Proietti FA, Carneiro-Proietti AB, Catalan-Soares BC, Murphy EL. contribute to better outcomes in HTLV-1-infected patients. HTLV-1 basic zip factor (HBZ) is also involved in viral chronicity and leukemic transformation (21). Therefore, similarly to a Tax-based vaccine, one could argue that vaccination against HBZ might prevent HTLV-1-induced leukemogenesis (22). Moreover, while Tax transcripts can be detected in only 40% of ATL patients, HBZ is expressed in all ATL patients (23, 24). In fact, Sugata and colleagues generated anti-HBZ-specific CD8+ T cells in mice as well as in rhesus macaques, using recombinant vaccinia viruses (25). Although this approach is encouraging, HBZ immunogenicity was poor compared to that of Tax and required multiple boosts. The efficiency of an HBZ-based vaccine will need to be tested against primary human ATL cells. Previous studies have indicated that HTLV-1 proviral load (PVL) is a major risk factor for HAM/TSP (26, 27). Tax-specific CD8+ T cells have been shown to reduce HTLV-1 PVL and to prevent asymptomatic carriers VTX-2337 from developing ATL VTX-2337 (28). These findings suggest that a reduction in the HTLV-1 PVL in circulating lymphocytes prevents HTLV-1 carriers from developing ATL and HAM/TSP. HTLV-1 is classified into six different subtypes, one cosmopolitan subtype (HTLV-1-a) (29), four subtypes restricted to Africa (HTLV-1-b, -d, -e, and -f) (30, 31), and one subtype in descendants of the first settlers of Melanesia and Australia (HTLV-1-c) (31). Simian T-lymphotropic virus type 1 (STLV-1) is closely related to HTLV-1 and infects several nonhuman primate species. Phylogenetic analysis of the conserved gene sequences indicates that STLV-1 and VTX-2337 HTLV-1 are evolutionarily related (32). Furthermore, STLV-1 Tax and STLV-1 bZIP factor (SBZ) have functions similar to those of their equivalents from HTLV-1 (19, 33). It is well established that Tax interacts with the host transcription factor NF-B, resulting in the activation of the NF-B pathway (19). This is critical for transformation, proliferation, and survival of HTLV-1-infected cells, especially in the Rabbit Polyclonal to JAB1 early phases of infection. Recent evidence showed that hunters in Africa can be infected by HTLV-1 strains that are genetically related to the strains circulating among local nonhuman primates (34). In STLV-1-infected macaques (study of asymptomatic baboons naturally infected with STLV-1 showed that induction of viral expression with valproate in combination with azidothymidine to prevent viral propagation resulted in a decrease in the PVL. Interestingly, the reduction of the PVL coincided with an accumulation of effector CD8+ T lymphocytes directed against the virus, indicating that these cells could have contributed to the positive outcome (45). As a prelude to the design of suitable vaccine inserts, we have defined the entire cellular immune response (CD4+ and CD8+ T cells) against STLV-1 in infected baboons. Here we show that cellular responses against STLV-1 are largely restricted to CD8+ T cells. Furthermore, as in HTLV-1-infected humans, Tax is the immunodominant virus-encoded protein target of baboon cellular responses. We have also identified six distinct Tax epitope-rich regions that are targeted by STLV-1-specific CD8+ T cells from assorted baboons. Our results support the use of baboons as models for HTLV-1 vaccine research and further suggest the inclusion of Tax in vaccine compositions. MATERIALS AND METHODS Research animals. The 22 animals used in this study were olive baboons (of the National Research Council (46), VTX-2337 as approved by the Texas Biomedical Research Institutional Animal Care and Use Committee. The study population included 18 STLV-1-infected baboons and 4 uninfected animals used as negative controls (Table 1). We excluded three animals from the study that were serologically reactive to STLV-1 but negative for STLV-1 PVL and CD8 responses. The numbers of male and female baboons were balanced in this study. STLV-1 serology was performed at the SNPRC according to the manufacturer’s protocol (47, 48) for the Macaque Tracking multiplexed fluorometric immunoassay (MFIA). This assay is a Luminex bead-based serology test developed by Charles River Labs (CRL) (Wilmington, MA). The performance (specificity and sensitivity) of the MFIA method is comparable to that of serology measurement by enzyme-linked immunosorbent assay (ELISA) (47). In brief, the STLV-1 Luminex multiplex assay used two different bead sets for anti-STLV-1 antibody detection. The first bead set uses HTLV-1 and HTLV-2 whole-virus lysates, whereas the second bead set uses a purified, truncated STLV-1 p21 (12-kDa) protein produced in insect cells. Additionally, beads coated with baculovirus were used as nonspecific assay controls. Data analysis was carried out by using the Charles River MFIA Results Excel Workbook (48) according to the manufacturer’s protocol. In summary, an assay score is created based on the reactivity against the HTLV- and STLV-specific beads minus the background. A sample was considered positive when reactivity against both specific beads exceeded the cutoff. The assay result was considered inconclusive if there was reactivity against only.