# CD8

Source: https://onco.cc/targets/cd8/  
OnCo record `cd8` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CD8 marks the T cells that kill: the ones that recognise a cancer cell and destroy it. How many CD8 cells sit inside a tumour, and where, is one of the few immune measurements that predicts how a cancer will behave.

## Summary

CD8 is the co-receptor that binds MHC class I and defines cytotoxic T cells, the cells that kill a target directly. It is the marker behind the phrase 'tumour-infiltrating lymphocytes' and behind the distinction between a hot and a cold tumour. Its density is prognostic rather than merely descriptive: the international consensus Immunoscore study quantified CD3 and CD8 densities in the tumour centre and the invasive margin in 1,885 stage I/II colon cancers across Canada, the United States, Europe and Asia, and a high Immunoscore carried the lowest risk of recurrence in both cohorts. CD8 is a two-chain receptor; CD8A is the alpha chain given here and CD8B (HGNC:1707) the beta.

## Fields

- Kind: Target
- Last checked: 2026-10-16
- Also known as: CD8a; CD8 alpha; T8
- Tags: immune-marker
- Symbol: CD8A
- Class: surface-antigen
- Biology: Co-receptor on cytotoxic T cells; binds MHC class I and marks the killing lineage. The beta chain is CD8B (HGNC:1707).
- Where found: Cytotoxic T cells; Some natural killer cells

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/CD8
- HGNC:1706: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:1706
- Consensus Immunoscore in stage I/II colon cancer (Cancers 2023): https://doi.org/10.3390/cancers15020418

## Connected records

- targets: [CD4](https://onco.cc/targets/cd4/), [CD57](https://onco.cc/targets/cd57/), [CXCR3](https://onco.cc/targets/cxcr3/), [PD-1](https://onco.cc/targets/pd1/)
- terms: [Hot vs cold tumours](https://onco.cc/terms/cold-vs-hot/), [T cell](https://onco.cc/terms/t-cell/), [T-cell exhaustion and CAR-T persistence](https://onco.cc/terms/t-cell-exhaustion-term/)

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JSON: https://onco.cc/api/v1/entities/cd8.json