Immunophenotypic features of the tumor substrate of Waldenström’s macroglobulinemia

Background. Waldenström’s macroglobulinemia (WM) is a lymphoplasmacytic lymphoma with a heterogeneous tumor substrate. Methods for selection and characterizing WM tumor cells using multicolor flow cytometry vary in the literature. Since the choice of optimal gating strategy directly impacts diagnostic accuracy and tumor volume assessment, developing a unified approach is a pressing issue.

Aim. To develop an optimal gating strategy for separating the tumor substrate in WM patients before initiating specific therapy and to study the immunophenotypic characteristics of each compartment.

Materials and methods. The study included 60 patients (31 men and 29 women) with a median age of 61 years. Bone marrow was analyzed using multicolor flow cytometry. A panel of antibodies against CD19, CD20, CD22, CD27, CD38, CD45, CD138, immunoglobulin M, and the light chains of immunoglobulins κ and λ was used.

Results. A unique gating strategy was proposed in the study, including the separation of the B-cell component, plasma cells (PCs), and intermediate lymphoplasmacytic cells (LPCs). Tumor B cells were detected in the bone marrow sample of 60 patients (100 %), tumor PCs in 53 (88 %), and LPCs in 45 (75 %). In all cases, tumor B cells and PCs demonstrated monoclonal restriction by immunoglobulin light chains (κ/λ) and immunoglobulin M expression. Tumor B cells, compared to normal B cells, had lower expression of CD19, CD20, CD22, and CD27 antigens. PCs differed from normal B cells by a higher density of CD20, CD45, and immunoglobulin M heavy chain antigen expression, as well as lower expression of CD38 and CD138.

Conclusion. The three-component strategy proposed for research purposes allows for a detailed characterization of WM tumor clone heterogeneity. However, for routine clinical diagnosis, a two-component approach (B cells + PCs), based on the inclusion of LPCs in the PC-compartment, is sufficient. Despite the identified heterogeneity, in clinical practice, we recommend combining LPCs with PCs due to the similarity of their immunophenotypes and the lack of additional diagnostic value when analyzed separately. Multicolor flow cytometry is a valuable adjunctive diagnostic method for patients with suspected WM.