Orphan Motif CpG Density for AAV Transgene Expression
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Solution Overview
Problem
Current gene therapy methods face challenges in achieving high and tissue-specific expression of heterologous nucleic acids, particularly due to limitations in packaging capacity of viral vectors like AAV, which restrict the size of genetic payloads and regulatory elements, and require improved calibration for therapeutic benefits.
Innovation Solution
Incorporation of a nucleic acid sequence with a CpG Observed over Estimated ratio (O/E ratio) greater than 0.6, bound by protein BANP, to regulate the expression of heterologous transgenes, allowing for controlled and enhanced expression of multiple transgenes on the same vector, with CpG density influencing activity and reducing risk of host cell integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AAV vectors are used to deliver heterologous nucleic acids, then transduction efficiency and long-term expression are improved, but the packaging capacity is limited to approximately 4.7 kb for single-stranded and 2.4 kb for self-complementary vectors
Solution Approach 1:
The regulatory elements are divided into multiple functional components: a tissue-specific promoter, an orphan motif sequence (SEQ ID NO: 1-3) with specific CpG density, and a transgene coding sequence. This segmentation allows optimization of each component independently while maintaining total packaging within AAV capacity limits.
Solution Approach 2:
The patent optimizes the CpG density parameter in the orphan motif sequence to achieve high expression levels. By adjusting the CpG Observed over Estimated ratio and the specific sequence composition, the patent achieves enhanced transcriptional activation while maintaining compact regulatory element size that fits within AAV packaging constraints.
2Productivity
If larger regulatory elements are included to enhance expression, then gene expression level is improved, but the size of the genetic payload increases beyond AAV packaging capacity
Solution Approach 1:
The patent achieves high gene expression by optimizing specific parameters of the orphan motif sequence, including CpG density and sequence composition (SEQ ID NO: 1-3). This allows compact regulatory elements to produce high expression levels without exceeding AAV packaging capacity.
Solution Approach 2:
The regulatory element is constructed as a composite sequence combining a tissue-specific promoter with an optimized orphan motif sequence containing specific CpG dinucleotide patterns. This composite structure achieves enhanced expression efficiency within a compact size that fits AAV packaging constraints.
3Productivity
If viral vectors are used for gene delivery, then delivery efficiency to target cells is improved, but the risk of host cell integration and immune response increases
Solution Approach 1:
The patent uses replication-deficient AAV vectors that have had the viral structural genes removed, eliminating the risk of viral replication and reducing integration risk. The vector retains only the essential ITR sequences for packaging and delivery, while the therapeutic payload consists of non-viral regulatory elements and transgene sequences.
Solution Approach 2:
The patent employs episomal persistence of the AAV vector in non-dividing cells, avoiding integration into the host genome. The vector functions as a temporary, non-integrating delivery vehicle that maintains transgene expression without permanent genomic alteration, reducing long-term safety risks.
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
This approach significantly increases the expression of heterologous transgenes by a factor greater than two, providing controlled and specific expression, while minimizing the risk of unintended host cell integration and immune response.
Implementation Method 1
a thus far orphaned regulatory motif in mammalian, when bound by protein BANP, acts as a strong transcriptional activator
Implementation Method 2
This strong activator effect is synergistically increased when more than one copy of the motif is present in front of a heterologous transgene
Data Source
AI summary
The present invention provides an isolated nucleic acid comprising more than 220 bp, one or more copy of a sequence selected from the group of SEQ ID NO:1, SEQ ID NO:2 and SEQ ID NO:3, and a CpG Observed over Estimated ratio (O/E ratio) larger than 0.6 in the N base pairs (bp) preceding and/or in the N bp following said one or more copy of a sequence selected from the group of SEQ ID NO:1, SEQ ID NO:2 and SEQ ID NO:3, wherein the CpG O/E ratio is determined by counting the number of CpG dinucleotides in the N bp-long sequences surrounding the at least one or more copy of a sequence selected from the group of SEQ ID NO:1, SEQ ID NO:2 and SEQ ID NO:3 and calculating the O/E ratio by multiplying the counted number of CpG dinucleotides by N and dividing the result by the product of the number of C and number of G present in the N bp (N*CpG/(C*G)), wherein N is between 50 and 1000 and is the length, in bp, of the sequence immediately preceding or immediately following said one or more copy of a sequence selected from the group of SEQ ID NO:1, SEQ ID NO:2 and SEQ ID NO:3.