Background: Small bowel allografts can either be placed heterotopically or orthotopically. In heterotopic small bowel transplantation (H-SBT), the host small intestine containing a substantial amount of gut-associated lymphoid tissue is removed, whereas in conventional orthotopic small bowel transplantation (O-SBT) it is retained. This study compared the allograft survival of H-SBT and O-SBT and evaluated the effect of retaining the host intestine in O-SBT in an altered O-SBT (AO-SBT) model.
Methods: SBT was performed in a high-responder rat stain combination (blood group D Agouti --> Lewis). Immunosuppressive treatment consisting of a short course of FK506 (2 mg/kg/day IM for 3 days before transplantation and 0.3 mg/kg/day for 14 days after transplantation) was used.
Results: Survival (mean +/- SD) of H-, O-, and AO-SBT untreated animals was 6.25+/-0.58 days, 6.5+/-0.58 days, and 6.7+/-0.25 days, respectively. With FK506 immunosuppression, survival of H-SBT animals was 49.3+/-13.17 days, whereas 75% (12/16) and 80% (4/5), respectively, of O-SBT and AO-SBT animals achieved indefinite survival (>120 days) with functioning grafts.
Conclusion: Our data suggest that heterotopic placement of intestinal allografts results in a more severe graft rejection than orthotopic placement. The indefinite survival of O-SBT is not due to of the removal of host intestine carrying a heavy load of gut-associated lymphoid tissue.