Influence of ara-c on effector activity of cytotoxic t-lymphocytes in vitro?

Mouse T-lymphocytes carrying the H-2?^d haplotype were sensitized in vitro? against allogeneic spleen cells homozygous for the H-2?^b haplotype. Cytolytic T-lymphocytes (CTL) were tested in a 4 hr cytotoxicity assay against ⁵¹Cr-labeled H-2?^b RBL-5 lymphoma cells. The cytotoxic activity of CTL was markedly increased by preincubation with Ara-C (1 through 1000 μg/ml, 1 hr at 37°C). Limited but significant increase of cytotoxicity occurred when the drug was added to the effector-target mixture, or when target cells were preincubated with Ara-C using the same conditions adopted for the in vitro ?treatment of CTL. It is suggested that the present findings would contribute to elucidate the mechanism underlying anti-tumor synergistic effects between host's responses and treatment with antineoplastic agents.