Induction of kidney transplantation tolerance across major histocompatibility complex barriers by bone marrow transplantation in miniature swine.

Previous studies from our laboratory have shown that permanent lymphohematopoietic chimerism can be induced in MHC-disparate miniature swine by bone marrow transplantation after lethal total-body irradiation. The purpose of the present study was to determine in this large animal model whether such chimerism would lead to permanent tolerance to a vascularized allograft without a requirement for exogenous immunosuppression. Eight miniature swine that had received MHC-mismatched BMT more than five months earlier underwent kidney transplantation (KTx) from a donor MHC matched (n = 5) or MHC mismatched (n = 3) with the BMT donor. All animals had regained in vitro responsiveness to third-party MHC antigens, as measured by mixed lymphocyte reaction (MLR), before KTx but remained nonresponsive to MHC antigens of the BMT donor and self. All three animals that received KTx mismatched for BMT donor MHC rejected promptly (mean survival time 7.0 days). Of the five animals that received KTx matched for BMT donor MHC, four showed no evidence of rejection and have functioning KTx greater than 200 days after KTx. The fifth animal had excellent renal function for 60 days but then developed a slowly rising BUN and serum creatinine, and died 75 days after KTx. The course of this animal's rejection is consistent with that previously described for rejection due to minor antigen disparities. The difference in survival of KTx matched or mismatched for the MHC of the BMT donor was statistically significant (P = 0.0062). The survival of KTx matched for the MHC of the BMT donor was significantly different from that of control animals without BMT receiving KTx mismatched for MHC (P = 0.0018). We therefore conclude that BMT is an effective means for induction of tolerance to an MHC mismatched KTx in this large animal model.