Delivery is vital: before CRISPR genome editing materials can execute a therapeutic change, they must reach their destination. Today, viral delivery is the delivery of choice in vivo. Viruses have evolved many strategies to inject their material into a host cell, and these can be harnessed to deliver the editing cargo. Two problems with viruses are that they may be too small for the cargo, and that they may trigger the body’s immune system. Synthetic organisms like viruses engineered to be bigger and/or evade immune response will help. More speculatively, engineered somatic cells could be delivery vehicles. Allogeneic cell therapy can create “universal cells” to carry synthetic biology circuits; they are less prone to rejection, and can be used to make any tissue in any part of the body.

Experimental organisms will be accelerated by the recent rapid advances in stem cell engineering, synthetic embryos, organoids (artificial and simplified versions of an organ), and tissue engineering. These techniques can provide human physiological models to study and predict the functionalities of genome editors outside the human body and before clinical applications. This is the approach prioritised by the NIH Common Fund’s Somatic Cell Genome Editing and other funding agencies.