Expression of Tryptophan Metabolism Enzymes in Patients with Diffuse Large B‐cell Lymphoma and NK/T‐cell Lymphoma

Abstract Background Metabolites of tryptophan (Trp) metabolism in the tumor microenvironment play crucial immunosuppressive roles in various cancers. However, the role of Trp metabolism in diffuse large B‐cell lymphoma (DLBCL) or natural killer/T‐cell lymphoma (NK/TCL) remains unelucidated. Methods We investigated the potential role of Trp metabolism in a cohort of 43 patients with DLBCL and 23 with NK/TCL. We constructed tissue microarrays and performed in situ staining of Trp‐catabolizing enzymes and PD‐L1 using immunohistochemistry (IHC). Results We observed 14.0% positive staining of IDO1 in DCBCL and 60.9% in NK/TCL; 55.8% of IDO2 in DCBCL and 95.7% in NK/TCL; 79.1% of TDO2 in DCBCL and 43.5% in NK/TCL; 29.7% of IL4I1 in DCBCL and 39.1% in NK/TCL. However, IDO1, IDO2, TDO2, and IL4I1 positivity did not significantly differ between PD‐L1+ and PD‐L1− biopsy tissue samples of NK/TCL; nonetheless, a positive correlation of IDO1 (r = 0.87, p