Pig Embryonic Pancreatic Tissue as a Source for Transplantation in Diabetes: Transient Treatment With Anti-LFA1, Anti-CD48, and FTY720 Enables Long-Term Graft Maintenance in Mice With Only Mild Ongoing Immunosuppression

Objective: Defining an optimal co-stimulatory blockade based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice. Research Design and Methods: Considering that anti-CD40L was found to be thrombotic in humans we sought to test alternative co-stimulatory blockade agents already in clinical use, including CTLA4-Ig, anti-LFA1 and anti-CD48. These agents were tested in conjunction with T cell debulking by anti-CD4 and anti-CD8 antibodies, or with conventional immunosuppressive drugs. Engraftment and functional development of E42 pig pancreatic tissue was monitored by immunohistology and by measuring pig insulin blood levels. Results: Fetal pig pancreatic tissue harvested at E42, or even as early as at E28, was fiercely rejected in C57BL/6 mice and in Lewis rats. A novel immune suppression comprised of anti-LFA1, anti-CD48, and FTY720 afforded optimal growth and functional development. Cessation of treatment with anti-LFA1 and anti-CD48 at 3 months post transplant did not lead to graft rejection, and graft maintenance could be achieved for more than 8 months with twice weekly low dose FTY720 treatment. These grafts exhibited normal morphology and were functional, as revealed by the high pig insulin blood levels in the transplanted mice, and by the ability of the recipients to resist alloxan induced diabetes. Conclusions: This novel protocol, comprised of agents that simulate those approved for clinical use, offer an attractive approach for embryonic xenogeneic transplantation. Further studies in non-human primates (NHP) are warranted.