Preclinical Characterization of Prgn-3006 Ultracar-T™ for the Treatment of AML and MDS: Non-Viral, Multigenic Autologous CAR-T Cells Administered One Day after Gene Transfer

Relapsed/refractory (r/r) acute myeloid leukemia (AML) is an aggressive malignancy with poor prognosis and limited treatment options underscoring the need for new therapies. Traditional methods for generating CAR-T cells require extensive ex vivo expansion following viral vector transduction, adding time and high cost to manufacturing with a centralized manufacturing process and prolonging the waiting period between apheresis and administration of CAR-T therapy to a patient. Time is of the essence for advanced cancer patients including patients with r/r AML. The UltraCAR-T™ platform addresses shortcomings of current CAR-T technologies by streamlined rapid manufacturing process that can be performed in a local hospital's GMP facility following apheresis from the patient providing a potential solution for broader adoption of CAR-T therapies. The UltraCAR-T™ platform utilizes Precigen's advanced non-viral multi-gene delivery system and the rapid manufacturing process with high cell viability that allows for administration of autologous CAR-T cells one day after gene transfer. PRGN-3006 UltraCAR-T™ cells, utilizing Precigen's UltraVector® platform, co-express CD33 CAR, membrane bound IL-15 (mbIL15) and a kill switch. Expression of mbIL15 provides CAR-T cells with a source of cytokine without the need for exogenous cytokines to further enhance the expansion potential in the presence of tumor antigen and the overall persistence for PRGN-3006 in. The expression of mbIL15 on PRGN-3006 eliminates any need for ex vivo expansion of T cells prior to cell administration. Co-expression of kill switch provides a mechanism for selective depletion of PRGN-3006 post administration and improves therapeutic control. We manufactured PRGN-3006 UltraCAR-T™ cells using non-viral gene transfer and rapid streamlined manufacturing process from multiple donor T cells. Co-expression of CAR, mbIL15 and kill switch was confirmed by flow cytometry and western blot analyses. PRGN-3006 demonstrated robust expansion in presence of CD33 antigen, lack of autonomous expansion in absence of CD33, and prolonged persistence in absence of exogenous cytokines in in vitro tests. The redirected specificity was demonstrated by the specific killing of CD33+ tumor cells as well as significant release of inflammatory cytokines such as IFNγ upon co-culture with AML tumor cells. We also demonstrated specific elimination of PRGN-3006 cells by kill switch activator antibody treatment. In vivo, a single administration of PRGN-3006 UltraCAR-T™ cells only one day after gene transfer effectively eliminated tumor burden and significantly improved overall survival (p<0.01) of tumor bearing mice compared to CAR-T cells lacking mbIL15 expression (conventional CAR-T) in an aggressive xenograft model of AML in immunocompromised (NSG) mice. PRGN-3006 demonstrated engraftment and significantly higher expansion and persistence in mice compared to CAR-T cells lacking mbIL15 (conventional CAR-T). These pre-clinical data provide a strong rationale to evaluate PRGN-3006 UltraCAR-T™ in a clinical trial for treatment of AML. The FDA has approved an investigational new drug application for PRGN-3006 UltraCAR-T™ and the first in human Phase 1 clinical trial for treatment of patients with relapse/refractory AML and high-risk myeloid dysplastic syndrome is currently ongoing (ClinicalTrials.gov Identifier: NCT03927261). Figure: Antitumor activity of PRGN-3006 UltraCAR-T™ cells in an established model of AML. MOLM-13 tumor cells were engrafted into NSG mice on Day 0 and PRGN-3006 were administered on Day 6 (arrow). Data shown is tumor burden (expressed as total flux in photons/sec) as the mean±SEM for each group of mice shown, with n=6-7 mice mice/group at the start of the study. Figure Disclosures Chan: Precigen: Employment. Ma:Precigen, Inc.: Employment. Carvajal-Borda:Precigen, Inc.: Employment. Velez:Precigen, Inc.: Employment. Plummer:Precigen, Inc.: Employment. Shepard:Precigen, Inc.: Employment. Shah:Precigen, Inc.: Employment; Intrexon Corp.: Equity Ownership. Sallman:Celyad: Membership on an entity's Board of Directors or advisory committees. Sabzevari:Precigen, Inc.: Employment.