Selective effects of cyclosporin A on colony-forming lymphoid and myeloid cells in man

THE properties of the fungus metabolite, cyclosporin A, have suggested its potential as a clinically valuable immunosup-pressive agent(1,2). Experiments in animals have demonstrated that its suppressive action against cell-mediated and humoral immunity is not accompanied by any appreciable myelotoxicity(3,4). In this respect, cyclosporin A contrasts with other immunosuppressants in current use, such as antilymphocyte globulin and azathioprine. There are, however, few data to substantiate a selective toxicity of cyclosporin A against human lymphocytes. Here, we have compared its effects against human lymphoid and myeloid cells, using colony formation by the different cell types as the end point. We found that the compound exhibited far greater toxicity towards a sub-population of T cells than towards either B lymphocytes or haematopoietic precursor cells.