Clinical application of AAV vectors containing targeted nucleases such as CRISPR-Cas9

COGEM was asked to advise on whether or not the use of targeted nucleases, such as CRISPR-Cas9, in AAV vectors in clinical trials meets the requirements of the generic environmental risk assessment for AAV vectors, and on the need for additional containment measures. COGEM was also asked if its answer also applies to future gene-editing applications in combination with AAV vectors. The term ‘targeted nucleases’ refers to certain enzymes (nucleases) which can induce breaks at specific sites in the DNA. With these applications, targeted modifications of DNA (gene editing) can be made. Targeted nucleases include CRISPR-Cas systems, zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and meganucleases. CRISPR-Cas systems are currently the subject of much research. Besides bringing about desired effects in patients, targeted nucleases can also cause unwanted effects, both at the intended position in the DNA and at other positions (off-target effects). Such unwanted effects present a risk mainly to the patient, but shedding of vector particles can potentially lead to third-party exposure to these vectors. Although exposure of third parties to AAV vectors containing targeted nucleases will be limited, the possibility of this leading to unwanted effects cannot be ruled out for all possible cases. COGEM therefore advises that clinical applications involving AAV vectors containing targeted nucleases should be subject to a further condition requiring additional hygiene measures to be taken after administering the AAV vector. This condition may be waived if an applicant provides a sound argument for doing so. COGEM points out that AAV vectors containing CRISPR-Cas sequences or sequences of other targeted nucleases have an increased risk of integration into the genome and therefore advises that to prevent any possible germline gene editing, such AAV vectors should not be administered in the sex organs of participants in clinical trials. Lastly, COGEM is of the opinion that future gene-editing applications in combination with an AAV vector should fall under the generic environmental risk assessment if these future applications have an effect comparable to the current known systems and the above-mentioned additional conditions are observed.