Modeling Vesicular Stomatitis Virus Using Ion Exchange Chromatography

A team of scientists from ViraTherapeutics modeled ion exchange chromatography’s effects on the elution behavior and convective entrapment of the vesicular stomatitis virus. Their findings were published in the Journal of Chromatography A (1).

Group of cows at cowshed eating hay or fodder on dairy farm. | Image Credit: © littlewolf1989 - stock.adobe.com

Vector-based therapy involves injecting a gene therapy into specific body parts so that new genetic instructions can be directly delivered to cells within the body (2). Viral vector-based therapeutics and their potential for handling diseases have advanced significantly in recent years, with therapeutic potential, safety, and efficacy being particularly enhanced. For example, a 2020 article published in Frontiers of Medicine focused on the development of oncolytic virotherapy (OVT), which a type of immunotherapy that uses natural or genetically modified viruses to selectively replicate in and kill malignant cells (3). Developments like these reflect the current clinical landscape, highlighting the demand for suitable bioprocesses for viral vector production.

Virus particles (VPs) are large, complex biomolecules with unique structures, sizes, and shapes. The attributes of VPs can vary greatly across different viruses, which creates unique challenges for process development and makes it difficult to establish standard platform processes. Enveloped viral particles can be susceptible to malformation and possible degradation during bioprocessing. This necessitates development for model production processes with short processing times and a minimal number of unit operations.

In this study, the scientists observed an unexpected fluid-dynamic effect while eluting enveloped virus particles from an ion exchange chromatography monolith. They used a modified vesicular stomatitis virus (VSV) of the Rhabdoviridae family known as VSV-GP, an enveloped virus particle with a bullet-shaped morphology of dimensions of approximately 70 × 200 nm. VSV is a contagious disease among livestock, primarily transmitted by biting flies and mainly affecting horses and cattle (4). Though this disease rarely causes high mortality rates, it can impact animal movement and international trade, causing economic losses for livestock producers. Production involves propagation in a mammalian cell suspension, and purification by filtration and chromatography steps.

The capture step involves a cationic exchange chromatography (CEX) monolith. During characterization, peak tailing was observed for VSV-GP eluting in a salt gradient, something that could not be explained by current understanding of fluid dynamics and particle-resin interaction in the monolith. This effect also led to the separation of virus particle subpopulations, with convective entrapment being identified as a plausible explanation. This fluid-dynamic effect can cause retention of large biomolecules dependent on the convective flow and biomolecules’ diffusional parameters. In response, the researchers found that–to the best of their knowledge–the entrapment had not been simulated in a chromatographic model, so they extended their experiment to include the retention of bioparticles resulting from convective entrapment. Following this, the introduced approach with the combined steric mass-action (SMA) isotherm proved capable of representing tailing effects, and consequently, separation of population due to different convective entrapment behaviors. This allowed them to investigate the effect in silico without analytical panels, which were not available to them. However, the presented isotherm approximates the entrapment and neglects dependencies, such as flow rate and particle diffusion rate. Altogether, with simplification, some misalignments are still observed, meaning that model application must be considered limited.

The observed convective entrapment effect has implications for both preparative runs and analytical methods using resins with convective channels and large biomolecules. Polymerization processes of monoliths are intended to keep channel sizes constant across scales, and it is expected that scaled-up columns should behave like scaled-down columns, as was shown for laboratory-scale columns.

Overall, the scientists demonstrated the relevance to consider the entrapment effect, and though the proposed modeling approach could properly describe this effect, further studies and suitable analytical methods are needed to gain more knowledge about this effect and its consequences.

References

(1) Schimek, A.; Ng, J.; Will, F.; Hubbuch, J. Mechanistic Modeling of the Elution Behavior and Convective Entrapment of Vesicular Stomatitis Virus on an Ion Exchange Chromatography Monolith. J. Chromatogr. A 2025, 1748, 465832. DOI: 10.1016/j.chroma.2025.465832

(2) Vectors 101. American Society of Gene + Cell Therapy 2024. https://patienteducation.asgct.org/gene-therapy-101/vectors-101 (accessed 2025-3-16)

(3) Lan, Q.; Xia, S.; Wang, Q.; Xu, W.; et al. Development of Oncolytic Virotherapy: From Genetic Modification to Combination Therapy. Front. Med. 2025, 1747, 465815. DOI: 10.1016/j.chroma.2025.465815

(4) Vesicular Stomatitis Virus. USDA Animal and Plant Health Inspection Service 2024. https://www.aphis.usda.gov/livestock-poultry-disease/cattle/vesicular-stomatitis (accessed 2025-3-16)