Angiogenesis in multiple myeloma: correlation between in vitro endothelial colonies growth (CFU-En) and clinical–biological features

Mouse models and studies performed on fixed bone marrow (BM) specimens obtained from patients with multiple myeloma (MM) suggest that plasma cell growth is dependent on endothelial cell (EC) proliferation within the BM microenvironment. In order to assess whether EC overgrowth in MM reflects a spontaneous in vitro angiogenesis, BM mononucleated cells from 13 untreated (UT) MM, 20 treated (11 with melphalan and nine with DAV schedule) MM, eight patients with monoclonal gammopathy of uncertain significance (MGUS) and eight controls were seeded in an unselective medium to assess EC proliferation. Furthermore, the influence of IL6 on the EC growth was investigated. Endothelial colonies (CFU-En) appeared as small clusters, formed by at least 100 slightly elongated and sometimes bi-nucleated cells expressing factor VIII, CD31 and CD105 (endoglin). The CFU-En mean number/106 BM mononucleated cells in untreated MM samples (2.07 s.d. ± 1.3) was significantly higher than in normal BM (0.28 ± 0.48), while no difference was seen between normal BM and MGUS (0.28 ± 0.54). Interestingly, the mean number of CFU-En in the DAV group (1.88 ± 1.6) did not differ from the UT, while it was found to be lower in the melphalan group (0.31 ± 0.63). The addition of anti-IL6 monoclonal antibody induced a reduction of both the plasma cells in the supernatant and the CFU-En number. This study describes a rapid and feasible assay providing support for the association between EC and plasma cells further suggesting that the in vitro angiogenesis process may parallel that observed in vivo.