RELATIONSHIP BETWEEN IMMUNE STATE AND TUMOR-GROWTH RATE IN RATS BEARING PROGRESSIVE AND NONPROGRESSIVE MAMMARY-TUMORS

Impaired immune responses occur frequently in cancer patients or in tu mor-bearing animals, but the mechanisms of the tumor-induced immune de fects remain poorly understood. The aim of the present study was to de termine the relevance of the immune system in the control of tumor gro wth. We have developed a model of progressive and non-progressive mamm ary tumor, chemically induced in female Wistar rats. In this model we evaluated the development of an immune response after immunization of rats bearing progressive and non-progressive tumors with a non-related antigen, such as sheep red blood cells. We also studied the activatio n state of peritoneal macrophages from animals bearing tumors by evalu ating the production of free radicals. Our findings indicated that the cell-mediated immunity in rats bearing progressive tumors fails to re spond to heterologous antigen in vivo, as demonstrated by a negative d elayed-type hypersensitivity reaction, and is accompanied by minor nit ric oxide production by peritoneal exudate cells as well as a lower ca pacity for macrophage activation. The study of non-progressive tumor-b earing rats indicated that the cell-mediated immune response was intac t and an activated state of macrophages was found in vivo. The results described in this paper should be taken into account when therapies b ased on cancer vaccines are chosen for the treatment of cancer.