No abstract

B-cell chronic lymphocytic leukemia (B-CLL) has long been considered a disease of "accumulation," due to a presumed defect in programmed cell death. Recent data, however, suggest that B-CLL cells are born at a normal to an accelerated rate, with the rate of proliferation varying among patients. In addition, differences in birth rates, activation state, and inducibility appear to exist among subpopulations of cells within individual leukemic clones. The extent to which such dissimilarities influence clinical course and outcome is still unclear. This review examines the evidence supporting the existence of a proliferative compartment in B-CLL and the role that proliferating cells might play in the progression and evolution of this disease.

Cellular immunophenotypic studies were performed on a cohort of randomly selected IgM+ B-chronic lymphocytic leukemia (B-CLL) cases for which Ig VH and VL gene sequences were available. The cases were categorized based on V gene mutation status and CD38 expression and analyzed for treatment history and survival. The B-CLL cases could be divided into 2 groups. Those patients with unmutated V genes displayed higher percentages of CD38+ B-CLL cells (≥30%) than those with mutated V genes that had lower percentages of CD38+ cells (<30%). Patients in both the unmutated and the ≥30% CD38+ groups responded poorly to continuous multiregimen chemotherapy (including fludarabine) and had shorter survival. In contrast, the mutated and the <30% CD38+ groups required minimal or no chemotherapy and had prolonged survival. These observations were true also for those patients who stratified to the Rai intermediate risk category. In the mutated and the <30% CD38+ groups, males and females were virtually equally distributed, whereas in the unmutated and the ≥30% CD38+ groups, a marked male predominance was found. Thus, Ig V gene mutation status and the percentages of CD38+B-CLL cells appear to be accurate predictors of clinical outcome in B-CLL patients. These parameters, especially CD38 expression that can be analyzed conveniently in most clinical laboratories, should be valuable adjuncts to the present staging systems for predicting the clinical course in individual B-CLL cases. Future evaluations of new therapeutic strategies and drugs should take into account the different natural histories of patients categorized in these manners.

Cellular immunophenotypic studies were performed on a cohort of randomly selected IgM+ B-chronic lymphocytic leukemia (B-CLL) cases for which Ig VH and VL gene sequences were available. The cases were categorized based on V gene mutation status and CD38 expression and analyzed for treatment history and survival. The B-CLL cases could be divided into 2 groups. Those patients with unmutated V genes displayed higher percentages of CD38+ B-CLL cells (≥30%) than those with mutated V genes that had lower percentages of CD38+ cells (&lt;30%). Patients in both the unmutated and the ≥30% CD38+ groups responded poorly to continuous multiregimen chemotherapy (including fludarabine) and had shorter survival. In contrast, the mutated and the &lt;30% CD38+ groups required minimal or no chemotherapy and had prolonged survival. These observations were true also for those patients who stratified to the Rai intermediate risk category. In the mutated and the &lt;30% CD38+ groups, males and females were virtually equally distributed, whereas in the unmutated and the ≥30% CD38+ groups, a marked male predominance was found. Thus, Ig V gene mutation status and the percentages of CD38+B-CLL cells appear to be accurate predictors of clinical outcome in B-CLL patients. These parameters, especially CD38 expression that can be analyzed conveniently in most clinical laboratories, should be valuable adjuncts to the present staging systems for predicting the clinical course in individual B-CLL cases. Future evaluations of new therapeutic strategies and drugs should take into account the different natural histories of patients categorized in these manners.

B-cell chronic lymphocytic leukemia (B-CLL) has long been considered a disease of "accumulation," due to a presumed defect in programmed cell death. Recent data, however, suggest that B-CLL cells are born at a normal to an accelerated rate, with the rate of proliferation varying among patients. In addition, differences in birth rates, activation state, and inducibility appear to exist among subpopulations of cells within individual leukemic clones. The extent to which such dissimilarities influence clinical course and outcome is still unclear. This review examines the evidence supporting the existence of a proliferative compartment in B-CLL and the role that proliferating cells might play in the progression and evolution of this disease.

Previous studies suggest that the diversity of the expressed variable (V) region repertoire of the immunoglobulin (Ig)H chain of B-CLL cells is restricted. Although limited examples of marked constraint in the primary structure of the H and L chain V regions exist, the possibility that this level of restriction is a general principle in this disease has not been accepted. This report describes five sets of patients, mostly with unmutated or minimally mutated IgV genes, with strikingly similar B cell antigen receptors (BCRs) arising from the use of common H and L chain V region gene segments that share CDR3 structural features such as length, amino acid composition, and unique amino acid residues at recombination junctions. Thus, a much more striking degree of structural restriction of the entire BCR and a much higher frequency of receptor sharing exists among patients than appreciated previously. The data imply that either a significant fraction of B-CLL cells was selected by a limited set of antigenic epitopes at some point in their development and/or that they derive from a distinct B cell subpopulation with limited Ig V region diversity. These shared, stereotyped Ig molecules may be valuable probes for antigen identification and important targets for cross-reactive idiotypic therapy.

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

Due to its relatively slow clinical progression, B cell chronic lymphocytic leukemia (B-CLL) is classically described as a disease of accumulation rather than proliferation. However, evidence for various forms of clonal evolution suggests that B-CLL clones may be more dynamic than previously assumed. We used a nonradioactive, stable isotopic labeling method to measure B-CLL cell kinetics in vivo. Nineteen patients drank an aliquot of deuterated water ( 2 H 2 O) daily for 84 days, and 2 H incorporation into the deoxyribose moiety of DNA of newly divided B-CLL cells was measured by gas chromatography/mass spectrometry, during and after the labeling period. Birth rates were calculated from the kinetic profiles. Death rates were defined as the difference between calculated birth and growth rates. These analyses demonstrated that the leukemic cells of each patient had definable and often substantial birth rates, varying from 0.1% to greater than 1.0% of the entire clone per day. Those patients with birth rates greater than 0.35% per day were much more likely to exhibit active or to develop progressive disease than those with lower birth rates Thus, B-CLL is not a static disease that results simply from accumulation of long-lived lymphocytes. Rather, it is a dynamic process composed also of cells that proliferate and die, often at appreciable levels. The extent to which this turnover occurs has not been previously appreciated. A correlation between birth rates and disease activity and progression appears to exist, which may help identify patients at risk for worsening disease in advance of clinical deterioration.