Suramin inhibits the mixed lymphocyte reaction by suppressing lymphokine production.

New compounds with a greater potency than cyclosporin A (CyA) for thwarting host rejection of organ transplantation are being sought. Suramin sodium may be a novel drug to prevent or delay graft rejection and graft-vs-host disease (GVHD), because of its in vitro and in vivo immunosuppressive properties. Since the allogeneic mixed lymphocyte reaction (MLR) is considered to be the in vitro counterpart of the initial T-lymphocyte recognition and response to allogeneic histocompatibility antigens on grafted tissue or organ and to GVHD, we initially evaluated the in vitro suppressive effect of suramin in the allogeneic MLR. Suramin inhibited the H-2- and HLA-incompatible MLR in a dose-dependent manner. The suppressive effect was observed both in the primary and in the secondary MLR. The suppression of the MLR by suramin is due predominantly to the inhibition of interleukin-2 (IL-2) production by the responding T cells.