CCL21 and Opportunistic infection: Implantation of PDL1‐CTLA4Ig‐expressing MHC‐matched islets into diabetic NOD mice resulted in protection of allogeneic islets from acute rejection, although islet grafts were eventually rejected.[73] Freddy et al., developed Ins2‐CCL21 transgenic NOD mice which express chemokine (C‐C motif) ligand 21 (CCL21) in pancreatic β‐cells and avoided developing autoimmune diabetes.[74] All the above studies represent localized immunosuppression strategies which allow for reduced or even no systemic immunosuppression, thus decreasing opportunistic infections.