By Lina carolina 
Researchers at the Francis Crick Institute and Barts Cancer Institute, Queen Mary University of London, have identified a crucial protein, CD74, that can serve as a significant indicator of which bowel cancer patients are most likely to benefit from life-extending immunotherapy treatments. This groundbreaking discovery, published in the esteemed journal Cancer Cell, holds the potential to expand eligibility for immunotherapy to hundreds of patients who are currently deemed unsuitable for this advanced form of cancer therapy.
Bowel cancer, a pervasive and often fatal disease, stands as the fourth most common cancer and the second leading cause of cancer-related deaths in the United Kingdom. The disease is broadly categorized into two main subtypes: the deficient subtype, characterized by a deficiency or absence of proteins responsible for repairing DNA errors, and the proficient subtype, where this DNA repair machinery remains intact. While immunotherapy drugs, designed to harness the body’s own immune system to combat tumors, have revolutionized the treatment landscape for the deficient subtype, their efficacy is limited, working for only about half of eligible patients. Critically, individuals with the proficient subtype, who constitute approximately 90% of all bowel cancer cases, are currently excluded from immunotherapy treatment. This new research offers a beacon of hope, suggesting a pathway to unlock the therapeutic potential of immunotherapy for a much larger patient population.
Unraveling the Immune Microenvironment’s Role in Treatment Efficacy
The investigative team embarked on a comprehensive study to understand the complex interplay between the tumor and its surrounding immune environment, recognizing its pivotal role in determining immunotherapy response. Their analysis encompassed tumor samples from both deficient and proficient subtypes, comparing individuals who responded positively to immunotherapy with those who did not. This meticulous examination revealed a critical requirement for the presence of three specific types of immune cells within the tumor microenvironment for a successful response to treatment. These essential players include cytotoxic T cells and Natural Killer (NK) cells, collectively known as "fighter cells," which are adept at directly eliminating cancer cells. Alongside these, macrophages were identified as crucial, acting as "presenter" cells that flag threats to the immune system by displaying antigens on their surfaces.
The research elucidated a vital signaling cascade: when all three immune cell populations – T cells, NK cells, and macrophages – were present and in close proximity to cancer cells, T cells released signaling molecules called interferons. These interferons, in turn, triggered a subsequent signal within macrophages and the tumor cells themselves. This amplified signaling pathway was significantly more pronounced in tumors of the deficient subtype that exhibited a positive response to immunotherapy. However, a surprising observation emerged: a subset of patients with the proficient subtype also demonstrated a comparable level of this signaling, suggesting that their immune systems might be primed and receptive to immunotherapy, even in the absence of the DNA repair deficiencies typically associated with responsiveness.
CD74: A Novel Biomarker for Immunotherapy Success
Building on these findings, the researchers sought a straightforward and reliable method to ascertain whether a patient’s immune system was optimally positioned for immunotherapy to achieve success. Employing a cutting-edge technological approach known as spatial transcriptomics, which allows for the analysis of gene expression within the spatial context of tissues, the team made a pivotal discovery. They observed that stimulated T cells were prompting nearby macrophages and tumor cells to produce a specific protein, CD74. Furthermore, tumors that were responding favorably to immunotherapy drugs exhibited significantly higher levels of CD74 expression.
To validate the potential of CD74 as a clinical marker for predicting immunotherapy response, the researchers extended their investigation to include samples from several international clinical trials. These trials specifically focused on patients with the proficient subtype of bowel cancer, who are typically ineligible for immunotherapy. The results were compelling: patients who responded to immunotherapy consistently displayed markedly higher levels of CD74 compared to those who did not experience a therapeutic benefit. This correlation held true irrespective of the tumor’s subtype, suggesting that CD74 levels could serve as a universal predictor of immunotherapy efficacy in bowel cancer.
The implications of this finding are profound. It indicates that measuring CD74 levels could become a standard clinical practice, enabling oncologists to more accurately identify patients who are likely to respond to immunotherapy. Crucially, this opens the door for individuals with the proficient subtype, who currently have limited treatment options beyond traditional chemotherapy and surgery, to potentially access and benefit from immunotherapy. This could dramatically alter the treatment paradigm for a substantial proportion of bowel cancer patients.
Expert Perspectives and Future Directions
Francesca Ciccarelli, Principal Group Leader of the Cancer Systems Biology Laboratory at the Crick and Professor of Cancer Genomics at Queen Mary University of London’s Barts Cancer Institute, highlighted the transformative potential of this research. "Immunotherapy drugs can be hugely successful for people with bowel cancer, but currently the majority of patients can’t be prescribed these drugs and, even when patients are eligible, we don’t know upfront who will respond," Professor Ciccarelli stated. "Our work suggests that testing for CD74 levels – which signal that the immune system is ‘just right’ to fight the tumour – could widen access to immunotherapy. This could revolutionise treatment for a sizeable fraction of people with the proficient bowel cancer subtype, which is a large number of patients across the UK in real terms. It could also be used to identify people with the deficient subtype who won’t respond, saving them from experiencing side effects unnecessarily."
Kalum Clayton, a former postdoc at the Crick and joint first author of the study, underscored the power of advanced technologies in addressing clinical challenges. "Our work shows how state-of-the-art technologies coupled with computational analysis can address important clinical questions," Clayton remarked. "As an early career research scientist, seeing the potential of our work to provide benefit to patients and their families is greatly rewarding."
The research team is actively pursuing the translation of these findings into a clinically applicable test. Collaborating with Cancer Research Horizons, they aim to develop a robust diagnostic tool that can be implemented in healthcare settings. Further research is also planned to investigate the underlying mechanisms by which macrophages and tumor cells overexpress CD74, and to explore whether this promising biomarker is also present and predictive in other cancer types.
Anna Kinsella, Science Engagement Manager at Cancer Research UK, emphasized the importance of fundamental biological research in advancing cancer treatment. "Immunotherapy treatments, such as immune checkpoint inhibitors, use the power of the immune system to fight cancer. Whilst these treatments benefit some people with bowel cancer, they aren’t effective for everyone," Kinsella explained. "Although further research is needed, studies like this – diving deep into the biology of tumours – help researchers find ways to predict when immunotherapy is likely to work. In the future, this could help clinicians tailor treatment and allow more people with bowel cancer to benefit from immunotherapy." She added, "Understanding the biology of cancer is vital to unlocking better ways to prevent, detect and treat it, so that people can live longer, better lives free from the fear of cancer. That’s why at Cancer Research UK, discovery research is at the heart of everything we do."
The collaborative nature of this research is also noteworthy, involving contributions from institutions such as UCL, the University of Pisa, King’s College London, the Sarah Cannon Research Institute, and the Veneto Institute of Oncology. This multi-institutional effort underscores the global commitment to advancing cancer care.
Broader Impact and Timeline of Discovery
The journey leading to this significant breakthrough involved a multi-stage research process. Initially, the team focused on understanding the fundamental immunological differences between responsive and non-responsive bowel tumors. This phase, likely spanning several years of experimental work and data analysis, culminated in the identification of the key immune cell populations and signaling pathways involved. The subsequent identification of CD74 as a potential biomarker was a critical turning point, achieved through the application of advanced spatial transcriptomics techniques. This technological leap allowed for precise localization and quantification of protein expression within the tumor microenvironment.
The validation of CD74 as a predictive marker then necessitated the analysis of retrospective data from international clinical trials. This phase, involving the careful curation and analysis of patient data and tumor samples, provided the robust evidence needed to support the clinical utility of CD74. The timeline for such research is typically measured in years, from initial hypothesis generation and laboratory experiments to large-scale clinical validation and the eventual translation into clinical practice.
The implications of this research extend beyond the immediate benefit to bowel cancer patients. The discovery of CD74 as a pan-subtype predictor of immunotherapy response could have a ripple effect across other cancer types where immunotherapy is being explored. If CD74 plays a similar role in modulating the immune microenvironment in other solid tumors, its measurement could become a broadly applicable tool in oncology. This could significantly accelerate the development and application of immunotherapies across a wider spectrum of cancers.
Furthermore, the ability to predict non-response to immunotherapy is equally valuable. By identifying patients unlikely to benefit, clinicians can avoid exposing them to the potential side effects of these powerful drugs, while also conserving valuable healthcare resources. This personalized approach to cancer treatment, guided by precise molecular biomarkers, represents the future of oncology.
The development of a diagnostic test based on CD74 measurement would likely involve several regulatory steps, including further clinical validation studies, regulatory approval from bodies like the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK, and integration into routine pathology workflows. This process can also take several years. However, the significant unmet need for effective immunotherapy prediction in bowel cancer, and potentially other cancers, provides strong motivation for rapid progress. The commitment from Cancer Research UK and the involvement of commercial partners like Cancer Research Horizons signal a clear intention to bring this promising discovery to patients as efficiently as possible. The scientific community will be closely watching the progression of this research, anticipating a future where more bowel cancer patients can confidently receive the most effective and personalized treatments available.
