INDUCTION OF TOLERANCE BY SIGNAL ONE BLOCKADE WITH ANTI-CD45RB REQUIRES NEGATIVE SIGNALING THROUGH CTLA-4.

Abstract

450 We have shown that blockade of Signal One with 3 doses of anti-CD45RB induces tolerance in 50-60% of murine islet allograft recipients (PNAS. 1998. 95:3821). Engagement of CTLA-4 is required for induction of tolerance to nominal antigen (Immunity. 1997. 6:411). Here, we evaluate the role of negative signaling through CTLA-4 in tolerance induction by anti-CD45RB in a murine islet allograft model through use of a blocking anti-CTLA-4 mAb. Chemically diabetic C57BL/6 mice were transplanted with 350-400 BALB/c islets under the left kidney capsule. Recipients were untreated, or treated with: anti-CD45RB (MB23G2), 100 ug IV on days −1,0, and 5; anti-CTLA-4 (UC10-4F10), 200 ug IP days −1, 0, 1; or the combination of anti-CTLA-4 plus anti-CD45RB. (Table)TableTreatment with anti-CTLA-4 alone had no effect on graft survival compared to untreated controls. Preliminary data indicate that anti-CTLA-4 does not affect CD45 isoform expression. In contrast, anti-CD45RB treatment induces a shift from high to low Mr (CD45RBLo) CD45 isoforms. Importantly, CD45RBLo T cells have been reported to exhibit increased CTLA-4 expression (J. Immunol. 1998. 161:5855). We hypothesize that the shift towards CD45RBLo isoforms induced by anti-CD45RB mAb augments CTLA-4 expression and that this contributes towards the generation of tolerance. Concordantly, blockade of CTLA-4-mediated negative signals with anti-CTLA-4 abrogates tolerance induction by anti-CD45RB. Understanding the role and mechanisms of negative signaling pathways in induction and maintenance of tolerance is critical for development of novel tolerance strategies in solid organ and cell transplantation.