# Buffer Valency Engineering Enables High-concentration and Shelf-stable DNA Transfection Particles for Viral Vector Production

## TL;DR

A new method improves DNA transfection particles for viral vector production, making them more stable and scalable.

## Contribution

A novel approach using trivalent citrate ions enables high-concentration, shelf-stable DNA transfection particles.

## Key findings

- Trivalent citrate ions enable uniform nanoparticle assembly and prevent aggregation at high concentrations.
- The method increases pDNA concentration tenfold and reduces dosing volume significantly.
- AAV production efficiency is equivalent to standard methods across various scales.

## Abstract

Cost-effective and scalable production is critical for advancing the clinical translation of adeno-associated virus (AAV)-mediated gene therapy. The widely used transient transfection method using plasmid DNA (pDNA)-loaded transfection particles for AAV production faces technical challenges due to instability of the particles and the concentration limits for particle preparation, hindering reproducibility and scalability. Here, we report a streamlined and scalable strategy to generate shelf-stable, highly concentrated pDNA/poly(ethylenimine) (PEI) transfection particles. By incorporating trivalent citrate ions in the dilution buffers, we kinetically modulate electrostatic complexation to achieve uniform nanoparticle assembly and prevent aggregation at high concentrations. This enables a tenfold increase in pDNA concentration in stabilized transfection particles from a typical range of 10–20 μg/mL to 200 μg/mL, while reducing the required dosing volume from 5–10% to 0.5% of the cell culture medium. The particle assembly process is robust to changes in mixing scale and timing and is compatible with standard workflows. We demonstrate equivalent AAV production efficiencies to standard methods and consistent performance in various production scales, which confirms the practical utility of this assembly method in developing robust, scalable, and cost-effective AAV manufacturing processes.