W143 - Lactic Acid Enhances Human Regulatory T Cell Phenotype and Function

Majid Mojibian – BC Children's Hospital Research Institute, University of British Columbia; Vivian Fung – BC Children's Hospital Research Institute, University of British Columbia; Manjurul Haque – BC Children's Hospital Research Institute, University of British Columbia; Dominic Boardman – BC Children's Hospital Research Institute, University of British Columbia; Ramon Klein Geltink – BC Children's Hospital Research Institute, University of British Columbia; Megan Levings – BC Children's Hospital Research Institute, University of British Columbia

Abstract Text: Cell therapy using regulatory T cells (Tregs) represents an approach for targeted suppression of pathological immune responses in autoimmunity and transplantation. Clinical translation of Treg therapy faces numerous challenges, one of which is expansion of homogenous and optimally suppressive cell populations. Given the association between lactic acid (LA) and enhanced Treg function in tumours, we hypothesised that supplementation of LA during expansion may be favourable for Treg expansion. To test this possibility, naïve human Tregs were stimulated with anti-CD3/CD28 beads with or without 15 mM LA from day 3 onwards. Without LA, Treg viability declined after day 9, which was fully prevented by LA supplementation. Culture in LA also significantly enhanced FOXP3 expression and suppressive function in vitro, accompanied by increased glycolysis. LA supplementation was also tested during the manufacture of Tregs expressing chimeric antigen receptors (CARs) targeting HLA-A2. Not only did LA enhance viability and purity, but it also significantly reduced exhaustion marker (PD-1, TIM-3, and LAG-3) expression, likely due to diminished CAR tonic signalling. In vivo experiments, in which human HLA-A2-CAR Tregs were injected into HLA-A2-transgenic immunodeficient mice, revealed that LA-cultured CAR Tregs maintained higher phenotypic stability and cell numbers over 4 weeks, with lower exhaustion marker expression in blood and tissues. Thus, LA has multimodal effects on human Treg manufacturing resulting in enhanced purity, viability, and function as well as reduced exhaustion. These data demonstrate the benefit of a straightforward culture media modification that leads to substantial improvement in expansion of optimal Treg products for cell therapy.