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.

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 × 10(8) 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.