Natural killer (NK) cells are key components of the innate immune system, known for their ability to directly kill tumour cells and coordinate broader anti-tumour immune responses. Despite their potent cytotoxic capacity, NK cells often fail to control tumour growth once they enter the tumour microenvironment (TME). The research article by Dean et al. (2024) investigates why this occurs, focusing on how NK cell function changes over time after they infiltrate tumours.
Rapid functional decline of NK cells in tumours
The study demonstrates that NK cells undergo rapid functional impairment shortly after entering tumours. Within as little as 24–72 hours, these cells lose their ability to kill cancer cells (reduced cytotoxicity), produce key immune signalling molecules such as IFN-γ, or recruit and activate other immune cells such as dendritic cells via chemokines like CCL5.
This decline occurs consistently across different tumour models, highlighting a general mechanism by which tumours suppress innate immunity.
Transition to a “tumour-retained” phenotype
As NK cells remain in the tumour, they adopt a distinct phenotype characterised by:
- Expression of CD49a, associated with tissue residency
- Loss of CD11b, a marker of mature circulating NK cells
- Upregulation of inhibitory receptors (e.g., PD-1, LAG-3)
This transformation reflects a shift from active tumour-fighting cells to a dysfunctional, tumour-adapted state, which the majority of retained NK cells eventually adopt.
Tumour-resident NK cells do not control tumour growth
When NK cells were experimentally depleted in established tumours, there was no significant effect on tumour growth. This indicates that once NK cells become dysfunctional within the TME, they no longer measurably impact tumour growth in these models.
Mechanisms driving NK cell dysfunction
The study investigated multiple contributors to NK cell impairment, including:
- TGF-β signalling
- Prostaglandin E₂ (PGE₂)
- Hypoxia (HIF-1α pathway)
Each had partial effects, but no single factor fully explained the dysfunction, suggesting that a combination of suppressive signals within the TME drives NK cell reprogramming.
Evidence from human tumours
Analysis of human colorectal cancer samples revealed similar patterns:
- Tumour-infiltrating NK cells predominantly exhibit a resting/inactive state
- Decreased expression of cytotoxic molecules (perforin, granzymes)
- Enrichment of CD49a⁺ dysfunctional NK cells, particularly in advanced tumours
This demonstrates that NK cell dysfunction is clinically relevant in humans.
Use of Bio X Cell antibodies in the study
Bio X Cell antibodies were used in this study specifically as isotype control reagents to ensure the validity and specificity of in vivo antibody-mediated experiments. The authors employed Bio X Cell’s InVivoMab mouse IgG2a and rat IgG2a isotype control antibodies, alongside functional antibodies such as anti-NK1.1, anti-CD8α, and anti-OX40 from elsewhere. These controls allowed the researchers to distinguish true biological effects of immune cell depletion or modulation from non-specific effects of antibody administration. For example, comparisons between isotype-treated and depletion-treated groups were essential in demonstrating that removal of NK cells or CD8⁺ T cells had specific and interpretable impacts on tumour growth and immune responses.
Bio X Cell’s isotype controls were critical for maintaining experimental rigor and ensuring accurate interpretation of immune manipulation experiments.
"To fully understand the role of NK cells in tumours, we needed an effective way to deplete these immune cells (and others) from tumours. We had access to functional antibodies to achieve this but needed suitable controls to verify the validity of results obtained. To ensure our experiments had appropriate controls we turned to Bio X Cell for their In Vivo antibodies, specifically their InVivoMab range which also consists of mouse and rat IgG isotype controls which we employed for our study. Bio X Cell have a reputation for high quality products for In Vivo use which were essential for this project, and their products remain a standard in my current research direction."
Dr Isaac Dean, Postdoctoral Training Fellow, Institute of Cancer Research.
Restoring NK cell function with IL-15
A key therapeutic finding was that enhanced IL-15 drives the formation of a distinct, highly functional NK cell population. Treatment with IL-15/IL-15Rα complexes:
- Prevented functional decline
- Increased cytotoxic molecule production
- Induced a hybrid NK cell state (both tissue-resident and highly active)
- Improved tumour control
Methodological approach
The researchers used a novel photoconversion labelling system in transgenic mice to track immune cells over time within tumours. Combined with single-cell RNA sequencing, flow cytometry and functional cytotoxicity assays, this approach enabled a detailed temporal map of NK cell fate from entry to dysfunction.
Implications for cancer immunotherapy
- Limits of current therapies: NK cells rapidly lose function in tumours, which may limit therapies relying on their cytotoxic activity.
- Targeting the tumour microenvironment: enhancing NK cell recruitment alone is insufficient; therapies must counteract suppressive TME signals.
- Promise of IL-15-based treatments: IL-15 therapies could restore NK function and work synergistically with other immunotherapies.
- Rethinking NK cell biology: dysfunction represents an adaptive reprogramming process rather than simple exhaustion.
Conclusion
Dean et al. provide a comprehensive view of NK cell dynamics in cancer, showing that these cells rapidly become dysfunctional after entering tumours and adopt a tissue-resident-like phenotype with reduced anti-tumour capacity. Crucially, this dysfunction can be treated, and therapeutic strategies such as IL-15 signalling can restore NK cell activity and improve tumour control.
These findings highlight both a major barrier to effective cancer immunity and a promising avenue for enhancing immunotherapy by reviving innate immune responses within the tumour microenvironment.
If you are working in cancer immunotherapy and would like to learn about how Bio X Cell's antibodies could support your research, get in touch with our specialists and get a 20% off introductory offer.
Reference
Dean, I., Lee, C.Y.C., Tuong, Z.K. et al. Rapid functional impairment of natural killer cells following tumor entry limits anti-tumor immunity. Nat Commun 15, 683 (2024). https://doi.org/10.1038/s41467-024-44789-z