Inhibitory effect of cyclosporin A on peripheral blood and bone marrow T lymphocyte colony formation

The effect of cyclosporin A on the formation of T lymphocyte colonies from human peripheral blood and bone marrow was tested using a double-layer technique. A moderate inhibition (27%) was observed on peripheral blood lymphocytes with concentrations of 0.1 microgram/ml of the drug; this increased to 57% with 1 microgram/ml and to almost 70% with 10 microgram/ml. Bone marrow cells were less sensitive to cyclosporin A. This was more evident at the lowest concentration of the drug (0.1 microgram/ml), with which a 14% inhibition was found. Higher concentrations (1--10 microgram/ml) produced 37 and 56% inhibition respectively. Overnight incubation with the drug followed by repeated washing of the cells did not influence colony growth. E-rosette formation was also not affected by cyclosporin A. The apparent greater sensitivity to the drug of peripheral blood than bone marrow T lymphocytes, possibly related to a different distribution of T colony-forming cells or of T lymphocyte subsets, may have some bearing on the clinical application of cyclosporin A in the prevention and treatment of graft-versus-host disease in man.