Adhesive interactions between tumour cells and bone marrow stromal elements in human multiple myeloma

Long-term bone marrow cultures (LTBMC) were established from marrow samples obtained from 6 myeloma patients and 5 healthy donors and were examined by in situ immunogold-silver staining. During the culture period, the established stroma in myeloma LTBMC revealed a lower level of confluency compared to the normal LTBMC. In addition, an increasing proportion of macrophages and osteoclasts was observed in the myeloma stroma throughout the culture period. Moreover, plasma cells were detectable by wk 8, mostly organized in small clusters. They strongly expressed VLA-4 (6/6), H-CAM (6/6), ICAM-1 (6/6) and N-CAM (3/6). In most cases, a weak expression of the other members of beta 1-integrins was observed. The expression of beta 2-integrins was always absent. Stromal fibroblasts were found to be weakly positive for VLA-2, VLA-3 and VLA-5 and showed strong expression of VCAM-1, H-CAM and ICAM-1. N-CAM expression could not be detected. By comparing the adhesion molecule profile of the stromal cells in myeloma cultures with normal bone marrow (BM) cultures, no particular defects could be observed. The stroma displayed most of the potential ligands which could interact with adhesion molecules detected on the myeloma cells. Among these ligands we could find fibronectin and VCAM-1 for VLA-4, collagen I for VLA-2 and VLA-3 and laminin for VLA-2, 3 and 6. Four myeloma cell lines, i.e. OPM-1, U266, RPMI 8226 and JJN3, with a representative phenotype, were used to study the adhesive interactions of myeloma cells with the BM microenvironnent. All the myeloma cell lines bound strongly to the marrow cell layers and also showed a high binding to purified fibronectin (FN). However, the adhesion of the cell lines to intact stroma could not be significantly inhibited by anti-FN receptors antibodies. Nor could it be prevented when the latter were combined with anti-H-CAM, V-CAM and ICAM-1 antibodies, as tested in the JJN3 cell line. This implies that other unknown mechanisms contribute to the myeloma cell binding.