Relative expression of IDO in biopsies from lower gastrointestinal tract as a function of GVHD grade at the time of biopsy. Relative expression of IDO (± SE) as assessed by quantitative RT-PCR is shown. Differences between patients without GVHD and GVHD grade 1 or 2 as well as severe GVHD were significant (P = .03).