A Novel Functional Role for Soluble CD27 in the Pathogenesis of Waldenstrom’s Macroglobulinemia.

The tumor necrosis factor (TNF) receptor family member, CD27, is a transmembrane co-stimulatory molecule present on primed T and B lymphocytes that also secrete a soluble form (sCD27). Recent evidence has suggested that interactions between CD27 and its TNF-like ligand, CD70, play a critical role in regulating B-cell activation and survival, though the detailed mechanism(s) by which this occurs remain unclear. Waldenstrom’s Macroglobulinemia (WM) represents a lymphoplasmacytic lymphoma characterized by a monoclonal IgM gammopathy and possesses a mast cell component that may contribute to its pathogenesis (Blood 104; 646a). Using ELISA assays, we observed that WM patients displayed significantly higher levels of sCD27 in their sera (median 7.45, range 0–19.42 U/ml) versus healthy donors (median 0, range 0–2.78 U/ml; p=2.5 x 10⁻⁷). CD27 was expressed in 7/7 patients using RT-PCR analysis, but was expressed on the cell surface of tumor cells in 5/12 patients using flow cytometric analysis. Conversely, CD70 expression was widely expressed on both tumor cells (6/6 patients) and mast cells (10/11 patients) using flow cytometric analysis. In order to define the functional role of sCD27 in WM, we cultured BCWM.1 (CD27⁻CD70⁺) WM cells, and LAD1 (CD27⁻CD70⁺) mast cells with sCD27 (0.1–50 ug/mL), and observed no effect on proliferation or induction of apoptosis. Culture of LAD1 cells with sCD27 did, however, result in marked upregulation of the TNF family ligands CD40L (CD154) and a proliferation induction ligand (APRIL), which previous work in our laboratory had implicated as mast cell proliferation and survival factors in WM. Taken together, these studies suggest a novel functional role for sCD27, and imply a pivotal role in the pathogenesis of WM.