Characterization of heterotypic adherence between transformed human lymphoblastic cells and marrow stromal cells: VCAM-1 is a ligand for one of the leukemia cell adhesion proteins.

Marrow stromal cells are important in normal myelopoiesis and support growth of leukemia/lymphoma (LL) cells in vitro. We have previously described the heterotypic adherence of a human B-lymphoblastic cell line (UTMB-460) to marrow stromal cells (MSC). We have extended these observations to a human T-lymphoblastic cell line (CEM) and characterized the heterotypic adherence of B- and T-lymphoblastic cell lines to human MSC. Electron microscopy demonstrated UTMB-460 cells were in very close apposition to the MSC, but no specific intercellular junctions were noted. Under the conditions employed, these MSC express extracellular fibronectin, collagen types I and IV, intracellular laminin, and vimentin, but no factor VIII-R antigen. In addition, the MSC had receptors for the lectin Ulex europaeus agglutinin I. UTMB-460 and CEM cells do not adhere to extracellular matrix (ECM) proteins secreted by the MSC, i.e., fibronectin, collagen types I, III, or IV, or laminin. Monoclonal antibodies (MoAbs) against CD11a, CD11b, CD18, and CD54 and a polyclonal anti-human fibronectin antibody do not inhibit attachment of either B- or T-lymphoblastic cells to MSC. Peptides GRGES and GRGDS did not inhibit adherence of UTMB-460 and CEM cells to MSC. In contrast, the anti-vascular cell adhesion molecule (VCAM)-1 MoAb (4b9) caused significant inhibition (p < 0.01) of the adherence of both UTMB-460 and CEM cells to normal human MSC monolayers. These data suggest: (1) that MSC to which lymphoblastic cells adhere are specialized mesenchymal cells; (2) that the membrane interactions between T- and B-lymphoblastic cells and MSC involve close apposition of cell membranes of MSC and the lymphoblastic cells; (3) that the heterotypic adherence between B- and T-lymphoblastic cell lines (UTMB-460 and CEM) and MSC does not involve the RGD recognition sequence of the integrin family, the B2 leukocyte integrins, CD44, LAM-1, or the ECM proteins examined; and (4) that VCAM-1 may at least be partially responsible for heterotypic adherence between human MSC and B- and T-lymphoblastic cells.