title: Anti-CD40 antibody binding modulates human multiple myeloma clonogenicity in vitro.
abstract: Ligand binding of the B-cell lineage antigen CD40 enhances growth and interleukin-6 (IL-6) secretion in human B cells (the CD40/IL-6 loop). IL-6 has an autocrine and paracrine role in human multiple myeloma (MM) cell growth. With the use of the CD40 monoclonal antibody (MoAb) G28-5, we examined CD40 expression and the effect of CD40 binding on MM clonogenic colony (MCC) formation to characterize the IL-6/CD40 loop activity in MM. CD40 was expressed on plasmacytoid cells in 21 of 28 plasma cell dyscrasia (PCD) bone marrow (BM) biopsies tested (10 of 14 MM, 2 of 2 Waldenstrom's macroglobulinemia [WM], 2 of 2 plasma cell leukemia [PCL], 6 of 8 monoclonal gammopathy of undetermined significance [MGUS], and 1 of 2 primary amyloidosis [AL]). G28-5 binding increased MCCs by 35% to 150% in 11 of 17 CD40+ PCD BM cultures, but did not affect MCC formation in CD40- specimens or normal BM colony forming units (CFU-GEMM, CFU-GM, BFU-E). Responsive cultures originated from BM of patients with MM (2 of 5 cases tested), WM (2 of 2), PCL (2 of 2), and MGUS (5 of 6). CD40-responsiveness was not significantly inhibited by the presence of an anti-IL-6 MoAb (2 of 2 MGUS cultures tested), and did not correlate with the capacity to respond to IL-6 stimulation (n = 17, P > .05) or a detectable level of endogenous IL-6 (n = 15, P > .05). Additional studies were performed with PCD cell lines to characterize the interrelationship of CD40 activation and IL-6 production. Fifty percent to greater than 95% of cells from the RPMI 8226 and ARH77 lines expressed CD40, whereas 6% of U266 cells were CD40+. For RPMI 8226, ARH-77, and U266 cells, the increased MCC formation after anti-CD40 stimulation was not affected by the presence of an anti-IL-6 neutralizing MoAb and was not accompanied by detectable IL-6 secretion. There was no apparent increase in IL-6 mRNA transcription following G28-5 treatment of U266 or RPMI 8226 cells. Our observations indicate that CD40 is expressed in a subset of human myeloma cells present in various PCDs. Cell-line studies suggest that the CD40+ myeloma cell may regulate MM clonogenic colony formation without activating the IL-6 pathway.
authors.affiliation: Cancer Immunology Research Laboratory, Charles A. Sammons Cancer Center, Baylor University Medical Center, Dallas, TX 75246.
authors.forename: A W
authors.initials: AW
authors.lastname: Tong
authors.forename: B Q
authors.initials: BQ
authors.lastname: Zhang
authors.forename: G
authors.initials: G
authors.lastname: Mues
authors.forename: M
authors.initials: M
authors.lastname: Solano
authors.forename: T
authors.initials: T
authors.lastname: Hanson
authors.forename: M J
authors.initials: MJ
authors.lastname: Stone
mesh_terms: D000937:Antigen-Antibody Reactions; D015703:Antigens, CD / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology*; D001853:Bone Marrow / Q000276:immunology / Q000473:pathology; D019013:CD40 Antigens; D002999:Clone Cells; D015870:Gene Expression; D006801:Humans; D015850:Interleukin-6 / Q000502:physiology; D009101:Multiple Myeloma / Q000276:immunology / Q000473:pathology*; D010265:Paraproteinemias / Q000276:immunology / Q000473:pathology*; D010950:Plasma Cells / Q000276:immunology / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D014407:Tumor Cells, Cultured
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D019013:CD40 Antigens; D015850:Interleukin-6; D012333:RNA, Messenger