The differential reactivity of benign and malignant nevomelanocytic lesions with mouse monoclonal antibody TNKH1

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Abstract
A mouse monoclonal antibody (TNKH1) which recognizes a marker of benign nevus cell nevus has been obtained for the first time. A375 human melanoma cells were induced to differentiate with n-butyric acid and used as immunogen. When frozen sections of nevomelanocytic lesions were tested with TNKH1 obtained by this method, 15 of 15 acquired nevus cell nevi, and two of two congenital melanocytic nevi showed strong reactivity; whereas five of five primary melanomas (three nodular, one lentigo maligna, and one subungual), as well as 10 of 10 metastatic melanomas were nonreactive. One superficial spreading melanoma showed residual TNKH1-positive nevus cells, and TNKH1-negative melanoma cells. Four of six dysplastic nevi, which would be precursors of some malignant melanomas, showed heterogeneity in staining intensity with TNKH1; indicating the initial change of malignant transformation. No reaction was found with normal melanocytes. Thus, the antigen that TNKH1 defines is present on benign nevus cells, and absent on malignant cells as well as normal melanocytes. TNKH1 could be a powerful tool not only for the diagnosis of malignant melanoma, but also for the assessment of the ontogeny of various melanomas.