Therapy with monoclonal antibody to interleukin 2 receptor spares suppressor T cells and prevents or reverses acute allograft rejection in rats.

The mouse hybridoma ART 18 monoclonal antibody (mAb), which binds to the rat interleukin 2 (IL-2) receptor, was studied for its effect on heterotopic cardiac allograft survival in two histoincompatible inbred rat strain combinations. Treatment with ART 18 mAb for 10 days after transplantation prolonged allograft survival in a dose-dependent fashion up to about 3 weeks (acute rejection normally occurs within 8 days). ART 18 mAb therapy started at 5 days after transplantation the time of major rejection activity) abrogated acute rejection and extended the survival to about 18 days. The dense cellular infiltrate noted histologically in acute rejection had virtually disappeared after ART 18 mAb treatment. Thus, IL-2 receptor-targeted therapy can be successfully used to prevent and/or treat acute rejection. When spleen cells from antibody-treated recipients bearing well-functioning allografts were adoptively transferred to normal untreated rats that received cardiac allografts 24 hr later, the survival of donor-specific, but not third-party, test cardiac allografts was prolonged significantly; this supports the idea that ART 18 mAb induced "sparing" of suppressor T lymphocytes. Combining infusion of ART 18 mAb with exogenous IL-2-rich conditioned medium produced the same effect as if the mAb alone had been administered, suggesting that an excess of IL-2 does not prevent binding of ART 18 mAb to IL-2 receptor-bearing cells in vivo. These results support the important role of the IL-2 receptor-bearing cells in the mechanism of allograft rejection; they may represent an important target for immunosuppression in clinical organ transplantation.