The usefulness of azathioprine (AZA), its metabolite 6-mercaptopurine (6-MP), cyclosporine, tacrolimus, and infliximab has been reported for the treatment of patients with ulcerative colitis (UC) refractory to conventional therapy. 1, 2 However, some patients with UC relapse, despite administration of these immunomodulators and biologics. Therefore, the management of patients with refractory UC is still challenging. Leukocyte removal therapy was reported to be effective for various disorders related to autoimmune responses. Recently, leukocytapheresis with a leukocyte removal filter (LCAP)(Cellsorba; Asahi Medical, Tokyo, Japan) is considered one of the promising treatments for UC patients, 3 although a possible mechanism of the therapeutic effect of LCAP on patients with UC has been unclear.

The CXCL12/CXCR4 chemokine axis has an important role in the migration of progenitors during embryonic development of the cardiovascular, hematopoietic, and central nervous system and several inflammatory diseases. 4, 5 Also, CXCR4 expression on T cells is induced by Th2 cytokine, which might be associated with the pathophysiology