Advances in CRISPR/Cas9 Technology for in Vivo Translation

An innovative CRISPR/Cas9 mouse model of human isolated microtia indicates the potential contribution of CNVs near HMX1 gene

BACKGROUND

Microtia is a prevalent congenital malformation, the precise etiology and pathogenesis of which remain elusive. Mutations in the non-coding region of the HMX1 gene have been implicated in isolated cases of microtia, emerging as a significant focus of contemporary research. Several pathogenic copy number variations (CNVs) proximal to the HMX1 gene have been documented in wild animal populations, whereas only a single large segmental duplication in this region has been identified in humans. However, the absence of a gene-edited animal model has impeded the investigation of the unclear gene function associated with HMX1 mutations in human isolated microtia. In this study, we sought to precisely identify the pathogenic mutation by analyzing three pedigrees alongside population controls. Subsequently, our objective was to develop a CRISPR/Cas9 gene-edited mouse model to elucidate the functional implications of the identified mutation.

METHODS

Genomic DNA was collected from 32 affected individuals across three pedigrees, as well as from 2000 control subjects. Comprehensive genomic analyses, including genome-wide linkage analysis, targeted capture, second-generation sequencing, and copy number analysis, were conducted to identify potential mutations associated with congenital auricle malformation. CRISPR/Cas9 gene-edited murine models were generated in response to the identified mutation. The auricular phenotypes of these gene-edited mice were systematically monitored. Small-animal Micro-CT scanning was employed to identify potential craniofacial or skeletal abnormalities. Furthermore, the expression of the HMX1 gene in the PA2 region of mouse embryos was quantified using RT-qPCR.

RESULTS

A co-segregated 600 base pair duplication located on chromosome 4 (chr4:8701900-8702500, hg19) was identified in affected individuals across three pedigrees, but was absent in healthy controls. Two types of CRISPR/Cas9 gene-edited mice were subsequently generated. The knock-in (KI) mouse model was engineered by inserting one copy of the duplicated sequence directly adjacent to the mutated site, whereas the knockout (KO) mouse model was created by excising the mutation sequence. The phenotypes of different group of CRISPR/Cas9 gene-edited mice demonstrated distinct auricular deformities. Furthermore, an increase in the copy number of the mutated sequence was associated with elevated expression levels of HMX1 in the gene-edited mouse model.

CONCLUSIONS

In this study, we further narrowed down and identified a 600 base pair copy number variation (CNV) located at chr4:8701900-8702500 (hg19), which is implicated in human bilateral, isolated microtia. Utilizing CRISPR/Cas9 technology, we developed novel mouse models harboring the identified mutation. These models serve as a robust platform for the comprehensive investigation of the underlying mechanisms of the disease.

A Multifunctional Aptamer Decorated Lipid Nanoparticles for the Delivery of EpCAM-targeted CRISPR/Cas9 Plasmid for Efficacious In Vivo Tumor Regression

Epithelial cell adhesion molecule (EpCAM) gene encodes a type-I trans-membrane glycoprotein that is overexpressed in many cancerous epithelial cells and promotes tumor progression by regulating the expression of several oncogenes like c-myc and other cyclins. Because of this tumorigenic association, the EpCAM gene has been a potential target for anti-cancer therapy in recent days. Herein, it is attempted to knockout the proto-oncogenic EpCAM expression by efficiently delivering an all-in-one Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) plasmid via a lipid nanoparticle system made out of synthetic stimuli-sensitive lipids. The plasmid possesses the necessary information in the form of a guide RNA targeted to the EpCAM gene. The aptamer decorated system selectively targets EpCAM overexpressed cells and efficiently inhibits the genetic expression. It has explored the pH-responsive property of the developed lipid nanoparticles and monitored their efficacy in various cancer cell lines of different origins with elevated EpCAM levels. The phenomenon has further been validated in vivo in non-immunocompromised mouse tumor models. Overall, the newly developed aptamer decorated lipid nanoparticle system has been proven to be efficacious for the delivery of EpCAM-targeted CRISPR/Cas9 plasmid.

Delivering the CRISPR/Cas9 system for engineering gene therapies: Recent cargo and delivery approaches for clinical translation

Clustered Regularly Interspaced Short Palindromic Repeats associated protein 9 (CRISPR/Cas9) has transformed our ability to edit the human genome selectively. This technology has quickly become the most standardized and reproducible gene editing tool available. Catalyzing rapid advances in biomedical research and genetic engineering, the CRISPR/Cas9 system offers great potential to provide diagnostic and therapeutic options for the prevention and treatment of currently incurable single-gene and more complex human diseases. However, significant barriers to the clinical application of CRISPR/Cas9 remain. While in vitro, ex vivo, and in vivo gene editing has been demonstrated extensively in a laboratory setting, the translation to clinical studies is currently limited by shortfalls in the precision, scalability, and efficiency of delivering CRISPR/Cas9-associated reagents to their intended therapeutic targets. To overcome these challenges, recent advancements manipulate both the delivery cargo and vehicles used to transport CRISPR/Cas9 reagents. With the choice of cargo informing the delivery vehicle, both must be optimized for precision and efficiency. This review aims to summarize current bioengineering approaches to applying CRISPR/Cas9 gene editing tools towards the development of emerging cellular therapeutics, focusing on its two main engineerable components: the delivery vehicle and the gene editing cargo it carries. The contemporary barriers to biomedical applications are discussed within the context of key considerations to be made in the optimization of CRISPR/Cas9 for widespread clinical translation.

Therapeutic Gene Editing with CRISPR: A Laboratory Medicine Perspective

Therapeutic gene editing with the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas system offers significant improvements in specificity and programmability compared with previous methods. CRISPR editing strategies can be used ex vivo and in vivo with many theoretic disease applications. Off-target effects of CRISPR-mediated gene editing are an important outcome to be aware of, minimize, and detect. The current methods of regulatory approval for personalized therapies are complex and may be proved inefficient as these therapies are implemented more widely. The role of pathologists and laboratory medicine practitioners is vital to the clinical implementation of therapeutic gene editing.

Efficient viral delivery of Cas9 into human safe harbor

Gene editing using CRISPR/Cas9 is a promising method to cure many human genetic diseases. We have developed an efficient system to deliver Cas9 into the adeno-associated virus integration site 1 (AAVS1) locus, known as a safe harbor, using lentivirus and AAV viral vectors, as a step toward future in vivo transduction. First, we introduced Cas9v1 (derived from Streptococcus pyogenes) at random into the genome using a lentiviral vector. Cas9v1 activity was used when the N-terminal 1.9 kb, and C-terminal 2.3 kb fragments of another Cas9v2 (human codon-optimized) were employed sequentially with specific single-guide RNAs (sgRNAs) and homology donors carried by AAV vectors into the AAVS1 locus. Then, Cas9v1 was removed from the genome by another AAV vector containing sgRNA targeting the long terminal repeat of the lentivirus vector. The reconstituted Cas9v2 in the AAVS1 locus was functional and gene editing was efficient.