Biomaterials coax immune cells to help heal damaged tissue

When bioengineers develop materials for medical implants, they often look for ways to avoid sparking an immune response that could lead to inflammation and formation of scar tissue.

But a study in Science reports that certain immune cells can promote healing in response to some biomaterials (2016, DOI: 10.1126/science.aad9272). The findings could lead to biomaterial-based therapies that regenerate tissue after injuries or infections.

“It’s almost the opposite of what you’d expect,” says Stephen F. Badylak of the University of Pittsburgh, who wrote a commentary accompanying the new report. “They’re suggesting working with the immune system instead of fighting it.”

A team led by Jennifer H. Elisseeff of Johns Hopkins University studied how wounds in the leg muscles of mice healed following injections of materials derived from pig bone and muscle. After examining the immune response at the injury site, the researchers hypothesized that type 2 helper T cells might be crucial for the resulting tissue regeneration. These cells normally fight off parasitic worm infections and are involved in some allergic reactions.

The team next studied similar injuries in mice engineered to lack T cells. After treatment with the biomaterials, these animals did not regrow much muscle tissue and struggled in a treadmill test of muscle function.

When the researchers injected some of these engineered animals with a mixture of normal T cells, they observed almost full functional recovery. But mice receiving injections of T cells incapable of becoming the type 2 helper form showed little improvement, indicating that activation of this cell type is necessary for regeneration.

“We can now use this information to try to induce this pathway with new biomaterials development,” Elisseeff says. One method, she says, could involve pairing biomaterials with small molecules that activate type 2 helper T cells.