Specific killing of tumor cells In vitro in the presence of normal lymphoid cells and sera from hosts immune to the tumor antigens

Evidence is presented for specific in vitro killing of neoplastic target cells in the presence of non‐sensitized lymphoid cells and heat decomplemented sera from mice bearing the respective neoplasms or whose tumors had been removed. Such an effect was observed with sera from mice bearing Moloney sarcoma virus (MSV)‐induced and 3‐methylcholanthrene (MCA)‐induced sarcomas, and from mice whose mammary tumor virus (MTV)‐induced adenocarcinomas had been removed. Neoplastic target cell death was not characteristically mediated by such sera alone or by normal lymphoid cells in the presence of serum from animals bearing some other tumor, but appeared to be a specific, synergistically produced cytotoxicity.