Establishment of a Waldenstrom’s Macroglobulinemia Cell Line (BCWM.1) with Productive In Vivo Engraftment in SCID-hu Mice.

Waldenstrom’s Macroglobulinemia (WM) is incurable B-cell malignancy characterized by the infiltration of the bone marrow infiltration with lymphoplasmacytic cells (LPC) and the presence of an IgM monoclonal gammopathy. A significant impairment in understanding the biology and advancing therapeutics for WM has been the lack of a representative cell line and animal model. We therefore report on work accomplished in our laboratories in establishing the BWMC.1 cell line, which was derived from long term culture of CD19⁺ selected lymphoplasmacytic cells isolated from the bone marrow (BM) aspirate of a previously untreated 55-year-old female patient with IgMk secreting WM. BCWM.1 cells morphologically resembled LPC and had prominent nucleoli and ample cytoplasm by Wright-Giemsa staining, and were propagated in RPMI 1640 medium supplemented with 10% FBS. Phenotypic characterization by flow cytometric analysis demonstrated typical WM LPC characteristics: CD5⁻, CD10⁻, CD19⁺, CD20⁺, CD23⁺, CD27⁻, CD38⁺, CD138⁺, CD40⁺, CD52⁺, CD70⁺, CD117⁺, cIgM⁺, cIgG⁻, cIgA⁻, ck⁺, cl⁻. BCWM.1 cells also expressed the survival proteins APRIL and B-Lymphocyte Stimulator (B-LYS), and their receptors TACI, BCMA and BAFF-R. ELISA studies demonstrated secretion of IgMk in culture. Karyotypic and M-FISH studies did not demonstrate cytogenetic abnormalities. Molecular analysis of BCWM.1 cells confirmed clonality by determination of IgH rearrangements through FR1c/JHc amplification of genomic DNA. BCWM.1 cells were positive for LMP1 expression by histochemical staining and PCR analysis. Importantly, inoculation of BCWM.1 cells directly into the human BM milieu of SCID-hu mice resulted in engraftment of tumor cells and serum detection of human IgMk in four of five SCID-hu mice within two weeks. In contrast, subcutaneous injection of BCWM.1 cells in SCID mice did not lead to engraftment, suggesting a role for the human BM microenvironment in supporting the expansion of BCWM.1 cells. These studies therefore support the use of BCWM.1 cells as an appropriate model for the study of WM, which in conjunction with the SCID-hu mouse model may be used as a convenient model for studies focused on both the pathogenesis and development of targeted therapies for WM.