By Lina carolina 
Researchers at the Francis Crick Institute and Barts Cancer Institute, Queen Mary University of London, have unveiled a significant breakthrough in the fight against bowel cancer, identifying a protein marker, CD74, that could revolutionize how immunotherapy is prescribed. This discovery promises to extend the reach of life-saving immunotherapies to hundreds, potentially thousands, of patients who were previously considered ineligible for such treatments. The findings, published in the prestigious journal Cancer Cell, mark a pivotal step in personalizing cancer care and maximizing the efficacy of existing therapeutic strategies.
Understanding the Landscape of Bowel Cancer Treatment
Bowel cancer, also known as colorectal cancer, remains a formidable health challenge in the United Kingdom, ranking as the fourth most common cancer and the second leading cause of cancer-related mortality. The disease is broadly categorized into two main subtypes based on DNA repair mechanisms: the deficient subtype, characterized by missing or deficient proteins crucial for correcting DNA errors, and the proficient subtype, where this DNA repair machinery remains intact.
Immunotherapy, a groundbreaking class of treatments that empowers the patient’s own immune system to identify and attack cancer cells, has already transformed the treatment paradigm for the deficient subtype of colorectal cancer. These therapies, often involving immune checkpoint inhibitors, have demonstrated remarkable success in prolonging survival and improving quality of life for many patients. However, their effectiveness is currently limited, with only approximately half of eligible patients experiencing a significant clinical benefit.
A more significant challenge lies with the proficient subtype, which accounts for a staggering 90% of all bowel cancer cases. Currently, patients with this subtype are generally not considered candidates for immunotherapy, leaving a vast majority of individuals without access to this potentially life-altering treatment modality. This disparity has been a major focus for researchers seeking to broaden the applicability of immunotherapy.
Unraveling the Immune Microenvironment’s Role
The research team embarked on an ambitious investigation to understand the underlying reasons for the differential response to immunotherapy and to identify strategies for expanding its benefits. Their inquiry delved deep into the complex interplay between cancer cells and the immune cells that infiltrate the tumor microenvironment. It is widely recognized that the composition and activity of these immune cells play a critical role in determining a patient’s response to immunotherapy.
By meticulously examining tumor samples from both deficient and proficient subtypes, and comparing individuals who responded to immunotherapy with those who did not, the researchers identified a crucial triumvirate of immune cells essential for therapeutic success: cytotoxic T cells and Natural Killer (NK) cells, often referred to as "fighter cells" due to their direct killing capabilities; and macrophages, which act as sentinels, presenting molecular flags to alert the immune system to threats.
The presence of all three cell types in close proximity to cancer cells was found to be a prerequisite for a robust anti-tumor immune response. When these immune cells were abundant and strategically positioned, T cells released signaling molecules called interferons. These interferons, in turn, triggered a cascade of signals within macrophages and tumor cells, effectively amplifying the immune attack.
While this signaling pathway was markedly pronounced in responsive tumors of the deficient subtype, the researchers made a surprising observation: a subset of patients with the proficient subtype also exhibited a comparable level of this immune signaling. This finding suggested that, despite their subtype classification, these patients’ immune systems might possess the necessary "readiness" to benefit from immunotherapy, a notion previously considered unlikely.
CD74: A Predictive Biomarker Emerges
The critical question then became: how can clinicians reliably identify these immune-ready patients, particularly within the large proficient subtype population? The researchers sought a straightforward and accessible method to assess the immune system’s preparedness for immunotherapy.
Leveraging cutting-edge spatial transcriptomics technology, a technique that allows for the detailed analysis of gene expression within specific locations in tissue, the team observed a direct link between T cell activity and the production of the protein CD74. They discovered that activated T cells stimulated neighboring macrophages and tumor cells to produce CD74. Crucially, tumors that were responding positively to immunotherapy drugs consistently showed higher levels of CD74 expression.
This pivotal discovery prompted the researchers to explore the potential of CD74 as a clinical biomarker. To validate their findings, they analyzed samples from several international clinical trials that had investigated immunotherapy in patients with the proficient subtype. The results were compelling: individuals who showed a positive response to immunotherapy exhibited significantly higher levels of CD74 compared to those who did not respond.
This evidence strongly indicates that measuring CD74 levels could serve as a reliable predictor of immunotherapy response, irrespective of the patient’s bowel cancer subtype. The implications are profound: a significant number of patients with the proficient subtype, who are currently excluded from immunotherapy, may now be eligible for this treatment. This could dramatically expand the pool of beneficiaries, offering a lifeline to individuals who previously had limited therapeutic options.
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, underscored the transformative potential of their findings. "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, expressed the profound personal reward of seeing scientific inquiry translate into tangible patient benefit. "Our work shows how state-of-the-art technologies coupled with computational analysis can address important clinical questions. As an early career research scientist, seeing the potential of our work to provide benefit to patients and their families is greatly rewarding," he remarked.
The research team is actively pursuing the translation of these discoveries into clinical practice. They are collaborating with Cancer Research Horizons, an organization focused on accelerating the development of research discoveries into new treatments, to create a diagnostic test for CD74 that can be implemented in clinics. Furthermore, ongoing research will investigate the precise mechanisms by which macrophages and tumor cells overexpress CD74 and explore whether this promising marker is also relevant in other cancer types.
Anna Kinsella, Science Engagement Manager at Cancer Research UK, highlighted the broader significance of this research within the context of advancing cancer treatments. "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," Ms. 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 emphasized the foundational role of discovery research: "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, with contributions from institutions including UCL, the University of Pisa, King’s College London, the Sarah Cannon Research Institute, and the Veneto Institute of Oncology, underscoring a global effort to combat cancer.
Broader Implications and the Road Ahead
The identification of CD74 as a predictive biomarker for immunotherapy response carries significant implications beyond bowel cancer. The principles underlying this discovery—understanding the immune microenvironment and identifying molecular signals that indicate immune readiness—are likely applicable to a wide range of solid tumors. This could pave the way for a paradigm shift in cancer treatment, moving towards a more personalized approach where therapies are tailored to the individual’s biological profile rather than solely their cancer subtype.
The current timeline for developing and implementing a new diagnostic test in clinical settings can vary, typically ranging from several years to over a decade. However, the robust nature of the findings and the ongoing collaboration with commercialization partners suggest a more accelerated path for CD74 testing. The immediate next steps involve rigorous validation in larger patient cohorts and regulatory approval processes.
The potential economic impact of this breakthrough is also substantial. By identifying patients who are most likely to respond to immunotherapy, clinicians can avoid administering expensive and potentially ineffective treatments to those who will not benefit, thereby optimizing healthcare resource allocation. Simultaneously, it opens up new revenue streams and investment opportunities in the development of companion diagnostics and further immunotherapy research.
In conclusion, the research conducted at the Francis Crick Institute and Barts Cancer Institute represents a beacon of hope for bowel cancer patients. The identification of CD74 as a predictive biomarker for immunotherapy response is a testament to the power of scientific inquiry and collaborative research. As this discovery moves from the laboratory to the clinic, it promises to not only improve treatment outcomes for countless individuals but also to reshape the future of cancer immunotherapy, making its life-saving benefits accessible to a much broader patient population. The journey from discovery to widespread clinical application is complex, but the potential rewards—saving lives and improving the quality of life for cancer patients—are immeasurable.
