Immunomodulation for intestinal transplantation by allograft irradiation, adjunct donor bone marrow infusion, or both

Background, The passenger leukocytes in the intestine have a lineage profil e that predisposes to graft-versus-host disease (GVHD) in some animal model s and have inferior tolerogenic qualities compared with the leukocytes in t he Liver, other solid organs, and bone marrow. Elimination by ex vivo irrad iation of mature lymphoid elements from the bowel allografts is known to el iminate the GVHD risk. We hypothesized that infusion of donor bone marrow c ells (BMC) in recipients of irradiated intestine would improve tolerogenesi s without increasing the risk. of GVHD. Methods. Orthotopic small intestine transplantation was performed with the GVHD-prone Lewis (LEW)-to-Brown Norway (BN) combination and the reverse GVH D-resistant BN-to-LEW model under a short course of tacrolimus treatment (I mg/kg/day, days 0-13, 20, 27). Grafts were irradiated ex vivo, using a Cs- 137 source. In selected experimental groups, donor BMC (2.5x10(8)) were inf used on the day of small intestine transplantation. Results. The unmodified LEW intestine remained intact, whether transplanted alone or with adjunct donor BMC infusion, but all of the BN recipients die d of GVHD after approximately 2 months. Intestinal graft irradiation (10 Gy ) effectively prevented the GVHD and prolonged survival to 92.5 days, but a ll of the BN recipients died with chronic rejection of the LEW grafts, whic h was prevented by infusion of adjunct donor BMC without causing GVHD. In t he GVHD-resistant reverse strain direction (BN --> LEW), all intestinal rec ipients treated for 27 days with tacrolimus survived greater than or equal to 150 days without regard for graft irradiation or adjunct BMC, but chroni c rejection was severe in the irradiated intestine, moderate in the unalter ed graft, and least in the irradiated intestine transplanted with adjunct B RIG. Mild arteritis in the 150 day allografts of both strain combinations ( i.e., LEW --> BN and BN --> LEW) may have been irradiation associated, but this was prevented when weekly doses of tacrolimus were continued for the d uration of the experiment rather than being stopped at 27 days. Conclusions. Recipients are protected from GVHD by irradiating intestinal a llografts, but the resulting leukocyte depletion leads to chronic rejection of the transplanted bowel. The chronic rejection is prevented with adjunct donor BMC without causing GVHD. Although application of the strategy may b e limited by the possibility of radiation injury, the results are consisten t with the paradigm that we have proposed to explain organ-induced graft ac ceptance, tolerance, and chronic rejection.