Abstract 23: The use of baboon envelope pseudotyped lentiviral (BaLV) vector allows high-efficiency transduction of CD8+ T cells
Authors: Kaplan Isabel , Sheffer Michal , Abdulhamid Yasmin , Bobilev Eden , Romee Rizwan 
Published: March 2024

Abstract
CAR-T (chimeric antigen receptors T) cell therapy has been proven to be effective in treating various types of cancers. To prevent graft vs. host disease, CAR-T cells are mostly produced from the patient’s own T-cells and transduced using pseudotyped vesicular stomatitis virus glycoprotein (VSV-G) lentivirus system. Typically, CD8+ effector T cells have relatively low transduction rates, compared with CD4+ T cells, and yet it is the CD8+ T cells that are the dominant effector immune cells in a CAR product. To achieve high efficacy of the CAR-positive effector T cells, a higher number of the patient’s CD8+ T cells are needed for transduction. However, cancer patients may not have enough T cells by the time they are eligible for CAR-T therapy due to multiple treatment cycles. One potential way to overcome this problem is to achieve a much higher transduction rate of the CD8+ T cells.
Recently, our lab published the use of pseudotyping CAR lentivirus with baboon endogenous retroviral envelope (BaEV) for the generation of CAR transduced natural killer (NK) cells, exhibiting high transduction rates of above 50%. BaEV lentivirus targets the amino acid transporter, SLC1A5 (ASCT2), to enter the cell. SLC1A5 is highly expressed on activated NK and T cells. Therefore, we hypothesized that CAR-T transduced with BaEV lentivirus will have increased transduction rates compared with VSV-G.
To assess transduction, we used anti-mesothelin (MSLN) CAR construct which consists of the mesothelin single chain variable fragment (scFv), CD8α hinge and transmembrane domain, 4-1BB costimulatory domain, and a CD3ζ activation domain, followed with GFP linked by self-cleavage P2A. The concentrated virus was titrated in Jurkat cells, resulting in 90% transduction efficiency with VSV-G and 50% with BaEV, for the same amount of virus.
Primary CD8+ T cells were isolated from the peripheral blood of 3 healthy donors and activated with CD3/CD28 beads for three days prior to transduction. Then, the cells were transduced with either VSV-G or BaEV meso-CAR pseudotyped lentiviruses. Transduction rates were measured by flow cytometry, 3 days post-transduction. In addition, the CAR-T cells were expanded in vitro to evaluate their cytotoxicity against the mesothelin-positive cell line OVCAR-8, for 24 hours. VSV-G led to 10-20% transduction rates, while BaEV exhibited much higher transduction rates (55-70%), leading to improved cytotoxicity against the tumor cells.
The successful increase of transduction rates for CD8+ CAR-T using our BaEV lentiviral system can be utilized in the clinic to treat patients that previously didn’t qualify for adoptive therapy, due to low lymphocyte counts. In addition, higher numbers of CD8+ CAR-T cells may result in better tumor control in both blood and solid tumor settings, compared with the traditional approach for CAR-T production.
Citation Format: Isabel Kaplan, Michal Sheffer, Yasmin Abdulhamid, Eden Bobilev, Rizwan Romee. The use of baboon envelope pseudotyped lentiviral (BaLV) vector allows high-efficiency transduction of CD8+ T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 23.