The body’s immune system is often likened to an army, and vaccines to training exercises that build up defenses against pathogens. By exposing the immune system to inactive forms of a virus or bacteria, a vaccine trains antibodies to fight off a real pathogen in the event of an invasion. However, while vaccines prepare antibodies to identify an attacker, they often don’t give specific instructions on exactly how to bring it down. Some antibodies may successfully hit a pathogen’s weak spot, while others may miss the mark entirely. That’s part of the reason why it normally takes several weeks or months for some vaccines to build up an effective immune response.
Now researchers at the Scripps Research Institute have developed preprogrammed chemicals that bind to antibodies and tell them how to recognize part of a pathogen, known as its epitope. In experiments, the team found that such chemicals prompted a therapeutic immune response that inhibited the growth of two types of tumors in mice. The researchers published their findings in the latest issue of the Proceedings of the National Academies of Science.
“We used a chemistry-based approach that wouldn’t induce antibodies that might be wasted,” says Carlos Barbas, a professor of molecular biology and lead investigator on the paper. “[This approach] could focus an immune response on functional epitopes of the pathogen, be it cancer or a virus.”
The group’s chemical-based vaccine may address a number of problems with some current vaccines, both in the clinic and in the lab. Today, there are only two FDA-approved, licensed cancer vaccines: one that targets Hepatitis B associated with liver cancer, the other for human papillomavirus (HPV), which leads to cervical cancer. For both vaccines, patients must go in for multiple immunizations to build up an effective defense over time. There are no licensed therapeutic vaccines that directly treat existing cancers, and researchers have found it difficult to train antibodies to attack cancer cells, since they arise from the body and are not generally regarded by the immune system as foreign.
In the past few years, however, researchers have identified cell-surface markers unique to cancer cells. There are molecules called adjuvants that attach to such markers and trick the immune system into recognizing and attacking tumors. Adjuvants are used in clinics today, but some come with unwanted side effects–for example, soreness, fever, and arthritis. Scientists are now looking for ways to genetically engineer monoclonal antibodies–antibodies created from a single cell line–to recognize tumor markers and attack cancer. But these methods are expensive, and Barbas says that a chemical-based approach may provide a cheaper and faster alternative.