Background:  The gut-associated lymphoid tissue (GALT) is an early target of HIV infection and site of severe CD4⁺ T cell depletion. Loss of CD4⁺ T cell help impedes anti-HIV CD8⁺ T cell responses. In contrast to peripheral blood, initiation of HAART results in delayed and variable GALT CD4⁺ T cell restoration. It is unknown whether a threshold level of GALT CD4⁺ T cell help would be sufficient for inducing effective anti-HIV CD8⁺ T cell responses that may be independent of complete GALT CD4⁺ T cell recovery. We investigated the effect of variable GALT CD4⁺ T cell restoration on the poly-functionality of anti-HIV CD8⁺ T cell responses in the context of viral suppression and control of GALT immune activation in HIV infected patients on long-term HAART (>5 years).

Methods:  We evaluated jejunal biopsies and peripheral blood of HIV-infected patients on HAART (n = 9), who had restored >50% or <50% CD4⁺ T cells, comparable with uninfected controls (n = 6), and HAART-naïve HIV-infected patients (n = 11). We evaluated the degree of CD4⁺ T cell restoration in correlation to memory subsets (central and effector memory) and the ability of CD4⁺ and CD8⁺ T cells to produce interleukin-2 (IL-2), interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and interleukin-17 (IL-17) in response to antigenic or mitogenic stimulation by multicolor flow cytometry. We also investigated viral burden and degree of immune activation and inflammation in GALT by immunohistochemistry and real-time real-time polymerase chain reaction (RT-PCR).

Results:  Our data demonstrate CD4⁺ T cell restoration in GALT during long-term HAART is variable. Inability to fully restore GALT CD4⁺ T cells was attributed to incomplete suppression of GALT viral replication and maintained stability of proviral burden in GALT CD4⁺ T cells despite long-term HAART. Increased CD4⁺ T cell restoration correlated with accumulation and maintenance of central memory CD4⁺ T cells, reduced immune activation and inflammation-associated gene expression, and poly-functional HIV-specific CD8⁺ T cell responses.

Conclusions:  Our findings suggest that >50% of GALT CD4⁺ T cell restoration during long-term HAART was sufficient to restore functional CD4⁺ T cells and overcome CD8⁺ T cell exhaustion, evidenced by enhanced poly-functional CD8⁺ T cell responses. These were linked to suppression of viral replication and mucosal immune activation and were independent of stable proviral reservoirs. Our results suggest that partial restoration of GALT CD4⁺ T cell help is sufficient for restoring mucosal immune functions.