Lactic acid improves Treg manufacturing and

Adoptive cell therapy using regulatory T cells (Tregs) is a promising approach to suppress immune responses in autoimmunity and transplantation, but it is challenging to expand pure and optimally suppressive cells. Lactic acid (LA) is associated with enhanced Treg function in tumors so we hypothesized that it may be beneficial during Treg expansion. We found that addition of LA at day 3 post-stimulation onwards improved viability and purity, increased glycolysis upon re-stimulation, and led to superior suppressive function. In Tregs expressing chimeric antigen receptors (CARs) specific for HLA-A2, LA not only enhanced viability and purity but also significantly reduced tonic signaling-associated expression of exhaustion-associated markers (PD-1, TIM-3, LAG-3, TOX, and BLIMP-1). The effects of LA were not fully recapitulated by either pH-neutral lactate or low pH. In immunodeficient mouse models of chronic stimulation and xenogeneic graft-versus-host disease, LA-conditioned human Tregs demonstrated enhanced stability, reduced exhaustion marker expression, and improved efficacy. Thus, LA has a multimodal effect on human polyclonal and CAR Treg purity, viability, and function, representing a method to generate an optimal Treg product for cell therapy.