Immunophenotypic analysis of Waldenstrom's macroglobulinemia

Abstract

Immunophenotyping has become an essential tool for diagnosis of hematological malignancies. By contrast, for diagnosis of Waldenstrom's macroglobulinemia (WM) immunophenotyping is used only occasionally. From 150 patients with a IgM monoclonal gammopathy we have selected 60 cases with (1) morphological lymphoplasmocytoid bone marrow (BM) infiltration (>20%); (2) IgM paraprotein (>10g/L); and (3) absence of features of other lymphoma types. Immunophenotypic analysis was based on the use of the triple or quadruple monoclonal antibody (MoAb) combinations. To increase the sensitivity of the analysis of antigen expression, selected CD19(+)CD20(+) B cells were targeted. We have also explored the antigenic characteristics of both the plasma cell (PC) and mast cell (MC) compartments present in the BM from 15 WM patients. Clonal WM lymphocytes were characterized by the constant expression of pan-B markers (CD19, CD20, CD22, CD24) together with sIg, predominantly kappa (5:1, kappa:lambda ratio). A high proportion of cases (75%) were positive for FMC7 and CD25, but in contrast to hairy cell leukemia (HCL), these lymphocytes were always negative for CD103 and CD11c. CD10 antigen was also absent in all WM patients and less than one fifth of patients were positive for CD5 and CD23, while CD27, CD45RA, and BCL-2 were present in most malignant cells. In two cases, the coexistence of two different clones of B lymphocytes was identified, and in eight additional cases, intraclonal phenotypic heterogeneity was observed. As far as PCs are concerned, in most patients (85%) the number of PCs was within the normal range (median, 0.36%). The antigenic profile of these PCs differed from that observed in normal and myelomatous PC (CD38(++)CD19(++/-)CD56(-)CD45(++)CD20(+)). In three cases, PCs showed aberrant expression for CD5, CD22, or FMC7. Finally, the number of mast cells was significantly higher (0.058 +/- 0.13) as compared to normal BM (0.019 +/- 0.02) (P <.01), although they were immunophenotypically normal (CD117(+)CD2(-)CD25(-)).