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Background:  Antigen-specific CD4⁺ T cells are believed to be generated during primary HIV-1 infection (PHI), but lost early in the course of infection. We recently found, in a long-term non-progressor, that HIV-specific CD4⁺ T cells expressed CCR5. These cells were also cytotoxic T lymphocytes (CTL). Therefore, we investigated whether we could detect HIV-specific CCR5⁺ CD4⁺ CTL during PHI.

Methods:  Fresh blood samples were obtained from 33 subjects enrolling in the Phaedra observational study of PHI. Subgroups were defined as early PHI (< 22 days following onset of symptoms; n = 21) or late PHI (28 to 122 days; n = 12). CD4⁺ T cells expressing CCR5 plus markers of activation (CD38), CTL (TIA-1, Granzyme B, Perforin), proliferation (Ki-67), and cell survival (Bcl-2) were analyzed by 6-color flow cytometry. The results were compared with 14 HIV-negative controls. Antigen-specific CD4⁺ T cells were measured in the last 14 consecutive PHI subjects (7 early and 7 late) by intracellular cytokine assay following incubation with HIV-1 Gag peptide pools.

Results:  CCR5⁺CD38⁺⁺⁺ CD4⁺ T cells were significantly elevated during early PHI, compared with late PHI and controls (medians: 4.8 vs 0.9 vs 0.3%, respectively). Also significantly elevated were CCR5⁺TIA-1⁺Ki-67⁺ CD4⁺ T cells (3.1 vs 0.9 vs 0.2%, respectively) and Perforin⁺GranzymeB⁺ CD4⁺ CTL (11.6 vs 5.0 vs 1.6%). For all comparisons between early PHI subjects and controls, or between early and late PHI, p values were < 0.001 and <0.01, respectively. HIV-1 Gag-specific IFN-γ-producing CD4⁺ T cells were readily detected in early PHI, compared with late PHI (medians: 0.58% vs 0.08%, respectively). These cells were predominantly CD38⁺⁺⁺Bcl-2low, TIA-1⁺Ki-67⁺, and CD40L⁺, while approximately 20% of IFN-γ⁺ cells also produced IL-2 and were IL-7R⁺. A very strong correlation was noted between the proportions of Gag-specific and CCR5⁺CD38⁺⁺⁺ CD4⁺ T cells at all stages of PHI (R² = 0.85). Further analysis of CCR5⁺CD38⁺⁺⁺ CD4⁺ T cells in early PHI showed an increased expression of CXCR3 and IL-12Rß1, consistent with Th1 effector cells. Limited expression of IL-2, IL-7R, and CCR7 by this population suggests it also contains precursors of central memory cells.

Conclusions:  These results suggest that the very early antiviral response in HIV-1 infection includes proliferating, highly activated CCR5⁺CD4⁺ effector cells, which are susceptible to both apoptosis and cytopathic infection with HIV-1, and rapidly decline.

Keywords: CD4; Antigen-specific ; CCR5