Tumor specific reactivity during development of N-methyl-N-nitrosourea-induced rat colon cancer

Invasive colon adenocarcinomas with lymph node metastases can be induced in Sprague-Dawley rats by 15 weekly intrarectal injections of 2 mg N-methyl-N-nitrosourea (NMU). Extracts were prepared from invasive adenocarcinomas and normal rat colon mucosa by a 2 phase gradient. Mixed leukocyte tumor interaction (MLTI) assays stimulating lymphocytes from tumor-bearing and normal rats were performed using these extracts. Quadruplicate cultures were established with 2 X 10(5) lymphocytes and tumor or normal colon extract. Cultures were pulsed with H3 thymidine at 7 days and harvested 6 hours later. Results were expressed as net counts (experimental CPM minus background CPM). Reactivity in tumor-bearing animals was first seen when rat colons showed intraepithelial dysplasia histologically and was maximal when early invasive colon tumors were present. No difference in stimulation was seen between tumor-bearing and normal animal lymphocyte reactivity with normal colon extract. In conclusion, animals with NMU-induced rat colon cancer show specific tumor reactivity in MLTI assays. Immune reactivity in these animals may provide clues to clinical tumor status by immunologic assay.