Prevention of chronic rejection and graft arteriosclerosis by tolerance induction.

Chronic rejection is a major cause of graft failure in solid organ transplants after the first year. A characteristic lesion in a variety of chronically rejecting organs is a fibrointimal proliferative arteriosclerosis. It has been speculated that approaches to tolerance induction may be effective in obviating not only acute, but also chronic, rejection. A picture of chronic rejection develops naturally in heart grafts transplanted from the Lewis-to-F-344 strain of rat. We examined whether tolerance induction by bone marrow transplantation and development of hematopoietic chimerism or tolerance induction by intrathymic inoculation of alloantigen could effectively prevent chronic rejection in an established model of chronic rejection. Bone marrow chimeras were developed in F-344 hosts by transplantation of T cell-depleted allogeneic marrow (TCD A BMT). Another set of F-344 hosts was inoculated with intrathymic allogeneic bone marrow cells. Heart grafts in these animals demonstrated tolerance for 120 days after transplantation. Control F-344 animals treated with a short course of cyclosporine consistently developed chronic rejection by 120 days following heart transplantation. Strikingly absent from the tolerant animals was any sign of graft arteriosclerosis, which was demonstrated in the vast majority of control animals. Analysis of cytokine mRNA profiles at 30 days following heart transplantation demonstrated differences between control and tolerant animals. These results suggest that tolerance induction can effectively prevent chronic rejection.