Scientists breed most human-like mice yet

For the first time, scientists have bred mice with fully fledged human immune systems. The researchers say these human-like animals will enhance drug development.

When faced with an infection, these "humanized" mice produce immune cells that mimic the structure and diversity of the immune cells made by humans. When injected with a chemical that triggers widespread inflammation in the body, the mice develop a version of the autoimmune disease lupus that closely resembles that seen in humans, the researchers discovered. 

The scientists described their findings in a paper published June 25 in the journal Nature Immunology. 

These are not the first humanized mice ever bred — the lab Animals are staples in research as they enable scientists to study features of the human immune system inside a living animal. This is helpful for testing the safety and effectiveness of new drugs, as well as vaccines against infectious diseases, before they are trialed in humans. 

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However, for years, researchers have struggled to create humanized mice that accurately respond to infection in the same way that humans do. Previous attempts have resulted in approximations of the human immune system, but these are missing certain human features, the team behind the new paper said in a statement. 

To develop a better humanized mouse, the researchers first bred mice that had been genetically modified to have a weakened immune system. When the mice were around 1 to 2 days old, the team injected human stem cells into the Animals' hearts. The stem cells, which had been extracted and purified from umbilical cord blood, were capable of becoming any type of immune cell.