Fig. 1

Protective mechanisms of MSCs in vivo. Both sole transplantation and co-transplantation of MSCs with islets or dissociated islet cells into the portal vein or the kidney capsule affect β-cell mass replenishment and transplantation outcome through indirect (immune and endothelial cells) and direct effects between MSCs and the β-cell. Danger signals sent out from the β-cell are detected by MSCs and tissue repair mechanisms are in place, e.g., via CXCL12/SDF signals, growth factor signals, N-cadherin-mediated direct cell–cell contacts, and secreted annexin, or by the formation of tunneling nanotubes which enable the exchange of mitochondria. In concert, these mechanisms promote β-cell survival/apoptosis protection, proliferation, and improved β-cell function