CRISPR-Cas9 gene editing therapeutics are advancing towards their first-ever human tests. However, a newly published research from Charité – Universitätsmedizin Berlin has overshadowed this advancement. The study has shown that a key component of CRISPR-Cas9 gene editing could attack, and possibly even be disabled by the human immune systems. Even more critical is the fact that this might be true for the large majority of people. Publication of a separate study in January, with a similar conclusion, had precipitated a massive drop in stock prices of CRISPR companies, such as CRISPR Therapeutics (NASDAQ: CRSP), Editas Medicine (NASDAQ: EDIT) and Intellia Therapeutics (NASDAQ: NTLA). While the previous paper only disrupted the stock market, the newly published paper in Nature Medicine has researchers concerned about the looming human trials.
In January, a research team led by Matthew Porteus of the Stanford School of Medicine 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.
The more recently published research from Charité – Universitätsmedizin Berlin has confirmed the results produced by The Porteus Lab. Blood samples from 48 healthy volunteers were exposed to Cas9 (a DNA-cutting enzyme) derived from a bacterium called Streptococcus pyogenes. Of the 48 volunteers, 41 (85%) samples had antibodies against Cas9, and 46 (96%) had T-cell based immunity.
The lead researcher, Michael Schmueck-Henneresse, said that he was initially surprised by the 96% finding. He wrote in an email,
“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.
In an email, Matthew Porteus of the Stanford School of Medicine said,
“The latest results show that issue of immunity to CRISPR-Cas9 remains one that needs to be closely considered.”
The Effects of These Results On CRISPR-based Therapeutics.
Schmueck-Henneresse urges caution going into clinical trials. He says, “At this point, we cannot predict what will happen [in humans],” it will depend on a variety of factors, such as how the CRISPR-Cas9 system is packaged and delivered throughout the body and what tissue is being targeted. He added, “CRISPR drug developers should minimize the amount of time Cas9 is active in cells, and they could consider giving the first patients immune-suppressing drugs.”
While other researchers have also raised a red flag around another CRISPR effect for unintended edits in off-target spots along the genome, Gaetan Burgio, a genome-editing expert at Australian National University, wrote on Twitter in April, “But pre-existing immunity to Cas9 is more of a worry than off-target edits”. However, in a tweet in response to the latest version of the paper, Burgio wrote that there are ways to circumvent the immunity issue.
Published now in @NatureMedicine on #CRISPR & Immunity to SpCas9. 6 months has past since the preprint was online & it is a long time in the CRISPR field. Since then additional work showed how to circumvented this by modifying Cas9 protein or using Cas9 orthologs. So No panic ! https://t.co/S9ZCAElH6X
— Dr Gaetan Burgio, MD, PhD. (@GaetanBurgio) October 30, 2018
Intellia Therapeutics, a leading biopharmaceutical company, has commented that they “have been on the lookout for T-cell based immunity against its CRISPR system.” They currently use lipid nanoparticles (LNPs) to deliver CRISPR to the liver. Intellia spokesperson Jenn Smoter said, “Intellia researchers have tested their LNPs in lab animals. We have seen no evidence of T-cell mediated cytotoxicity to the cells expressing Cas9”. Their other treatment programs use CRISPR to modify cells outside of the body, where this pre-existing immunity is less of an issue.
Nevertheless, by using other kinds of DNA-cutting enzymes, it is possible to solve the immunity issue. Indeed, his team tested other enzymes such as Cpf1 and found similar immune reactions. He suggests pursuing Cas9 from bacteria that are not known to infect humans.
However, Schmueck-Henneresse says, “There’s no reason to panic, our results are a warning, but immunogenicity has been a problem in the field of gene therapy for a long time”.