Transduction of producer cells during lentiviral vector (LVV) production causes the loss of 70–90% of viable particles. This process is called retro-transduction and it is a consequence of the interaction between the LVV envelope protein, VSV-G, and the LDL receptor located on the producer cell membrane, allowing lentiviral vector transduction. Avoiding retro-transduction in LVV manufacturing is crucial to improve net production and, therefore, the efficiency of the production process. Here, we describe a method for quantifying the transduction of producer cells and three different strategies that, focused on the interaction between VSV-G and the LDLR, aim to reduce retro-transduction.

Background/Objectives: To date, nearly 300 lentiviral-based gene therapy clinical trials have been conducted, with eight therapies receiving regulatory approval for commercialization. These advances, along with the increased number of advanced-phase clinical trials, have prompted contract development and manufacturing organizations (CDMOs) to develop innovative strategies to address the growing demand for large-scale batches of lentiviral vectors (LVVs). Consequently, manufacturers have focused on optimizing processes under good manufacturing practices (GMPs) to improve cost-efficiency, increase process robustness, and ensure regulatory compliance. Nowadays, the LVV production process mainly relies on the transient transfection of four plasmids encoding for the lentiviral helper genes and the transgene. While this method is efficient at small scales and has also proven to be scalable, the industry is exploring alternative processes due to the high cost of GMP reagents, and the batch-to-batch variability predominantly attributed to the transfection step. Methods: Here, we report the development and implementation of a reliable and clinical-grade envisioned platform based on the generation of stable producer cell lines (SCLs) from an initial well-characterized lentiviral packaging cell line (PCL). Results: This platform enables the production of VSV-G-pseudotyped LVVs through a fully transfection-free manufacturing process. Our data demonstrate that the developed platform will facilitate successful technological transfer to large-scale LVV production for clinical application. Conclusions: With this simple and robust stable cell line generation strategy, we address key concerns associated with the costs and reproducibility of current manufacturing processes.

Extensive studies about the human immunodeficiency virus type 1 (HIV-1) have allowed the generation of lentiviral vectors as gene delivery vehicles with enhanced safety and efficacy features. In this review, several strategies for controlling the molecular mechanisms occurring during the lentiviral vector manufacturing process are presented. Specifically, modifications focused on LVV manufacturing components, such as plasmids or the producer cell line, that enable increased safety, integrity, and potency of the produced LVV, as well as manufacturing efficiency. Considering the stochasticity of the LVV manufacturing process from plasmid transfection until the budding of the virus from the target cell, minimal modifications might have a huge impact on the final LVV yield. Indeed, the extent of a potential impact may vary depending on the specificities of each LVV regarding the particular genetic payload or the envelope protein. Thus, the feasibility of each of the optimizations described herein requires thorough evaluation. The second part of the review examines the potential multi-purpose nature of the LVV. Growing research in the field has enabled the development of new engineered modalities of LVV, expanding their application scope beyond the traditional ex vivo DNA delivery approach. LVVs are becoming a versatile tool for the packaging or delivery of cargo in the form of DNA, RNA, or protein, allowing their use for in vivo approaches, vaccinology, or gene editing, among others.

Background: The development of stable producer cell lines (SCLs) represents a promising alternative for lentiviral vector (LVV) manufacturing, offering improved reproducibility and reduced manufacturing costs. In previous work, our group established an SCL generation platform based on a well-characterized packaging cell line (PCL), demonstrating successful vector production at laboratory scale. However, translation of this platform to larger scales remains necessary for industrial applications. Objective: In this study, we aimed to evaluate the scalability of the existing platform and identify key parameters that influence the production performance (e.g., cell density, harvest timing or pH). Moreover, the platform was enhanced through extensive genetic characterization and improved integration methods. Results: Our findings suggest that mildly acidic culture conditions and extended harvest periods contribute to increased LVV titers. Furthermore, we conducted a comparative analysis of transgene integration strategies to determine the most suitable method for SCL generation. The results demonstrate that transposase-mediated integration provides a precise and stable approach, minimizing concatemer formation and tandem rearrangements. Conclusions: Collectively, these findings provide evidence that our stable producer cell line constitutes a scalable, genetically characterized and consistent LVV production platform, supporting its potential for large-scale LVV manufacturing.