Selective and non‐selective lymphocytotoxicity in human melanoma: Observation on the effect of long‐term culture and fetal bovine serum on target‐cell sensitivity to lymphocytes

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Abstract
In vitro cell mediated cytotoxicity (CMC) assays have been conducted in a human melanoma system with a 3H‐proline retention technique. Melanoma target cells from long‐term cultures (“cell lines”) are found to exhibit increased susceptibility for lymphocyte cytotoxicity in comparison to the same target cells from short‐term culture. The higher sensitivity of the “cell line” derived target cells is seen with lymphocytes, irrespective of diagnosis of the donor. In parallel experiments with the target cells grown in medium supplemented with fetal calf serum (FCS) and AB+ human serum (from a normal male donor), the melanoma target cells grown with FCS do not show any enhanced cytotoxicity, suggesting no causal relationship of such enhanced sensitivity of “cell line” ‐derived target cells to “heterologous melanoma antigens” that might have been acquired by the target cells following the use of FCS in tissue culture. In controlled assays of in vitro CMC, lymphocytes from melanoma patients (14/44) exhibited selective cytotoxicity (destruction of only one target‐cell type) against the melanoma target cells, whereas only 3/97 control lymphocytes (other malignancies and normal donors) showed such melanoma‐selective cytotoxicity. This difference is statistically significant at p<0.001. Non‐selective cytotoxicity (destruction of two or more unrelated target cell types) was seen with lymphocytes from 9/44 melanoma patients, 13/51 patients with other malignancies and 8/46 normal donors. No correlation of selective cytotoxicity could be established with donors' age, sex, stage of disease, therapy or history of blood transfusion. Such a correlation may emerge as our series becomes larger. Despite the lack of any correlation between selective cytotoxicity and disease status, our study reaffirms the existence of selective cytotoxicity by melanoma patients' lymphocytes against melanoma target cells.