Stem Cells as Anti-Cancer Vaccines?
Vaccines are routinely used to increase immunity against a variety of infectious diseases, such as influenza, measles, and chicken pox, to name a few. Rather than vaccinating against viral infectious diseases, however, imagine a vaccine that could prevent cancer.
Researchers have long been interested in developing a vaccine that can help the body’s immune system and fight abnormal, cancerous cells. Certain immune cells, called T cells, regularly scan the surface of every cell in the body and check if they appear normal. Imagine a cell is wearing a printed Hawaiian shirt: the pattern has several parts, such as palm trees and a beach scene, and it repeats. T cells check each cell to be sure that there are no irregularities to the pattern — i.e. changes to color, size, number of palm fronds, etc.
New patterns on a cell (such as a ketchup stain) may indicate that the cell is either infected by a virus or bacteria, or damaged in way that could cause cancer. When T cells identify damaged, aberrant cells they kill the cells so that they can’t grow or divide. Occasionally, however, T cells may not detect a problematic change, and the abnormal cell grows unrestrained, potentially into a tumor. Scientists are working on creating vaccines that could be used to help T cells identify cancerous cells, so they can be eradicated, preventing tumor formation.
Using vaccines to activate the immune system to fight cancer
Tumor cells have adapted mechanisms for evading the immune system, making this effort a challenge. Different types of cancer cells have their own unique differences compared to normal healthy cells, and in order to recognize problematic cells, the immune system needs to recognize many potential changes (different palm tree patterns, ketchup vs mustard stains, etc). Early cancer vaccines were not widely effective because they could only recognize a few of these differences.
Researchers from Stanford University recently tested a new vaccine, composed of stem cells, that may help the immune system recognize many different tumor proteins and stimulate an immune response against several types of cancer.
Vaccinating mice with iPS cells leads to an immune response against tumor cells
Interestingly, tumor cells share properties with cells that are found in early development. Researchers wondered whether they could use embryonic-like stem cells as a vaccine to elicit an immune response against cancer cells. They engineered mouse skin cells in the laboratory to become induced pluripotent stem cells (iPS cells), a process which causes mature cells to take on the characteristics of stem cells in the early embryo. These stem cells do indeed express many proteins that are found on tumor cells, making them intriguing candidates to use as a vaccine against tumor cells. Scientists wondered: if they vaccinated mice with stem cells, would T cells learn to recognize these proteins and be able to later attack the cancer cells that express them?
To test whether an iPS cell vaccine could be used to prevent cancerous cell growth, researchers stimulated the immune system of mice by first vaccinating them with irradiated iPS cells, and then injecting them with cancer cells (the irradiation serves to stop cell proliferation and prevents the iPS cells from forming tumors on their own). Strikingly, researchers found that mice that had been vaccinated with iPS cells initiated a strong immune response and had significantly less tumor progression compared to mice that weren’t vaccinated. The iPS cell vaccine was able to protect the mice against breast, skin, and lung cancer.
iPS cell vaccines may also prevent cancer recurrence
Surgery is a common treatment for cancer in humans, and although surgeons do their best to remove the entire tumor, in many cases a few cancer cells remain. If those cells are able to regrow over time, they may become another tumor, causing cancer recurrence. To test whether the iPS cell vaccine could be used to prevent cancer from recurring, scientists vaccinated mice with irradiated iPS cells after tumor removal. Researchers found that mice vaccinated with iPS cells after surgery were able to illicit an immune response and had significantly less tumor recurrence after surgery compared to mice that weren’t vaccinated.
Can the vaccines work in humans? The need for further study
The initial results of these studies in mice are promising, with evidence that an individual’s own cells can be engineered to make a robust vaccine against tumor cells, using the body’s natural immune system to fight cancer. This proof-of-principle study in mice is just the first step in testing the use of iPS cells as a cancer vaccine. If promising results continue, the vaccine may then be tested in humans in a series of clinical trials, which can take 10 to 12 years.
A single universal cancer treatment to prevent all cancer types has been the pinnacle goal of cancer research for decades. Unexpectedly, the answer could possibly lie in a stem cell vaccine. These remarkable preliminary results are sure to inspire many more studies as researchers work to confirm and further these compelling new findings.