A strong research paper from scientists at the Wellcome Sanger Institute has again raised doubts over the safety and accuracy of the CRISPR-Cas9 gene editing technique. The study suggests that the gene editing process can cause extensive unforeseen and unpredictable alterations to DNA sequences outside of the intended targets.

The new research systematically examined the broader effects of CRISPR-Cas9 gene editing in mouse and human cells. It was found that after the Cas9 enzyme made its initial cut to the desired DNA location, it unpredictably continued to make cuts that resulted in areas close to the target site being rearranged or inverted.

"This is the first systematic assessment of unexpected events resulting from CRISPR/Cas9 editing in therapeutically relevant cells, and we found that changes in the DNA have been seriously underestimated before now," explains Allan Bradley, corresponding author on the study. "It is important that anyone thinking of using this technology for gene therapy proceeds with caution, and looks very carefully to check for possible harmful effects."

Despite many human clinical trials using CRISPR being on the precipice of commencement, the last few months have not been kind to this potentially revolutionary but still quite nascent technique. Two studies published in early June raised concerns that the process could trigger mechanisms that increase the risk of cancer.

The concerns over the technique's off-target effects, or ability to initiate unintended genetic mutations, have been muted until now. A controversial study last year, claiming the technique introduces multiple off-target mutations, was ultimately retracted after a chorus of criticism attacked the veracity of the work. This new study, on the other hand, seems to be much more rigorous and well-supported according to several experts in the area.

Francesca Forzano, a consultant in Clinical Genetics and Genomics at Guy's & St Thomas' NHS Foundation Trust, suggests this is a good quality piece of research with important implications for all in the field.

"This work represents a milestone in the gene editing field and signpost that more caution should be exerted in the application of this technique and more research is needed before considering any possible clinical application," says Forzano.

Cristopher Galichet, from the Francis Crick Institute, also iterates the veracity of the study but questions the anomalous nature of this single paper. Galichet asks, "… how the type of mutations describe[d] in the paper, some of which being large deletions, were missed in previous studies."

The burgeoning multi-billion dollar CRISPR industry is also questioning what this research actually means in practice. With stocks of several publicly traded CRISPR companies losing tens of millions of dollars within minutes of this new research being published, some are simply claiming this new study is just not relevant to a great deal of current CRISPR work.

Tom Barnes from CRISPR company Intellia Therapeutics reported to Stat News that they have not, "seen any [cancer-causing] transformation of these cells, even with all the edits we've introduced." And, Robin Lovell-Badge, from the Francis Crick Institute suggests, "it is not at all clear that the specific protocols used in the paper would relate much to any sensible use of genome editing clinically."

Perhaps the clearest analysis of this new research comes from Australia National University geneticist Gaetan Burgio, who recognizes these potential limitations with Cas9 gene editing and suggests there are several new CRISPR techniques that can actually overcome the problems cited in this new research.

Burgio explains some newer forms of CRISPR don't aggressively cut DNA like the Cas9 technique. Instead, other techniques cut only RNA, or even simply rearrange the letters of DNA without carving it.

The overriding conclusion most experts are reaching in the wake of this new study is that gene editing may be a lot more difficult than we initially suspected. Still, human clinical trials are moving forward with work already underway in China, and studies in Europe and the United States set to commence later this year.

Will these early human trials prove disastrous, demonstrating dramatic unforeseen side effects? Or will they prove some of these preliminary concerns to be irrelevant? This is compelling uncharted territory for scientists.

The study was published in the journal Nature Biotechnology.