Donor-specific antigen transfusion-mediated skin-graft tolerance results from the peripheral deletion of donor-reactive CD8+ T cells

Background. The mechanism of donor-specific transfusion (DST)-induced long-term skin-graft survival is examined in 2CF1 (2C×dm2) transgenic and B6F1 (C57BL/6×dm2) nontransgenic mice in which CB6F1 (Balb/cxB6) DST and donor skin grafts differ from 2CF1 or B6F1 recipients only at major histocompatibility complex class I L^d. Methods. Saline (control) or allogeneic CB6F1 spleen cells were injected intravenously into 2CF1 and B6F1 mice. One week later, CB6F1 tail skin was transplanted onto the dorsum of these mice. Fluorescence-activated cell sorter analysis (flow cytometric analysis) of peripheral blood was performed 2 days before DST, 5 days after DST, and 7, 14, 21, 28, and 75 days after skin grafting. Splenocyte responsiveness was measured by in vitro mixed lymphocyte culture and cytotoxic T lymphocyte. Cytokine protein production (interleukin [IL]-2 and interferon-γ) was measured by enzyme-linked immunosorbent assay. Results. Whereas all CB6F1 skin grafts in control saline-treated 2CF1 and B6F1 mice were rejected, 100% of 2CF1 and B6F1 pretreated with CB6F1 DST accepted the class I L^d disparate donor skin indefinitely. DST followed by a CB6F1 skin graft led to a significant deletion of donor-reactive CD8+ T cells by fluorescence-activated cell sorter analysis and decreased production of the inflammatory cytokines IL-2 and interferon-γ. The hyporesponsiveness of residual CD8+ T cells in mixed lymphocyte culture and cytotoxic T lymphocyte to L^d after DST was restored to normal by IL-2. Conclusion. These findings demonstrate that administration of DST uniformly results in long-term L^d+ skin-allograft acceptance. This tolerance induction is related to both a significant decrease in donor-reactive CD8+ transgenic T cells and anergy of the residual CD8+ T cells.