A quantitative assay for tumor antigen based on inhibition of cytotoxicity of sensitized lymphocytes.

Specific inhibition of cell-mediated cytotoxicity can be used as a quantitative measure of soluble tumor antigen if highly cytolytic cells are obtained. In vitro secondary stimulation of spleen cells sensitized in vivo to the syngeneic 13762A mammary adenocarcinoma results in a lymphocyte population consistently more cytolytic than lymphocytes after primary stimulation. Maximal cytolysis requires removal of dead lymphocytes from the effector population. Soluble tumor antigen (STA) is detected only in supernatant: of 13762A mammary tumor cultures grown in the presence of the proteolytic enzyme inhibitor, e-amino caproic acid. Soluble MTM antigen preparations block lymphocytes immune to the mammary tumor but not lymphocytes immune to a second mammary adenocarcinoma (R3230) or to allogeneic spleen cells. Soluble antigen preparations from other tumors do not inhibit lymphocytes specifically cytolytic to the 13762A tumor. Additional evidence that the STA preparation contains tumor antigen is its ability to induce specific cytolytic lymphocytes and partial protection from challenge with live MTA tumor cells.