Modification of the immunologic response to human choriocarcinoma in the hamster cheek pouch by heterologous antilymphocyte serum.

Because the immune response to human choriocarcinoma growing in the hamster cheek pouch makes it difficult to evaluate the responsiveness of the tumor to drugs, we have studied this immune response in untreated hamsters and hamsters immunologically suppressed with heterologous antilymphocyte serum (ALS). Untreated animals were immunized by the tumor beginning as early as 6 days after implantation. Once an animal rejected the tumor, it would not accept a second implant of that or any other strain. This immune state was due to species-specific antigens, for it could be induced by injection of whole human blood. Treatment of hamsters with ALS resulted in a higher incidence of growth of tumors from a given donor tumor, increased tumor volume, and longer tumor survival. These effects were the result of the potent immunosuppressive action of ALS and may facilitate the establishment of heterotransplant tumors for each patient to be evaluated for therapy. Methotrexate had less oncolytic effect on choriocarcinoma in ALS-treated hamsters than in untreated hamsters. This suggests that the evaluation of drugs may be more reliable in the absence of the immune response to these xenogeneic tumors, for the strain of choriocarcinoma used was not responding to Methotrexate when obtained from the patient.