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Blood, 15 February 2008, Vol. 111, No. 4, pp. 2152-2154. Prepublished online as a Blood First Edition Paper on November 28, 2007; DOI 10.1182/blood-2007-10-116111.
IMMUNOBIOLOGY Levo- but not dextro-1-methyl tryptophan abrogates the IDO activity of human dendritic cells1 Department of General, Visceral and Transplant Surgery, University Hospital of Tubingen, Tubingen; 2 Institute for Cell Biology, Department of Immunology, Eberhard Karls University of Tubingen, Tubingen; 3 Institute of Clinical and Experimental Transfusion Medicine, Eberhard Karls University of Tubingen, Tubingen; and 4 Institute of Immunology, Department of Transplantation Immunology, University of Heidelberg, Heidelberg, Germany Clinical trials have been started with the aim of inducing tumor immunity by blocking the immunosuppressive action of indoleamine-2,3-dioxygenase (IDO) with the IDO2-inhibitor dextro-1-methyl-tryptophan (D-1MT). Here we show that human dendritic cells (DCs) express both IDO-1 and IDO-2, but that only IDO1 mediates tryptophan catabolism; furthermore, its activity is blocked by levo-1MT, whereas D-1MT is inefficient. Consequently, in humans any possible antitumor effects of D-1MT cannot be attributed to abrogation of IDO activity in DCs as described in this study.
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