For many people, the word “vaccine” is still associated with prevention: an injection given before a disease appears, designed to train the immune system against a virus or bacterium. But in oncology, the concept of a vaccine is evolving. Some cancer vaccines are not intended to prevent cancer from developing in the first place. Instead, they are designed to help the immune system recognize cancer that is already present, or to reduce the risk of cancer returning after surgery.
This is where personalized mRNA cancer vaccines have captured major scientific attention. mRNA, or messenger RNA, is a molecule that works like a temporary instruction for cells to produce a specific protein. In this case, those instructions are designed to help the immune system recognize signals that are unique to a patient’s tumor.
The COVID-19 pandemic introduced the world to a technology that science had been developing for decades: mRNA. COVID-19 vaccines demonstrated that this molecule could be used as a temporary instruction to train the immune system quickly and precisely. Today, that same platform is being explored in cancer with a more personalized goal: not to recognize a virus, but to help the immune system identify the unique signals of a tumor.
Instead of using a one-size-fits-all approach, personalized mRNA cancer vaccines are designed from the genetic characteristics of each person’s tumor. The goal is to teach immune cells to recognize “molecular fingerprints” found in cancer cells, helping the body identify and attack residual disease that may remain after treatment.
One of the most closely watched examples is intismeran autogene, also known as mRNA-4157 or V940, an investigational individualized neoantigen therapy developed by Moderna and Merck in combination with pembrolizumab, an anti-PD-1 immunotherapy. In high-risk melanoma after surgical resection, this approach has shown encouraging results in clinical trials, including sustained improvement in recurrence-free survival in longer follow-up analyses. However, it is important to note that this therapy remains investigational and is still being evaluated in larger trials.
Why Cancer Vaccines Are Different From Traditional Vaccines
Traditional vaccines usually work by exposing the immune system to a harmless version or fragment of a pathogen. This allows the body to build immune memory before a future infection. Cancer vaccines are more complex because cancer is not an external invader. It arises from the body’s own cells.
Cancer cells often look very similar to healthy cells, making them more difficult for the immune system to distinguish. However, as tumors grow, they accumulate mutations. Some of these mutations can produce abnormal proteins or protein fragments that do not exist in healthy cells. These signals are called neoantigens.
Neoantigens can be understood as small “identity marks” created by tumor mutations. When the immune system recognizes them, it can interpret that the cell is abnormal and should be attacked. The challenge is that neoantigens are often highly individual. Two patients with the same cancer type may have very different tumor mutations. This is one reason personalized cancer vaccines are so promising: they can be designed based on the specific neoantigen profile of a patient’s tumor.
How Personalized mRNA Cancer Vaccines Work
The process begins with tumor tissue, usually obtained during surgery or biopsy. Scientists analyze the genetic information of the tumor and compare it with normal tissue to identify mutations that may produce cancer-specific signals. Computational tools and machine learning algorithms then help select which of those signals are most likely to be recognized by the patient’s immune system.
Once the most promising neoantigens are selected, they are encoded into mRNA. This mRNA can be imagined as a temporary biological recipe: it does not change a person’s DNA, but gives cells a short-lived instruction to produce fragments related to the tumor.
The mRNA is packaged in lipid nanoparticles, small fat-like particles that help deliver the instructions into cells. After injection, cells read the mRNA and temporarily produce fragments of the selected neoantigens. These fragments are then processed and presented to the immune system, especially through antigen-presenting cells such as dendritic cells. These cells display the fragments using HLA molecules, which act like biological “display windows” that allow T cells to inspect what is being shown.
In simple terms, the vaccine gives the immune system a kind of personalized “wanted poster” of that patient’s cancer. This does not mean the vaccine contains live cancer cells or changes a person’s DNA. mRNA does not enter the nucleus, where DNA is stored. Instead, it acts as a temporary instruction molecule that helps train the immune system against tumor-specific signals.
Why Combine mRNA Vaccines With Immunotherapy
A personalized vaccine can help show the immune system what to look for. But cancer has many ways to evade immune attack. Tumors can create an environment that weakens immune responses, become less visible to the body’s defenses, or activate signals that “brake” immune cells.
That is why many mRNA cancer vaccine trials combine these vaccines with immune checkpoint inhibitors, such as pembrolizumab. Immune checkpoints are normal mechanisms the body uses to prevent excessive immune responses. They function like safety brakes. The problem is that some tumors learn to use these brakes to hide from the immune system. Pembrolizumab works by blocking one of these brakes, known as PD-1, and can help immune cells remain active against cancer.
The combination strategy makes biological sense: the vaccine helps educate the immune system about which tumor signals to recognize, while the checkpoint inhibitor helps prevent that response from shutting down too soon. In other words, one component helps identify the target, while the other helps sustain the immune attack.
What the Data in Melanoma Show So Far
The KEYNOTE-942/mRNA-4157-P201 study evaluated mRNA-4157/V940 plus pembrolizumab compared with pembrolizumab alone in patients with high-risk melanoma after complete surgical resection. This is an important setting because, even after visible disease has been removed, microscopic cancer cells may remain and later cause recurrence.
The publication in The Lancet described this study as an open-label, randomized, phase 2b trial in the adjuvant setting. This means it was evaluated after surgery as an additional strategy to reduce the risk of cancer returning. The goal was to analyze whether individualized mRNA-based neoantigen therapy plus pembrolizumab could improve recurrence-free survival and distant metastasis-free survival compared with pembrolizumab alone.
In the three-year analysis announced by Moderna and Merck in 2024, the combination reduced the risk of recurrence or death by 49% compared with pembrolizumab alone. It also reduced the risk of distant metastasis or death by 62%. The 2.5-year recurrence-free survival rate was 74.8% in the combination group compared with 55.6% in the pembrolizumab-alone group.
In January 2026, Moderna and Merck announced five-year follow-up data from the same phase 2b study. With a median pre-planned follow-up of five years, intismeran autogene plus pembrolizumab continued to show a 49% reduction in the risk of recurrence or death compared with pembrolizumab alone. The companies also reported that the phase 3 adjuvant melanoma trial, INTerpath-001, had completed enrollment, while other phase 3 and phase 2 studies were ongoing in different tumor types.
These findings are promising, but they should be interpreted with caution. The phase 2b trial included 157 patients, and larger phase 3 studies are needed to confirm whether this approach should become a standard treatment option. The therapy remains investigational.
Why Melanoma Is an Important Starting Point
Melanoma has long been one of the cancers most sensitive to immunotherapy. One reason is that many melanomas have a relatively high tumor mutational burden. This means their cells can accumulate many genetic alterations and, as a result, produce more abnormal signals that the immune system may recognize.
That is why melanoma is a logical starting point for testing personalized vaccines based on neoantigens. If a tumor produces more abnormal signals, there may be more opportunities for a vaccine to train the immune system against them.
However, melanoma is not the only target. The field is expanding into lung cancer, bladder cancer, kidney cancer, cutaneous squamous cell carcinoma, and other tumor types. Moderna and Merck have reported multiple phase 2 and phase 3 studies in different cancers, reflecting a broader effort to determine where individualized mRNA vaccines could offer meaningful clinical benefit.
The key question is not simply whether mRNA vaccines can generate immune responses. The deeper question is whether those responses are strong, specific, durable, and clinically relevant across different tumor types.
Figure 1. Tumor-informed mRNA delivers temporary instructions for producing antigen fragments that can be presented by dendritic cells to T cells, promoting T-cell activation and a targeted immune response against tumor cells carrying related signals.
The Promise and the Challenges
Personalized mRNA vaccines offer several potential advantages. First, they are highly individualized. Instead of targeting a general marker that may or may not be present in many patients, these vaccines are built around the molecular identity of a specific tumor.
Second, mRNA platforms can be relatively fast to design once tumor sequencing and neoantigen selection are complete. This matters in oncology, where time can be critical.
Third, the immune system has memory. If a vaccine succeeds in training T cells to recognize tumor signals, those cells may continue surveillance over time. In theory, this could help detect and eliminate residual cancer cells before they grow into a clinically visible recurrence.
Fourth, the platform is flexible. mRNA can be designed to include several instructions in a single vaccine. In Moderna’s approach, the possibility of selecting up to 34 neoantigen candidates has been described, allowing the immune system to be trained against a broader set of tumor-specific signals.
Despite the enthusiasm, important challenges remain. Neoantigen selection is complex. Not every mutation produces a useful immune signal. Some tumor fragments may not be effectively presented by HLA molecules, meaning T cells may not detect them. Tumors can also evolve over time, change their characteristics, or lose certain targets, making a sustained immune response more difficult.
Manufacturing is another challenge. Each vaccine must be produced for an individual patient, requiring tumor sequencing, computational analysis, quality-controlled manufacturing, and timely delivery. This creates logistical and cost barriers that are very different from mass-produced therapies.
Tumor biology also matters. Some cancers are “hot,” meaning they already contain immune cells and inflammatory signals that can facilitate an immune response. Others are “cold,” meaning they are less visible to the immune system and have less immune activity. In colder tumors, additional strategies may be needed to increase immune visibility.
This is where combination approaches become especially important. Cancer vaccines may need to be combined not only with checkpoint inhibitors, but also with local therapies, ablation techniques, immune stimulants, or other methods that help expose tumor antigens and remodel the tumor microenvironment.
A Realistic View of the Future
The progress in personalized mRNA cancer vaccines is important, but it should not be misunderstood. These vaccines are not currently a universal solution for cancer. They are not designed to prevent cancer in the general population in the same way that vaccines against infectious diseases prevent viral infections. They are therapeutic tools being studied in specific clinical contexts, often after surgery, with the goal of reducing recurrence risk.
The strongest evidence so far has emerged in high-risk melanoma, particularly in combination with pembrolizumab. Larger trials will determine whether these results hold in broader patient populations and in other tumor types.
Still, the direction is scientifically meaningful. Oncology is moving toward treatments that are more personalized, more immune-guided, and more biologically precise. Instead of treating cancer only by where it appears in the body, researchers are increasingly trying to treat it according to what makes it molecularly unique.
Personalized mRNA vaccines represent this shift. They translate the genetic language of a tumor into immune instructions. They attempt to turn tumor mutations into targets. And they may help the immune system recognize what was once hidden.
This article is for educational purposes and does not replace professional medical advice. Patients should consult their oncology team about their treatment options, individual risks, and treatment availability.
Main reference:
Weber, J. S., Carlino, M. S., Khattak, A., Meniawy, T., Ansstas, G., Taylor, M. H., Kim, K. B., McKean, M., Long, G. V., Sullivan, R. J., Faries, M., Tran, T. T., Cowey, C. L., Pecora, A., Shaheen, M., Segar, J., Medina, T., Atkinson, V., Gibney, G. T., Luke, J. J., … Zaks, T. (2024). Individualised neoantigen therapy mRNA-4157 (V940) plus pembrolizumab versus pembrolizumab monotherapy in resected melanoma (KEYNOTE-942): a randomised, phase 2b study. Lancet (London, England), 403(10427), 632–644. https://doi.org/10.1016/S0140-6736(23)02268-7
Other references:
Fan, S. (2024, junio 26). MRNA cancer vaccines spark renewed hope as clinical trials gain momentum. SingularityHub. https://singularityhub.com/2024/06/26/mrna-cancer-vaccines-spark-renewed-hope-as-clinical-trials-gain-momentum/
Moderna. (2024, June 3). Moderna and Merck announce 3-year data for mRNA-4157 (V940) in combination with KEYTRUDA® (pembrolizumab) demonstrated sustained improvement in recurrence-free survival, distant metastasis-free survival in patients with high-risk melanoma. Issuer Direct. https://feeds.issuerdirect.com/news-release.html?newsid=7833349731277438&symbol=MRNA
