MHC class II antigen and immunoglobulin expression in spontaneous phenotypic variants of the Burkitt's lymphoma cell line Namalwa.

Phenotypic variant sublines of the Burkitt's lymphoma cell line Namalwa were examined with cDNA probes for the different MHC class II beta chain genes and with monoclonal antibodies specific for the corresponding cell surface antigens (DP, DQ and DR antigens). Expression of MHC class II antigens in the Namalwa sublines (known as CSN/70, IPN/45, PNT and KN2) was compared with that of the B-lymphoblastoid cell line DEW1, which is identical to Namalwa in DR allotype (DR 2,4). There were markedly different levels of expression of MHC class II antigens among the cell lines: in DEW1 and the Namalwa KN2 subline DP, DQ and DR antigens were expressed on almost all the cells. On the PNT and IPN/45 sublines, DR antigens were expressed on all the cells, and DP and DQ antigens were expressed at detectable levels on only a proportion of cells. On CSN/70, there was weak expression of DR antigens on a minority of cells and no detectable expression of DP and DQ antigens. When examined with MHC class II-specific cDNAs, restriction fragment patterns of DNA were identical for all the cell lines, suggesting that they had structurally identical MHC class II genes. In the Namalwa cell lines the synthesis of Ig and the expression of MHC class II antigens were coordinately regulated.

Tumorigenicity of human lymphoblastoid cell lines, acquired during in vitro culture and associated with chromosome gains.

Tumorigenicity of human lymphoma and lymphoblastoid B-cell lines was assessed by their ability to form growing and transplantable masses on subcutaneous inoculation into neonatally thymectomized, Ara-C-protected, total-body-irradiated mice. By these criteria, 12 lines of known malignant origin were tumorigenic, 11 lymphoblastoid lines, tested after less than one year of in vitro growth, were non-tumorigenic and 8/18 long-established lymphoblastoid lines produced transplantable tumours. All of the long-established lines had acquired karyotypic changes on prolonged culture, the predominant characteristic being a gain of whole chromosomes or of major chromosome segments. None showed the classical 8:14 translocation associated with Burkitt's lymphoma. Comparisons with nontumorigenic precursors (recovered from liquid nitrogen storage) and with other non-tumorigenic but chromosomally abnormal, lymphoblastoid lines suggest that imbalance of the dosage of genes carried on chromosomes 7,8 and 9 may be important in determining the tumorigenic phenotype.