Contribution of CD8+ T Cells to Containment of Viral Replication and Emergence of Mutations in Mamu-A*01-Restricted Epitopes in Simian Immunodeficiency Virus-Infected Rhesus Monkeys▿ †

Here, we investigated the containment of virus replication in simian immunodeficiency virus (SIV) infection by CD8+ lymphocytes. Escape mutations in Mamu-A*01 epitopes appeared first in SIV Tat TL8 and then in SIV Gag p11C. The appearance of escape mutations in SIV Gag p11C was coincident with compensatory changes outside of the epitope. Eliminating CD8+ lymphocytes from rhesus monkeys during primary infection resulted in more rapid disease progression that was associated with preservation of canonical epitopes. These results confirm the importance of cytotoxic T cells in controlling viremia and the constraint on epitope sequences that require compensatory changes to go to fixation

Increased Loss of CCR5+ CD45RA− CD4+ T Cells in CD8+ Lymphocyte-Depleted Simian Immunodeficiency Virus-Infected Rhesus Monkeys▿

Previously we have shown that CD8+ T cells are critical for containment of simian immunodeficiency virus (SIV) viremia and that rapid and profound depletion of CD4+ T cells occurs in the intestinal tract of acutely infected macaques. To determine the impact of SIV-specific CD8+ T-cell responses on the magnitude of the CD4+ T-cell depletion, we investigated the effect of CD8+ lymphocyte depletion during primary SIV infection on CD4+ T-cell subsets and function in peripheral blood, lymph nodes, and intestinal tissues. In peripheral blood, CD8+ lymphocyte-depletion changed the dynamics of CD4+ T-cell loss, resulting in a more pronounced loss 2 weeks after infection, followed by a temporal rebound approximately 2 months after infection, when absolute numbers of CD4+ T cells were restored to baseline levels. These CD4+ T cells showed a markedly skewed phenotype, however, as there were decreased levels of memory cells in CD8+ lymphocyte-depleted macaques compared to controls. In intestinal tissues and lymph nodes, we observed a significantly higher loss of CCR5+ CD45RA− CD4+ T cells in CD8+ lymphocyte-depleted macaques than in controls, suggesting that these SIV-targeted CD4+ T cells were eliminated more efficiently in CD8+ lymphocyte-depleted animals. Also, CD8+ lymphocyte depletion significantly affected the ability to generate SIV Gag-specific CD4+ T-cell responses and neutralizing antibodies. These results reemphasize that SIV-specific CD8+ T-cell responses are absolutely critical to initiate at least partial control of SIV infection

Effect of CD8(+) Lymphocyte Depletion on Virus Containment after Simian Immunodeficiency Virus SIVmac251 Challenge of Live Attenuated SIVmac239Δ3-Vaccinated Rhesus Macaques

Although live attenuated vaccines can provide potent protection against simian immunodeficiency virus (SIV) and simian-human immunodeficiency virus challenges, the specific immune responses that confer this protection have not been determined. To test whether cellular immune responses mediated by CD8(+) lymphocytes contribute to this vaccine-induced protection, we depleted rhesus macaques vaccinated with the live attenuated virus SIVmac239Δ3 of CD8(+) lymphocytes and then challenged them with SIVmac251 by the intravenous route. While vaccination did not prevent infection with the pathogenic challenge virus, the postchallenge levels of virus in the plasmas of vaccinated control animals were significantly lower than those for unvaccinated animals. The depletion of CD8(+) lymphocytes at the time of challenge resulted in virus levels in the plasma that were intermediate between those of the vaccinated and unvaccinated controls, suggesting that CD8(+) cell-mediated immune responses contributed to protection. Interestingly, at the time of challenge, animals expressing the Mamu-A*01 major histocompatibility complex class I allele showed significantly higher frequencies of SIV-specific CD8(+) T-cell responses and lower neutralizing antibody titers than those in Mamu-A*01(−) animals. Consistent with these findings, the depletion of CD8(+) lymphocytes abrogated vaccine-induced protection, as judged by the peak postchallenge viremia, to a greater extent in Mamu-A*01(+) than in Mamu-A*01(−) animals. The partial control of postchallenge viremia after CD8(+) lymphocyte depletion suggests that both humoral and cellular immune responses induced by live attenuated SIV vaccines can contribute to protection against a pathogenic challenge and that the relative contribution of each of these responses to protection may be genetically determined