CD4 and diabetes mellitus: Similarly, the transfer of 3.5 × 105 purified CD25+ CD4+ T cells (containing largely Treg cells, see Fig. 3b) from vaccinated/ppins-primed, but not from non-immunized donor mice into PD-L1−/− hosts one week after the injection of the diabetogenic pCI/ppins DNA efficiently suppressed diabetes induction (Fig. 6b).