Responder peripheral blood lymphocytes (PBL) were plated in triplicate in 96-well flat-bottom plates (Costar, Cambridge, MA) at a final concentration of 4 × 105 cells/well in RPMI 1640 supplemented with 6% fetal pig serum and were stimulated by an equal number of irradiated (2500 cGy) stimulator PBL as previously described (14 (link)). For tests of mixed lymphocyte reaction (MLR) in the presence of cyclosporine, the drug was added to the medium at a final concentration of 0, 5, 10, 20 and 40 ng/mL.