Bendix et al found that long-term administration of vitamin D3 on patients with Crohn’s disease promoted PD-1 expression on CD4+ CD25int T cells,38 and Sheikh et al showed that stimulation of CD4+ T cells with vitamin D3 in vitro enhanced the expression of PD-1.39 In contrast, Pincikova et al reported that vitamin D treatment on patients with cystic fibrosis was associated with reduced PD-1 expression on both CD4+ and CD8+ T cells.40 Our results showed that 1α,25(OH)2D3 could reverse exhaustion of CD4 T cells derived from PBMCs of healthy donors in vitro. Here, CD4 is linked to cystic fibrosis.