ASSESSMENT OF DONOR BONE-MARROW CELL-DERIVED CHIMERISM IN TRANSPLANTATION TOLERANCE USING TRANSGENIC MICE

Allospecific skin graft prolongation can be induced in mice using anti thymocyte globulin and allospecific donor bone marrow cells (DBMC). Th is enhancement may be due to the persistence of chimeric cells of dono r origin in the host. In this study, we systematically investigated DB MC-derived chimerism in various lymphoid and nonlymphoid tissues over time. To do this, transgenic mice were used as a source of DBMC to cle arly distinguish chimerism due only to the injected DBMC. Chimerism in various tissues was assessed at several times points after DBMC infus ion by polymerase chain reaction amplification of tissue DNA using tra nsgene specific primers. A cDNA probe specific for the transgene was u sed to demonstrate DBMC-derived chimerism in polymerase chain reaction products by the method of Southern. Although chimerism was initially detectable in most tissues tested 1 day after DBMC infusion, the prese nce of chimeric cells generally diminished over time. At 4 weeks or lo nger, chimerism was consistently confined to recipient skin. Furthermo re, the chimeric cells in recipient skin persisted even after the allo graft was rejected. In contrast to chimerism in recipient skin, chimer ism became undetectable in donor skin as early as 2 weeks after DBMC i nfusion. The loss of chimerism in donor skin showed a temporal correla tion with a reduction of chimerism in host bone marrow and lymphoid ti ssues that preceded rejection in all experiments by a range of 7-14 da ys. The use of DBMC from transgenic mice allowed a unique opportunity to monitor the kinetics of DBMC-derived chimerism. The presence of chi merism in the skin of mice in temporal association with chronic allogr aft rejection suggests that chimerism per se is not a reliable index o f allogeneic unresponsiveness.