Reduced Expression of Vascular Cell Adhesion Molecule-1 on Bone Marrow Stromal Cells Isolated from Marrow Transplant Recipients Correlates with a Reduced Capacity to Support Human B Lymphopoiesis in Vitro

A common sequela to allogeneic or autologous bone marrow transplantation (BMT) is a delay in the reconstitution of a functional B-cell immune response. Therefore, we examined whether the posttransplant BM microenvironment is deficient in supporting the proliferation and/or differentiation of B-cell precursors. BM stromal cell cultures were established from patients who received allogeneic or autologous BMT for acute lymphoblastic leukemia, Hodgkin's disease, or non-Hodgkin's lymphoma. These cultures were then compared with normal donor BM stromal cell cultures for expression of adhesion molecules and the capacity to support the adhesion and interleukin-7 (IL-7)-dependent growth of normal B-cell precursors. Analysis of BM stromal cell cultures established from 28 BMT recipients showed a significantly reduced expression of cell surface vascular cell adhesion molecule-1 (VCAM-1/CD106), compared with normal donor BM stromal cells. Transplant BM stromal cell CD106 expression was responsive to regulatory cytokines in a manner qualitatively comparable with normal donor BM stromal cells. The level of B-cell precursor adhesion to transplant BM stromal cells correlated with the level of CD106 expression. Of 19 evaluable transplant BM stromal cell cultures, eight exhibited a reduced capacity to support the growth of CD19⁺/light chain^- normal B-cell precursors. The capacity of transplant BM stromal cells to support B-cell precursor growth correlated with the level of CD106 expression, and the level of B-cell precursor adhesion. Our collective results may provide new mechanistic insight into why B-cell recovery is delayed post-BMT and underscore the importance of VCAM-1/CD106 in regulating B lymphopoiesis.