Dual-Vector CRISPR/Cas9 Delivery for Self-Inactivating Expression
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Solution Overview
Problem
Long-term expression of CRISPR/Cas9 can lead to undesirable immune responses and off-target cleavages, complicating the treatment of genetic diseases like Huntington's disease.
Innovation Solution
A dual vector system is employed, where a first vector delivers Cas9 and a specific sgRNA targeting a genomic locus, and a second vector delivers an sgRNA to target and disrupt Cas9 expression, achieving transient Cas9 expression and reducing off-target effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If long-term Cas9 expression is maintained to ensure sufficient gene editing activity, then gene editing efficacy is improved, but off-target cleavages and immune responses increase
Solution Approach 1:
The patent employs a dual vector system where Cas9 expression is dynamically controlled through two opposing sgRNAs: one maintains Cas9 expression for sustained gene editing activity, while the other gradually reduces it to minimize off-target effects. This dynamic balance allows the system to adapt Cas9 expression levels over time, achieving both high editing efficacy and reduced harmful effects.
Solution Approach 2:
The system implements a feedback mechanism where the expression of sgRNA2 (which targets Cas9) is activated by Cas9 itself, creating a self-regulating loop. As Cas9 expression increases, so does the production of sgRNA2, which subsequently reduces Cas9 levels. This feedback control prevents excessive Cas9 accumulation and minimizes off-target cleavages while maintaining sufficient editing activity.
2Reliability
If Cas9 expression is sustained to achieve complete gene editing, then editing completeness is improved, but duration of Cas9 expression increases causing more off-target effects
Solution Approach 1:
The patent creates a periodic oscillation in Cas9 expression levels through the interaction of two sgRNAs. Cas9 is initially expressed at high levels to drive gene editing, then gradually reduced as sgRNA2 accumulates, creating cycles of expression and suppression. This periodic action ensures complete editing while limiting the total duration of high Cas9 expression to reduce off-target effects.
Solution Approach 2:
The system performs preliminary gene editing during the initial phase of high Cas9 expression before implementing the suppression mechanism. By completing the majority of editing tasks early when Cas9 levels are high, the system then reduces Cas9 expression to minimal levels needed for maintaining editing completeness, thereby reducing the overall duration of harmful Cas9 activity.
3Device complexity
If a single vector system is used to simplify delivery, then device complexity is reduced, but control over Cas9 expression precision is worsened
Solution Approach 1:
The patent divides the gene editing system into two separate vector components: one delivering Cas9 and sgRNA1 (for maintaining expression), and another delivering sgRNA2 (for suppressing expression). This segmentation allows independent optimization and precise control of each component's expression, enabling fine-tuned regulation of Cas9 activity that would be difficult to achieve in a single vector system.
Solution Approach 2:
The patent introduces sgRNA2 as an intermediary molecule that mediates the suppression of Cas9 expression. This intermediary acts as a controlled inhibitor, allowing precise temporal and quantitative regulation of Cas9 activity. The intermediary mechanism provides a layer of control that enhances precision without requiring complex single-vector designs.
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 system effectively edits target genes while minimizing off-target events and providing precise control over Cas9 expression, thereby enhancing the safety and efficacy of gene editing.
Implementation Method 1
The gRNA has two parts, crRNA, which is nucleotide sequence complementary to the target DNA, and tracrRNA, which is a nucleotide sequence that functions as a binding scaffold for the Cas nuclease
Implementation Method 2
A double strand break (DSB) at the target sequence is then formed by the Cas9 nuclease
Implementation Method 3
The DSB triggers endogenous DNA repair mechanisms, namely homology directed repair (HDR), and non-homologous end joining (NHEJ)
Implementation Method 4
The DSB triggers endogenous DNA repair mechanisms, namely homology directed repair (HDR), and non-homologous end joining (NHEJ)
Data Source
AI summary
A self-inactivating CRISPR/Cas9 delivery system utilizes a dual vector system. The first viral vector includes a unit for expression of a Cas9 nuclease and a nucleotide sequence encoding an sgRNA targeting a specific genomic locus. The second viral vector includes a nucleotide sequence encoding the sgRNA targeting expression of the Cas9 nuclease by the expression unit. The self-inactivating CRISPR/Cas9 dual vector delivery system can be used treating a genetic disease or genetic disorder and for treating a gene-associated disease or condition.