Andrea Anichini , Giuseppe Fossati , and Giorgio Parmiani

The analysis o f cell surface antigenic determinants associated with malignant t ransformation of cells in the melanocyte lineage has been carried out in recent years (1-4) with autologous sera as well as with mAb to H L A and melanomaassociated antigens (MAA). This approach has revealed the existence of a high degree of phenotypic heterogeneity not only among tumors derived from different patients (4), but also between autologous primary and metastatic lesions (5), among different metastases removed from the same patient (6) and even among clones isolated from the same cell line (7, 8). The differential expression of tumor-associated antigens (TAA) on different melanomas and in different cells of the same tumor has profound implications for the design of both diagnostic and therapeutic approaches with antibodies to MAA, since neoplastic clones not expressing the relevant antigen will not be detected or affected by these methods. The outcome of alternative therapeutic strategies, now under study in many laboratories, which are based on the infusion of autologous activated cytotoxic lymphocytes as ant i tumor reagents (9), might be equally influenced by the differential expression of the target structure recognized by the cytolytic effectors in a single melanoma. At the present time, however, no information is available concerning the heterogeneity of a single human tumor as determined by susceptibility to autologous CTL. To address this issue, we used cloned CTL, previously shown (10) to react against the autoiogous metastatic melanoma (Me28) to screen 31 clones derived from Me28. We looked for significant differences in the cytotoxic activity of the C T L tested against the clones of the tumor and the uncloned melanoma line.