FCRL2 Expression Is Predictive of IgV_H Mutation Status and Clinical Progression in Chronic Lymphocytic Leukemia.

B cell chronic lymphocytic leukemia (CLL) is a heterogeneous malignancy of two subtypes that can be stratified according to the mutation status of the immunoglobulin heavy chain variable region gene (IgV_H). Because the clinical course of this disease differs dramatically between these subgroups, accurately identifying indolent patients (mutated-MT IgV_H) from aggressive ones (unmutated-UM IgV_H) is of increasing importance. CD38 and ZAP-70 expression are both considered useful prognostic markers in CLL and are utilized by most clinical laboratories. Although they are associated with Ig mutation status and predictive of clinical course, both proteins have some limitations and demonstrate variable discordance with IgV_H mutation status. Thus, the proper diagnostic use of these indicators and their optimal detection remains under investigation. The identification of additional diagnostic and prognostic markers would not only be helpful for subgrouping CLL patients and choosing appropriate treatment options, but could also be informative for understanding the cellular origins and biological defects underlying this lymphoproliferative disorder. Recent characterization of five human Fc receptor-like (FCRL1–5) molecules possessing tyrosine-based activating and/or inhibitory potential that are expressed by distinct B cell subpopulations, suggests they could be useful diagnostic, prognostic and/or therapeutic markers in B lineage malignancies. To determine their prognostic potential in CLL, FCRL1–5 surface expression was evaluated with a panel of specific monoclonal antibodies by flow cytometry and compared with currently established markers of prognosis including IgV_H mutation status, as well as CD38 surface expression, ZAP-70 cytoplasmic expression, and clinical parameters from 107 CLL cases. Our results demonstrate that FCRL1–3, and FCRL5 are expressed by CLL cells, but FCRL4 is not. Except for FCRL1, the expression of FCRL2, FCRL3, and FCRL5 was found at significantly higher levels on CLL cells than the polyclonal CD19⁺ B cell population in normal individuals. Univariate analysis revealed that all four FCRLs, as well as CD38 and ZAP-70, were significantly associated with IgV_H mutation status. However multivariate logistical analysis confirmed that only FCRL2 and ZAP-70 maintain predictive value. Furthermore, significant negative correlations between FCRL2 and ZAP-70 expression (r=0.60, P<0.0001), and FCRL2 and CD38 expression (r=0.49, P<0.0001) were identified. Strikingly, FCRL2 provided excellent sensitivity and specificity, demonstrating 94.4% concordance with IgV_H mutation compared to 77.6% for CD38 and 80.4% for ZAP-70. In a subset of patients for which clinical data were initially available, log-rank analysis revealed that similar to IgV_H mutation status, FCRL2 can predict disease progression; the median time to first therapy was 13 years for FCRL2 high expressers compared to 4 years for FCRL2 low individuals. Our data indicate that FCRL2 is a novel prognostic marker of IgV_H mutation status and clinical progression that may complement the clinical prognostic significance of CD38 and ZAP-70, and further improve therapeutic strategies for patients afflicted with CLL.