Effects of immunosuppression on the rejection of methylcholanthrene tumor isografts

The effect of immunosuppression with azathioprine, methylprednisolone, or both, on primary and secondary immune responses to a transplanted tumor was studied. The ability to reject a methylcholanthrene-induced squamous cell carcinoma of the prostate in Lewis rats was determined by rechallenge with tumor cells after amputation of the primary transplant. Oral azathioprine (20 mg/kg/day) increased the incidence of tumors in a primary challenge, but did not affect the ability of immunized rats to reject subsequent tumor isografts. Similar results were obtained with 2 mg/kg day intraperitoneal (IP) azathioprine, 2 mg/kg IP methylprednisolone, and the combination of 2 mg/kg/day IP methylprednisolone and 10 mg/kg/day IP azathioprine. It appears that immunosuppression by azathioprine affects the proliferation of sensitized cells during the immunological response to antigens of this specific tumor. Immunosuppression does not appear to alter substantially the processing of tumor-specific antigens or the cytotoxic effectiveness of the immune system. This data is reassuring to the concern of whether transplantation in patients previously cured of cancer is safe.