Excess bone marrow mast cells constitutively express CD154 (CD40 ligand) in Waldenstrom's macroglobulinemia and may support tumor cell growth through CD154/CD40 pathway

Abstract

6555 Background: Excess mast cells (MC) have been described in Waldenstrom's macroglobulinemia (WM), though the frequency of detection of MC and their role in the pathogenesis of WM remains to be clarified. Methods: BM biopsies of 188 patients diagnosed with an IgM monoclonal gammopathy at our institution were reviewed. Excess MC were observed in 123/171 (71.9%) cases of WM, but not in IgM MGUS (n=14), IgM myeloma (n=3), or in 5 healthy donors. To determine if WM patient MC were activated and expressed ligands which could support the growth of WM cells, we used multicolor flow cytometry, immunohistochemistry, and/or RT-PCR to examine BM MC (CD117+ FceRI+) for expression of CD154 (CD40 ligand) and CD153 (CD30 ligand). BM LPC were also evaluated for expression of CD30 and CD40, the signaling receptors for CD154 and CD153. BM LPC proliferation by CD40 stimulation was also evaluated by 3H-thymidine uptake. The secretion of cytokines which could support the growth and survival of MC was also evaluated by ELISA. Results: CD154 and CD153 were expressed on BM MC from 14/15 (93.3%) and 6/6 (100%) patients with WM, respectively, but not on normal donor BM MC. Immunohistochemistry and/or RT-PCR analysis further confirmed expression of CD154 and CD153 on WM MC, but not normal donor MC. Bright CD40 expression was observed on LPC in most patients, whereas CD30 was weakly positive in 3/12 patients. Given the above, we next evaluated purified BM LPC for growth induction by CD40 stimulation, and demonstrated dose dependent uptake of 3H-thymidine. Lastly, in an evaluation of mast cell growth factors, we observed elevated levels of IL-3, but not IL-4, IL-5, IL-6, IL-9, IL-13, IL-15 and SCF in patients with WM (n=41) versus healthy donors (n=20) (p=0.01). Conclusions: The results suggest that MC may play a central role in the growth of WM tumor cells through the CD154/CD40 pathway. Moreover, WM tumor cells may provide support for MC growth and survival by secretion of IL-3. These data provide the rationale for targeting MC-WM tumor cells interactions in the treatment of WM. No significant financial relationships to disclose.