Locally expressed CTLA4-Ig in a pancreatic beta-cell line suppresses accelerated graft rejection response induced by donor-specific transfusion

Aims/hypothesis. This study examined whether locally expressed CTLA4-Ig can suppress the accelerated islet allograft rejection that is induced by donor-specific transfusion. Methods. CTLA4-Ig-transfected or parental MIN6 cells were transplanted subcutaneously into the right flank of streptozotocin-induced diabetic C3H/Hej mice with or without donor-specific transfusion. For donor-specific transfusion, spleen cells from C57BL/6 mice were injected i.v. at the time of transplantation. In other experiments, CTLA4-Ig-transfected and parental MIN6 cells were transplanted separately into each flank, together with donor-specific transfusion. Rejection was defined as a blood glucose concentration of more than 300 mg/dl in two consecutive measurements, and graft survival was confirmed by hyperglycaemia after the grafts were removed. The effect of an anti-CTLA4 antibody on the survival of CTLA4-Ig-transfected MIN6 cells was also examined. Results. In 7 of 12 donor-specific transfusion sensitised mice, CTLA4-Ig-transfected MIN6 cells remained viable 20 days after grafting, whereas all parental MIN6 cells (n = 10) were rejected promptly, within 14 days. The prolonged allograft survival was observed even in the absence of detectable levels of serum CTLA4-Ig, while the surviving allografts continued to produce CTLA4-Ig in situ. This protection was abrogated by an anti-CTLA4 antibody, but not by a control antibody. Furthermore, six animals that maintained normoglycaemia after the separate transplantation of parental and CTLA4-Ig-transfected MIN6 cells into each flank all showed abrupt hyperglycaemia after the CTLA4-Ig/MIN6 graft was removed, suggesting that this protection operated locally. Conclusion/interpretation. A beta-cell line genetically engineered to secrete CTLA4-Ig can protect a graft locally from the alloimmune response induced by donor-specific transfusion.