Can radiation help activate the immune system to fight cancer? How radioimmunotherapy affects immune response in patients with non-small cell lung cancer.
Over the past decade, significant progress has been achieved in treating lung cancer, particularly for individuals with non-small cell lung cancer (NSCLC). In particular, the development of immune checkpoint inhibitors – which harness a patient’s immune system to fight cancer – has resulted in significant improvements in patient outcomes. Immune checkpoint inhibitors work by blocking inhibitory molecules that cancer cells use to evade immune surveillance, enabling the patient’s immune system to target cancer cells. This therapeutic approach is entirely unlike chemotherapy, which targets all rapidly dividing cells and thus has the potential to target some healthy cells – e.g., hair cells and cells in the lining of the digestive tract.
Still, not all patients attain clinical benefit from these novel immunotherapies. Some lung cancers harbor an “immunologically cold” phenotype, meaning they are more likely to evade immune recognition and elimination by the immune system even when treated with immune checkpoint inhibitors. For example, tumors with fewer somatic mutations, which are considered to have a low tumor mutation burden (TMB), and tumors with no PD-L1 expression, generally show a poorer response to immunotherapy. This raises the question of how we can improve responses to immunotherapy in patients with tumors that are predisposed to resistance.
Preclinical evidence suggests that radiation therapy (RT) could help circumvent immunotherapy resistance. When cancer cells are subjected to RT, they release antigens into the nearby environment, known as the tumor microenvironment (TME). The immune system can then recognize these antigens and tailor immune responses to the molecular “blueprint” of the cancer. In this way, RT may be able to enhance anti-tumor immune responses, both at the primary tumor treated with radiation and systemically, and at distant metastases far from the site of radiation. This effect is known as the abscopal effect of radiation (‘ab’ meaning away from, and ‘scopus’ meaning target).
These findings suggest that RT could enhance the response to immunotherapy, even at distant metastatic sites. However, this effect has not been consistently shown, especially in human biospecimens. To bridge this gap, we studied how lung cancers responded to immunotherapy in a phase 2 randomized clinical trial of patients with NSCLC receiving combination radioimmunotherapy. In one arm of this trial, patients received radiotherapy together with pembrolizumab, while in the control arm, patients received pembrolizumab alone.
To study each tumor’s response to therapy at the molecular and cellular level, our team analyzed 293 tissue and blood specimens derived from patients in this trial, from both pre-therapy and on-therapy timepoints. Using whole-exome sequencing and gene expression analyses, we identified tumors that harbored features of immunotherapy resistance and immunologically cold phenotypes. We were particularly interested in patients with this immunologically cold tumor phenotype and hypothesized that radiotherapy may circumvent immunotherapy resistance and sensitize such lung cancers to pembrolizumab. Below are the main insights from our research study.
We found that patients who received combination immunotherapy with RT showed enhanced anti-tumor immune responses, including in metastatic sites that were not irradiated. We examined gene expression patterns in the TME and observed an upregulation of key genes involved in inflammatory response and immune cell activation. This was also reflected in a greater number of T-cells, B-cells, macrophages, and natural-killer cells being recruited to the TME. As these phenomena were notes in tumors that harbored characteristics of immune resistance due to an immunologically cold TME, our findings supported a cold-to-hot transition of the TME, that we posit was driven by radiotherapy. This rewiring of the TME towards a more inflamed, immunologically “hot” phenotype enabled better clinical responses with immunotherapy.
Our second key finding was that, in the combination radioimmunotherapy arm, existing T-cells increased in density in both the blood and tissue compartments together with the appearance of new T cell clones. T-cells rely on T-cell receptors (TCRs) to recognize antigens, including tumor-associated and neoantigen-associated neoantigens. We employed T-cell receptor sequencing focusing on the antigen-recognizing domains to study changes in the T cell repertoire with radioimmunotherapy. Our hypothesis going into these analyses, based on our transcriptomic data, was that we would observe a reshaping of the T cell repertoire characterized by an influx and expansion of T cells in non-irradiated sites for patients who received radiation in addition to immunotherapy. Indeed, we found that patients who received RT in addition to immunotherapy exhibited an expansion of both existing and new TCRs, consistent with an enhanced immune response.
But were these T cells targeting the cancer cells? To answer this question, we cultured T-cells ex vivo from selected patients who attained long-term clinical outcomes with radioimmunotherapy despite their tumors having molecular features of resistance to immunotherapy. This led to our third key finding – that mutation-associated neoantigens elicited tumor-reactive clonotypic T cell expansions. This provided definitive evidence of the presence and enhancement of anti-tumor immune responses in the context of radioimmunotherapy.
Ultimately, when examining the clinical outcomes of patients who received radioimmunotherapy, we found that the phenomenon of the TME in non-irradiated metastatic sites warming up with radiotherapy was mainly observed in patients with the longest survival. Overall, patients who received radioimmunotherapy had significant tumor shrinkage at non-irradiated metastatic sites. This was especially evident in patients with tumors that initially exhibited an immunologically cold phenotype, and as a result, were not expected to benefit from immunotherapy.
Ultimately, our study highlights the potential application of RT in combination with immunotherapy for treating patients with NSCLC, particularly those with immunologically cold tumors who may otherwise have a poor response to immunotherapy alone. Taken together, our findings at the molecular, cellular, and systemic levels suggest that combination radioimmunotherapy may help circumvent immunotherapy resistance.
Our open-access study (DOI) was published in Nature Cancer on Tuesday, July 22nd, 2025.
