Mixed chimerism, heart, and skin allograft tolerance in cyclophosphamide-induced tolerance

We elucidated the possible role of chimerism in skin and heart allograft to lerance using cyclophosphamide (CP)-induced tolerance. When C3H (H-2(k); Th y1.2, Mls-1(b)) mice were i.v. primed with 1x10(8) spleen cells (SC) from H -2 matched AKR (H-2(k); Thy1.1 Mls-1(a)) mice and then treated i.p. with 20 0 mg/kg of CP, the survivals of both AKR skin grafts and heart grafts (HG) were permanently prolonged in a tolerogen-specific fashion. After this trea tment, a minimal degree of mixed chimerism, the clonal destruction of Mls-1 (a)-reactive CD4(+)V beta 6(+) T cells in the periphery, and the clonal del etion of V beta 6(+) thymocytes were all observed. When AKR SC and 100 mg/k g CP were used for conditioning, the AKR HG were permanently accepted, but the survival of the AKR skin grafts was only mildly prolonged. The clonal d estruction of CD4(+)V beta 6(+) T cells in the periphery and the intrathymi c clonal deletion of V beta 6(+) thymocytes were induced in both the SC and the 100 mg/kg CP-treated C3H mice. A minimal degree of mixed chimerism was detectable at 4 and 12 weeks after AKR SC and 100 mg/kg CP treatment, and still did not disappear at 40 weeks, The degree of mixed chimerism induced with SC and 100 mg/kg CP was significantly lower than that with SC and 200 mg/kg CP during the observation. No posttransplant cardiac allograft vascul opathy (CAV) was observed to develop, while both the Th1 type (interferon-g amma) and Th2 type (interleukin-4 and -10) cytokine expressions decreased i n the AKR HG of the tolerant C3H mice treated with both AKR SC plus 200 mg/ kg CP, and AKR SC pins 100 mg/kg CP, A second set of skin grafts from donor AKR mice survived for more than 100 days in a tolerogen-specific fashion i n all C3H mice treated with AKR SC and 200 mg/kg CP and also accepted the A BR HG for over 200 days, while 80% of the C3H mice treated with AKR SC and 100 mg/kg CP and accepted the AKR HG; for more than 200 days. These results strongly suggested the following conclusions: 1) the degree of chimerism c an strongly influence the induction of skin and heart allograft tolerance, 2) posttransplant CAV does not develop in the donor HC; maintained by chime rism-based CP-induced tolerance, 3) the mRNA expression of both Th1 and Th2 type cytokine decreased in the donor HG maintained by chimerism-based CP-i nduced tolerance, and 4) the induction of skin allograft tolerance is more difficult than the prevention of posttransplant CAV.