Vitamin C promotes the proliferation and effector functions of human γδ T cells

γδ T cells are of interest as effector cells for cellular immunotherapy due to their HLA-non-restricted lysis of many different tumor cell types. Potential applications include the adoptive transfer of in vitro-expanded γδ T cells. Therefore, it is important to optimize the culture conditions to enable maximal proliferative and functional activity. Vitamin C (L-ascorbic acid) is an essential vitamin with multiple effects on immune cells. It is a cofactor for several enzymes, has antioxidant activity, and is an epigenetic modifier. Here, we investigated the effects of vitamin C (VC) and its more stable derivative, L-ascorbic acid 2-phosphate (pVC), on the proliferation and effector function of human γδ T cells stimulated with zoledronate (ZOL) or synthetic phosphoantigens (pAgs). VC and pVC did not increase γδ T-cell expansion within ZOL- or pAg-stimulated PBMCs, but increased the proliferation of purified γδ T cells and 14-day-expanded γδ T-cell lines in response to γδ T-cell-specific pAgs. VC reduced the apoptosis of γδ T cells during primary stimulation. While pVC did not prevent activation-induced death of pAg-restimulated γδ T cells, it enhanced the cell cycle progression and cellular expansion. Furthermore, VC and pVC enhanced cytokine production during primary activation, as well as upon pAg restimulation of 14-day-expanded γδ T cells. VC and pVC also increased the oxidative respiration and glycolysis of γδ T cells, but stimulus-dependent differences were observed. The modulatory activity of VC and pVC might help to increase the efficacy of γδ T-cell expansion for adoptive immunotherapy.