High-level chimerism after rhesus HSCT. (A) Rhesus macaque HSCT strategy. Each component of CoBS immunosuppression (anti-CD40 monoclonal antibody, CTLA4Ig, sirolimus) is shown, along with the total body irradiation (TBI)–based conditioning regimen. Control animals received only TBI-based conditioning but no posttransplantation immunosuppression. (B) Whole-blood chimerism in recipients who did not receive posttransplantation immunosuppression (R.1-R.3). (C) Whole-blood chimerism in recipients who received CoBS (R.4-9). (D) T-cell chimerism in the transplant recipients.