Transcriptional profiles of sorted CD8+ and CD4+ memory T cells from CP and NP and unvaccinated control RM 7 days prior to, and 4 and 14 days after wt SIVmac239 challenge by microarray analysis.

Live-attenuated SIV vaccines (LAVs) remain the most efficacious of all vaccines in nonhuman primate models of HIV/AIDS, yet the basis of their robust protection remains poorly understood. Here, we demonstrate that the degree of LAV-mediated protection against intravenous (IV) wildtype (wt) SIVmac239 challenge strongly correlates with the magnitude and function of SIV-specific, effector-differentiated T cells in lymph node (LN), but not with such T cell responses in blood or with other cellular, humoral and innate immune parameters. Maintenance of protective T cell responses was associated with persistent LAV replication in LN, which occurred almost exclusively in follicular helper T cells. Thus, effective LAVs maintain lymphoid tissue-based, effector-differentiated, SIV-specific T cells that intercept and suppress early wt SIV amplification and, if present in sufficient frequencies, can completely control and perhaps clear infection -- an observation that provides rationale for development of safe, persistent vectors that can elicit and maintain such responses. There are two protection outcome groups, complete protect (CP) and non-protect (NP) animals. Memory T cells (CD4+ or CD8+) were sorted for three time points, seven days pre-challenge, four days post-challenge and fourteen days post-challenge.