In situ detection of Gag-specific CD8+ cells in the GI tract of SIV infected Rhesus macaques

Background: SIV and HIV predominantly replicate in lymphoid tissue, but the study of virus specific CD8(+) T cells in intact lymphoid tissue is difficult, as traditional in situ tetramer staining requires fresh tissue. Results: In this report, we demonstrate a novel technique using Qdot 655-conjugated peptide-MHC multimers to directly visualize SIV specific cells in cryopreserved tissue biopsies from chronically SIVmac239 infected Rhesus macaques. Qdot 655 multimers showed similar sensitivity and specificity to APC-conjugated tetramers by flow cytometry analysis, but yielded ten-fold higher signal intensity when imaged by fluorescence microscopy. Using this technique, we detected CD8(+) T cells which recognize an immunodominant epitope (Gag CM9) in the spleen, lymph nodes, ileum and colon. In all these tissues, the Gag CM9 positive cells were mainly located in the extra follicular T cell zone. In the ileum and colon, we found Gag CM9 positive cells concentrated in Peyer's patches and solitary lymphoid follicles, a pattern of localization not previously described. Conclusions: The use of Qdot multimers provide an anatomic and quantitative evaluation of SIV specific CD8(+) T cell responses in SIV pathogenesis, and may prove useful to studies of SIV specific CD8(+) T cell responses elicited by vaccines and other immunotherapies in the non-human primate model.