Modified Cas9 Nuclease Fused with HDR Factors
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Solution Overview
Problem
Current gene therapy methods using viral vectors for immunodeficiency treatment face safety concerns due to random integration, and HDR-based genome editing is inefficient, limiting precise modification and increasing the risk of cancer.
Innovation Solution
A modified Cas9 nuclease fused with HDR factors like RAD51, RAD52, and MRE11, along with CtIP, is used to promote homologous recombination, increasing the frequency of HDR-mediated genome editing and reducing the reliance on error-prone NHEJ repair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If viral vectors are used for gene therapy, then gene expression can be reconstituted, but random integration may lead to cancer
Solution Approach 1:
The patent introduces a targeted integration system that acts as an intermediary between the viral vector and host genome. Instead of random integration, the system uses a specific integrationase enzyme and attP/attB sites to mediate precise integration at safe harbor locations, eliminating the harmful random integration effect while preserving gene expression reconstitution
Solution Approach 2:
The patent changes the integration parameter from random to targeted by modifying the integration mechanism. By using site-specific recombination with defined attP and attB sequences, the integration location is precisely controlled to safe harbor sites, transforming the uncontrolled random process into a controlled targeted process that avoids oncogenes
2Manufacturing precision
If HDR-based genome editing is used for precise modification, then gene editing precision is improved, but editing frequency remains too low for therapeutic benefit
Solution Approach 1:
The patent merges the Cas9 nuclease with CtIP protein to create a fusion enzyme. This combination brings together the DNA-cutting capability of Cas9 with the HDR-promoting function of CtIP at the same location, ensuring that HDR factors are immediately available when the DSB is created, thereby significantly increasing HDR frequency while maintaining precision
Solution Approach 2:
The patent performs preliminary action by pre-assembling the Cas9-CtIP fusion protein that already contains HDR-promoting activity before the DSB occurs. The CtIP domain is prepared in advance and positioned to act immediately upon DSB formation, eliminating the delay that would otherwise exist for recruiting HDR factors to the break site
3Productivity
If small molecule drugs are used to block NHEJ and promote HDR, then HDR frequency increases, but cellular safety concerns arise
Solution Approach 1:
The patent uses the Cas9-CtIP fusion protein as an intermediary that directly promotes HDR without requiring small molecule drugs. The fusion protein acts as a built-in mediator that naturally biases repair toward HDR by having CtIP activity integrated into the Cas9 complex, eliminating the need for external chemical compounds that cause cellular toxicity
Solution Approach 2:
The system performs self-service by incorporating HDR-promoting activity directly into the Cas9 enzyme through the CtIP fusion. The Cas9-CtIP complex autonomously promotes HDR at the DSB site without requiring external small molecule assistance, making the system self-sufficient and avoiding the safety issues associated with pharmacological agents
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modified Cas9 system significantly enhances the frequency of HDR-mediated repair events, making precise genome editing more efficient and potentially applicable for therapeutic benefits in gene therapy, particularly in hematopoietic stem cells.
Implementation Method 1
The correction of DNA breaks can occur either by homology-directed repair (HDR) which is typically much less efficient than the non-homologous end-joining (NHEJ) repair. The modified Cas9 system significantly enhances the frequency of HDR-mediated repair events
Data Source
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Figure 3A~3B
AI summary
The present invention relates to modified Cas9 nuclease comprising a substantial part of a Cas9 nuclease and covalently linked thereto at least one of a protein domain of a HDR factor selected from the group consisting of RAD51, RAD52, RAD54, MRE11, PALB2, FANCD2 and EXO1.