Purpose: Clinical application of composite tissue allograft transplants opened discussion on the restoration of facial deformities by allotransplantation. We have achieved operational tolerance in fully MHC mismatched rat hemifacial allograft model under low dose of cyclosporine-A (CsA) monotherapy. The potential of graft-derived dendritic cells (DC) on chimerism induction was tested in hemiface allografts under CsA monotherapy across MHC barrier. Methods: Twenty-four hemiface transplantations were performed in 4 groups (6 rats each). Rejection controls included semi-allogenic LBN(RT1^l+n) (Group-1) and fully-allogenic ACI(RT1^a) (Group-2) donors. Group-3 (LBN donors) and Group-4 (ACI donors) received tapered dose of CsA monotherapy. At different time-point (7, 28, 63, 100 day) samples from lymphoid organs and blood were harvested. Flow cytometry monitored donor-specific chimerism (MHC class-I RT1ⁿ and RT1^a antigens). Mechanism of allograft acceptance was assessed by the presence of donor dendritic cells (DDC) (immunofluorescence) and apoptotic cells (TUNEL technique) within lymphoid organs. Results: Face transplants under CsA monotherapy from LBN and ACI donors displayed presence of passenger leukocytes within lymphoid organs of recipients. At day 7 post-transplant DDC and donor leukocytes were detected within spleen and lymph nodes of recipients. During follow-up, the number of donor-origin DC significantly increased within spleen but only single cells were present within lymph nodes. DDC were not detected within thymus. Donor-specific chimerism in the peripheral blood of recipients at day 100 measured: LBN recipients at 1.4% for CD4/RT1ⁿ, 0.5% for CD8/RT1ⁿ and 2.6% for CD45RA/RT1ⁿ; for ACI recipients at 16.8% for CD4/RT1^a, 3.7% for CD8/RT1^a and 0.2% for CD45RA/RT1^a. Apoptotic cells were detected at day 7 and during entire follow-up period (100 days) in the lymphoid organs of recipients. Conclusions: CsA monotherapy promoted T-cell tolerogenicity of DDC in hemifacial allograft transplants due to functional stabilization of DDC at the immature state. Migration and localization of graft-derived DDC into lymphoid organs of recipient confirmed immunomodulatory function of DDC for skin allograft acceptance in hemifacial allograft model. Anergy of T cells, demonstrated by the presence of apoptotic cells, contributed to long-term hemifacial skin allograft survival.
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