Cytotoxic T lymphocyte response against multiple simian immunodeficiency virusA (SIV) proteins in SIV-infected macaques.

To identify the target proteins of CD8+ T lymphocytes we have explored the cytolytic immune responses of 12 rhesus macaques experimentally infected with the simian immunodeficiency virus (SIVmac). Target cells were autologous B cell lines presenting SIVmac proteins after infection with recombinant vaccinia viruses. The eight following proteins were studied: ENV, POL, GAG, NEF, VIF, REV, TAT, and VPX. Macaque PBMC stimulated with Con A and expanded in T cell growth factor-containing medium produced cell lines with cytolytic activity in the majority of infected animals (9/12). The structural proteins ENV, POL, and GAG were recognized by cell lines derived from nine, eight, and six macaques, respectively. The small regulatory proteins also represented efficient CTL targets, a specific activity being detected against NEF (8/12), REV (7/12), VPX (7/12), TAT (6/12), and VIF (5/12). Most cytotoxic responses (except those directed against ENV) were mediated by CD8 cells and were MHC class I restricted. Limiting dilution analysis allowed us to quantify the frequency of CTL precursors and confirmed the high immunogenicity of multiple SIV proteins. Three different patterns of response could be defined: six animals were able to recognize at least six of the eight tested target proteins, two of them reacting with all eight target proteins. The other three responder macaques reacted only against a few SIV proteins, whereas no cytotoxic activity was detected in the three remaining infected macaques and in the nine negative controls. The six animals responding against multiple proteins were still healthy 12 to 22 mo after infection with two of them presenting a decrease in circulating CD4 cells concurrently to the disappearance of the CTL response. Conversely, three nonresponder or low responder macaques developed an overt disease after 4 to 12 mo, and two other presented a very low level of CD4 cells, suggesting that the pattern of response may be of prognostic value.