T cell lines and variant subclones with differing susceptibility to tumor promoters

The effect of tumor-promoting phorbol esters on cloned cytotoxic T cell (CTL) lines, H-2 restricted and specific for minor histocompatibility antigens, was studied. We found that two of the three CTL lines tested can be induced by 12-O-tetradecanoylphorbol 13 acetate (TPA or PMA) to synthesize DNA. One of the lines did not respond. TPA concentrations in the range of 1 nmol were active, and induction of DNA synthesis was independent from cell densities. Testing of other phorbol esters showed correlations with their tumor-promoting activity, because TPA and phorbol 12,13-didecanoate were active, whereas phorbol and 4 alpha phorbol 12,13-didecanoate had no effect. Interestingly, two subclones isolated from one of the lines responding to TPA behaved differently: one of the subclones synthesized DNA when incubated with TPA, whereas the other remained completely negative. This difference was reflected also in the dissimilarity of morphologic alterations (observed by scanning electron microscopy) occurring in the responding cells. The nonresponsiveness, in terms of DNA synthesis, by some of the CTL lines is not due to a lack of interaction between TPA and the cells. When incubated simultaneously with TPA and T cell growth factor (IL 2), all lines responded with greater DNA synthesis than when incubated with IL 2 or TPA alone, thus demonstrating a synergistic action between TPA and IL 2. We have also done experiments to test whether TPA induces the synthesis and secretion of a factor leading to proliferation of the cells. From bystander experiments it appears that the action of TPA is not mediated by a secreted product but is a direct one.