HETEROTYPIC ADHERENCE BETWEEN HUMAN B-LYMPHOBLASTIC AND PRE-B-LYMPHOBLASTIC CELLS AND MARROW STROMAL CELLS IS A BIPHASIC EVENT - INTEGRIN VERY LATE ANTIGEN-4-ALPHA MEDIATES ONLY THE EARLY PHASE OF THE HETEROTYPIC ADHESION

Heterotypic adherence between marrow stromal cells (MSC) and lymphobla stic cells is essential for normal lymphopoiesis and malignant lymphob lastic development. However, the detailed molecular mechanisms by whic h this heterotypic adherence occurs are poorly understood. The cell-ce ll interactions between a B-lymphoblastic cell line (UTMB-460) and a p re-B-cell line (NALM-6) with MSC were chosen as models to investigate potential mechanisms and adhesion molecules involved in the apposition between normal and malignant lymphoblastic cells and MSC. A parallel- flow detachment assay (PFDA) and a Cr-51 detachment assay, coupled wit h monoclonal antibody (MoAb) blocking experiments, were used to quanti fy the attachment of lymphoblastic cells to confluent monolayers of MS C. The apposition between MSC and B-lymphoblastic cells (UTMB-460 cell s) was investigated for variable time periods, ranging from 1 minute t o 4 hours. Results from the temporal study suggest that the heterotypi c adherence of the B-lymphoblastic cells to MSC is a biphasic event an d the interactions occur rapidly (less than or equal to 1 minute) afte r the two cells come into contact. More specifically, the early phase of adherence (less than or equal to 15 minutes) solely involves very l ate antigen-4 alpha (VLA-4 alpha)/vascular cell adhesion molecule 1 (V CAM-1) interactions, as evidenced by the nearly complete inhibition (9 3%) of UTMB-460 cell adherence in the presence of anti-VLA-4 alpha. Th e late phase (greater than or equal to 30 minutes) proceeds despite th e continuous presence of anti-VLA-4 alpha. In addition, the late-phase adherence is not affected by MoAbs to LFA-1, CD44, VCAM-1, E-selectin , or L-selectin, which suggests the possible involvement of other adhe sion molecules. Adherence of pre-B-lymphoblastic cells (NALM- 6) to MS C is also biphasic. Integrin VLA-4 is again a major player in the earl y phase of pre-B-lymphoblastic cell/MSC interactions. The early phase of adherence may be important in homing of the malignant lymphoblastic cells to the MSC and the late phase in retention of malignant lymphob lastic cells in the bone marrow. (C) 1995 by The American Society of H ematology.