High-Integrating Loci for Stable Transgene Expression
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Solution Overview
Problem
Current site-specific integration (SSI) methods for recombinant protein expression in mammalian cells face challenges such as instability and reduced production due to random integration of recombination target sites, leading to variable expression levels and phenotypic heterogeneity, and cumulative SSI methods require multiple rounds of integration to achieve stable expression.
Innovation Solution
The use of 3D genome mapping techniques like Hi-C and Promoter Capture Hi-C to identify high-integrating loci (HI loci) within transcriptionally active and stable chromatin regions for targeted integration of recombination target sites, ensuring predictable and stable expression of heterologous genes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If random integration (RI) processes are used to integrate expression cassettes, then integration is simple and takes advantage of existing double strand breaks, but the number of gene copies integrated and expression characteristics are highly variable leading to phenotypic heterogeneity and requiring expensive screening
Solution Approach 1:
The patent applies preliminary action by pre-integrating recombination target sites (RTS) into the genome at specific locations before introducing the expression cassette. This preparatory step creates predetermined integration sites that ensure consistent and controlled integration of the expression cassette, eliminating the variability associated with random integration while maintaining process simplicity.
2Productivity
If gene amplification methods are used to increase expression, then production levels increase, but genome instability arises including deletions, duplications, translocations and expression-modifying epigenetic actions
Solution Approach 1:
The patent uses preliminary action by pre-establishing stable integration sites with RTS before introducing the expression cassette. This ensures that the cassette integrates at controlled locations without requiring subsequent gene amplification, thereby maintaining genome stability while achieving consistent expression levels.
Solution Approach 2:
The recombination target site acts as an intermediary element that facilitates controlled integration of the expression cassette. This intermediary mechanism allows for precise integration at predetermined locations, avoiding the genome instability associated with gene amplification methods while maintaining productivity.
3Manufacturing precision
If site-specific integration (SSI) is used with recombination target sites, then integration is more controlled and directional, but RTS insertion itself is carried out by random integration or into limited genomic regions resulting in similar instability and reduced production over time
Solution Approach 1:
The patent applies preliminary action by selecting and validating specific genomic loci in advance that are known to provide stable long-term expression. The RTS are then integrated into these pre-selected stable loci, ensuring both controlled integration and long-term production stability, avoiding the instability issues of random RTS insertion.
Solution Approach 2:
The patent changes the parameter of integration location from random or limited regions to specifically selected stable genomic loci. This parameter change ensures that both the controlled integration benefit of SSI and the long-term stability required for industrial production are achieved simultaneously.
4Quantity of substance
If cumulative SSI is used with repeated rounds of RMCE, then multiple copies of rP expression cassettes can be loaded into a single site, but the process is complex and requires multiple integration rounds
Solution Approach 1:
The patent merges multiple expression cassettes into a single integrated construct that contains multiple genes of interest flanked by RTS. This allows all cassettes to be introduced in a single transformation event rather than requiring multiple sequential RMCE rounds, thereby reducing process complexity while achieving the desired quantity of expression cassettes.
Data Source
AI summary
Mammalian cells are described that includes a recombination target site integrated within high integrating locus. Recombinant protein producer cell lines incorporating the mammalian cells and methods for forming the mammalian cells are also described. The high integrating loci have been developed through understanding and mapping of the three dimensional hierarchical structure of chromatin in mammalian cells. The high integrating loci are present in transcriptionally active environments that can provide both chromatin accessibility and epigenetic stability. As such, the recombinant mammalian cells can provide predictable and stable transgene production.