A vaccine is a biological preparation that stimulates the immune system to recognize and defend against specific diseases. It typically contains weakened or inactivated forms of viruses, bacteria, or other infectious agents, or components of these microorganisms, such as their proteins or sugars. The main purpose of a vaccine is to mimic an infection without causing the disease itself. When a vaccine is administered, the immune system recognizes these harmless antigens as foreign invaders and mounts an immune response. This response includes the production of antibodies, specialized immune cells, and memory cells that “remember” the specific antigens. If the vaccinated person is later exposed to the actual infectious agent, their immune system can quickly recognize and destroy it, preventing or significantly reducing the severity of the disease. Vaccines not only protect individuals who receive them but also contribute to community immunity, reducing the spread of infectious diseases within a population. Several vaccines are commonly used worldwide to prevent various infectious diseases. Some of the most widely administered vaccines include, MMR vaccine which protects against measles, mumps, and rubella, DTaP (DPT) vaccine against diphtheria, tetanus, and pertussis, Polio vaccine, immunizes against poliovirus, which can cause polio, a highly infectious disease that can lead to paralysis, Hepatitis B vaccine which protects against the hepatitis B virus, which can cause liver disease, Hib vaccine against Haemophilus influenzae type b, Pneumococcal vaccine, Rotavirus vaccine, Varicella (Chickenpox) vaccine, HPV vaccine, Influenza vaccine against seasonal influenza viruses and lastly, COVID-19 vaccines which prevent infection with the SARS-CoV-2 virus, the cause of the COVID-19 pandemic. These vaccines are recommended by health authorities worldwide and are typically included in routine vaccination schedules for infants, children, adolescents, and adults based on age, health status, and potential exposure risks. They have played a significant role in preventing the spread of diseases and reducing their impact on public health.
What are Cancer vaccines?
Cancer vaccines are a form of immunotherapy that aims to stimulate the body’s immune system to recognize and attack cancer cells. There are two main types:
- Preventive vaccines, these are designed to prevent certain types of cancers by targeting viruses known to cause them. For instance, the human papillomavirus (HPV) vaccine can prevent cervical, anal, and other cancers caused by HPV infections. Hepatitis B vaccine also reduces the risk of liver cancer associated with chronic hepatitis B infections.
- Therapeutic Vaccines: These are used to treat existing cancers by helping the immune system recognize and attack cancer cells more effectively. Unlike traditional vaccines that prevent diseases by priming the immune system beforehand, therapeutic cancer vaccines are administered after cancer diagnosis to boost the immune response against the cancer cells.
Therapeutic cancer vaccines function by showing the immune system specific parts of cancer cells, like little flags or markers. This helps the immune system recognize these markers as something foreign or harmful. As a result, the immune system gears up to attack and eliminate the cancer cells containing these markers. They can be designed using various approaches like tumour-associated antigen vaccines, dendritic cell vaccines and genetic vaccines. Research in cancer vaccines is ongoing, aiming to improve their efficacy, reduce side effects, and expand their application to various types of cancers. While some cancer vaccines have shown promise in clinical trials, many are still in development and require further study to confirm their effectiveness.
How does preventive vaccines work?
Preventive vaccines work by training the immune system to recognize and mount a defence against specific viruses, thereby preventing infections and the subsequent development of virus-associated cancers. Here is how they typically function:
Introducing Antigens: Vaccines contain weakened or inactivated parts of the virus (antigens) or substances that mimic the virus. These antigens are not harmful but are recognizable by the immune system as foreign.
Immune Response Activation: When the vaccine is administered, the immune system recognizes these antigens as potential threats. This triggers the immune system to produce antibodies and activate immune cells (such as T cells) that specifically target and eliminate the virus or infected cells.
Memory Cells Formation: After the initial exposure to the vaccine, the immune system retains a memory of the antigens. If the individual encounters the actual virus later in life, their immune system can quickly recognize and respond to the virus, preventing infection or reducing its severity. For example, the HPV vaccine contains proteins from the outer coat of the virus, which triggers the immune system to produce antibodies against those specific proteins. If a person is later exposed to HPV, their immune system recognizes the virus and can mount a swift defence, preventing a persistent infection that could lead to HPV-related cancers. Similarly, the hepatitis B vaccine contains a part of the hepatitis B virus that stimulates the immune system to produce antibodies against the virus. If a vaccinated individual comes into contact with the hepatitis B virus, their immune system is prepared to neutralize it before it causes infection or leads to chronic liver disease and potential liver cancer. Overall, these vaccines prime the immune system to recognize and respond effectively to specific viruses, thereby preventing infections and reducing the associated risk of developing virus-induced cancers.
Preventive vaccines in cancer primarily focus on preventing infections by specific viruses that are known to significantly increase the risk of developing certain types of cancers. These vaccines target viruses rather than cancer cells directly. Here are some examples:
Human Papillomavirus (HPV) Vaccine: HPV infections are linked to several cancers, including cervical, anal, vaginal, vulvar, penile, and some oropharyngeal cancers. The HPV vaccine targets various strains of the virus to prevent these infections. It is most administered to adolescents and young adults before they become sexually active to provide protection against HPV-related cancers.
Hepatitis B Virus (HBV) Vaccine: Chronic hepatitis B infections can lead to liver cancer (hepatocellular carcinoma). Vaccination against hepatitis B significantly reduces the risk of contracting the virus and lowers the risk of liver cancer.
Hepatitis C Virus (HCV) Vaccine (Under Development): As hepatitis C infections can also lead to liver cancer, researchers are working on vaccines to prevent HCV infections and reduce the associated cancer risk. However, an effective vaccine against hepatitis C is still in the developmental stage.
Epstein-Barr Virus (EBV) Vaccine (Under Investigation): EBV is associated with several types of cancer, including Burkitt lymphoma, Hodgkin’s lymphoma, and nasopharyngeal carcinoma. Vaccines targeting EBV are being researched to prevent these infections and potentially lower the risk of developing these cancers. It is important to note that while these vaccines significantly reduce the risk of associated cancers, they do not eliminate all potential risks. Regular screenings and other preventive measures are still recommended for individuals even after vaccination to ensure early detection and appropriate management if cancer does develop.
Therapeutic vaccines in cancer treatment are designed to stimulate the body’s immune system to recognize and attack cancer cells more effectively. Unlike preventive vaccines that aim to prevent infections, therapeutic vaccines are used after a cancer diagnosis to help the immune system target and destroy existing cancer cells. Here is how they generally work:
Identifying Targets: Therapeutic cancer vaccines are developed based on specific antigens or markers found on cancer cells. These antigens can be unique to cancer cells or more prevalent on them compared to healthy cells.
Stimulating Immune Response: The vaccine contains the cancer-specific antigens or substances that resemble them. When administered, the vaccine prompts the immune system to recognize these antigens as foreign or harmful.
Immune Activation: The immune system responds by generating an immune response against the antigens present in the vaccine. This includes the production of immune cells (such as T cells and B cells) and antibodies that are capable of targeting and attacking cancer cells bearing these antigens.
Enhancing Immune Recognition: The goal of therapeutic vaccines is to enhance the immune system’s ability to identify and eliminate cancer cells. By training the immune system to recognize cancer-specific antigens, these vaccines aim to improve the body’s natural defences against the tumour. There are different types of therapeutic Vaccines:
Tumour-associated antigen vaccines: These vaccines target specific proteins or antigens found on cancer cells. For instance, prostate cancer vaccines might target prostate-specific antigen (PSA), and breast cancer vaccines might target HER2/neu.
Dendritic cell vaccines: These vaccines involve extracting a patient’s own immune cells (dendritic cells), loading them with cancer-specific antigens in a laboratory, and then reintroducing these modified cells into the patient. Dendritic cells are potent activators of the immune system and can trigger a robust response against cancer cells.
Genetic vaccines: DNA or RNA-based vaccines deliver genetic material encoding tumour antigens directly into cells. These vaccines aim to prompt the patient’s cells to produce specific cancer antigens, triggering an immune response against these antigens.
Therapeutic cancer vaccines are an active area of research and clinical trials. While some have shown promise in activating the immune system against cancer cells, their effectiveness can vary among different types of cancers and among individuals. Research continues to explore ways to enhance the efficacy of these vaccines and broaden their application in cancer treatment. Few examples of therapeutic vaccines under research include
Sipuleucel-T (Provenge): This is a therapeutic vaccine used for advanced prostate cancer. It is a personalized vaccine made from a patient’s own immune cells (dendritic cells) that are exposed to a protein found in prostate cancer cells. Once activated, these cells are reintroduced into the patient to trigger an immune response against prostate cancer cells.
GVAX: GVAX is a cancer vaccine that uses genetically modified cancer cells to produce proteins that stimulate an immune response against the cancer. It has been studied in various cancers, including pancreatic cancer and leukaemia.
Tecentriq (atezolizumab) in combination with Cancer Vaccine: Tecentriq is an immune checkpoint inhibitor used in combination with cancer vaccines in some clinical trials. This combination aims to enhance the immune response against specific tumour antigens. Tumour-specific antigen peptides targeting melanoma-specific antigens, MAGE-A3 vaccine against various cancers, including melanoma, lung, and head and neck cancers.
The COVID-19 vaccines and cancer vaccines serve different purposes and target different health conditions: COVID-19 vaccines are designed to prevent infection with the SARS-CoV-2 virus, which causes COVID-19, a respiratory illness. These vaccines stimulate the immune system to recognize and fight the specific virus that causes COVID-19. They contain genetic material, proteins, or weakened forms of the virus to trigger an immune response. This response prepares the body to defend against the virus if a vaccinated person is exposed to it. The primary goal of COVID-19 vaccines is to prevent individuals from contracting the virus, reduce the severity of illness if infection occurs, and help control the spread of the virus within communities. In summary, COVID-19 vaccines aim to prevent viral infections caused by the SARS-CoV-2 virus, while cancer vaccines, particularly therapeutic ones, are focused on boosting the immune system’s ability to recognize and attack cancer cells within the body.
Cancer vaccines, like other medical treatments, may come with potential side effects, though they can vary widely depending on the specific type of vaccine, individual patient factors, and the stage of research or development. Here are some possible side effects associated with cancer vaccines: local reactions, systemic reactions, allergic reactions, overstimulation or under stimulation, vaccine-specific reactions and treatment-specific effects. It’s important to note that many cancer vaccines are still in clinical trial phases, and the side effect profiles can vary between different vaccines and patient populations. Monitoring and managing these side effects are critical aspects of the ongoing research and development of cancer vaccines. Lastly theoretical risk as few people might worry that stimulating the immune system in this way could potentially promote the growth of cancer cells. This concern arises from the complex interactions of the immune system with cancer cells, where in certain contexts, immune responses could inadvertently aid cancer growth or progression. However, this is still an area of ongoing research and remains a theoretical consideration rather than a proven risk in most cases.
Overall, the goal of cancer vaccines is to provide a targeted and