Reviewing the Present State of Cancer Vaccines
Cancer vaccines are an area of active development, but have yet to succeed in obtaining clinical approval. The principle is much the same as any vaccine: deliver a suitably designed molecule or combination of molecules that will provoke the immune system into recognizing a distinctive feature of the target cell, pathogen, or other structure as a candidate for attack and destruction. Unfortunately tumor cells employ a wide range of mechanisms to suppress, co-opt, and subvert the activities of immune cells, and so it may well be the case that cancer vaccines will remain poorly effective without the addition of means to block these mechanisms.
Despite advancements in traditional cancer treatments such as surgery, chemotherapy, and radiotherapy, many cancers remain difficult to cure, particularly in advanced stages where treatment options are limited. Recently, immunotherapies such as immune checkpoint inhibitors (ICIs), adoptive cell therapy (ACT), and cancer vaccines have emerged as promising approaches to leverage the host immune system against malignancies. While ICIs and ACT have shown efficacy in specific patient populations, their success remains limited, with only a subset of patients achieving sustained responses. Cancer vaccines, however, offer a unique advantage by priming new T cells, potentially targeting a broader array of tumor antigens and inducing more durable immune responses.
Cancer vaccines deliver target antigens, often in combination with adjuvants, to evoke or amplify the host immune system, especially T-cell immunity, to recognize and eliminate malignant cells. They are broadly categorized into two types: therapeutic and prophylactic cancer vaccines. Therapeutic cancer vaccines are post-exposure treatments that induce potent cellular immune responses to eliminate existing cancer cells and establish long-lasting immune memory to prevent recurrence. In contrast, prophylactic cancer vaccines are designed to stimulate the immune system in tumor-free individuals, generating antibodies and immune memory cells that reduce the risk of cancer development.
Numerous cancer vaccines have progressed to clinical evaluation, demonstrating the ability to elicit strong immune responses. However, despite some early successes, the majority have not achieved durable responses or significant clinical efficacy in large phase III trials, presenting both opportunities and challenges for future development. Decades of research have greatly deepened our understanding of cancer vaccines, and the design of an optimal vaccine remains a delicate process. This process requires careful consideration of antigen selection, adjuvant incorporation, administration methods, combination with other therapies, and identification of the appropriate patient population.