Cell Phenotype Evaluation at Various Sites After Skin Transplantation and FTY720 Plus Sirolimus Therapy

Cell phenotype evaluation enables better understanding of the rejection process in experimental transplantation. We studied allograft survival and the mechanisms associated with rejection in a murine model of skin transplantation in the absence of immunosuppression or after FTY720 or sirolimus (SRL) administration for 21 days. Leukocyte phenotype was evaluated in the peripheral blood, spleen, axillary lymph nodes, thymus gland, and skin graft using flow cytometry at 5 days posttransplantation. Treatment with FTY720 plus SRL increased skin allograft survival in association with lymphopenia, reduced CD11b+ and CD3+CD4+ cell percentages in the graft, decreased CD3+CD4+, CD3+CD8+, and CD11b+ cell counts in lymphoid organs, and decreased CD4+CD8+ cell count in the thymus. These results suggest that increased allograft survival in animals treated with FTY720 plus SRL is due to possible impairment of antigen presentation or recognition in the graft and secondary lymphoid organs, and decreased emigration of mature thymocytes to the periphery.