A paradoxical pattern of indoleamine 2,3-dioxygenase expression in the colon tissues of patients with acute graft-versus-host disease.

Indoleamine 2,3-dioxygenase (IDO) is a rate-limiting enzyme for tryptophan catabolism that plays an important role in the induction of immune tolerance. It is induced in the colon and exerts its effects there, regulating T-cell proliferation and survival. To address the role of IDO in acute graft-versus-host disease (AGVHD) after human allogeneic hematopoietic stem cell transplantation, we analyzed the relationship between IDO expression in colon tissues and clinical outcomes among 41 AGVHD patients who were diagnosed as gut AGVHD by a colon mucosal biopsy within 100 days posttransplantation. By in situ immunohistochemical analyses, IDO expression was measured in colon mucosal mononuclear cells (MNCs) and endothelial cells (ECs) in GVHD areas. High IDO expression in MNCs and low IDO expression in ECs had a trend toward a lower nonrelapse mortality (p = 0.157 and p = 0.062, respectively). Multivariate analysis showed that high MNC combined with low EC IDO expression (p = 0.046), as well as low disease risk (p = 0.012), are associated with lower nonrelapse mortality. Paradoxical upregulation of IDO expression in colon MNCs and ECs may represent a new predictive factor for prognosis in gut AGVHD after human allogeneic hematopoietic stem cell transplantation.