Cationic Metal Affinity Chromatography for AAV Capsid Purification
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Solution Overview
Problem
Current methods for purifying Adeno-associated virus (AAV) capsids, such as affinity chromatography and IMAC, fail to effectively separate full capsids from empty capsids and contaminating DNA, leading to incomplete purification and potential safety concerns for gene therapy applications.
Innovation Solution
A method using immobilized metal affinity chromatography with a cationic metal affinity ligand that captures AAV without His-tags, employing a pH gradient, salt gradient, or metal ion gradient in the presence of multivalent cations to separate full AAV capsids from empty capsids, and combining with anionic exchange chromatography or density-gradient centrifugation to reduce DNA contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If affinity chromatography or IMAC is used to purify AAV capsids, then the purification process is operationally simple, but full capsids cannot be effectively separated from empty capsids and contaminating DNA
Solution Approach 1:
The invention divides the purification process into two distinct chromatography steps: first capturing full capsids on a cationic substrate, then separating them from empty capsids and DNA on an anionic substrate. This segmentation allows each step to target specific contaminants, achieving effective separation while maintaining operational simplicity.
Solution Approach 2:
The invention uses oppositely charged substrates (cationic then anionic) as intermediaries to selectively bind and release different components. The cationic substrate captures full capsids while allowing empty capsids and DNA to pass through, then the anionic substrate further purifies by binding remaining contaminants, achieving high purification effectiveness through sequential mediation.
2Productivity
If IMAC with nickel ions is used to capture His-tagged AAV, then capture efficiency is improved, but nickel removal becomes difficult and toxic waste disposal costs increase
Solution Approach 1:
The invention replaces permanent nickel ion binding with transient cationic substrate binding that can be easily reversed. The cationic substrate captures full capsids efficiently but allows easy release through pH or ionic strength changes, eliminating the need for difficult nickel removal and reducing toxic waste disposal requirements.
Solution Approach 2:
The invention uses changes in pH and ionic strength as controllable parameters to modulate the binding affinity between the cationic substrate and full capsids. By adjusting these parameters, efficient capture is achieved during binding, then easy release is achieved during elution, maintaining high productivity while eliminating toxic metal contamination.
3Manufacturing precision
If strong anion exchangers are used to reduce empty capsid content, then empty capsid removal is effective for some AAV serotypes, but the method offers little utility with others and fails to remove contaminating DNA to sufficient levels
Solution Approach 1:
The invention uses a cationic substrate that captures full capsids through positive charge interactions, a mechanism that is universally effective across different AAV serotypes regardless of their surface charge variations. This universal capture mechanism, followed by anionic substrate purification, achieves both empty capsid removal and DNA reduction across all serotypes.
Solution Approach 2:
Instead of using anion exchangers to capture empty capsids (the conventional approach), the invention inverts the strategy by using a cationic substrate to capture full capsids. This inversion allows selective retention of full capsids while allowing empty capsids and DNA to pass through, then uses the anionic substrate to remove remaining contaminants, achieving superior purification across all serotypes.
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 method achieves efficient separation of full capsids from empty capsids and reduces DNA contamination more effectively than existing methods, ensuring higher purity and safety for therapeutic applications.
Implementation Method 1
contacting the buffered mixture with a cationic solid phase
Implementation Method 2
contacting the buffered mixture or the purified full AAV capsid fraction with an anionic solid phase
Implementation Method 3
combining with anionic exchange chromatography or density-gradient centrifugation to reduce DNA contamination
Data Source
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AI summary
A method for separating full Adeno-associated virus (AAV) capsids from empty AAV capsids in a buffered mixture comprising full AAV capsids, empty AAV capsids, comprising the steps of - contacting the buffered mixture with a first substrate bearing a metal affinity ligand, said metal affinity ligand having the ability to complex metal ions via three or more nitrogen atoms, - separating empty AAV capsids from full AAV capsids by eluting with a pH gradient, a salt gradient, a metal ion gradient or a combination thereof in the presence of multivalent cations bound to the metal affinity ligand to obtain a purified full AAV capsid fraction. For removing contaminating DNA in the mixture or purified AAV capsid fraction, the method of the invention can be combined with contacting of the buffered mixture or the purified full AAV capsid fraction with a second substrate bearing a metal affinity ligand in the presence of multivalent cations bound to the metal affinity ligand, said metal affinity ligand comprises two or more carboxylic acid residues.