Adhesion of synchronized human hematopoietic progenitor cells to fibronectin and vascular cell adhesion molecule-1 fluctuates reversibly during cell cycle transit in ex vivo culture

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Abstract
Ex vivo expansion of hematopoietic stem/progenitor cells may result in defective engraftment. Human cord blood CD34+ progenitor cells were synchronized and assayed for adhesion and migration onto fibronectin (Fn) and vascular cell adhesion molecule-1 (VCAM-1) at different stages of a first cell cycle executed ex vivo. During S phase transit, adhesion to Fn was transiently increased while binding to VCAM-1 was reversibly decreased, after which adhesion to both ligands returned to baseline levels with cell cycle completion. Transmigration across Fn and VCAM-1 decreased irreversibly during S phase progression. The function of α4 and α5 integrins was assessed with specific neutralizing antibodies. In uncultured CD34+ cells and long-term culture-initiating cells (LTC-ICs), both adhesion and migration on Fn were inhibited by anti-α4 but not by anti-α5 antibodies. In mitotically activated CD34+ cells and LTC-ICs, adhesion and migration on Fn were mainly dependent on α5 integrin and to a lesser extent on α4 integrin. Changes in integrin function were not dependent on parallel modulation of integrin expression. In conclusion, Fn and VCAM-1 binding of progenitor cells fluctuates reversibly during cell cycle transit ex vivo. In addition, our data show that mitogenic activation induces a shift from a dominant α4 to a preferential α5 integrin–dependent interaction with Fn.

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