Abstract
A new cytotoxicity assay for the study of tumor antigens is described. Splenocytes from normal and mammary‐tumor‐bearing BALB/c mice were depleted of glass‐adherent cells, exposed to various concentrations of tumor extracts and mixed with ^51^Cr‐labelled chick red blood cells. Cytolysis evidenced by ^51^Cr release was determined 20 h after incubation at 37°C. Lymphocytes from tumor bearers exerted no cytotoxic action per se, but became cytolytic after confrontation with immunogenic tumor extracts. Although this cytotoxicity is expressed against targets other than the cells containing the sensitizing antigen, i.e., a non‐specific activity, its induction is strictly specific as evidenced by the following: (1) extracts of D1‐DMBA‐3 tumors exerted an inductive effect only in lymphocytes from mice bearing this tumor and not in lymphocytes from normal mice; and (2) extracts of normal tissues or of a non‐immunogenic mammary tumor, D1‐DMBA‐2, did not induce cytotoxicity in lymphocytes from normal or tumor‐bearing mice. This approach may provide a useful method for in vitro determination of cell‐mediated immunity in which specific reactions can be induced by tumor extracts as opposed to intact tumor cells.