INS and type 1 diabetes mellitus: This study reveals that MDSC not only have the capacity to spontaneously differentiate into insulin-expressing and insulin-secreting clusters of beta-like cells in vitro, but also can be used directly in vivo without predifferentiation by direct intraperitoneal (IP) injection into mouse models of T1DM where they are recruited to pancreatic islets within 48 h and differentiate into insulin-expressing beta-like cells within 10 days of injection.