CD274 and diabetes mellitus: However, the role of PD-L1 in the regulation of T-cell tolerance to islets needs to be further investigated because the transgenic expression of PD-L1 on islets in mice with a C57BL/6 background induced T-cell-mediated spontaneous diabetes [25], and transgenic expression of B7-H1 (PD-L1) on peri-islet Schwann cells unexpectedly accelerated rather than suppressed diabetes progression [26].