Theileria parvacandidate vaccine antigens recognized by immune bovine cytotoxic T lymphocytes

Abstract

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 ...

Mucosal HIV-1 Pox Virus Prime-Boost Immunization Induces High-Avidity CD8+ T Cells with Regime-Dependent Cytokine/Granzyme B Profiles

“…ϩ CTL play a pivotal role in the control of many acute and chronic viral infections (1)(2)(3)(4) including HIV-1 (5-7). Depletion of CD8 ϩ lymphocytes from rhesus macaques during chronic SIV infection can result in a rapid increase in viremia, which can subsequently be controlled by reintroduction of SIV-specific CD8 ϩ T cells (8).…”

Extensive Polymorphism and Evidence of Immune Selection in a Highly Dominant Antigen Recognized by Bovine CD8 T Cells Specific for Theileria annulata

“…A total of 70 T. annulata cDNAs containing 66 unique sequences were used for antigen screening (the genes are listed in Table S1 in the supplemental material). These comprised a set of 10 cDNAs representing T. annulata orthologues of T. parva genes previously identified as encoding antigens recognized by CD8 T cells in animals immune to T. parva (19) and a further set of 60 cDNAs originally selected for their potential involvement in host cell transformation (four genes were represented in both sets). The latter set of 60 cDNAs were identified as described previously (51), by using bioinformatic analyses of available Theileria genome sequences and a set of expression sequence tags obtained from a cDNA library representing purified T. annulata macroschizonts.…”

Extensive Genotypic Diversity in a Recombining Population of the Apicomplexan ParasiteTheileria parva

“…First, the availability of the T. parva genome sequence has allowed assembly of a genome-wide panel of satellite markers for high-resolution genotyping of parasite populations. Second, a number of parasite antigens recognized by bovine CTL have been identified (9) and located within the genome. We have exploited these developments to undertake a broad genotypic analysis of a recombining population of T. parva before and after transmission through a naive calf and the tick vector.…”