Pretransplant injection of allograft recipients with donor blood or lymphocytes permits allograft tolerance without the presence of persistent donor microchimerism

Donor-recipient microchimerism has recently been suggested to play a critical role in the induction and maintenance of allograft tolerance. In this study we sought evidence for this hypothesis using the LEW-to-ACI cardiac allograft as a model system. Donor-specific tolerance to cardiac allografts was induced by intravenous or intraportal injection of graft recipients with donor peripheral blood, T cells, or B cells 7 days before transplantation. All the graft recipients injected with donor antigens accepted donor heart grafts indefinitely when compared with control recipients that rejected donor allografts in 12 days. Long-term graft survivors rejected third-party BN heart allografts in 14 days without an adverse effect on the survival of the first LEW heart allografts, demonstrating the specificity of the tolerance. Tissue lysates prepared from heart, kidney, liver, bone marrow, thymus, lymph nodes, and spleen of tolerant (>120 days) graft recipients were analyzed for the presence of donor DNA using LEW T cell receptor C beta gene-specific primers for polymerase chain reaction that detects donor DNA at > or = 1:10,000 dilution. Donor DNA was detected in 77% of tolerant graft recipients. Chimeric recipients showed variations in the levels and presence of donor DNA in different tissues. The status of donor microchimerism, with respect to its presence and tissue distribution, was dependent upon the donor cell type and route of injection used for the induction of tolerance. Intraportal injection of the graft recipients with donor peripheral blood resulted in the highest degree of chimerism, whereas intravenous injection with donor B cells did not induce detectable microchimerism in this group of recipients. These data clearly demonstrate that the presence of microchimerism is common following administration of donor cells, but that its presence is not an absolute requirement for the long-term survival of allografts.