# IDO1

Source: https://onco.cc/targets/ido1/  
OnCo record `ido1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

IDO1 is an enzyme tumours use to burn up tryptophan, starving T cells and producing by-products that switch them off. Epacadostat blocked it but its programme ended in failure; the IO102-IO103 vaccine instead teaches T cells to attack the IDO1-expressing cells themselves.

## Summary

IDO1 (chromosome 8p11.21) catalyses the first, rate-limiting step of tryptophan catabolism along the kynurenine pathway; the tryptophan shortage stops T lymphocytes dividing and the catabolites induce T-cell apoptosis and regulatory T-cell differentiation, so the enzyme maintains peripheral tolerance, protects the fetus from maternal rejection, limits intracellular pathogens and suppresses anti-tumour immunity (UniProt P14902). In OnCo, IDO1 is the target of epacadostat, a selective reversible enzyme inhibitor recorded as a negative programme in melanoma, and one of the two antigens (with PD-L1) of the IO102-IO103 peptide vaccine in phase 3 for melanoma and head and neck cancer.

## Fields

- Kind: Target
- Last checked: 2026-09-22
- Also known as: IDO; INDO; indoleamine 2,3-dioxygenase 1
- Tags: wave5-target
- Symbol: IDO1
- Class: enzyme
- Biology: The two corpus approaches differ in kind: epacadostat blocked the enzyme's chemistry, while IO102-IO103 raises T cells against cells that express IDO1 or PD-L1 in the tumour microenvironment, turning the suppressive cells themselves into targets.
- Where found: Tumour cells and myeloid cells of the tumour microenvironment; Melanoma and head and neck cancer (IO102-IO103); melanoma (epacadostat)

## Notes

- Prevalence not recorded in this wave: HGNC and UniProt carry no positivity rates and no other source was consulted.

## Sources

- HGNC HGNC:6059: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:6059
- UniProt P14902: https://www.uniprot.org/uniprotkb/P14902/entry
- NCBI Gene 3620: https://www.ncbi.nlm.nih.gov/gene/3620

## Connected records

- targets: [PD-L1](https://onco.cc/targets/pdl1/)
- cancers: [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/), [Melanoma](https://onco.cc/cancers/melanoma/)
- technologies: [Immune checkpoint inhibitors](https://onco.cc/technologies/checkpoint-inhibitor/)
- drugs: [Epacadostat](https://onco.cc/drugs/epacadostat/), [IO102-IO103](https://onco.cc/drugs/io102-io103/)
- pathways: [Cold tumours: immune deserts and exclusion](https://onco.cc/pathways/immune-desert-exclusion/), [Nutrient competition & metabolic immunosuppression](https://onco.cc/pathways/nutrient-competition-tme/), [The cancer-immunity cycle](https://onco.cc/pathways/cancer-immunity-cycle/)

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JSON: https://onco.cc/api/v1/entities/ido1.json