In vivo suppression of EL 4 lymphomas by rabbit antitumor sera.

Three of more than 50 batches of rabbit antisera raised against the mouse EL 4 lymphoma could inhibit the growth of the tumor in the syngeneic C57BL/6J mice either after exposure of the tumor cells to the antitumor globulin (ATG) in vitro or after the administration of ATG in mice preinoculated with various numbers of EL 4 cells, even though the ATG was not cytotoxic to the tumor cells in the presence of complement. The outcome of immunotherapy with ATG in tumor-bearing C57BL/6J mice depended on the tumor load, the interval between tumor inoculation and the institution of therapy, the total dose, and the schedule of administration of ATG. Complete tumor suppression could be obtained in a proportion of mice preinoculated with 10(5) EL 4 cells, i.e., 10(4) times more than the minimum number of EL 4 cells necessary for 100% tumor takes. Whole-body irradiation (400 rads) or complement depletion of tumor host by cobra venom factor had no effect on tumor suppression by ATG. No evidence of immunity against the EL 4 lymphoma could be detected in EL 4-bearing mice that survived after serotherapy. Anti-EL 4 sera raised in goats and goat and rabbit antisera raised against a lymphoma in the AKR mice have, so far, failed to show any tumor inhibition.