As the smoke clears from Jiankui He’s bombshell germline editing announcement, the gap between where the gene editing field is now and where it would need to be to support responsible germline editing has become sharply visible.
Extending the field’s growing capacity to assess gene editing accuracy in somatic cells to embryos would be a logical place to start, but there is little sign existing government-backed consortia, therapeutics companies or diagnostics developers are ready to step up to the plate.
On Nov. 25, He jolted the gene editing space by announcing he had edited the CCR5 gene in human embryos that gave rise to twin girls. The revelation unleashed a debate on ethical, regulatory and scientific questions the field has largely kept on the back burner, even as the technology has moved forward (see “China’s Germline Growing Pain”).
From a technical point of view, the boundary-crossing study has sharpened the need for methods to reliably characterize edits in embryos.
In a presentation at the Second International Summit on Human Genome Editing in Hong Kong on Nov. 28, He detailed the steps he took to preclinically screen guide RNAs for off-target edits, including in silico predictions, cell-free approaches and human embryo cell culture experiments. He also described the pre-implantation sequencing tests and post-implantation cell-free DNA (cfDNA) monitoring he performed for the edited embryos (see “Sidebar: No Rules for He’s Road”).