Marrow Fibroblasts: A Requirement for CD44 and Adhesion of Multiple Myeloma Peripheral Blood B Cells to Bone

We have earlier described the presence of phenotypically unusual monoclonal B cells within the peripheral blood ofmultiple myeloma (MM) patients. To determine the biological properties of these B ceHs as corn pared to B cells from normal donors, we investigated the potential of CD19@MMbloodB cells to adhereto endothelialcell and bonemarrow (BM)-fibroblast rnonolayers. We find that 30—60%of freshly isolated CD19' MM blood B cells adhere to endothelialcell monolayers,and 50—80%adhere to BM fibroblast monolayers. The adhesion ofMM blood B cells to either monolayerwas not increasedby in vitroactivation, suggesting that these cells were activated in vivo. In contrast, fewer than 10%of CD19@B cells fromperipheralbloodof nonnaldonorsadhered. Function-blocking monoclonal antibodies (mAbs) were used to determine which adhesion receptors were involved in CD19@ MM blood B cell interaction with BM fibroblasts. mAbs against very late antigen 4, the @-integrin subunit, and CD44, but not mAbs against very late antigen 5 and j3@,inhibited adhesion 61, SO, and 30%, respectively. The lack of inhibition with mAbs against fi@ implicates aj3.@ but not aji@ in adhesion of CD19@MM blood B cells. To determine the a@fi@ligand that mediated MM blood B cell adhesion, mAbs against vascular cellular adhesion molecule 1 and fibronectin, as well as CS! and RGD peptides, were used as inhibitors. These were unable to reduce the adhesion of CDl9@ MM bloodB cells to BM fibroblasts,suggestingthat fibronectinand vascular cellular adhesion molecule 1 are not involved in adhesion. Also, adhesion of MM blood B cells to mucosal addressin cell adhesion molecule 1-tram fected Chinese hamster ovary cells was not enhanced compared to control transfected Chinese hamster ovary cells, suggesting that mucosal ad dressin cell adhesion molecule 1 was not promoting adhesion of these cells. These data implicate CD44:HA interactions, as well as a4fi@and an as yet unidentified ligand in the adhesion of in vivo activated MM blood B cell adhesion to BM flbroblasts. The adhesion properties of MM CD19@B cells distinguishes them from normal B cells. Although the malignant status ofthese cells is as yet undefined, their adhesion properties implicate MM blood B cells in migratory spread of the disease.