{"entity":{"id":"tdo2","kind":"target","name":"TDO2","aka":["tryptophan 2,3-dioxygenase","TDO"],"tldr":"TDO2 does the same job as IDO1, breaking down tryptophan into kynurenine, which quietens T cells. It is one reason IDO1 inhibitors alone may not have been enough; no TDO2 drug has reached late trials.","summary":"TDO2 (chromosome 4q32.1) is a haem-dependent dioxygenase that catalyses the oxidative cleavage of the L-tryptophan pyrrole ring, converting it to N-formyl-L-kynurenine (UniProt P48775). IDO1 and TDO2 catalyse the commitment step of the kynurenine pathway; kynurenine activates the aryl hydrocarbon receptor, generating immune-tolerant dendritic cells and regulatory T cells and a tumour microenvironment defective at recognising cancer cells (Cheong and Sun 2018, Trends Pharmacol Sci). No TDO2-selective agent was found in ClinicalTrials.gov under the names the corpus knows.","asOf":"2026-09-24","links":[{"label":"HGNC HGNC:11708","url":"https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:11708"},{"label":"UniProt P48775","url":"https://www.uniprot.org/uniprotkb/P48775/entry"},{"label":"NCBI Gene 6999","url":"https://www.ncbi.nlm.nih.gov/gene/6999"},{"label":"Cheong and Sun 2018 (Europe PMC)","url":"https://europepmc.org/article/MED/29254698"}],"tags":["checkpoint-map"],"related":["ido1","epacadostat"],"cancers":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":["cancer-immunity-cycle"],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":["Prevalence not recorded: HGNC and UniProt carry no positivity rates."],"provenance":{"editedBy":"OnCo checkpoint map (HGNC REST, UniProt REST, ClinicalTrials.gov v2)","editedOn":"2026-09-24"},"symbol":"TDO2","role":["immune-checkpoint"],"sources":[{"label":"HGNC HGNC:11708","url":"https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:11708","note":"approved symbol, name, aliases and cross-references"},{"label":"UniProt P48775","url":"https://www.uniprot.org/uniprotkb/P48775/entry","note":"protein name, function and tissue specificity"}],"specificitySources":[],"hgnc":"HGNC:11708","ensembl":"ENSG00000151790","uniprot":"P48775","entrez":"6999","biology":"The liver-type tryptophan dioxygenase; UniProt records no tissue distribution for the human protein, so none is claimed here.","whereFound":["Not recorded by UniProt for the human protein"],"targetClass":"enzyme","prevalence":[]},"route":"/targets/tdo2/","neighbours":{"target":[{"id":"ido1","kind":"target","name":"IDO1","route":"/targets/ido1/"}],"drug":[{"id":"epacadostat","kind":"drug","name":"Epacadostat","route":"/drugs/epacadostat/"}],"pathway":[{"id":"cancer-immunity-cycle","kind":"pathway","name":"The cancer-immunity cycle","route":"/pathways/cancer-immunity-cycle/"}],"term":[{"id":"checkpoint","kind":"term","name":"Checkpoint (two meanings)","route":"/terms/checkpoint/"}]}}