A resurgence in clinical trials using RNA interference (RNAi) occurred in 2012. Although there were initial difficulties in achieving efficacious results with RNAi without toxic side effects, advances in delivery and improved chemistry made this resurgence possible. More than 20 RNAi-based therapeutics are currently in clinical trials, and several of these are Phase III trials. Continued positive results from these trials have helped bolster further attempts to develop clinically relevant RNAi therapies. With a wide variety of disease targets to choose from, the first RNAi therapeutic to be clinically approved is not far off. This review covers recently established and completed clinical trials.

CRISPR-Cas genome-editing nucleases hold substantial promise for developing human therapeutic applications but identifying unwanted off-target mutations is important for clinical translation. A well-validated method that can reliably identify off-targets in vivo has not been described to date, which means it is currently unclear whether and how frequently these mutations occur. Here we describe 'verification of in vivo off-targets' (VIVO), a highly sensitive strategy that can robustly identify the genome-wide off-target effects of CRISPR-Cas nucleases in vivo. We use VIVO and a guide RNA deliberately designed to be promiscuous to show that CRISPR-Cas nucleases can induce substantial off-target mutations in mouse livers in vivo. More importantly, we also use VIVO to show that appropriately designed guide RNAs can direct efficient in vivo editing in mouse livers with no detectable off-target mutations. VIVO provides a general strategy for defining and quantifying the off-target effects of gene-editing nucleases in whole organisms, thereby providing a blueprint to foster the development of therapeutic strategies that use in vivo gene editing.