivered with adjuvants.

In this study, we report on the safety and skin delayed-type hypersensitivity (DTH), responses of the Leishmania donovani whole cell sonicate antigen delivered in conjunction with alum-BCG (AlBCG), Montanide ISA 720 (MISA) or Monophosphoryl lipid A (MPLA) in groups of vervet monkeys. Following three intradermal injections of the inoculums on days 0, 28 and 42, safety and DTH responses were assessed. Preliminary tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) levels were also measured and these were compared with DTH. Only those animals immunized with alum-BCG reacted adversely to the inoculum by producing ulcerative erythematous skin indurations. Non-parametric analysis of variance followed by a post-test showed significantly higher DTH responses in the MISA+Ag group compared with other immunized groups (p < 0.001). The MPLA+Ag group indicated significantly lower DTH responses to the sonicate antigen compared with the AlBCG+Ag group. There was a significant correlation between the DTH and cytokine responses (p < 0.0001). Based on this study we conclude that Leishmania donovani sonicate antigen containing MISA 720 is safe and is associated with a strong DTH reaction following immunization.

In vitro and in vivo antileishmanial efficacy of a combination therapy of diminazene and artesunate against Leishmania donovani in BALB/c mice.

The in vitro and in vivo activity of diminazene (Dim), artesunate (Art) and combination of Dim and Art (Dim-Art) against Leishmania donovani was compared to reference drug; amphotericin B. IC50 of Dim-Art was found to be 2.28 ± 0.24 µg/mL while those of Dim and Art were 9.16 ± 0.3 µg/mL and 4.64 ± 0.48 µg/mL respectively. The IC50 for Amphot B was 0.16 ± 0.32 µg/mL against stationary-phase promastigotes. In vivo evaluation in the L. donovani BALB/c mice model indicated that treatments with the combined drug therapy at doses of 12.5 mg/kg for 28 consecutive days significantly (p < 0.001) reduced parasite burden in the spleen as compared to the single drug treatments given at the same dosages. Although parasite burden was slightly lower (p < 0.05) in the Amphot B group than in the Dim-Art treatment group, the present study demonstrates the positive advantage and the potential use of the combined therapy of Dim-Art over the constituent drugs, Dim or Art when used alone. Further evaluation is recommended to determine the most efficacious combination ratio of the two compounds.

Treatment of cattle with DNA-encoded Flt3L and GM-CSF prior to immunization with Theileria parva candidate vaccine antigens induces CD4 and CD8 T cell IFN-γ responses but not CTL responses.

Theileria parva antigens recognized by cytotoxic T lymphocytes (CTLs) are prime vaccine candidates against East Coast fever in cattle. A strategy for enhancing induction of parasite-specific T cell responses by increasing recruitment and activation of dendritic cells (DCs) at the immunization site by administration of bovine Flt3L and GM-CSF prior to inoculation with DNA vaccine constructs and MVA boost was evaluated. Analysis of immune responses showed induction of significant T. parva-specific proliferation, and IFN-γ-secreting CD4(+) and CD8(+) T cell responses in immunized cattle. However, antigen-specific CTLs were not detected. Following lethal challenge, 5/12 immunized cattle survived by day 21, whereas all the negative controls had to be euthanized due to severe disease, indicating a protective effect of the vaccine (p<0.05). The study demonstrated the potential of this technology to elicit significant MHC class II and class I restricted IFN-γ-secreting CD4(+) and CD8(+) T cells to defined vaccine candidate antigens in a natural host, but also underscores the need to improve strategies for eliciting protective CTL responses.