On the other hand, mice that did not receive donor leukocyte infusion did not express IDO1 and IFN‐γ, implying that IDO inhibition can be advantageous for anti‐tumour therapy when used in conjunction with reduced‐intensity allogeneic haematopoietic stem cell transplant with donor leukocyte infusion.31 This evidence concerns the gene IDO1 and neoplasm.