Flow cytometric analysis of chimerism in the rat tolerant to a renal allograft.

BACKGROUND

Chimerism, produced by the two-way migration of cells between graft and host, is a proposed mechanism by which tolerance occurs. The appearance of donor/recipient chimeras in tolerant ACI to Lewis rat heterotopic renal transplants was assessed in peripheral blood leukocytes using flow cytometry after staining with monoclonal antibodies.

MATERIALS AND METHODS

ACI and Lewis rats were used as donor and recipient, respectively, after Rapamycin and Cyclosporin immunosuppression with or without donor blood or bone marrow transfusion. ACI and Lewis animals were also used for isograft and single-kidney controls. Animals were sacrificed at various time points after initial operation. Flow cytometry was performed on isolated peripheral blood leukocytes at sacrifice. Histologic and functional data were also obtained. The monoclonal antibody panel included RT1(a) (ACI, MHC I) combined with CD2, CD4, CD8, CD16, and CD25 or RT1(a,c) (bone marrow chimeras).

RESULTS

RT1(a)+, CD8+ cells were transiently present in the peripheral blood leukocytes of Lewis recipients with the exception of allogeneic bone marrow recipients. No significant number of RT1(a)+, CD16+ ("dendritic" cell-line) chimeras was seen. Veto cells (RT1(a,c)+) were transiently present in the bone marrow recipients, but they did not lead to improved outcome. Furthermore, no correlation was made between histologic tolerance and any of these donor-derived cells.

CONCLUSION

Donor/recipient chimerism, and the veto cell phenomenon are not operational tolerance mechanisms in this stringent model of ACI to Lewis rat renal transplantation.