Kinetics of cellular cytotoxicity mediated by cloned cytotoxic T lymphocytes

Kinetic methods can provide significant information concerning the mechanism of cellular cytotoxicity reactions. Previous kinetic studies of cytotoxic T lymphocytes (Tc) have been hampered by the heterogeneity of the effector cell population tested. We therefore examined the kinetics of lysis mediated by cloned, IL 2 and antigen-dependent murine Tc cells with strong cytotoxic activity that is restricted to distinct tumor-associated antigens on P815 mastocytoma target cells. Initial velocity measurements for cytotoxicity mediated by these clones fit a simple Michaelian kinetic model. Specific activity values obtained from these initial rate measurements are compared to those obtained for polyclonal Tc preparations, NK cells, and activated killer cells. Whereas the initial rate of lytic programming mediated by these cloned cells was very rapid, the rate of cytolysis mediated by the cloned cells decreased significantly within one hour. Since this decrease was observed over a wide range of E:T ratios, it is unlikely to result from product inhibition or a significant decrease in the concentration of unlysed target cells, but may be due to a decrease in the rate of programming and/or effector cell recycling. These results indicate that a simple Michaelian kinetic model is not adequate for tumor cell cytolysis by Tc cells in vitro.