Persistence of Gene Expression Profile in CD200 Transgenic Skin Allografts Is Associated With Graft Survival on Retransplantation to Normal Recipients

Background. Expression of CD200 increases allograft survival by suppressing inflammation and acquired immunity. Increased allograft survival in transgenic mice overexpressing CD200 (CD200(tg)) occurs in association with increased intragraft expression of messenger RNAs (mRNAs) for genes associated with altered T-cell differentiation. Methods. We investigated whether donor CD200(tg) BL/6 skin grafts taken from primary control or CD200(tg) recipient BALB/c mice persisted after retransplantation at 14 days to control (nontransgenic) secondary BALB/c recipients, with or without transfer of splenocytes from autologous primary recipients. Splenocytes from primary and secondary recipients were analyzed 14 days after grafting, using in vitro mixed leukocyte cultures (MLCs) incubated with irradiated BL/6 (or third-party C3H/HeJ) stimulator cells and assayed for antigen-specific cytotoxic T lymphocyte. Cytotoxic T lymphocyte responses were correlated with changes in the mRNA gene expression profile observed in the skin tissue harvested from primary or secondary recipients on day 14 after grafting, using real-time polymerase chain reaction to compare quantitative mRNA expression in the graft tissue of primary/secondary recipients. Results and Conclusions. Adoptive transfer of tolerance in MLC to BL/6 grafts was most evident when both skin and splenocytes were transferred from primary BALB/c recipients, although there was an attenuation of MLC responses after graft transfer alone. Adoptive transfer of tolerance occurred concomitant with persistent overexpression of genes encoding Foxp3, transforming growth factor beta, interleukin 10, and PD-1 (and PD-L1/PD-L2) in tolerant skin grafts and increased expression of mRNAs for indoleamine 2,3-dioxygenase and the subunits encoding interleukin 35. Infusion of anti-CD4 or anti-transforming growth factor beta to secondary recipients on retransplantation abolished increased graft survival, suggesting the importance of each to the final outcome.