104. A Gene Deleted High Capacity Adenoviral Vector for Efficient Delivery of a Multiplex DMD Specific CRISPR/Cas9 Machinery

Abstract

Recent advances in the field of designer nuclease directed genome editing hold great promise to correct underlying mutations leading to Duchenne muscular dystrophy. Especially the CRISPR/Cas9 system provides an easy way to design and to assemble RNA guided nucleases offering the potential to develop personalized treatments to correct the multiple different mutations leading to this fatal disease. Recent studies showed efficient genome editing in a myoblast cell line derived from DMD patients and mdx mice. Nevertheless viral delivery of all required CRISPR/Cas9 components including Cas9 and one or multiple guide RNA (gRNA) expression units has not been fully exploited. Gene deleted high-capacity adenoviral vectors (HCAdVs) offer the packaging capacity to deliver the complete CRISPR/Cas9 machinery including several gRNA expression units using a single viral vector. By using a new toolbox that facilitates customization, cloning and production of CRISPR-HCAdVs, we assembled a HCAdV genome containing a Streptococcus pyogenes Cas9 (spCas9) gene including two guide RNA (gRNA) expression units specific for DMD that have shown efficiency to delete exon 51 in dystrophic human myoblasts. CRISPR-HCAdV was amplified in medium scale using a shortened protocol yielding high titers. Infection of cultured HEK293 cells and primary human myoblasts with purified DMD specific CRISPR-HCAdV at different MOIs resulted in strong locus specific deletion efficiency for DMD exon 51 as shown with locus specific PCR. As a comparison we also designed and produced DMD-specific TALEN encoding HCAdVs which allow delivery of a complete TALEN pair using a single vector. We found that it was more complicated to produce double TALEN-HCAdVs compared to multiplex CRSIPR/Cas9-HCAdV as they require controlled expression of TALEN genes by inducible promotors. Furthermore the TALEN system is not suitable for multiplexing and showed less efficiency in T7E1 assays. Our platform enables cloning and production of gene deleted adenoviral vectors for the delivery of a DMD specific CRISPR/Cas9 system within a short time providing a valuable tool for viral delivery of customized CRISPR/Cas9 for DMD treatment. Additional gRNAs or gRNAs with other specificities can be easily included in the vector allowing personalized molecular design of the gene transfer vector. We expect that this may pave the way towards broader applications of the CRISPR technology for DMD treatment including preclinical and eventually clinical studies.