ADHESIVE INTERACTIONS BETWEEN TUMOR-CELLS AND BONE-MARROW STROMAL ELEMENTS IN HUMAN MULTIPLE-MYELOMA

Long-term bone marrow cultures (LTBMC) were established from marrow sa mples obtained from 6 myeloma patients and 5 healthy donors and were e xamined by in situ immunogold-silver staining. During the culture peri od, the established stroma in myeloma LTBMC revealed a lower level of confluency compared to the normal LTBMC. In addition, an increasing pr oportion of macrophages and osteoclasts was observed in the myeloma st roma throughout the culture period. Moreover, plasma cells were detect able by wk 8, mostly organized in small clusters. They strongly expres sed VLA-4 (6/6), H-CAM (6/6), ICAM-1 (6/6) and N-CAM (3/6). In most ca ses, a weak expression of the other members of beta 1-integrins was ob served. 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 expr ession could not be detected. By comparing the adhesion molecule profi le of the stromal cells in myeloma cultures with normal bone marrow (B M) cultures, no particular defects could be observed. The stroma displ ayed 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, U 266, RPMI 8226 and JJN3, with a representative phenotype, were used to study the adhesive interactions of myeloma cells with the BM microenv ironnent. All the myeloma cell lines bound strongly to the marrow cell layers and also showed a high binding to purified fibronectin (FN). H owever, the adhesion of the cell lines to intact stroma could not be s ignificantly inhibited by anti-FN receptors antibodies. Nor could it b e prevented when the latter were combined with anti-H-CAM, V-CAM and I CAM-1 antibodies, as tested in the JJN3 cell line. This implies that o ther unknown mechanisms contribute to the myeloma cell binding.