Evidence of the nonimmune regression of chemically induced papillomas in mouse skin.

To determine the degree to which host immunity is responsible for papilloma regression, 3-methylcholanthrene-treated allografts were placed on maximally immunodepressed recipients (thymectomy + 450 R radiation and weekly antithymocyte serum injections). Almost 80% of the papillomas on the allografts regressed. Cellular or humoral immune capacity in the recipient animals could not be detected by conventional means. Therefore, the regressions were probably the result of a nonimmunologic mechanism. The data showed that more papillomas regressed on multiples of 21 ± 4 days, from the day of grafting, than in the intervening periods. This clustering pattern of regressions was not observed in immunocompetent animals. In competent mice, two or more mechanisms, one of which is immunity, may contribute to the regression of chemically induced skin papillomas.-J Nat Cancer Inst 47: 653-665, 1971.