New Strategy Blocks NMD, Unmasks Hidden Tumor Antigens, and Boosts Immunotherapy

A new study led by UCL researchers suggests that making cancer cells more visible to the immune system could broaden the impact of immunotherapy across multiple tumor types. Published in Immunity and based on data from more than 1,000 patients, the research shows that inhibiting nonsense-mediated mRNA decay (NMD) exposes hidden tumor antigens, boosts T-cell recognition, and enhances checkpoint inhibitor activity, including in low-mutation tumors and checkpoint inhibitor-resistant settings.

Cancer immunotherapy has changed the trajectory of care for many patients, yet one stubborn problem remains: a large share of tumors still evade immune detection. A new study points to a possible way around that barrier, not by adding more immune stimulation, but by making cancer cells easier to see.

The work centers on nonsense-mediated mRNA decay, or NMD, a cellular surveillance system that normally removes faulty RNA before it can be translated into defective proteins. In healthy tissues, that function is protective. In tumors, however, it may also serve as an unexpected shield.

Researchers led by Dr Roberto Vendramin at the UCL Cancer Institute found that blocking NMD allows faulty RNA transcripts to persist inside cancer cells. Those transcripts are then translated into abnormal proteins, which are chopped into peptide fragments and displayed on the cell surface through MHC class I molecules. In effect, inhibiting NMD exposes a previously hidden set of antigens that the immune system can recognize.

As Dr Roberto Vendramin explained: “Immunotherapy has already transformed cancer care, but too many patients still don’t benefit because their tumours remain effectively invisible to the immune system. By preventing the destruction of faulty RNA, we allow them to produce abnormal proteins which eventually become antigens and make cancer cells easier to see. Increasing the visibility of antigens on cancer cells may help the immune system target cancers with few genetic mutations.

“Once successfully developed into a treatment, our approach could benefit a wide range of cancer patients, particularly those whose tumours do not currently respond well to immunotherapy. It has the potential to improve immunotherapy response rates, which could translate into improved long-term survival and better outcomes for patients.”

What makes the study notable is not only the mechanism, but the scale of the evidence behind it. Using multi-omics and checkpoint inhibitor response data from more than 1,000 patients, the investigators identified reduced activity of SMG1, a key NMD pathway kinase, as a predictor of improved response to checkpoint blockade. Pharmacologic inhibition of SMG1 stabilized transcripts carrying premature termination codons, most of them arising not from DNA mutations, but from non-mutational RNA errors such as retained introns, pseudogenes, and long non-coding RNAs.

That distinction matters. Cancer immunotherapy has largely been built around neoantigens generated by DNA mutations, especially in tumors with high mutational burden. This study suggests that tumors may harbor a much broader antigenic reservoir, one created by abnormal RNA processing. By unlocking that reservoir, NMD inhibition raised neoantigen abundance to levels comparable to tumors with high mutation burden, even in cancers that would ordinarily appear less immunogenic.

The biological effects extended beyond antigen display. In vitro, NMD inhibition enhanced antigen-dependent T cell killing. In patient-derived ex vivo models, it activated tissue-resident T cells. In vivo, it improved the efficacy of PD-1 blockade, including in a checkpoint inhibitor resistant setting. The strongest ex vivo effects were seen in effector memory T cells, raising the possibility that some tumors already prime immune responses against these hidden antigens, but keep them below the threshold needed for durable activation.

This is especially relevant for low-TMB cancers, which make up the majority of solid tumors and often respond poorly to current immunotherapies. The findings also suggest a potential role in tumors that already contain immune infiltrates, such as some colorectal, breast, and kidney cancers, but are not adequately controlled by them.

The strategy remains early, and important questions about safety, dosing, and duration still need to be answered. NMD is a fundamental pathway, and prolonged suppression could theoretically drive chronic inflammation or immune exhaustion. Still, the authors argue that acute, transient inhibition of SMG1 may offer a more selective and clinically workable approach, one that boosts tumor immunogenicity without widespread toxicity.

About Author: Hüseyin Kandemir

As a medical journalist with over 20 years of experience, I have served as an Editor and Reporter for various magazines, newspapers, and online broadcasting platforms, consistently demonstrating a strong commitment to excellence in journalism. My specialization includes medical science, digital health, AI for health, data science, and biotechnology.