Correlation of chimerism with graft size and revascularization in vascularized and nonvascularized skin allografts.

The high antigenicity of skin components of composite tissue allografts is the most challenging factor in achieving long-term viability after composite tissue allografts transplantation. The vascularization pattern of vascularized skin allografts (VSA) and nonvascularized skin allografts (NVSA) differs significantly and these differences may alter host immune responses. We hypothesized that vascularized grafts contribute to better engraftment and long-term survival. We have tested our hypothesis by transplantation of different sizes (2 x 2 cm, 4 x 4 cm, 6 x 6 cm) of VSA and NVSA across major histocompatibility complex barrier between LBN (RT1(1+n)) and Lewis (RT1(1)) rats. Correlation of revascularization process with development of donor-specific chimerism was tested. We found that the highest chimerism levels (8%-12.2% in VSA groups; 2.53%-3.92% in NVSA groups) were reached as early as 7 days in both VSA and NVSA. Chimerism decreased in both groups during 100-day follow-up and higher chimerism was found only in VSA in late posttransplant period. Revascularization, assessed by the presence of CD31 positive vessels, was significantly higher in VSA compared with NVSA and to controls (P < 0.05). A direct correlation was seen between increased skin diameter and donor chimerism in VSA, whereas inverse correlation was tested in NVSA. We have confirmed that allograft size and vascularization pattern contribute to donor chimerism development and maintenance.