Another study investigating the function of IDO inhibition using a mouse graft‐versus‐tumour model of reduced‐intensity allogeneic haematopoietic stem cell transplant, followed by donor leukocyte infusion found that an IDO inhibitor decreased the growth of the tumour and increased the expression of IDO1 and IFN‐γ in mice that received donor leukocyte infusion.31 This evidence concerns the gene IDO1 and neoplasm.