Mobilization of bone marrow cells by leukocytapheresis in patients with ulcerative colitis

While several trials have suggested that leukocytapheresis by filtration can benefit patients with active ulcerative colitis (UC), mechanisms underlying these benefits are largely unknown. We studied how leukocytapheresis mobilizes bone marrow cells into the peripheral circulation in patients with active UC. Leukocytapheresis transiently reduced peripheral leukocytes, followed by an overshoot increase with emergence of immature leukocytes. The numbers of colonies and CD34(+) cells were comparable between UC patients and normal controls. Shortly after leukocytapheresis, the numbers of both colonies and CD34(+) cells increased significantly in UC patients (P < 0.0001 and P = 0.0372, respectively). This was not associated with changes in the concentration of circulating cytokines or epinephrine. These results indicate that leukocytapheresis mobilizes bone marrow cells into the circulation. This cell replacement may partly explain the therapeutic benefit in UC. The functional role of the mobilized bone marrow cells in affected intestine remains to be characterized.