Operational Tolerance Permitted Under a Low Dose of Cyclosporine Monotherapy in Facial Tissue Allograft Transplants

The clinical application of composite tissue allograft transplants has opened a discussion on the restoration of facial deformities by allotransplantation. Here the authors introduced a hemi-facial allograft transplant model to investigate the rationale for development of operational tolerance across the MHC barrier.

Thirty rats in five groups (6 animals each) were studied. Composite hemi-face isograft transplantations were performed in Group 1; allograft rejection controls included semi-allogenic transplantations from LBN (RT1l + n) donors to LEW (RT1l) recipients in Group 2; and fully allogenic transplants from Acl (RT1a) donors in Group 3. In allograft treatment groups, recipients of LBN grafts in Group 4 and of ACl grafts in Group 5 were treated with CsA monotherapy at a dose of 16 mg/kg/day, tapered to 2 mg/kg/day and maintained at this level thereafter. Flow cytometry was used to evaluate donor-specific chimerism for MHC class l-RT1n and RT1a-specific antigens. Immunocytochemical method evaluated the migratory potential of donor-derived cells into the lymphatic tissues of recipients. The mechanism of allograft tolerance was assessed by the presence of apoptotic cells using the TUNEL technique. The mixed lymphocyte reaction (MLR) for donor-specific tolerance in vitro was tested at day 160 post transplant. Following H&E staining, histological grading of graft rejection was established.

Isograft controls survived indefinitely. All non-treated allografts were rejected within 5 to 9 days post transplant. Face transplants under CsA monotherapy from LBN and ACl donors survived up to 440 and 400 days, respectively. Donor-specific chimerism at day 160 showed LBN recipients: 10.2% CD4/RT1n and 6.4% CD8/RT1n T-lymphocytes and 10.0% CD45RA/RT1n B-lymphocytes, ACl recipients: 17.5% and 9.3% for CD4/RT1a andCD8/RT1a, respectively. The presence of donor-derived passenger leukocytes in the lymph nodes and spleens of recipients confirmed donor chimerism. Apoptotic cells were detected at day 7 and during the entire follow-up period (> 300 days) in the lymphatic tissues of recipients. MLR assay at day 160 post transplant revealed suppressed response in semi-allogenic transplants and moderate reactivity to donor antigens (ACl) in fully MHC mismatched transplants. Skin biopsies taken at sign of rejection demonstrated Grade II histopathologic lesions in LBN and ACl recipients at days 140 and 180 post transplant.

Operational tolerance was induced in hemifacial allograft transplants across the MHC barrier under CsA monotherapy protocol. This was associated with the presence of donor-specific chimerism in the blood and lymphatic tissues of face recipients. Anergy of T cells, which could contribute to operational tolerance in this model, was confirmed by the presence of apoptosis at day 7 post transplant.