Therapeutic vaccines are designed to treat existing diseases rather than prevent them. These treatments leverage the immune system to combat various illnesses. Their purpose is to stimulate or enhance an immune response that targets specific disease-causing agents or abnormal cells. This approach aims to help the immune system recognize, attack, and manage ongoing conditions.
Distinguishing Therapeutic from Preventive Vaccines
The distinction between therapeutic and preventive vaccines lies in their timing and objective. Preventive vaccines are administered before exposure to a pathogen or disease, building immunity to prevent future infection. They prepare the immune system to recognize and neutralize threats before an illness can take hold, much like a shield.
In contrast, therapeutic vaccines are given after a disease has developed. Their purpose is to help the body fight an existing condition by enhancing the immune system’s ability to recognize and eliminate the specific cells or pathogens causing the illness. For example, a preventive vaccine might protect a healthy person from contracting the flu, while a therapeutic vaccine would aim to help someone already infected with a chronic virus manage or clear that infection.
How Therapeutic Vaccines Function
Therapeutic vaccines operate by presenting antigens to the immune system. These antigens are unique identifiers found on the surface of diseased cells, such as cancer cells, or on infectious agents like viruses. By introducing these antigens, the vaccine effectively informs the immune system about the specific threat it needs to address.
Once introduced, these antigens are taken up by specialized immune cells called antigen-presenting cells (APCs), such as dendritic cells. APCs process the antigens and display fragments of them on their surface using major histocompatibility complex (MHC) molecules. This presentation is an important step, as it allows other immune cells, particularly T-cells, to recognize the foreign or abnormal material.
The activation of T-cells is an important part of the therapeutic vaccine’s mechanism. Cytotoxic T-cells (CD8+ T cells) identify and destroy cells displaying the target antigens, like infected cells or tumor cells. Helper T-cells (CD4+ T cells) play a coordinating role, assisting in the activation and regulation of other immune cells, including cytotoxic T-cells and B-cells. B-cells, when activated, produce antibodies that specifically target and neutralize pathogens or mark diseased cells for destruction. This coordinated immune response aims to clear or control the existing disease.
Applications Across Diseases
Therapeutic vaccines are being developed for various conditions, particularly cancer and chronic infectious diseases. In cancer, these vaccines aim to stimulate an immune response against tumor cells. For instance, Sipuleucel-T, an approved therapeutic vaccine for prostate cancer, targets cancer cells. Research also explores vaccines for melanoma, breast cancer, and other malignancies by targeting tumor-specific antigens or neoantigens, which are newly formed proteins on cancer cells.
For chronic infectious diseases, therapeutic vaccines seek to boost the immune response against persistent pathogens. In cases like HIV, the goal is to control viral replication and potentially clear viral reservoirs. Hepatitis B (HBV) and Hepatitis C (HCV) are also targets, where therapeutic vaccines aim to activate T-cells to eliminate infected liver cells and achieve sustained viral control. Efforts are also underway for Human Papillomavirus (HPV), which can cause chronic infection and lead to certain cancers.
Current State of Therapeutic Vaccine Research
The field of therapeutic vaccine development is actively progressing, with numerous candidates currently undergoing investigation in clinical trials. While many are still in various phases of testing, some therapeutic vaccines have received regulatory approval for specific conditions. Sipuleucel-T, for example, gained approval for certain forms of prostate cancer in 2010.
Ongoing research focuses on identifying new and more effective antigens to target, and improving vaccine delivery methods to enhance immune responses. Scientists are exploring different platforms, including protein-based, peptide-based, whole-cell, and nucleic acid-based vaccines like mRNA and DNA vaccines. Researchers are also investigating combination therapies, where therapeutic vaccines are used alongside other treatments such as immune checkpoint inhibitors or chemotherapy, to potentially improve overall patient outcomes.