Regulatory B cell frequency correlates with markers of HIV disease progression and attenuates anti-HIV CD8⁺ T cell function in vitro

HIV infection is associated with elevated expression of IL-10 and PD-L1, contributing to impairment of T cell effector functions. In autoimmunity, tumor immunology, and some viral infections, Bregs modulate T cell function via IL-10 production. In this study, we tested the hypothesis that during HIV infection, Bregs attenuate CD8⁺ T cell effector function, contributing to immune dysfunction. We determined that in vitro, TLR2-, TLR9-, and CD40L-costimulated Bregs from HIV^- individuals exhibited a high frequency of cells expressing IL-10 and PD-L1. Compared with Bregs from HIV⁺ individuals, a significantly higher percentage of Bregs from HIV⁺ individuals spontaneously expressed IL-10 (P=0.0218). After in vitro stimulation with HIV peptides, Breg-depleted PBMCs from HIV⁺ individuals exhibited a heightened frequency of cytotoxic (CD107a⁺; P=0.0171) and HIVspecific CD8⁺ T cells compared with total PBMCs. Furthermore, Breg depletion led to enhanced proliferation of total CD8⁺ and CD107a⁺CD8⁺ T cells (P=0.0280, and P=0.0102, respectively). In addition, augmented CD8⁺ T cell effector function in vitro was reflected in a 67% increased clearance of infected CD4⁺ T cells. The observed Breg suppression of CD8⁺ T cell proliferation was IL-10-dependent. In HIV⁺ individuals, Breg frequency correlated positively with viral load (r=0.4324; P=0.0095), immune activation (r=0.5978; P=0.0005), and CD8⁺ T cell exhaustion (CD8⁺PD-1⁺; r=0.5893; P=0.0101). Finally, the frequency of PD-L1-expressing Bregs correlated positively with CD8⁺PD-1⁺ T cells (r=0.4791; P=0.0443). Our data indicate that Bregs contribute to HIV-infection associated immune dysfunction by T cell impairment, via IL-10 and possibly PD-L1 expression.