Persistence of High Viral Load Abrogates Long-Term HIV-Specific Memory CD4 T-Cells Producing Interleukin-2.

Abstract

Virus-specific CD4 T-cells are believed to play a critical role in determining the persistence of memory and effector CD8 T-cell responses during viral infections. However, the reasons for which human immunodeficiency virus (HIV)-specific CD4 cells fail to generate effective CD8 cell responses remain incompletely understood. In this study, we analyzed the HIV-specific CD4 cells in 10 aviremic (viral load < 50 copies/ml) and 8 viremic (mean viral load 45,295 copies/ml) patients treated during primary HIV infection and followed for up to 6 years. At the time of apheresis, median CD4 T cell counts for aviremic and viremic patients were 671 cells/μl and 485 cells/μl respectively. Using Gag and Nef overlapping HIV peptides, the highly sensitive CFSE-based proliferation assay and intracellular staining techniques, we observed that proliferative Gag and Nef peptide-specific CD4 cell responses were 30-fold higher in aviremic patients compared to viremic. Several subsets of HIV-specific memory CD4 cells endowed with different proliferative and functional capacities were identified. We observed two subsets of HIV-specific memory CD4 cells in aviremic patients, CD45RA− CCR7+ central memory cells (Tcm) producing exclusively IL-2 and CD45RA− CCR7− effector memory cells (Tem) that produced both IL-2 and IFN-γ. In contrast, in viremic patients, Tem were found to unexpectedly produce IFN-γ exclusively. Longitudinal data showed that only cells, which were capable of producing IL-2, persisted as long-term memory cells. In viremic patients, HIV-specific CD4 cells that produce INF-γ were found only during periods of elevated viral loads. To test if the presence of IL-2 could restore the proliferation of these cells, we stimulated CD4 cells from viremic patients with a pool of peptides, which gave strong IFN-γ responses in these patients in the presence of exogenous IL-2. The addition of IL-2 during the in vitro peptide stimulation dramatically increased the fraction of proliferating cells. This experiment strongly suggests that the impaired proliferation of CD4 cells from viremic patients is not caused by a virus-mediated destruction of proliferating cells but a lack of producing IL-2. Altogether, these results indicate that long-term memory HIV-specific CD4 cell produce mainly IL-2, while those producing IFN-γ are short-lived. These findings favor a model in which Tcm are continuously produced in limited numbers but under continuous viral stimulation are rapidly induced to differentiate into IFN-γ only-producing cells that lack the capacity for self-renewal.These findings also indicate that treatment strategies aimed to increase the long-term memory CD4 cells are needed for future HIV vaccine development.