Measurement of cell mediated cytotoxicity by post-labeling surviving target cells

The 51Cr release assay (CRA) is the commonly accepted technique for measurement of cell mediated cytotoxicity. This assay shows some disadvantages when mononucleated cells of human peripheral blood (MNC) are used as effector and target cells. The uptake of 51Cr by PHA stimulated lymphocytes is low compared to the spontaneous release. In an attempt to develop a cytotoxicity assay suitable for human lymphocytes we used 14C-TdR to label target cells surviving after contact with effector cells. Cytotoxic lymphocytes were generated by incubation of MNC with irradiated allogeneic MNC for 6 days. On day 6 the effector cells are irradiated and co-cultured with PHA stimulated target cells. Twenty-four hours later 14C-TdR is added. After an additional 24 h the cultures are harvested and 14C-TdR taken up by target cells is measured. It is shown that the effector cells are still cytotoxic after irradiation. These cells do not take up 14C-TdR. Cell-free supernatants do not influence the uptake of 14C-TdR by target cells. The results obtained with this assay correlate very well with those obtained by the CRA, if the spontaneous release does not exceed 30%.