IL4I1

Interleukin 4 Induced 1 (IL4I1) is a secreted L-amino acid oxidase (LAAO) with alias LAAO1. Induced by IL4 and IFN-γ, it catalyzes oxidative deamination of aromatic amino acids (e.g., phenylalanine, tryptophan) to generate hydrogen peroxide, ammonia, and keto acids. This activity suppresses T cell proliferation and cytokine secretion, modulating adaptive immunity and tumor immune evasion pathways.
IL4I1 is upregulated in tumor-associated macrophages across melanoma, colorectal, and breast cancers, correlating with poor prognosis. Preclinical small-molecule inhibitors targeting its LAAO activity restore T cell function, enhancing anti-tumor immunity in mouse models. These agents are being explored for combination with immune checkpoint therapies to overcome resistance.