14 . Brandacher G , Perathoner A , Ladurner R , Schneeberger S , Obrist P , Winkler C , et al . Prognostic value of indoleamine 2 , 3 - dioxygenase expression in colorectal cancer : effect on tumor - infiltrating T cells . Clin Cancer Res 2006 ; 12 ( 4 ) : 1144 - 51 doi 10 . 1158 / 1078 - 0432 . CCR - 05 - 1966 .