How immunology is learning to recognize individual cancer

Personalized vaccines against tumors have become one of the most notable topics in modern oncology because they change the usual understanding of a vaccine. In the classical sense, a vaccine is used to prevent an infectious disease: it introduces the immune system to a pathogen in advance and forms a protective response. In oncology, the logic is different. A cancer vaccine is usually created after the diagnosis of cancer and is directed not against a virus or bacterium, but against the individual features of tumor cells in a specific patient.

The main idea is to find unique tumor targets. A malignant cell differs from a normal cell not only by rapid division, but also by a set of genetic changes. Some of these changes lead to the appearance of neoantigens — altered protein fragments that can be recognized by the immune system as foreign. If such neoantigens can be accurately identified, they can be used as the basis for a vaccine. The goal is to activate T lymphocytes and direct them against cells carrying these tumor-specific features.

The process of creating a personalized vaccine begins with the analysis of tumor tissue and a normal sample from the patient. Sequencing is used to identify mutations that are characteristic specifically of the tumor. Then bioinformatic algorithms evaluate which of these mutations are most likely to become strong immune targets. After that, an individual construct is created, most often based on mRNA or peptides, encoding the selected neoantigens. Such a vaccine is not a standard drug that is the same for all patients. It is essentially manufactured for the specific molecular profile of one tumor.

Why mRNA has become a convenient platform. mRNA technology allows cells to receive instructions for synthesizing specific protein fragments relatively quickly. In the case of an oncological vaccine, these fragments are tumor neoantigens. After administration, cells present these antigens to the immune system, and T cells receive a signal to recognize similar structures on tumor cells. Unlike preventive vaccines against infections, the task here is not to create a barrier against infection, but to strengthen an existing or potential antitumor immune response.

The most notable clinical data are associated with melanoma. Individualized mRNA therapy has been studied in combination with immune checkpoint inhibitors in patients with high-risk melanoma after complete surgical removal of the tumor. This approach is important because melanoma often has a high mutational burden, meaning it may produce more neoantigens that can be recognized by the immune system. The combination of a personalized vaccine with immunotherapy is biologically logical: one component shows the immune system what to attack, while the other helps preserve immune activity against the tumor.

It is important to understand that such a vaccine usually does not work in isolation. In many studies, it is used together with a PD-1 inhibitor or another form of immunotherapy. A checkpoint inhibitor helps remove one of the braking mechanisms of the immune response, while the vaccine provides the immune system with more precise targets. This is why the combination looks biologically justified: one component defines the target, and the other helps the immune system remain active against cancer. The combination of personalized antigen stimulation and immune checkpoint therapy has therefore become one of the leading directions of research.

The clinical value of personalized vaccines is especially visible after surgery. Even if a tumor has been completely removed, some patients remain at risk of microscopic residual disease. Such cells cannot be seen using ordinary imaging methods, but they may become the source of recurrence. Adjuvant therapy is intended to reduce this risk. In this situation, a personalized vaccine may theoretically help the immune system recognize and destroy remaining tumor cells if they carry the same neoantigens that were found in the removed tumor.

However, the technology remains complex. Its use requires obtaining a high-quality tumor sample, performing sequencing, conducting bioinformatic analysis, selecting targets, manufacturing an individual product and delivering it to the patient within a clinically reasonable timeframe. Every stage requires standardization. An error in antigen selection, insufficient material quality or production delay may reduce efficacy. Therefore, a personalized vaccine is not only a drug, but an entire technological chain in which laboratory medicine, molecular oncology, immunology and manufacturing must work as a single system.

Another important issue is tumor heterogeneity. Cancer cells within one tumor can differ from one another. Some mutations are present in all tumor cells, while others are found only in individual subclones. If a vaccine targets antigens that are not present in all cells, part of the tumor may escape immune pressure. For this reason, the selection of neoantigens requires not only technical analysis, but also an understanding of tumor evolution. The more accurately common and immunogenic targets are selected, the higher the probability of clinical benefit.

Research is gradually expanding beyond melanoma. Personalized mRNA vaccines are being studied in lung cancer, bladder cancer, kidney cancer and other tumors. At the same time, results cannot be automatically transferred from one cancer type to another. Melanoma usually has a high mutational burden and is more responsive to immunotherapy, whereas other tumors may be less immunogenic or may have a more complex microenvironment. This means that the success of personalized vaccines will depend on the biology of each tumor type and on the ability to combine vaccination with other treatment strategies.

A separate direction concerns tumors in which the immune response is traditionally considered more difficult. For example, personalized neoantigen vaccines are being studied in breast cancer, pancreatic cancer and other diseases where standard immunotherapy has not always produced strong results. These studies are important because they test whether individualized immune targeting can expand the possibilities of immunotherapy beyond tumors that are already known to be highly immunogenic. However, small early studies cannot yet determine the real effect on survival, recurrence risk or long-term disease control. Larger trials are needed.

Safety also requires careful observation. A cancer vaccine must activate immunity, but not cause excessive inflammation or autoimmune complications. In combination with immune checkpoint inhibitors, the risk of immune-related adverse events may increase because the immune system becomes more active. Therefore, clinical studies assess not only recurrence rates, but also tolerability, types of adverse reactions, the need for immunosuppressive therapy and the impact of treatment on quality of life.

The main limitation of personalized vaccines is that they are not yet a universal treatment for cancer. This is a highly specialized approach for specific clinical situations where there is a clear tumor target, preserved immune reactivity and the ability to perform complex molecular preparation. But this is exactly why they are important: oncology is gradually moving from diagnosis by organ to diagnosis by tumor biology. In the future, a vaccine for melanoma, lung cancer or breast cancer may not mean one standard drug, but an individual immune instruction created from a specific tumor.

Personalized cancer vaccines show that modern medicine is moving toward more precise and dynamic treatment. A tumor is no longer viewed only as a mass of cells that must be removed or suppressed. It becomes a source of molecular information that can be used against the tumor itself. If future studies confirm sustained clinical benefit, such vaccines may become an important part of combined oncological therapy. Their development will depend on the quality of molecular diagnostics, speed of manufacturing, strict regulatory assessment and the ability of physicians to choose patients for whom this approach truly makes sense.