Tumorigenic conversion of xeroderma pigmentosum lymphoblastoid cells without karyotypic alteration

In order to examine the process of malignant transformation of human somatic cells, we studied the tumorigenic conversion of an Epstein-Barr-virus-immortalized lymphoblastoid cell line (LCL) derived from a patient with xeroderma pigmentosum (XP) complementation group A. Repeated irradiation of the XP cells, XP7NI, with UV-light and subsequent treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in the acquisition of tumorigenicity in athymic nude mice. The tumorigenicity of XP7NI cells was also induced by TPA treatment alone. The tumors formed in athymic mice were of B-cell lymphoma with characteristic histology, cell surface immunoglobulins and an antigen as detected by a B-cell-specific monoclonal antibody (MAb), CD20. The surface immunoglobulins and the HLA type of these tumor cells were identical with those of the parental cells. These malignantly transformed cells retained the same UV sensitivity, serum requirement, colony-forming ability in soft agar, and normal human karyotype as the parental cells. Unlike other tumorigenic lymphoblastoid cell lines, this XP lymphoblastoid cell line provides a unique case in that process(es) leading to tumorigenicity may be induced by UV and TPA without apparent karyotypic changes.