In vitro cell‐mediated immune reactions of melanoma and colorectal carcinoma patients demonstrated by long‐term 51chromium assays

In a series of consecutive 51chromium (51Cr) assays, 21 melanoma and 14 colo‐rectal carcinoma patients were tested for their in vitro cell‐mediated immune reactions to melanoma, rectal adenocarcinoma, and normal fibroblast target cells. Blood lymphocytes (BL) from four individuals were included in each experiment. In 9/14 experiments the BL effects of 2 melanoma patients were compared to BL effects of 2 colorectal carcinoma patients. In two experiments, BL from 1 melanoma patient and 1 colorectal carcinoma patient were compared for cytotoxic effect with each other and with BL from 2 normal healthy donors, and in the remaining 3 experiments BL from 2 melanoma patients were compared with BL from 1 healthy donor and one patient bearing a tumor which was neither a melanoma nor a colorectal carcinoma. Eleven out of 14 experiments were performed in a criss‐cross manner. Target cells in the first three tests of this series consisted of tumor cells and fibroblasts explanted from a single melanoma patient. In all of the remaining experiments, each BL population was tested for cytotoxicity against both a tumor‐fibroblast target cell pair explanted from one of two melanoma patients and a tumor‐fibroblast target cell pair explanted from a rectal adencarcinoma patient. Out of 35 tumor patients, 27 (77%) demonstrated a selective cytotoxic effect on the tumor target cells compared to the corresponding fibroblasts, while 4 patients (11%) showed a selective effect on the fibroblasts and 6/29 patients showed a selective effect on the other type of tumor cells compared to matching fibroblasts. In 8/11 experiments (including two repeat tests) tumor‐specific BL effects were demonstrated in a criss‐cross manner. BL effects were demonstrated in a criss‐cross manner. BL separations and 51Cr tests were repeated in 11 of the 35 patients 2‐4 weeks after their original tests. BL populations from these 11 patients reproduced their individual earlier effects, whether these effects showed specific, non‐specific, or no cytotoxicity. In each assay, differences in sensitivity between fibroblasts and tumor target cells in matched pairs were analyzed by comparing the effects of BL from the two controls. No differences in target‐cell sensitivity could be demonstrated.