PDCD1 and diabetes mellitus: Liposomes encapsulating the CD4+ peptide [BDC2.5mim, has a high affinity for islet autoantigen chromogranin a (ChgA)] and 1α,25-dihydroxy vitamin D3 (calcitriol) suppressed diabetes progression by activating ChgA-specific forkhead box P3 (Foxp3)+ and Foxp3- programmed cell death 1 (PD1)+ CD73+ inducible T cell costimulator (ICOS, also named CD278)+ IL-10+ peripheral regulatory T cells (21), suggesting that CD4+ peptide combination with calcitriol decreased diabetes progression by enhancing CD73+ expression.