*Purpose: Using donor splenocytes fixed with cross-linker ethylcarbodiimide (ECDI-SPs), our lab has induced tolerance in a variety of murine and non-human primate models when one dose of ECDI-SPs is administered before transplant and one dose after. We aimed to identify a method to induce tolerance post-transplant (delayed tolerance) in a murine model.

*Methods: We transplanted BALB/c pancreatic islets under the kidney capsule of C57BL/6J mice. Prior to islet harvest, donors were treated with either anti-CSF1R antibody to deplete macrophages or an isotype control. Recipients were made diabetic with one dose of streptozotocin one week before transplant. Recipients received one or two doses of ECDI-SPs following transplant. Graft rejection was defined as hyperglycemia for two consecutive days.

*Results: Multiple dosing schedules of anti-CSFR1 antibody were tested to determine an effective schedule to deplete macrophages. Complete depletion of CD11b^hiF4/80⁺ macrophages required two doses of 500ug of antibody at days -11 and -7 prior to transplant. We demonstrate a specific and complete depletion of donor macrophages in murine pancreatic islets using this method. To establish delayed tolerance, we tested single and multiple doses of post-transplant ECDI-SPs. A single dose at day +1 after islet transplant was insufficient to induce tolerance. However, transplantation of macrophage-depleted islets followed by two doses of ECDI-SPs at days +1 and +7 post-transplant resulted in greatly extended graft survival.

*Conclusions: Depletion of macrophages in donors prior to murine islet transplant allows for post-transplant tolerization of grafts. Our delayed tolerance strategy significantly lengthened graft survival. The development of a post-transplant tolerization model could lead to tolerization for recipients of organs from deceased donors.

« Back to 2022 American Transplant Congress