Assessing non-classical antigen presentation in HIV-infected CD4+ T cells.

Abstract

Abstract CD4+T cells recognize peptides presented by MHC Class II (MHC-II) molecules on B cells, dendritic cells, and macrophages. Interestingly, in humans, activated CD4+ T cells themselves express MHC-II molecules (HLA-DR, -DP, -DQ), but their potential role as antigen processing cells has not been well characterized. Recent promising data in a simian immunodeficiency (SIV) model suggest that antigen presentation by CD4+ T cells may be important in immunity. In these studies, a vaccine incorporating SIV antigens into a cytomegalovirus vector induced MHC-II restricted CD8+ T cells in macaques. Notably, these non-canonical cells were also observed in HIV patients. Clones generated from these MHC-II restricted CD8+ T cells killed autologous HIV-infected CD4+ T cells, suggesting that HIV is processed and presented on MHC-II on CD4+ T cells. To investigate this potentially novel form of antigen presentation, we eluted peptides from HLA-DR on activated CD4+T cells and sequenced them by LC-MS/MS. We show for the first time that human primary CD4+ T cells indeed process and present peptides on HLA-DR. We are currently applying this approach to HIV-infected cells to detect HIV peptides. Given the low sensitivity of untargeted MS for rare viral peptides, we are also generating a library of MHC-II HIV epitopes presented on HLA-DR to help guide more targeted MS analysis. To create this library, we are using a MHC-II cell-free processing system. We have already identified several epitopes from HIV Gag, Pol, Env, Vif, Rev, and Tat, some of which we show elicit memory responses in HIV patients. Our studies reveal a novel role for CD4+ T cells in antigen presentation and show that a cell-free processing system can predict HIV epitopes that may be presented on these cells.