Hot Versus Cold Tumours: What T-Cell Infiltration Means

Defining the Categories

A hot (inflamed) tumour has T cells distributed through the tumour body, often alongside interferon-signature gene expression and PD-L1. A cold (immune desert) tumour has few or no T cells anywhere. An intermediate immune-excluded pattern has T cells stuck at the tumour margin, unable to penetrate.

Hot tumours are more likely to respond to checkpoint inhibitors because the drugs act by reinvigorating T cells that are already present; if no T cells are there, releasing their brakes achieves little.

What Makes a Tumour Cold

Contributing factors include low neoantigen load, defective antigen presentation, a stroma that physically excludes T cells, immunosuppressive cell populations such as regulatory T cells and myeloid-derived suppressor cells, and oncogenic signalling (for example WNT/beta-catenin activation) that reduces dendritic-cell recruitment.

Because the causes differ, the strategies proposed to warm a cold tumour also differ, from vaccines to stroma-modifying agents to combination targeted therapy.

Limits of the Label

Infiltration can vary markedly between areas of the same tumour and between the primary and metastases, so a single biopsy may misclassify. Quantitative tools such as the Immunoscore, which counts T-cell subsets in the tumour core and margin, formalise the assessment in colorectal cancer.

Hot versus cold is a helpful concept for discussion but is not by itself a validated companion diagnostic.

Strategies to Warm a Cold Tumour

Because a tumour can be cold for different reasons, the approaches under study are correspondingly varied: radiotherapy or certain chemotherapies to release antigen, oncolytic viruses and STING agonists injected into the tumour, targeted therapy to lift oncogene-driven immune exclusion, and drugs that deplete or reprogramme suppressive myeloid and regulatory-T-cell populations.

Most of this is investigational, and results have been inconsistent. The clearest routine use of the hot-versus-cold idea is to set expectations: a checkpoint inhibitor is more likely to help an inflamed tumour, and a cold tumour usually needs a combination or a different modality.

Key Takeaways

• ·Hot tumours have infiltrating, active T cells; cold tumours have few or none; excluded tumours trap them at the margin.
• ·Checkpoint inhibitors mostly work on hot tumours because they reinvigorate T cells already present.
• ·Infiltration varies within and between tumour sites, so the label is a spectrum, not a fixed property.