A novel cell type carrying both Th and Tc/s markers in the blood of cyclosporine-treated, allografted rats.

During treatment of heart-grafted rats with cyclosporine, an unusual large lymphocyte appears in the blood. These cells constitute up to 40% of the peripheral blood leukocyte population and carry both the T helper/DTH and T cytotoxic/suppressor differentiation antigens. They require both the allograft and CsA for their generation and are not recently thymus-derived. They gradually disappear after stopping CsA treatment, although the treated rats remain tolerant of the graft.