Significance of VLA-4-VCAM-1 interaction and CD44 for transendothelial invasion in a bone marrow metastatic myeloma model

In previous work, we established the B9/BM1 syngeneic murine bone marrow me tastasis model. Interleukin (IL)-6-dependent, IL-1-producing B9/BM1 cells, which colonize the vertebral and femoral marrow after i.v. injection, show great similarity in cell surface phenotype to human myeloma cells, especial ly the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-1. Here we investigated the function of these adhesion molecules by binding and transe ndothelial invasion assays using a newly established bone marrow-derived en dothelial cell line (BMEC). A combination of monoclonal antibodies against CD44 and VLA-4 significantly inhibited the adherence of B9/BM1 cells to BME C and anti-CD44 mAb especially blocked B9/BM1 transendothelial invasion of unstimulated BMEC cells. Results of additional experiments, in which the ce lls were treated with anti-CD44 and hyaluronidase, demonstrated that the in teraction of CD44 molecules on B9/BM1 cells with hyaluronan on BMEC cells w as a critical factor in both adhesion and transendothelial invasion in this model. However, stimulation of BMEC with TNF alpha resulted in increased i nvasion by B9/BM1 cells, which was completely suppressed by anti-VCAM-1 mAb , implicating a significant role of this adhesion molecule in this process during inflammation.