Challenges and opportunities in continuous bioprocessing of lentiviral vectors and adeno-associated viral vectors

Adeno-associated viral (AAV) and lentiviral (LV) vectors are pivotal gene delivery vehicles for in vivo and ex vivo gene therapies, respectively. The broad adoption of these therapies depends on developing scalable manufacturing processes that can increase yields while simultaneously reducing costs. Continuous bioprocessing offers a transformative solution for viral vector manufacturing by minimising inter-campaign downtime, streamlining time- and labour-intensive steps, integrating serial operations, and mitigating vector losses from instability. This review critically examines advancements in upstream bioprocessing of AAVs and LVs, with a focus on the applicability of transient transfection for continuous production and the progress in stable cell line development. Furthermore, the development of downstream processing (DSP) technologies designed to handle the large size and limited stability of viral vectors is explored. Recent innovations in continuous DSP, including single-pass tangential flow filtration and continuous chromatography, are discussed alongside emerging strategies for continuous clarification and nucleic acid reduction. As enhanced process control is vital for continuous bioprocesses, the suitability of current process analytical technologies for monitoring is assessed. Finally, the techno-economic implications of transitioning to continuous bioprocessing are examined.