Cancer vaccine

Introduction

A cancer vaccine is a type of vaccine that either treats existing cancer or prevents the development of cancer. Vaccines that treat existing cancer are known as therapeutic cancer vaccines. Some vaccines are "autologous," being prepared from samples taken from the patient, and are specific to that patient. Some researchers claim that cancerous cells routinely arise and are destroyed by the immune system (immunosurveillance); and that tumors form when the immune system fails to destroy them. Some types of cancer, such as cervical cancer and some liver cancers, are caused by viruses (oncoviruses). Traditional vaccines against those viruses, such as the HPV vaccine and the hepatitis B vaccine, prevent those types of cancer. Other cancers are to some extent caused by bacterial infections (e.g., stomach cancer and Helicobacter pylori). Traditional vaccines against cancer-causing bacteria (oncobacteria) are not yet available.

Mechanism of Action

Cancer vaccines work by stimulating the immune system to attack cancer cells. The immune system recognizes antigens on the surface of cancer cells as foreign and mounts an immune response against them. This process involves several steps:

1. **Antigen Presentation**: Cancer cells express abnormal proteins (antigens) on their surface. These antigens are taken up by antigen-presenting cells (APCs) such as dendritic cells. 2. **Activation of T Cells**: The APCs process the antigens and present them on their surface to T cells. This activates the T cells, which then proliferate and differentiate into effector T cells. 3. **Targeting Cancer Cells**: The effector T cells recognize and kill cancer cells that express the specific antigens.

Types of Cancer Vaccines

Preventive (Prophylactic) Vaccines

Preventive cancer vaccines are designed to prevent cancer from developing in healthy people. The most well-known preventive cancer vaccines are the HPV vaccine and the hepatitis B vaccine. These vaccines target viruses that can cause cancer.

Therapeutic Vaccines

Therapeutic cancer vaccines are designed to treat existing cancer by strengthening the body's natural defenses against the cancer. Examples include:

**Sipuleucel-T (Provenge)**: This vaccine is used to treat prostate cancer. It involves collecting a patient's dendritic cells, exposing them to a protein found on prostate cancer cells, and then reinfusing them into the patient.
**Talimogene laherparepvec (T-VEC)**: This oncolytic virus vaccine is used to treat melanoma. It involves injecting a modified herpes simplex virus directly into tumors, where it replicates and produces a protein that stimulates an immune response.

Development and Challenges

The development of cancer vaccines involves several stages, including preclinical studies, clinical trials, and regulatory approval. Some of the challenges in developing effective cancer vaccines include:

**Tumor Heterogeneity**: Cancer cells within the same tumor can be genetically diverse, making it difficult to target all cancer cells with a single vaccine.
**Immune Evasion**: Cancer cells can develop mechanisms to evade the immune system, such as downregulating antigen presentation or secreting immunosuppressive factors.
**Safety and Efficacy**: Ensuring that cancer vaccines are both safe and effective is crucial. This requires extensive testing in clinical trials.

Current Research and Future Directions

Research on cancer vaccines is ongoing, with several promising approaches being investigated:

**Personalized Vaccines**: These vaccines are tailored to the specific mutations found in an individual's cancer. This approach aims to target the unique antigens present in each patient's tumor.
**Combination Therapies**: Combining cancer vaccines with other treatments, such as immune checkpoint inhibitors, can enhance the overall immune response against cancer.
**Neoantigen Vaccines**: These vaccines target neoantigens, which are new antigens that arise from mutations in cancer cells. Neoantigen vaccines are highly specific to the tumor and have shown promise in early clinical trials.