PROLONGATION OF IMPURE MURINE ISLET ALLOGRAFTS WITH ANTILYMPHOCYTE-SERUM AND DONOR-SPECIFIC BONE-MARROW

The inclusion of contaminating nonislet tissue in allografts of purified islets of Langerhans has been shown to decrease allograft survival times in unimmunosuppressed mice. Our current work examines the effectiveness of antilymphocyte serum and donor bone marrow cell infusion on the survival of very impure islet allografts. Treatment of B6AF1 mice with peritransplant antilymphocyte serum plus posttransplant infusion of donor (C3H/HeJ) bone marrow was very effective at prolonging contaminated allograft survival. ALS plus BMC was also effective for even more immunogenic allograft situations; mice that received contralateral transplants of adult and neonatal tissue, and mice that received dual transplants of adult islets. Long-term graft-bearing mice that originally received ALS and BMC were challenged with C3H/HeJ skin grafts. These mice exhibited several different types of response. Four of thirteen appeared sensitized to donor antigen, four rejected the skin grafts in approximate first-set fashion, and five showed limited prolongation, with skin grafts surviving 20-48 days. Long-term graft-bearing mice were also tested in in vitro proliferative assays. As responders in mixed lymphocyte reactions, splenocytes (SPC) from only one of eight appeared to show specific unresponsiveness to donor cells. Four of eight had a normal proliferative response and stimulation index to stimulation with C3H/HeJ SPC. SPC from three did not produce a normal stimulation index, but had an abnormally high (3x normal) background proliferation. SPC from seven of eight of these mice were able to suppress the proliferative response of naive B6AF1 SPC to C3H/HeJ cells. Our conclusions are that while ALS plus BMC are very effective in prolonging islet allograft survival, this treatment does not appear to be uniformly inducing a state of immunologic unresponsiveness in these mice. It appears that multiple mechanisms are acting to maintain islet allografts in this system, either independently or sequentially.