CONFIRMATION OF RB GENE DEFECTS IN B-CLL CLONES AND EVIDENCE FOR VARIABLE PREDOMINANCE OF THE RB DEFECTIVE CELLS WITHIN THE CLL CLONE

In 70 B-CLL patients, deletion or translocation, at or near the retino blastoma (Rb) site, was detected in 20 by cytogenetic analysis. Purifi ed B cell clones from 13 of these B-CLL patients were isolated and stu died for Rb gene status, Rb mRNA and the Rb protein product. Southern blot analysis of the Rb site detected internal deletions (N = 1) or a single allele loss (N = 2) in five patients. Northern blots detected r educed Rb mRNA in four patients. Immunoblot of whole cell lysate revea led reduced levels of unphosphorylated Rb protein in six CLL patients. No CLL B cell clone contained phosphorylated Rb species. These molecu lar studies have confirmed the cytogenetic alteration of 13q12-14 site s in B-CLL cells. In addition, cytogenetic and molecular biologic anal ysis suggest heterogeneity in the B cell clone for Rb gene abnormality . B-CLL patients with abnormalities in both cytogenetic and Rb DNA/RNA analysis will have a dominance of B cells with an Rb abnormality (N = 5). In patients whose Rb defective CLL cells constitute only a minor subpopulation of the total B cell clone, only cytogenetic defects woul d likely be detected (N = 7).