Jag1‐overexpressing dendritic cells (DCs) enhanced Foxp3+ regulatory T‐cell expansion in vitro. (a) In the mixed lymphocyte reaction, Jag1‐DCs from BALB/c mice were co‐cultured with naive CD4+ T cells from C57BL/6 mice. (b) For the ovalbumin (OVA) ‐specific CD4+ T‐cell response, differently treated DCs from BALB/6 mice were co‐cultured with syngeneic OT‐II CD4+ T cells. Anti‐PD‐L1 antibodies were used to block the PD‐L1/PD‐1 signaling pathway between DCs and T cells. After 5 days of culture, CD4+ T cells were collected and further analyzed by flow cytometry. Representative dot plots show expressions of CD25 and Foxp3 on gated CD4+ T cells. The percentage was calculated, and results are expressed as the mean ± SEM of three independent experiments. *P < 0·05, ***P < 0·001 versus Jag1‐DCs.