Expression of the cellular immune response during tumor development in an animal model of bladder cancer

Papillary and solid transitional cell cancers were induced in the bladders of Fischer rats by ingestion of the carcinogen N-[4-(5-nitro-furyl)-2-thiazolyl]formamide. At sequential regular intervals, purified splenic, peripheral blood, regional lymph node, and thymus lymphocytes were harvested from tumor-bearing and age-matched control animals and tested for cytotoxicity against a variety of cell lines. Lymphocytes were also tested in mixed lymphocyte cultures for blastogenesis. Tumor development was accompanied by decreased lymphocyte cytotoxicity against bladder tumor targets at each interval tested. This decrease was in addition to the age-related decrease in cytotoxicity expressed by lymphocytes from control animals. No corresponding differences were seen in lymphocyte subpopulations as determined by immunofluorescence or in lymphocyte blastogenesis. Suppressor cell activity in tumor-bearing animals could not be demonstrated, and no cause-effect relationship between cytotoxicity depression and tumor development in these experiments was apparent.