Constitutive expression of IL-12Rβ2 on human multiple myeloma cells delineates a novel therapeutic target

The interleukin-12 (IL-12) receptor (R) B2 gene acts as tumor suppressor in human acute and chronic B-cell leukemias/ lymphomas and IL-12rb2-deficient mice develop spontaneously localized plasmacytomas. With this background, we investigated the role of IL-12802 in multiple myeloma (MM) pathogenesis. Here we show the following: (1) IL-128[32 was expressed in primary MM cells but downregulated compared with normal polyclonal plasmablastic cells and plasma cells (PCs). IL-6 dampened IL-12R[32 expression on polyclonal plasmablastic cells and MM cells. (2) IL-12 reduced the proangiogenic activity of primary MM cells in vitro and decreased significantly (P =.001) the tumorigenicity of the NCIH929 cell line in SCID/NOD mice by inhibiting cell proliferation and angiogenesis. The latter phenomenon was found to depend on abolished expression of a wide panel of proangiogenic genes and upregulated expression of the antiangio- genic genes IFN-y, IFN-a, platelet factor-4, and TIMP-2. Inhibition of the angiogenic potential of primary MM cells was related to down-regulated expression of the proangiogenic genes CCL11, vascular endothelial-cadherin, CD13, and AKT and to up-regulation of an IFN-yrelated antiangiogenic pathway. Thus, IL-128(32 directly restrains MM cell growth, and targeting of IL-12 to tumor cells holds promise as new therapeutic strategy.