VLA‐4 and VCAM‐1 are the principal adhesion molecules involved in the interaction between blast colony‐forming cells and bone marrow stromal cells

Summary. The molecular basis and functional significance of interactions between haemopoietic progenitor cells and the stromal microenvironment is still poorly understood. Here we investigated a broad panel of surface adhesion molecules for their involvement. For this purpose, the colony‐forming capacity of stroma‐adherent Bl‐CFC, BFU‐E and GM‐CFC was studied. Both mononuclear bone marrow cells (BMC) and bone marrow‐derived stromal cells (BMSC) express a wide variety of adhesion molecules. However, only antibodies against β1‐, α4‐integrin (both chains of the very late activation antigen‐4 (VLA‐4)) and vascular cell adhesion molecule (VCAM‐1) inhibited colony formation from stroma‐adherent Bl‐CFC by 50% or more. Antibodies against a panel of other adhesion molecules, including the α5‐integrin chain, were without effect. Subsequent pretreatment experiments revealed that VLA‐4 on progenitors interacted with stromal VCAM‐1. The inhibitory antibodies did not interfere with the clonogenic capacity of but with adhesion of BFU‐E and GM‐CFC. Whether the inhibitory antibodies act similarly on progenitors which depend on BMSC for growth and/or differentiation, such as Bl‐CFC, remains to be determined.