Absence of graft-versus-host disease in the isolated vascularized bone marrow transplant.

An isolated vascularized bone marrow transplant (iVBMT) model was developed to study the contribution of the bone marrow component in a composite tissue allograft. We hypothesized that the iVBMT would be functional and cause graft-versus-host disease (GVHD) in a fraction of the recipients. Lewis iVBMT grafts were transplanted to Lewis-Brown Norway recipients. Animals were sacrificed at various times from 1 to 14 weeks. Polymerase chain reaction for microchimerism was performed on the host's marrow. No animals exhibited signs of GVHD at death. Histologic examination of the grafts showed a normal mix of hematopoietic and fatty elements and appeared to be functional. Tissues usually affected-tongue, ear, liver, and gut-also showed no evidence of disease. Polymerase chain reaction demonstrated microchimerism in both groups. These findings suggest that the vascularized bone marrow within a composite tissue allograft is not the component that causes GVHD; rather, it may serve an immunomodulatory function for tolerance induction.