Abstract:Stable suspension producer cell lines for the production of vesicular stomatitis virus envelope glycoprotein (VSVg)-pseudotyped lentiviral vectors represent an attractive alternative to current widely used production methods based on transient transfection of adherent 293T cells with multiple plasmids. We report here a method to rapidly generate such producer cell lines from 293T cells by stable transfection of a single DNA construct encoding all lentiviral vector components. The resulting suspension cell line… Show more
“…To facilitate this, all packaging components (Gag-pol, VSVg, and Rev) were assembled into modules on a single construct in a manner that maintained independent expression of each component ( Figure 4 A). 22 This reduced the complexity of transient transfections from a 4-construct to a 2-construct system, enabling relative quantities of packaging components and transfer plasmid to be easily modified. Figure 4 Varying the packaging to transfer plasmid transfection ratio impacts packaging efficiency (A) The single packaging construct used in co-transfections is illustrated.…”
Lentiviral vectors are showing success in the clinic, but producing enough vector to meet the growing demand is a major challenge. Furthermore, next-generation gene therapy vectors encode multiple genes resulting in larger genome sizes, which is reported to reduce titers. A packaging limit has not been defined. The aim of this work was to assess the impact of genome size on the production of lentiviral vectors with an emphasis on producer cell mRNA levels, packaging efficiency, and infectivity measures. Consistent with work by others, vector titers reduced as genome size increased. While genomic infectivity accounted for much of this effect, genome sizes exceeding that of clinical HIV-1 isolates result in low titers due to a combination of both low genomic infectivity and decreased packaging efficiency. Manipulating the relative level of genomic RNA to gag-pol mRNA in the producer cells revealed a direct relationship between producer cell mRNA levels and packaging efficiency yet could not rescue packaging of oversized genomes, implying a de facto packaging defect. However, independent of genome size, an equimolar ratio between wild-type gag-pol mRNA and vector genomic RNA in producer cells was optimal for titer.
“…To facilitate this, all packaging components (Gag-pol, VSVg, and Rev) were assembled into modules on a single construct in a manner that maintained independent expression of each component ( Figure 4 A). 22 This reduced the complexity of transient transfections from a 4-construct to a 2-construct system, enabling relative quantities of packaging components and transfer plasmid to be easily modified. Figure 4 Varying the packaging to transfer plasmid transfection ratio impacts packaging efficiency (A) The single packaging construct used in co-transfections is illustrated.…”
Lentiviral vectors are showing success in the clinic, but producing enough vector to meet the growing demand is a major challenge. Furthermore, next-generation gene therapy vectors encode multiple genes resulting in larger genome sizes, which is reported to reduce titers. A packaging limit has not been defined. The aim of this work was to assess the impact of genome size on the production of lentiviral vectors with an emphasis on producer cell mRNA levels, packaging efficiency, and infectivity measures. Consistent with work by others, vector titers reduced as genome size increased. While genomic infectivity accounted for much of this effect, genome sizes exceeding that of clinical HIV-1 isolates result in low titers due to a combination of both low genomic infectivity and decreased packaging efficiency. Manipulating the relative level of genomic RNA to gag-pol mRNA in the producer cells revealed a direct relationship between producer cell mRNA levels and packaging efficiency yet could not rescue packaging of oversized genomes, implying a de facto packaging defect. However, independent of genome size, an equimolar ratio between wild-type gag-pol mRNA and vector genomic RNA in producer cells was optimal for titer.
“…The development of stable producer cell lines for lentivectors pseudotyped with VSV-G is challenging, owing to the cytotoxicity associated with this envelope, which is not the case with other vector envelopes. While several lentiviral packaging cell lines have been described, none is commercially available-an unmet need in the vector production space (98)(99)(100)(101).…”
As of April 2021, there are five commercially available chimeric antigen receptor (CAR) T cell therapies for hematologic malignancies. With the current transition of CAR T cell manufacturing from academia to industry, there is a shift toward Good Manufacturing Practice (GMP)-compliant closed and automated systems to ensure reproducibility and to meet the increased demand for patients with cancer. In this review, we describe current CAR T cell clinical manufacturing models and discuss emerging technologic advances that embrace scaling and production optimization. We summarize measures being used to shorten CAR T cell manufacturing times and highlight regulatory challenges to scaling production for clinical use.
Significance:As the demand for CAR T cell cancer therapy increases, several closed and automated production platforms are being deployed, and others are in development. This review provides a critical appraisal of these technologies, which can be leveraged to scale and optimize the production of nextgeneration CAR T cells.
iNtRODUctiONChimeric antigen receptor (CAR)-modified T cells have emerged as an efficacious treatment for patients with certain hematologic malignancies (1). Currently, five CAR T cell products are approved for commercial use and available on the U.S. market: three for B-cell leukemia and lymphoma (tisagenlecleucel, axicabtagene ciloleucel, lisocabtagene maraleucel), one for mantle cell lymphoma (brexucabtagene autoleucel), and one for multiple myeloma (idecabtagene vicleucel; refs. 2-8). These therapies involve genetically modifying patient-derived (autologous) peripheral blood T cells to express a CAR directed against antigens present on the surface of targeted tumor cells, such as the CD19 molecule, or, in the case of idecabtagene vicleucel, B-cell maturation antigen (BCMA;. After antigen recognition, the intracellular signaling domains activate the immune effector and memory functions of the CAR T cells. Once activated, these T cells proliferate, infiltrate tumor sites, secrete cytokines, and release cytolytic granules to eliminate targeted cells in an antigen-dependent manner (1). All approved CAR T cell products are second-generation CARs that incorporate CD28 or CD137 (4-1BB) costimulatory signals, which are essential for eliciting a clinically relevant immune response (9-15). These CAR T cells were able to elicit complete responses (CR) in 32% to 67% of patients with lymphoma and showed better CR rates in patients with leukemia (16)(17)(18)(19).The increasing success of CAR T immunotherapies in relapsed/refractory hematologic malignancies sparked the interest of pharmaceutical companies, and several products targeting a variety of cancers are currently in the pipeline (20). However, many limitations to current CAR T cell manufacturing must be overcome before this modality can be fully integrated into routine clinical practice. First, most CAR T cell trials to date have used autologous peripheral blood and apheresis as the main cell sources for manufacturing
“…A possible reason that vector titre did not increase could be that the cytoplasmic abundance of the genomic RNA is in excess of the amount required for efficient packaging. While we did these experiments using small scale three plasmid transfection of HEK293T or HEK293Tsa cells, it will be interesting in the future to compare the titre of the pLV and pLV-RRE genomes in a more clinically relevant setting, such as the recently described bacterial artificial chromosome system 56 , in which the relative abundance of the vector genome and viral proteins may be different. Another possible reason that vector titre did not substantially increase for pLV-RRE compared to pLV is that the threefold increase in the proportion of the unspliced RNA is not large enough to raise the titre.…”
Many lentiviral vectors used for gene therapy are derived from HIV-1. An optimal vector genome would include only the viral sequences required for transduction efficiency and gene expression to minimize the amount of foreign sequence inserted into a patient’s genome. However, it remains unclear whether all of the HIV-1 sequence in vector genomes is essential. To determine which viral sequences are required, we performed a systematic deletion analysis, which showed that most of the gag region and over 50% of the env region could be deleted. Because the splicing profile for lentiviral vectors is poorly characterized, we used long-read sequencing to determine canonical and cryptic splice site usage. Deleting specific regions of env sequence reduced the number of splicing events per transcript and increased the proportion of unspliced genomes. Finally, combining a large deletion in gag with repositioning the Rev-response element downstream of the 3’ R to prevent its reverse transcription showed that 1201 nucleotides of HIV-1 sequence can be removed from the integrated vector genome without substantially compromising transduction efficiency. Overall, this allows the creation of lentiviral vector genomes that contain minimal HIV-1 sequence, which could improve safety and transfer less viral sequence into a patient’s DNA.
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