Mycobacteria‐reactive γδ T cells in HIV‐infected individuals: lack of Vγ9 cell responsiveness is due to deficiency of antigen‐specific CD4 T helper type 1 cells

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Abstract
Human γδ T lymphocytes expressing the variable T cell receptor elements Vγδ paired with Vδ2 are activated by antigen derived from Mycobacterium tuberculosis (M. tb.) and presented by antigen‐presenting cells (APC). The subsequent proliferation is strictly dependent on the presence of CD4+TCRαβ+ T helper type 1 (Th1) cells producing interleukin‐2 (IL‐2). In this study, we report that the reactivity of Vγ9 cells to M. tb. stimulation in vitro was drastically decreased or absent in the majority of the analyzed HIV‐1‐infected individuals (CDC stages III and IV). We show that the failure of Vγ9 cells frim HIV− individuals to proliferate following M. tb. stimulation was not due to an intrinsic qualitative or quantitative defect of γδ T cells but rather to a deficiency of M. tb.‐reactive CD4 Th1 cells. Thus, Vγ9 responsiveness could be restored if cultures of M. tb.‐stimulated T cells from HIV+ donors were reconstituted with one of the following: (i) exogenous IL‐2; (ii) purified CD4T cells from allogeneic donors; or (iii) T cell‐depleted APC from allogeneic donors. In the majority of HIV+ patients, the defective Th1 activity of M. tb.‐stimulated CD4 T cells could be increased neither by cytokines known to favor Th1 development (IL‐12, interferon‐γ) nor by neutralization of the Th1‐suppressing Th2 cytokine IL‐10. We suggest that measurement of Vγ9 cell expansion within M. tb.‐stimulated peripheral blood mononuclear cells provides a sensitive assay for the functional capacity of antigen (M. tb.)‐specific CD4 Th1 cells in HIV‐infected individuals.