TRAIL-mediated PMN-MDSC depletion prevents CD4 ⁺ T cell loss in HIV-infected humanized mice

Myeloid-derived suppressor cells (MDSCs) are critical regulators of HIV immunity, but the mechanisms behind their expansion and value as a therapeutic target remain unclear. We investigated MDSC function in HIV using a humanized mouse model. Acute HIV-1 infection triggered the systemic expansion of polymorphonuclear MDSCs (PMN-MDSCs), with their frequency correlating positively with plasma viral load. Notably, PMN-MDSC expansion increased further when natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) were depleted, suggesting these immune cells restrain MDSC proliferation. We identified Tumor necrosis factor related apoptosis-inducing ligand (TRAIL)-induced apoptosis as a regulatory mechanism, as MDSCs expressed high levels of TRAIL receptor 2 (R2), while NK cells and CTLs upregulated TRAIL expression during HIV infection. Treating HIV-1-infected mice with a TRAIL-R2 agonist significantly reduced MDSC levels to those of uninfected mice and significantly improved NK cell and CTL immune function. Crucially, in viremic humanized mice, the treatment prevented CD4+ T cell loss, a hallmark of HIV-1 pathogenesis and acquired immune deficiency syndrome (AIDS) progression. These findings reveal the therapeutic potential of targeting MDSC apoptosis to mitigate CD4+ T cell depletion and enhance HIV-specific immunity, offering a new clinical target to prevent AIDS and insights into MDSC– NK/CTL cross-regulation during HIV-1 infection.