Results of an unpublished pilot study performed in this laboratory suggested increased incidence of fibrosarcomas at the site of subcutaneous plastic film implants in immunosuppressed mice as compared with normal mice. Plastic-induced tumors, like most spontaneous tumors, have low antigenicity (1) and should provide a better model than highly antigenic chemically or virally induced tumors for studying the relationship between the immune system and tumor development. The experiment was expanded as is described below.

Ninety C3H/St male mice were operated on at 60 ± 7 days; half of these were thymectomized and the rest sham-thymectomized. Eight days later, whole body irradiation at 350 R was carried out, a procedure previously shown by Miller to produce moderate, prolonged immunosuppression (2). (Concurrent experiments in our laboratory showed significant immunosuppression induced by this method, with 100% of 30 thymectomized, irradiated C3H mice succumbing within 30 days to an inoculum of allogeneic tumor (TA3) which was lethal for only 53 ± 9% of control C3H mice.)

1

This study was supported by United States Public Health Service Grant CA11091.

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