In addition to using ex vivo-sorted epitope-specific CD8+T cells, we shortened the viral suppression assay to 48 h. ex vivo-sorted simian immunodeficiency virus (SIV)-specific CD8+T cells to suppress viral replication from SIVmac239-infected CD4+T cells. Using this assay, we established an antiviral hierarchy when we compared CD8+T cells specific for 12 different epitopes. Antiviral efficacy was unrelated to the disease Enecadin status of each animal, the protein from which the tested epitopes were derived, or the major histocompatibility complex (MHC) class I restriction of the tested epitopes. Additionally, there was no correlation with the ability to suppress viral replication and epitope avidity, epitope affinity, CD8+T-cell cytokine multifunctionality, the percentage of central and effector memory cell populations, or the expression of PD-1. The ability of virus-specific CD8+T cells to suppress viral replication therefore cannot be decided using conventional assays. Our results suggest that a single definitive correlate of Enecadin immune control may not exist; rather, a successful CD8+T-cell response may be comprised of several factors. CD8+T cells may play a critical role in blunting peak viremia and controlling human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication. The transient depletion of CD8+cells in SIV-infected macaques results in increased viral replication (26,31,51,70). The emergence of virus-specific CD8+T cells coincides with the reduction of peak viremia (12,39,42,63), and CD8+T-cell pressure selects for escape mutants (6,9,13,28,29,38,60,61,85). Furthermore, particular major histocompatibility complex (MHC) class I alleles are overrepresented in SIV- and HIV-infected elite controllers (15,29,33,34,46,56,88). Because it has been difficult to induce broadly neutralizing antibodies (Abs), the AIDS vaccine field is currently focused on developing a vaccine designed to elicit HIV-specific CD8+T cells (8,52,53,82). Investigators have tried to define the immune correlates of HIV control. Neither the magnitude nor the breadth of epitopes recognized by virus-specific CD8+T-cell responses correlates with the control of viral replication (1). The quality of the immune response may, however, contribute to the antiviral efficacy of the effector cells. It has been suggested that the number of cytokines that virus-specific CD8+T cells secrete may correlate with viral control, since HIV-infected nonprogressors appear to maintain CD8+T cells that secrete several cytokines, compared to HIV-infected progressors (11,27). An increased amount of perforin secretion may also be related to the proliferation of HIV-specific CD8+T cells in HIV-infected nonprogressors (55). While those studies offer insight into the different immune systems of progressors and nonprogressors, they did not address the Enecadin mechanism of viral control. Previously, we found no association between the ability of SIV-specific CD8+T-cell clones to suppress viral replication in vitro and their ability to secrete gamma interferon (IFN-), tumor necrosis factor alpha (TNF-), or interleukin-2 (IL-2) (18). Evidence suggests that some HIV/SIV proteins may be better vaccine targets than others. CD8+T cells recognize epitopes derived from Gag as early as 2 h postinfection, whereas CD8+T cells specific for epitopes in Env recognize infected cells only at 18 h postinfection (68). Additionally, a previously reported study of HIV-infected individuals showed that an increased breadth of Gag-specific responses was associated with lower viral loads (35,59,65,66). CD8+T-cell responses specific for Env, Rev, Tat, Vif, Vpr, Vpu, and Nef were associated with higher viral loads, with increased breadth of Env in particular being significantly associated with a higher chronic-phase viral set point. None of the many sophisticated methods employed for analyzing the characteristics of HIV- or SIV-specific immune responses clearly demarcate the critical qualities of an effective antiviral response. In an attempt to address these questions, we developed a new assay to measure the antiviral efficacy of individual SIV-specific CD8+T-cell responses sorted directly from fresh peripheral blood mononuclear cells (PBMC). Using MHC class I tetramers specific for the epitope of interest, we sorted freshly isolated virus-specific CD8+T cells and decided their ability to suppress virus production from SIV-infected CD4+T cells. We then looked for a common characteristic of efficacious epitope-specific CD8+T cells using traditional methods. == MATERIALS AND METHODS == == SIVmac239 virus stocks. == SIVmac239 (GenBank accession no.M33262) was generated as previously described (23). Briefly, Vero cells were transfected with plasmid DNA encoding the SIV proviral sequences. One day after transfection, CEMx174 cells were added to the Vero cultures. Virus was expanded on CEMx174 cells, and cell-free supernatant was collected 2 days after peak syncytium formation. Harvested virus was analyzed by Gag p27 enzyme-linked immunosorbent assay (ZeptoMetrix Corporation) and quantitative reverse transcription (RT)-PCR prior to use in ex vivo studies. == Animals and viral load analysis. DES == Indian rhesus macaques (Macaca mulatta) from the Wisconsin National Primate Research Center were cared for according to the regulations and guidelines of the University.