1,25-Dihydroxyvitamin D3 impairs the differentiation of effector memory T cells in vitro in multiple sclerosis patients and healthy controls

•The effects of 1,25-(OH)2 vitamin D on MS and healthy control PBMCs were examined.•Vitamin D reduced the differentiation of effector memory T cells in both groups.•Vitamin D led to an increased percentage of naïve T cells in both groups.•We report a novel effect of vitamin D on T cell memory.

Vitamin D deficiency is associated with increased susceptibility to multiple sclerosis (MS) and increased disease activity. Vitamin D is a potent immunomodulator but the effects of vitamin D treatment on T cell memory have not been explored. We studied the effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on T cell memory in MS patients (n = 10) and healthy controls (n = 10). In vitro treatment of PBMC cultures with 1,25(OH)2D3, led to a decrease in the proportion of effector memory T cells with an increase in naïve T cells, compared to vehicle in both groups. Further studies to unravel the mechanism of this effect and to understand its long-term implications are required.