In ancient Greek mythology, a Chimera was a creature that was usually depicted as a lion with an additional goat head and a serpent for a tail. Due to the Chimera’s animal hybrid nature, the term “chimeric” came to fruition in the scientific community as a way to describe an organism containing two or more different sets of DNA.

A CIRM-funded study conducted by Dr. Mathew Blurton-Jones and his team at UC Irvine describes a way for human brain immune cells, known as microglia, to grow and function inside mice. Since the mice contain a both human cells and their own mice cells, they are described as being chimeric.

In order to develop this chimeric “mighty mouse” model, Dr. Blurton-Jones and his team generated induced pluripotent stem cells (iPSCs), which have the ability to turn into any kind of cell, from cell samples donated by adult patients. For this study, the researchers converted iPSCs into microglia, a type of immune cell found in the brain, and implanted them into genetically modified mice. After a few months, they found that the implanted cells successfully integrated inside the brains of the mice.

By finding a way to look at human microglia grow and function in real time in an animal model, scientists can further analyze crucial mechanisms contributing to neurological conditions such as Alzheimer’s, Parkinson’s, traumatic brain injury, and stroke.

For this particular study, Dr. Blurton-Jones and his team looked at human microglia in the mouse brain in relation to Alzheimer’s, which could hold clues to better understand and treat the disease. The team did this by introducing amyloid plaques, protein fragments in the brain that accumulate in people with Alzheimer’s, and evaluating how the human microglia responded. They found that the human microglia migrated toward the amyloid plaques and surrounding them, which is what is observed in Alzheimer’s patients.

In a press release, Dr. Blurton-Jones expressed the importance of studying microglia by stating that,

“Microglia are now seen as having a crucial role in the development and progression of Alzheimer’s. The functions of our cells are influenced by which genes are turned on or off. Recent research has identified over 40 different genes with links to Alzheimer’s and the majority of these are switched on in microglia. However, so far we’ve only been able to study human microglia at the end stage of Alzheimer’s in post-mortem tissues or in petri dishes.”

Furthermore, Dr. Blurton-Jones highlighted the importance of looking at human microglia in particular by saying that,

“The human microglia also showed significant genetic differences from the rodent version in their response to the plaques, demonstrating how important it is to study the human form of these cell.”

The full results of this study were published in Cell.