The immune systems of a large majority of people could already be primed to attack and possibly even disable a key component of CRISPR-Cas9 gene editing Today’s paper, published in the peer-reviewed journal Nature Medicine, suggests those results from January weren’t a fluke. In the latest research, a team of scientists in Germany exposed blood samples from 48 healthy volunteers to Cas9 (a DNA-cutting enzyme) derived from a bacterium called Streptococcus pyogenes. (Cas9 from S. pyogenes is one of the most common DNA-cutting enzymes used in CRISPR R&D, if not the most commonly used.) The researchers found that 96 percent of the people in the study had T-cell based immunity against Cas9, and 85% had antibodies against it. Those are higher rates than what the other research team, led by Matthew Porteus of the Stanford School of Medicine, showed in January. The Porteus group found that 65% of donors had antibodies against Cas9 from S. pyogenes, but couldn’t detect T cell activity against that enzyme. Previous research from other teams has shown pre-existing immunity in lab animals. Michael Schmueck-Henneresse of Charité University Medicine Berlin, who led today’s study, said that he was initially surprised by the 96% finding. “But it made sense because the Streptococcus pyogenes bacterium is one of the most common causes for bacterial infections in humans and we have all been through multiple infections and potentially even been colonized by it,” he wrote in an email.