CD8-mediated virus inhibition can be detected in HIV-1-positive subjects who naturally control virus replication. Characterizing the inhibitory function of CD8+ Τ cells during acute HIV-1 infection (AHI) can elucidate the nature of the CD8+ responses that can be rapidly elicited and that contribute to virus control. We examined the timing and HIV-1 antigen specificity of antiviral CD8+ Τ cells during AHI. Autologous and heterologous CD8+ Τ cell antiviral functions were assessed longitudinally during AHI in five donors from the CHAVI 001 cohort using a CD8+ Τ cell-mediated virus inhibition assay (CD8 VIA) and transmitted/ founder (T/F) viruses. Potent CD8+ antiviral responses against heterologous T/F viruses appeared during AHI at the first time point sampled in each of the 5 donors (Fiebig stages 1/2 to 5). Inhibition of an autologous T/F virus was durable to 48 weeks; however, inhibition of heterologous responses declined concurrent with the resolution of viremia. HIV-1 viruses from 6 months postinfection were more resistant to CD8+-mediated virus inhibition than cognate T/F viruses, demonstrating that the virus escapes early from CD8+ Τ cell-mediated inhibition of virus replication. CD8+ Τ cell antigen-specific subsets mediated inhibition of T/F virus replication via soluble components, and these soluble responses were stimulated by peptide pools that include epitopes that were shown to drive HIV-1 escape during AHI. These data provide insights into the mechanisms of CD8-mediated virus inhibition and suggest that functional analyses will be important for determining whether similar antigen-specific virus inhibition can be induced by Τ cell-directed vaccine strategies. [ABSTRACT FROM AUTHOR]