Potential significance of the cellular immune response against the macaque strain of simian immunodeficiency virus (SIVMAC) in immunized and infected rhesus macaques.

The cellular immune response of seven rhesus macaques immunized with Tween-ether-treated macaque strain of simian immunodeficiency virus (SIVMAC) and three non-vaccinated control animals was investigated. Immunization elicited antigen-specific proliferating CD4+ cells in five of seven monkeys. Proliferating T cells were found in all animals protected from a first virus challenge. Cytotoxic T lymphocytes (CTLs) were not induced by the immunization. After the second challenge, the four formerly protected animals became infected, despite a strong proliferative CD4+ cell activity in three of them. All animals lost their proliferative activity 2 weeks after infection. After the first challenge four of the six infected animals exhibited a CTL response and after the second challenge, one of four newly infected macaques acquired a CTL response. The five animals with a CTL activity against SIVMAC proteins were protected from severe thrombocytopenia, which appeared in the five CTL-negative animals after infection. Our data show the induction of proliferative T cells by immunization with soluble SIVMAC antigen. This T cell reactivity was found in all animals protected from the first virus challenge, but did not confer protection from the second challenge. Interestingly, the proliferative T cell reactivity disappeared 2 weeks after virus infection. Furthermore a CTL response against viral proteins seems to protect infected animals from severe thrombocytopenia which is an early sign of AIDS in monkeys.