Project description:Prime editing is a highly versatile CRISPR-based genome editing technology with the potential to correct the vast majority of genetic defects1. However, correction of a disease phenotype in vivo in somatic tissues has not been achieved yet. Here, we establish proof-of-concept for in vivo prime editing, that resulted in rescue of a metabolic liver disease. We first develop a size-reduced prime editor (PE) lacking the RNaseH domain of the reverse transcriptase (SpCas9-PERnH), and a linker- and NLS-optimized intein-split PE construct (SpCas9-PE p.1153) for delivery by adeno-associated viruses (AAV). Systemic dual AAV-mediated delivery of this variant in neonatal mice enables installation of a transversion mutation at the Dnmt1 locus with 15% efficiency on average. Next, we targeted the disease-causing mutation in the phenylalanine hydroxylase (Pah)enu2 mouse model for phenylketonuria (PKU). Correction rates of 1.5% using the dual AAV approach could be increased to up to 14% by delivery of full-length SpCas9-PE via adenoviral vector 5 (AdV5), leading to full restoration of physiological blood phenylalanine (L-Phe) levels below 120 µmol/L. Our study demonstrates in vivo prime editing in the liver at two independent loci, emphasizing the potential of PEs for future therapeutic applications.
Project description:Prime editors (PEs) can mediate versatile genome editing but their efficiency remains low. Here, we developed spegRNA by introducing same-sense mutations at proper positions in the reverse-transcription template of pegRNA to increase PE’s single-base editing efficiency or apegRNA by altering the pegRNA secondary structure to increase PE’s indel-editing efficiency . When used in PE3 and PE5, the efficiencies of sPE3, aPE3, sPE5 and aPE5 were all enhanced significantly.
Project description:Prime editing enables the precise modification of genomes through reverse transcription of template sequences appended to the 3′ ends of CRISPR–Cas guide RNAs. To identify cellular determinants of prime editing, we developed scalable prime editing reporters and performed genome-scale CRISPR-interference screens. From these screens, a single factor emerged as the strongest mediator of prime editing: the small RNA-binding exonuclease protection factor La. Further investigation revealed that La promotes prime editing across approaches (PE2, PE3, PE4 and PE5), edit types (substitutions, insertions and deletions), endogenous loci and cell types but has no consistent effect on genome-editing approaches that rely on standard, unextended guide RNAs. Previous work has shown that La binds polyuridine tracts at the 3′ ends of RNA polymerase III transcripts. We found that La functionally interacts with the 3′ ends of polyuridylated prime editing guide RNAs (pegRNAs). Guided by these results, we developed a prime editor protein (PE7) fused to the RNA-binding, N-terminal domain of La. This editor improved prime editing with expressed pegRNAs and engineered pegRNAs (epegRNAs), as well as with synthetic pegRNAs optimized for La binding. Together, our results provide key insights into how prime editing components interact with the cellular environment and suggest general strategies for stabilizing exogenous small RNAs therein.
Project description:Viruses and virally-derived particles have the intrinsic capacity to deliver molecules to cells, but the difficulty of readily altering cell-type selectivity has hindered their use for therapeutic delivery. Here we show that cell surface marker recognition by antibody fragments displayed on membrane-derived particles encapsulating CRISPR-Cas9 protein and guide RNA can target genome editing tools to specific cells. These Cas9-packaging enveloped delivery vehicles (Cas9-EDVs), programmed with different displayed antibody fragments, confer genome editing in target cells over bystander cells in mixed cell populations both ex vivo and in vivo. This strategy enabled the generation of genome-edited chimeric antigen receptor (CAR) T cells in humanized mice, establishing a new programmable delivery modality with the potential for widespread therapeutic utility.
Project description:Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo. Using engineered murine leukemia virus-like particles loaded with Cas9/sgRNA ribonucleoproteins (“Nanoblades”), we were able to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades were also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for “all-in-one” homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.