ANALYSIS OF REARRANGED IMMUNOGLOBULIN GENES INDICATING A PROCESS OF CLONAL EVOLUTION IN CHRONIC LYMPHOCYTIC-LEUKEMIA

Chronic lymphocytic leukaemia (CLL) is known to be a stable monoclonal neoplasm. In contrast to early studies demonstrating no more than two hybridizing immunoglobulin heavy chain bands corresponding to the two expected alleles, we have demonstrated an unexpected multiband patter n when the HindIII-digested DNA samples from 38 CLL patients were anal ysed by Southern blot hybridization using JH and Cu gene probes. In or der to characterize the genetic basis for the multiband pattern, we mo lecularly cloned the immunoglobulin heavy chain genes of one of the pa tients whose leukaemic DNA sample demonstrated three hybridizing JH ba nds and a loss of the germline band. The cloned rearranged immunoglobu lin genes could be divided, based on the restriction mapping and the h ybridization with the various probes, into two basic patterns represen ting two alleles. In one of the cloned rearranged immunoglobulin genes a secondary rearrangement occurred that resulted in the addition of 3 00 base-pair long sequence into the switch region, and the creation of a HindIII restriction site. The results of the study suggest that clo nal evolution occurs in some CLL, and that many of these neoplasms are indeed oligoclonal due to the accumulation of secondary genetic chang es.