Vascular cell adhesion molecule‐1 expression by hematopoiesis‐supporting stromal cells is not essential for lymphoid or myeloid differentiation in vivo or in vitro

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Abstract
Binding of myeloid and lymphoid precursors to stromal cells in bone marrow has been suggested to be mediated through α4 integrins (α4) and vascular cell adhesion molecule-1 (VCAM-1) expressed on hematopoietic progenitors and stromal cells, respectively. It has not been shown, however, how essential the VCAM-1/α4 interaction is for hematopoiesis in vivo and whether or not other adhesion pathways can provide similar functional binding between stromal cells and hematopoietic progenitors. We addressed this issue by analyzing myeloid and lymphoid differentiation in vivo in mice with VCAM-1-null or -hypomorphic mutations and in vitro in long-term hematopoietic cultures with stromal cell clones from wild-type mice, which express or do not express VCAM-1. Mice bearing VCAM-1 mutations had no gross hematopoietic insufficiencies in the myeloid or lymphoid compartments and the distribution of myeloid progenitors between bone marrow and periphery was normal. In Dexter type long-term bone marrow cultures from mutant mice, the formation of supportive stromal cell layers and myeloid proliferation and differentiation were not affected by the absence of VCAM-1. Long-term maintenance and proliferation of clonable pre-B cells, cobblestone formation and differentiation to IgM-secreting, mature B cells was equally possible on VCAM-1+ and VCAM-1− stromal cell clones. We conclude from our data that VCAM-1 is not essential for the functional interaction between hematopoietic progenitors and stromal cells required for myeloid and B-lymphoid development in vivo or in vitro.