Disappearance of a tumor-associated antigen in malignant melanoma after imidazole carboxamide therapy

Abstract

Tumor fluid from a patient with cystic malignant melanoma contained a homogeneous protein, which induced in vitro stimulation of autologous lymphocyte DNA synthesis. The protein is believed to be a soluble tumor-associated antigen. Following therapy with dimethyl triazeno imidazole carboxamide (DTIC) the tumor antigen disappeared. Post-treatment lymphocytes of this patient were incubated with pre- and post-treatment tumor fluid. In the latter case, they were shown to be unaffected, and in the former to have a reduction of stimulation. In addition, homologous pretreatment lymphocytes from other melanoma patients showed cross reaction to pretreatment tumor fluid from the index patient, but had marked reduction in responsiveness to tumor fluid removed during treatment. These studies suggest that the anticancer drug DTIC may inhibit the synthesis of tumor-associated antigens, as well as lymphocyte mediated immunosensitivity to them.