In summary, these results indicate that CD8+ T cells of LTNP/EC possess greater SIV-specific cytotoxic capacity on a per-cell basis than those of progressors and that changes in both the numbers of virus-specific CD8+ T cells and in their per-cell cytotoxic capacity following re-stimulation with SIV-infected targets are required for maximal cytotoxicity, as had been observed in human HIV infection [12]–[14]. This evidence concerns the gene CD8A and HIV infectious disease.