The induction of pseudo-graft-versus-host disease following syngeneic bone marrow transplantation using FK 506.

CYCLOSPORINE (Cy A)-induced pseudo-graft-versus-host disease (GVHD) developing in syngeneic rat bone marrow chimeras has features resembling classical acute and later chronic GVHD in the fully allogeneic bone marrow chimera. 1 These features develop in the early post-CyA period, and usually result in a mild, acute form of GVHD, followed by a more chronic autoimmunelike syndrome in a high percentage of animals, particularly with high doses of Cy A. 1 Cy A-induced thymic changes, which include disruption of thymocyte maturation while on therapy, are thought to be the mechanisms responsible for these effects following the discontinuation of Cy A therapy. I Since FK 506, like CyA. affects the thymic microenvironment.2 we decided to observe the nature of any pseudo-GVHD reactions induced by the abrupt assation of FK 506 therapy following syngeneic BMT in the Lewis rat.