Efficacy of an HTLV-1 subunit vaccine in prevention of a STLV-1 infection in pig-tailed macaques.

Three pig-tailed macaques were vaccinated twice, four weeks apart, with a human T-cell lymphotropic virus type 1 (HTLV-1) subunit vaccine. Four weeks post-vaccination, the vaccinated macaques and two control monkeys were challenged with a simian T-cell lymphotropic virus type 1 (STLV-1)-infected cell line. Following the first vaccination, an antibody response developed to HTLV-1 and STLV-1 viral proteins as visualized by Western blot. The antibody recognized both gag and env protein precursors and the titer remained elevated after the second vaccination. After challenge, the antibody titers of the vaccinates increased. The controls also developed HTLV-1 and STLV-1 specific antibody which recognized the gag precursor and to a lesser extent the putative tax protein. Immunized monkeys also produced syncytium inhibiting antibody primarily toward HTLV-1-infected cells and to a lesser extent toward STLV-1-infected cells. Control monkeys produced negligible amounts of syncytium inhibiting antibody. Additionally, both polymorphonuclear (PMN) and mononuclear (MNC) cells were examined. The PMN population was tested for its ability to generate an oxidative burst. Neither vaccination nor challenge had any significant effect on the PMN CL response. The MNCs were tested for their capability to proliferate after stimulation. Again, no significant change occurred. However, when examined for cell-mediated cytotoxicity, the MNCs from immunized monkeys produced greater cytotoxic activity against the HTLV-1-infected cell line than the MNCs from control monkeys. In order to determine if the immunized monkeys were protected by the subunit vaccine against the STLV-1 challenge, reverse transcriptase (RT) activity was measured in the five monkey's MNCs. RT activity was exclusively present in the non-immunized, control monkeys implying that the HTLV-1 subunit vaccine was successful in protecting the pig-tailed macaques from the STLV-1 infection.