Critically, the Kyn–AhR axis exerts profound immunosuppressive effects: it promotes the differentiation and functional activity of regulatory T cells, induces CD8+ cytotoxic T cell apoptosis or dysfunction and facilitates recruitment and polarisation of tumour‐associated macrophages (TAMs) toward an immunosuppressive phenotype.70, 71. The gene discussed is AHR; the disease is neoplasm.