Allograft mass as a possible contributing factor to the skin transplant outcome

A composite tissue consists of tissues derived from ectoderm and mesoderm typically containing skin, fat, muscle, nerves, lymph nodes, bone, bone marrow or any combination of these. Solid organ transplants possessing larger allograft mass were reported to survive better. As for the vascularized composite tissues however, thus far no study has comparatively studied the survival of grafts possessing different tissue burdens. The purpose of this study was to explore the effect of transplanted tissue burden and tissue type on survival of skin element of composite tissues.

Forty-five transplantations were performed using four different vascularized composite tissue allotransplantation models. The survival periods and rejection severity of the skin parts of the transplants were compared by histological, immunological, and macroscopic evaluation: (a) under no immunosuppressive treatment (control group) (n = 21); (b) after 1 week of Cyclosporine (CsA) treatment (16 mg/kg) (experimental group) (n = 24). Total rejection was defined as necrosis of >90% of the skin flaps. Histopathologic evaluation and flow cytometric analysis to detect chimerism rates in the blood was performed in the CsA treated animals on day 18.

The differences of mean survival times between and within the experimental and control groups were statistically significant (P < 0.05). Histopathological outcomes showed lower rejection grades in skin allografts transplanted with a higher tissue burden. Total CD4+ and CD8+ T-cell chimerism rates were less than 1% in isolated skin transplant groups and ranged from 6.1 to 33.5% in skin flaps transplanted with the entire hindlimb or a part of it.

The transplanted tissue burden as well as the tissue type can be an important factor for the skin transplant outcome.