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Ultraviolet Radiation-induced Murine Tumors Produced in the Absence of Ultraviolet Radiation-induced Systemic Tumor Immunosuppression¹

Department of Veterinary Pathology, University of Sydney, Sydney 2006 [S. W. M., G. E. G., V. E. R., C. H. G.], and Lidcombe Hospital Dermatology Centre, Lidcombe, New South Wales 2141 [S. W. M.], Australia

Using micro-UV-irradiation versus whole-dorsal irradiation for inducing cutaneous carcinomas in Skh:HRI mice and an assay for UV radiation (UVR)-induced systemic tumor immunosuppression, the dependence upon systemic immunosuppression for the growth of UVR-induced carcinomas was examined. Squamous cell carcinomas were produced by repeated microirradiation of 0.8-cm² middorsal skin with xenon arc solar-simulated UVR. These tumors were excised from tumor-bearing animals who 7 days later were inoculated ventrally with a cloned UVR-induced squamous cell carcinoma cell line, the T51/6. This cell line only grows in UVR-induced immunosuppressed Skh:HRI mice. In two separate experiments T51/6 inocula failed to grow significantly in the previously tumor-bearing animals (1 of 13) and in unirradiated mice (0 of 19), whereas it grew in 100% (15 of 15) of animals given a whole-dorsal subcarcinogenic UVR dose from a filtered fluorescent tube solar simulator. No sinecomitant immune response to the T51/6 was found in previously UVR-induced tumor-bearing animals. In contrast to whole-dorsal UVR-induced tumors, microirradiation-induced squamous cell carcinomas, whose original growth environment lacked UVR-induced systemic tumor immunosuppression, did not grow preferentially in mice given an immunosuppressive dose of UVR. However both the whole-dorsal and microirradiation-induced tumors were shown to be poorly antigenic, since they lacked preferential growth in athymic nude mice. These observations provide evidence that UVR-induced systemic tumor immunosuppression is not necessary for the production of UVR-induced tumors. However, it does cause a positive selection pressure during tumor formation, independent of the carcinogenic effect of UVR, which affects the transplantation biology of a tumor.

¹ This research was supported by the University of Sydney Cancer Research Fund.

² To whom requests for reprints should be addressed.

Received 9/ 7/89. Accepted 3/13/91.