Chromosome abnormalities of leukaemic B lymphocytes in chronic lymphocytic leukaemia

Abstract

Chromosome analyses have revealed abnormalities in many cases of lymphoma, non-lymphocytic leukaemia and acute lymphoblastic leukaemia. Most studies on chronic lymphocytic leukaemia (CCL), however, have shown normal karyotypes^1–4 although chromosomal abnormalities have been reported^5,6 . In most of these studies specific surface marker analyses on leukaemic lymphocytes have not been carried out. It has been difficult to establish whether the metaphases seen in the majority of the CLL studies were from normal or from leukaemic cells. Recently, in one of our laboratories special interest has centred on cases of CLL with monoclonal serum protein bands; in two such cases with immunoglobulin M (IgM) bands, it was demonstrated with idiotypic antisera against the serum IgM band that the leukaemic lymphocytes were the precursors of plasma cells responsible for the monoclonal serum IgM^7,8. In addition, the leukaemic lymphocytes of these patients could be stimulated in vitro to divide and to differentiate to plasma cells⁸. Epstein–Barr virus (EBV)-transformed lymphoblastoid cell lines were obtained from the two patients. With the idiotypic determinants as leukaemia specific markers, certain of these lines were shown to be derived from leukaemic cells⁹. Thus, rapidly proliferating populations of cells, which could be identified with certainty as being of CLL origin, were available for chromosome analysis. In the present study, conventional G- and Q-banding techniques for karyotypic analysis were carried out on the leukaemic lymphocytes induced to divide in vitro and on the cells of the leukaemic lymphoblastoid lines. Aneuploid karyotypes were found in the leukaemic B cells of both patients.