Specific Desensitization of Resistance against a Syngeneic Methylcholanthrene-induced Sarcoma in C3Hf Mice1

The effect of residual or reinjected tumor tissues on specific host antitumor resistance has been studied with a syngeneic methylcholanthrene-induced fibrosarcoma. Sensitized mice showed a strong resistance to the growth of injected fibrosarcoma cells if the sensitizing tumor implants were removed before the time of challenge. If large sensitizing tumors were left in situ until after the challenge injection of tumor cells or if suspensions of killed tumor cells were injected into sensitized, surgically cured tumor hosts, the immune resistance of the hosts was impaired but not abrogated. Injection of graded doses of killed tumor cells about the time of challenge showed that the depression of host resistance was dose related. Small (6x 6-mm) sensitizing tumors left in situ after challenge injection of tumor cells did not affect the resistance of the hosts, whereas larger (13x 13-mm) tumors had a depressive effect. Depression of resistance by injection of killed tumor cells was most effective during the week following challenge. The depression was specific, and resistance was not impaired by the presence of a growing implant or by injected, killed cells of an antigenically unrelated syngeneic mammary carcinoma. The depression of host resistance by antigenic tumor tissue appeared not to be mediated by specific immunoglobulins (enhancement), since repeated injections about the time of challenge with serum from tumor-carrying mice or from hyperimmunized mice did not impair resistance.