Our immune system could block some gene therapies based on the CRISPR-Cas9 enzyme – at least according to one study  pre-published on the bioRxiv site on 5 January.
CRISPR-Cas9 is a primitive immune system of many bacteria. Today, it is used to correct gene mutations. However, according to this latest study, foreign proteins such as Cas9 could trigger immune responses in humans, blocking gene therapy and posing a health risk to the person receiving the treatment. Indeed, two of the most widely used versions of the Cas9 enzyme come from widespread bacteria against which humans have already been able to develop immune reactions and, therefore, antibodies.
In fact, scientists found that 79% of the study participants  produced antibodies against Cas9 derived from Staphylococcus aureus and 65% against Cas9 derived from Streptococcus pyogenes, i.e. the two bacteria from which Cas9 enzymes are derived.
The threat posed by immune responses is well known to gene therapy scientists. To guard against this, those patients at risk can be screened before treatment is administered. This step should be incorporated in the development of “CRISPR-Cas9 therapy”. However, the finding would have fewer implications for procedures treating cells in vitro before reinjecting them into patients. Another solution would be to replace these at-risk Cas9 enzymes with others obtained from bacteria that do not colonise or infect humans.
Nature, Heidi Ledford (8/01/2018)