Immune stimulation, as a vaccine

Immune stimulation refers to the stimulation of the immune system by an external source. The stimulation can confer a protective effect against microorganisms . As well, immune stimulation shows promise as a means of obtaining an immune response to conditions such as cancer.

Conventionally, the immune system is stimulated into producing antibodies or other infection-fighting constituents in response to an infection. Immune stimulation seeks to elicit the immune reaction before infection or other malady strikes, as a means of preventing the infection or malady. This approach is analogous to the administration of components of weakened or inactive influenza virus to protect people from the subsequent onset of influenza.

The roots of the use of immune stimulation as a vaccine date back to the late nineteenth century. Then, William Coley, a New York bone surgeon, began treatments in which he injected cancer sufferers with a preparation consisting of dissolved Streptococcus pyogenes bacteria . Anecdotal evidence claimed remission of tumor growth in 40% of the treated patients. Then, in the 1980s, it was discovered that the observed anti-tumor activity of a bacteria known as Bacillus Calmette-Guerin was a property of the construction of the bacterial genetic material. Indeed, the bacterial genetic material is able to stimulate the immune system such that the target sequence of the bacterial gene is distinguished from the host genetic material. The resulting immune stimulation boosts antibody levels as well as another aspect of the immune system known as cell-mediated immunity .

Synthetic peptides have also proved useful as agents of immune stimulation. These compounds are made up of chains of amino acids. They are called synthetic because they are not naturally occurring, but rather are constructed in the laboratory. The peptide can contain amino acids in which a chemical group is oriented in a mirror image of that which is normally found in nature.

The mirror image arrangement proves lethal to various bacteria. For example, synthetic peptides swiftly kill populations of Staphylococcus aureus and Enterococcus faecium that are resistant to an array of antibiotics . The peptide binds to the outer surface of the bacterium and is able to punch a hole through the cell wall. The punctured bacteria die. Furthermore, as the bacteria release their contents, the immune system is stimulated to produce antibodies to the bacterial constituents. The synthetic peptide both kills bacteria directly and stimulates an immune response that acts to kill more bacteria.

Thus far, immune stimulation as a vaccine has been developed towards so-called extracellular infections. These are infection caused by bacteria that adhere to host cells or that proliferate in fluids such as blood. For these types of infections, the immune stimulation aims to produce antibodies. Defense against intracellular infections, which are caused by bacteria invading host cells, requires the stimulation of other immune components, such as phagocytic cells. Furthermore, defense against viral infections requires stimulation of immune components called killer cells.

Synthetic peptides can also stimulate the immune system to recognize a surface constituent of a certain type of cancer cell called a melanoma cell. Melanoma is also commonly referred to as skin cancer. The synthetic peptide can mimic the peptide produced on a tumor that the immune system can recognize and respond to. By supplying the target externally, the immune system has more opportunity to mount a defense against the offending peptide. The resulting antibody molecules would target the peptide on the tumor cells.

While shrinkage of tumors was evident in laboratories studies, confirmation of the clinical power of the technique requires a clinical trial where many people are given the treatment and their progress monitored. Nonetheless, it has been demonstrated that synthetic peptides are capable of stimulating the ability of the immune system to distinguish between antigens that are an innate part of the body from those antigen that come from outside of the body. In the case of many cancers, such immune stimulation is required, as the disease can compromise the natural immune defenses.

See also Immunization; Immunologic therapies