Role of plasma cells in Waldenström macroglobulinaemia.

Waldenström macroglobulinaemia (WM) is an indolent mature B cell lymphoma characterised by an infiltrate of heterogeneous B cells and hypersecretion of IgM. There are two distinct cellular populations that can be distinguished on morphology and immunophenotyping within the bone marrow. The predominant lymphoplasmacytic compartment arises at an earlier stage in ontogeny, and is responsible for the cytopenias noted during the symptomatic phase of the disease. This population is ably targeted by B cell immunodepletion. The smaller plasma cell compartment has been shown to be monotypic and to carry the MYD88L265P mutation noted in >90% of WM. Further, pathogenic IgM levels tend to correlate better with plasma cell burden as compared to lymphoplasmacytic cell burden within the bone marrow. B cell immunodepletion does not eradicate the plasma cell compartment resulting in persistent IgM levels and poor complete remission rates. In this review we discuss the different cellular compartments in WM and highlight evidence regarding the significance and impending function of the plasma cell compartment in WM. We suggest detection of plasma cells be incorporated into routine diagnostic algorithms, and highlight the need to trial incorporation of plasma cell depleting therapy into treatment algorithms to deepen responses and improve clinical outcomes.