Simultaneous Blockade of Costimulatory Signals CD28-CD80 and CD40-CD154 Combined with Monoclonal Antibody against CD25 Induced a Stable Chimerism and Tolerance without Graft-versus-Host Disease in Rat

Abstract

Background: The conditioning regimen to induce chimerism for immune tolerance is usually accompanied by high toxicity and graft-versus-host disease (GVHD). Our aim was to explore a nontoxic strategy for the induction of mixed chimerism by pretreatment with anti-CD25 monoclonal antibody (mAb), cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4Ig) and anti-CD154 mAb. Methods: A total of 30 Lewis recipient rats (RT1l) were randomly divided into control (A and B) and treated (C, D and E) groups. Recipients serving as controls were without any pretreatment (group A) or pretreated with anti-CD25 mAb, CTLA4Ig and anti-CD154 mAb on days 0, 2, 4, 6 and 8 without bone marrow transplantation (BMT; group B). In the treated groups, the recipients were pretreated with anti-CD25 mAb and CTLA4Ig (group C), with anti-CD25 mAb and anti-CD154 mAb (group D) or with anti-CD25 mAb, CTLA4Ig and anti-CD154 mAb (group E) on days 0, 2, 4, 6 and 8 plus BMT [2 × 10⁸ unmodified whole bone marrow cells from Brown Norway donor rats (RT1n)] on day 0. Full-thickness skin grafts from donor-specific Brown Norway rats were grafted to the dorsal thoracic wall of Lewis recipients on day 8. GVHD was assessed after BMT, and chimerism and T cell apoptosis on days 7, 21, 35 and 49 were detected by flow cytometry. Results: GVHD was not observed in any groups. On days 7, 21 and 35, hematopoietic chimerism was present and maintained in the recipients of the 3 treated groups (groups C, D and E), and thereafter disappeared on day 49. The rate of chimerism in group E was significantly higher compared to that in group C on day 7 and that in group C or D on day 21, but there was no significant difference on day 35 among the 3 groups. The rate of T cell apoptosis in group C, D or E was significantly higher than in group A or B on days 14, 21 and 35. The grafted skin survival in group C, D or E was longer than in group A or B, and survival was significantly longer in group E than in group C or D. Conclusion: Preconditioning with anti-CD25 mAb, CTLA4Ig and anti-CD154 mAb could effectively induce chimerism and immune tolerance without GVHD in a major histocompatibility complex-disparate rat model. This strategy may be attractive for induction of transplantation tolerance. T cell apoptosis is one of the important considerations in tolerance induction.