East Coast fever, caused by the tick-borne intracellular apicomplexan parasite Theileria parva, is a highly fatal lymphoproliferative disease of cattle. The pathogenic schizont-induced lymphocyte transformation is a unique cancer-like condition that is reversible with parasite removal. Schizont-infected cell-directed CD8 ؉ cytotoxic T lymphocytes (CTL) constitute the dominant protective bovine immune response after a single exposure to infection. However, the schizont antigens targeted by T. parva-specific CTL are undefined. Here we show the identification of five candidate vaccine antigens that are the targets of MHC class I-restricted CD8 ؉ CTL from immune cattle. CD8 ؉ T cell responses to these antigens were boosted in T. parva-immune cattle resolving a challenge infection and, when used to immunize naïve cattle, induced CTL responses that significantly correlated with survival from a lethal parasite challenge. These data provide a basis for developing a CTL-targeted anti-East Coast fever subunit vaccine. In addition, orthologs of these antigens may be vaccine targets for other apicomplexan parasites.cattle ͉ East Coast fever ͉ immunoscreening ͉ protozoan parasite ͉ vaccination A single inoculation with a potentially lethal dose of Theileria parva sporozoites and simultaneous treatment with a longacting oxytetracycline induces solid immunity to homologous and, in certain instances, heterologous parasite challenge (1, 2). This methodology has been adopted as a live vaccine for the control of East Coast fever (ECF) (3). The long-lasting immunity to ECF contrasts with the partial immunity to malaria that develops after only several years of exposure to T. parva-related Plasmodium spp. (4). Manufacture and delivery of the live ECF vaccine is difficult to sustain, but it has enabled elucidation of the dominant protective immune response against the disease. Kinetic and adoptive cell transfer studies (5, 6) have demonstrated that protection of cattle is mediated by MHC class I-restricted CD8 ϩ cytotoxic T lymphocytes (CTL) that destroy schizontinfected lymphocytes, the pathogenic life-cycle stage of T. parva. In addition, there is a strong correlation between the specificity of the CTL response and cross-immunity profiles of distinct parasite strains (2). The identification of schizont antigens targeted by CTL from T. parva-immune cattle has been elusive but should pave the way for the development of a subunit vaccine against ECF and provide a long-term solution to a socioeconomically important constraint to livestock agriculture in Africa (7). We adopted two approaches to antigen identification, both dependent on screening of transiently transfected antigenpresenting cells with fully characterized CTL (8, 9) from live vaccine-immunized cattle of diverse bovine leukocyte antigen (BoLA) MHC class I genotypes. First, in a targeted gene approach, we immunoscreened genes that were predicted by using preliminary sequence data from one of the four T. parva chromosomes (10) to contain a secretion signal. The approach was ...

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.

No abstract

No abstract

The research objective was to develop a thermostable vaccine against peste des petits ruminants (PPR), a morbilliviral disease of small ruminants targeted for eradication that is a major constraint on the livelihoods of the rural poor throughout much of Africa and Asia. Although existing PPR vaccines provide life-long immunity, they require continuous refrigeration. This limits their utility in developing countries. Methods for the lyophilization of a related morbillivirus, rinderpest (RP), resulted in vaccine that could be used in the field for up to 30days without refrigeration which was a major contribution to the global eradication of RP completed in 2011. The present research applied the rinderpest lyophilization method to the attenuated Nigeria 75/1 PPR vaccine strain, and measured thermostability in accelerated stability tests (AST) at 37°C. The shelf-life of the vaccine was determined as the time a vial retained the minimum dose required as a 25-dose presentation at the specified temperature. A lactalbumin hydrolysate and sucrose (LS) stabilizer was compared to stabilizers based on trehalose. PPR vaccine produced using the Xerovac drying method was compared to vaccine produced using the rinderpest lyophilization method in AST. LS vaccine was evaluated in AST at 37, 45 and 56°C and an Arrhenius plot was constructed for estimation of stability at temperatures not tested. Vaccines produced using LS and the rinderpest method of lyophilization were the most stable. The shelf-life of the Xerovac preparation was 22.2days at 37°C. The three LS vaccine batches had shelf-lives at 37°C of 177.6, 105.0 and 148.9days, respectively, at 37°C. At 56°C, the shelf-life was 13.7days. The projected half-life at 25°C was 1.3years. This is sufficient thermostability for use without a cold chain for up to 30days which will greatly facilitate the delivery of vaccination in the global eradication of PPR.