Pharmaceutical developers Merck and Moderna announced that an experimental mRNA cancer vaccine combined with Keytruda has met its primary endpoint in a Phase 3 clinical trial, successfully preventing recurrence and spread in patients with resected melanoma. According to the companies, the late-stage trial evaluated the personalized neoantigen therapy in more than a thousand patients with high-risk melanoma who had their tumors surgically removed.
Phase 3 Trial Design and Patient Outcomes
The randomized trial compared a combination of the personalized mRNA vaccine, designated intismeran, and the monoclonal antibody Keytruda against the administration of Keytruda alone. According to Dr. Janice Mehnert, an oncologist and researcher at NYU Perlmutter Cancer Center who serves as a principal investigator for the study, participants experienced manageable side effects. Patients reported feeling unwell for a few days and missing a day or two of work, but experienced no life-threatening complications, according to Dr. Mehnert.
The Phase 3 evaluation follows earlier findings from a Phase 2 trial published in June, which indicated that the vaccine regimen reduced the risk of recurrence or death by 49 percent. While the earlier mid-stage trial focused on advanced disease stages, the Phase 3 cohort encompassed a larger and broader group of participants, according to Dr. Mehnert. Large-scale Phase 3 trials provide the statistical cohort size required to establish new standards of care by comparing outcomes across distinct patient groups.
Personalized mRNA Technology and Neoantigens
Unlike traditional broad-spectrum cancer therapies that administer identical treatments across large patient populations, mRNA cancer vaccines are custom-built for individuals. According to Dr. Catherine Wu, a physician and researcher at the Dana-Farber Cancer Institute at Harvard University whose team first demonstrated the feasibility of mRNA cancer vaccines in 2017, the approach creates bespoke treatments tailored to specific patient mutations.
The manufacturing process begins with a sample of the patient’s tumor obtained via biopsy or complete surgical removal. Researchers sequence the tumor DNA and compare it with healthy tissue from the same individual to identify genetic mutations. Machine learning algorithms then predict which neoantigens—proteins produced by those specific mutations—will trigger the strongest immune response. Because each patient’s human leukocyte antigen (HLA) profile is unique, researchers encode customized instructions into an mRNA molecule. This molecule is wrapped in a lipid nanoparticle and injected intramuscularly, functioning similarly to standard influenza immunizations to guide the immune system toward the cancer cells, according to Dr. Mehnert.
With the Phase 3 trial meeting its primary endpoint, the companies plan to submit their data to the U.S. Food and Drug Administration (FDA) to seek formal regulatory approval. Dr. Mehnert confirmed that research teams are fully prepared to scale the treatment for worldwide manufacturing if the FDA grants authorization based on the data review.
Clinical evaluation of the mRNA platform is already expanding beyond skin cancer. Researchers are currently testing similar personalized vaccines against lung and bladder cancers, according to Dr. Mehnert. Dr. Nina Bhardwaj, director of immunotherapy at the Icahn School of Medicine at Mount Sinai in New York, whose foundational research contributed to the vaccine’s development, stated that the treatment could prove revolutionary for patients with surgically excised tumors who face high risks of relapse.
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