A recent study has pointed out that instead of IDO1, interleukin 4 induced 1 (IL4I1) is the novel and the main Trp‐catabolic enzyme in glioma and chronic lymphocytic leukemia, which explains the major reason why the clinical trials of IDO1 inhibitors are a failure.16 The gene discussed is IL4I1; the disease is B-cell chronic lymphocytic leukemia.