Anti-CD25 mAb, Anti-IL2 mAb, and IL2 Block Tolerance Induction Through Anti-CD154 mAb and Rapamycin in Xenogeneic Islet Transplantation

Abstract

Background We have used anti-CD154 monoclonal antibody (mAb; MR1) and rapamycin (rapa) to induce tolerance to islet xenografts. The aim of this study was to investigate whether classical anergy and/or regulation by interleukin (IL)2-dependent CD25 + T regulatory cells played roles in the induction and maintenance of tolerance in this model. Methods Streptozotocin-induced diabetic mice were transplanted with rat islets. We performed the following groups: control group, islet transplantation without therapy; rapamycin group, 0.2 mg/kg by oral gavage on days 0, 1, 2, and every other day to day 14; anti-CD154 mAb (MR1) group, 0.5 mg intraperitoneally on days 0, 2, and 4; combination therapy group with rapa and MR1. We then administered in addition to the combination therapy with early (from days 0 to 14 [for IL2] or to 28 [for anti-IL2 mAb and anti-CD25 mAb] post-transplantation) or late (from days 100 to 114 [for IL2] or to 128 [for anti-IL2 mAb and anti-CD25 mAb] posttransplantation) recombinant IL2 (2000 U, intraperitoneally twice a day), a neutralizing anti-IL2 mAb (S4B6-1, 0.3 mg intraperitoneally twice weekly), and a depleting anti-CD25 mAb (PC61, 0.3 mg intraperitoneally twice weekly), respectively. Histology was performed at time of rejection. Results Rapa and MR1 therapy alone significantly prolonged xenograft survival compared to the control group: median graft survival was 34 days versus 17 days ( P < .05) and 98 days versus 17 days ( P < .05), respectively, but rejection still occurred. Combination therapy with MR1 and rapa allowed indefinite graft survival (median graft survival [MGS] >200 days, P < .001). When exogenous IL2 was administered early with MR1 and rapa, rapid rejection developed in 18 of 18 mice (MGS 7 days), whereas when IL2 was given late, only 3 of 10 developed rejection. Early administration of anti-IL2 mAb led to rejection in 10 of 10 mice (MGS 42 days), whereas late administration led to rejection in only one of four mice. Early administration of anti-CD25 mAb led to rejection in eight of nine mice (MGS 49 days), whereas late administration led to rejection in only three of seven mice. Conclusions Rapa and MR1 allowed indefinite graft survival of islet xenografts. Classical anergy and regulation by IL2-dependent CD25 + T regulatory cells were critical in the induction of tolerance in the immediate posttransplantation period and less important for maintenance of tolerance.