Despite multiple lines of evidence suggesting their involvement, the precise role of CD8+ T cells in controlling HIV replication remains unclear. To determine whether CD8+ T cells can limit retroviral replication in the absence of other immune responses, we transferred 1–13× 10 9 allogeneic in vitro expanded SIV-specific CD8+ T cell clones matched for the relevant restricting MHC-I allele into rhesus macaques near the time of iv SIV challenge. Additionally, in vitro expanded autologous SIV-specific CD8+ T cell clones were infused 4–9 mo postinfection. Infused cells did not appreciably impact acute or chronic viral replication. The partially MHC-matched allogeneic cells were not detected in the blood or most tissues after 3 d but persisted longer in the lungs as assessed by bronchoalveolar lavage (BAL). Autologous cells transferred iv or ip were found in BAL and blood samples for up to 8 wk postinfusion. Interestingly, despite having a nominally activated phenotype (CD69+ HLA-DR+), many of these cells persisted in the BAL without dividing. This suggests that expression of such markers by T cells at mucosal sites may not reflect recent activation, but may instead identify stable resident memory T cells. The lack of impact following transfer of such a large number of functional Ag-specific CD8+ T cells on SIV replication may reflect the magnitude of the immune response required to contain the virus.