Induction of operational tolerance and generation of regulatory cells after intratracheal delivery of alloantigen combined with nondepleting anti-CD4 monoclonal antibody

Background. We previously showed that intratracheal delivery of alloantigen induced prolonged survival of fully allogeneic cardiac grafts in mice. Here, this treatment protocol was combined with nondepleting anti-CD4 monoclonal antibody (mAb) to induce operational tolerance. Methods. CBA (H-2(k)) mice were pretreated with intratracheal delivery of whole splenocytes from C57BL/10 (H-2(b)) mice or a 15-mer K-b peptide, with or without intraperitoneal administration of nondepleting anti-CD4 mAb (YTS177). Seven days later, C57BL/10 hearts were transplanted into the pretreated CBA mice. In addition, some naive CBA mice underwent adoptive transfer of splenocytes from pretreated CBA mice and transplantation of a C57BL/10 heart on the same day. Results. Untreated CBA mice rejected C57BL/10 cadiac grafts acutely (median survival time, 12 days). Mice given intratracheal delivery of whole splenocytes or K-b peptide demonstrated prolonged graft survival (median survival time, 84 and 76 days, respectively). Concurrent administration of YTS177 and intratracheal. delivery of splenocytes or K-b peptide resulted in indefinite graft survival. Mice with long-surviving C57BL/10 cardiac grafts showed acceptance of skin grafts from C57BL/10 mice but not BALB/c mice, demonstrating that operational tolerance had been induced. Adoptive transfer of splenocytes from mice pretreated. with intratracheal delivery of splenocytes or K-b peptide plus YTS177 induced indefinite survival of cardiac grafts in secondary recipients, indicating that regulatory cells had been generated. Conclusion. In a murine model, intratracheal delivery of donor splenocytes or K-b peptide combined with YTS177 induced operational tolerance and generated regulatory cells.