Action of three nitrosoureas on human lymphocytes. Hypothesis of a specific effect on lymphocyte subpopulations.

RFCNU [(chloro-2-ethyl)-1-(ribofuranosylisopropylidene-2',3'-paranitrobenzoate-5')-3- nitrosourea], RPCNU [(chloro-2-ethyl)-1-(ribopyranosyltriacetate-2',3',4')-3-nitrosourea] and CCNU [(chloro-2-ethyl)-1-cyclohexyl-3-nitrosourea) were found cytotoxic in vitro for human blood lymphocytes from healthy donors at doses higher than 50 micrograms/ml. Blood lymphocytes from different individuals displayed different behaviors both in their sensitivity to nitrosoureas and in their proliferative response to mitogenic lectins. With pokeweed-mitogen-stimulated lymphocytes the main effect of all three drugs (10 micrograms/ml) was an increase of [3H]-thymidine uptake. This facilitation effect was found only in half of the experiments with phytohemagglutinin-stimulated lymphocytes, while the stimulation by concanavalin A was inhibited under the same conditions. The hypothesis that nitrosoureas might be selectively cytotoxic for a suppressor cell subpopulation might explain the observed increase of thymidine uptake.