Oral Vaccine Shows Promise in Fighting Colorectal Cancer | Futurity

A new strategy involving an oral vaccine based on a modified Listeria monocytogenes bacterium is showing promise in the fight against colorectal cancer. Researchers at Stony Brook University have engineered a version of the common bacterium to stimulate an immune response directly within the gut, potentially offering a more targeted and effective approach to immunotherapy for this challenging disease.

Colorectal cancer remains a significant global health concern. The American Cancer Society projects over 150,000 new diagnoses and more than 55,000 deaths in the United States alone for 2026. Current statistics highlight the urgent need for improved treatment options, particularly as many colorectal cancers do not respond well to existing immunotherapies.

Harnessing the Power of Listeria

Listeria monocytogenes, while known as a foodborne pathogen, has been investigated for its potential as a cancer immunotherapy. Previous research focused on intravenous administration of Listeria-based vaccines, aiming to generate tumor-reactive CD8 T cells – a type of immune cell crucial for fighting cancer. However, clinical trial success has been limited. This new research, published in the Journal for the ImmunoTherapy of Cancer, takes a different approach: oral delivery.

The team, led by Stony Brook immunologist Brian Sheridan, engineered a strain of Listeria by deleting key genes responsible for causing illness (virulence genes). This attenuated strain, dubbed InlAM Lm-ova, retains the ability to access the intestinal immune system, triggering an anti-tumor response without causing Listeriosis. The vaccine is delivered via consumption of inoculated bread, a method designed to target gastrointestinal tissues directly.

Localized Immune Response and Minimal Side Effects

In mouse models of colorectal cancer, the oral vaccine induced a robust CD8 T cell response comparable to that achieved with fully virulent Listeria. Importantly, the vaccine remained contained within the intestinal tissues, without spreading to other organs or causing significant side effects like weight loss. This localized approach is a key advantage, ensuring the immune system focuses on the site where colorectal cancer typically develops, minimizing damage to healthy tissues.

The study utilized two murine models of colorectal cancer: a cell line expressing ovalbumin (MC38) and genetically engineered organoids (AKPS) as well expressing low levels of ovalbumin. Researchers tested the vaccine’s efficacy in both prophylactic (preventative) and therapeutic settings, and also explored its potential in combination with immune checkpoint inhibitors (ICIs).

Synergy with Immune Checkpoint Inhibitors

While the vaccine alone showed some success in curtailing local tumor growth, its true potential emerged when combined with ICIs. Immune checkpoint inhibitors work by releasing the brakes on the immune system, allowing it to more effectively attack cancer cells. The combination of the oral vaccine and ICIs led to profound tumor control in the mouse models, suggesting the vaccine can “turn on” the immune system in tumors previously resistant to standard immunotherapy.

Specifically, the research demonstrated that oral immunization, coupled with ICIs, induced the accumulation of tumor-specific CD8 T cells within the tumor environment. These specialized immune cells remain stationed in the gut, providing immediate and long-lasting protection against cancer cells – a response not achieved through vaccination or ICIs alone.

What In other words for Patients

The findings suggest a potential new avenue for treating advanced or metastatic colorectal cancer, where therapeutic options are often limited. The oral vaccine strategy could not only prevent the onset of disease but also enhance the effectiveness of existing immunotherapies. However, it’s crucial to remember that this research is currently in the pre-clinical stage, conducted on mouse models. Significant further research is needed to determine if these results will translate to humans.

The study’s success hinges on the targeted delivery of the vaccine to the gut, stimulating a localized immune response. This contrasts with traditional systemic immunotherapies, which can sometimes cause widespread inflammation and off-target effects. The attenuated Listeria strain is designed to minimize the risk of infection, but careful monitoring for any adverse effects will be essential in future clinical trials.

The Path Forward: Clinical Trials and Further Research

According to Sheridan, the clinical significance of these laboratory findings underscores the vaccine’s performance in treating established tumors. The next steps involve rigorous testing in human clinical trials to assess the vaccine’s safety, efficacy, and optimal dosage. Researchers will also need to investigate the long-term durability of the immune response and identify potential biomarkers that can predict which patients are most likely to benefit from this therapy.

The study was supported by funding from the Department of Defense, the National Institutes of Health’s National Institute of Allergy and Infectious Diseases (NIAID), the Research Foundation for the State University of New York, and several charitable foundations. This collaborative effort highlights the importance of continued investment in cancer research to develop innovative and effective treatments.

Looking ahead, this research could pave the way for a new generation of cancer vaccines designed to both prevent disease and enhance the efficacy of existing immunotherapies. The oral delivery method offers a convenient and potentially cost-effective approach, making it accessible to a wider range of patients. While challenges remain, this study represents a significant step forward in the fight against colorectal cancer.