Manipulating IL-2 Availability Amid Presentation of Donor MHC Antigens Suppresses Murine Alloimmune Responses by Inducing Regulatory T Cells

Abstract

BackgroundMajor histocompatibility complex (MHC) antigens are important for alloimmune responses as well as immune tolerance. Previous studies have shown that presentation of donor MHC antigens by donor-specific transfusion prior to or upon transplantation promotes transplant tolerance induced by other agents. However, it is unclear whether presentation of donor MHC antigens by DNA vaccination induces long-term allograft survival.Methodology/Principal FindingsWe investigated whether presentation of MHC class-II and/or class-I donor antigens by DNA vaccination suppresses alloimmune responses and promotes long-term allograft acceptance. We initially found that presentation of both MHC donor antigens by DNA vaccination itself prior to transplantation fails to significantly prolong islet allograft survival in otherwise untreated mice. However, islet allograft survival was significantly prolonged when MHC class-II DNA vaccination was accompanied with IL-2 administration (MHCII + IL-2) while MHC class-I DNA vaccination was followed by IL-2 and subsequent neutralizing anti-IL-2 treatments (MHCI + IL-2/anti-IL-2). Especially, this protocol promoted long-term allograft survival in the majority of recipients (57%) when combined with low doses of rapamycin post-transplantation. Importantly, MHCII + IL-2 induced FoxP3+ Treg cells in both spleens and grafts and suppressed graft-infiltrating CD4+ cell proliferation, whereas MHCI + IL-2/anti-IL-2 mainly inhibited graft-infiltrating CD8+ cell proliferation and donor-specific CTL activity. The combined protocol plus rapamycin treatment further reduced both CD4+ and CD8+ T cell proliferation as well as donor-specific CTL activity but spared FoxP3+ Treg cells. Depleting CD25+ Treg cells or adoptive transfer of pre-sensitized CD8+ T cells abolished this long-term allograft survival.Conclusions/SignificanceManipulating IL-2 availability during presentation of MHC class-II and class-I donor antigens by DNA vaccination pre-transplantation induces Treg cells, suppresses alloimmune responses and promotes long-term allograft survival.

Immunosuppression induced by apoptosis of mixed lymphocyte culture is associated with p53

“…An aliquot of frozen D2 (Bm) was washed with RPMI-1640 medium and then counted. The cell concentration was diluted to 1x10 6 /ml with RPMI-1640 containing 20% fetal bovine serum. RPMI-1640 liquid (100 µl) was used as a blank control, and 50 µl PMLC was used as a control.…”

“…The fixed TCR-β chain caused a defective response to alloantigen, which was measured as decreased IL-2 generation and utilization, followed by an abnormally decreased graft-versus-host response (GVHR). Another opposite opinion, however, deemed that IL-2 induced immune tolerance via regulatory T cells (5)(6)(7)(8).…”