Abstract 2476: Electroporation-mediated novel albumin-fused Flt3L DNA delivery promotes cDC1-associated anticancer immunity
Authors: Hu Ming-Hung , Wu Tzyy-Choou , Hung Chien-Fu 
Published: March 2024

Abstract
Introduction: Dendritic cells (DCs) constitute a distinct type of immune cell found within tumors, serving a central role in mediating tumor antigen-specific immunity against cancer cells. Frequently, DC functions are dysregulated by the immunosuppressive signals present within the tumor microenvironment (TME). Consequently, DC manipulation holds great potential to enhance the cytotoxic T cell response against cancer diseases. The Fms-like tyrosine kinase receptor 3 ligand (Flt3L) is a pluripotent growth factor that regulates the maturation and differentiation of DCs in hematopoiesis. The in vivo administration of Flt3L itself is limited by its short serum half-life. To overcome this major drawback, our group developed a novel fusion protein albumin-Flt3L (alb-Flt3L), which is the conjugation of albumin to Flt3L. Our hypothesis is that the Flt3L, which has extended bioavailability, is a feasible therapeutic strategy to overcome these treatment limitations.
Method: A novel alb-Flt3L DNA, a plasmid encoding the alb-Flt3L protein, was administrated for its anti-tumor effect on TC-1 tumor-bearing C57BL/6 mice. For the generation of pcDNA3-albFlt3L, mouse Flt3 ligand was amplified by PCR using cDNA template of pcDNA3-Flt3L1 and a set of primers, 5′- TTTGAATTCGGGACACCTGACTGTTACTTC-3′ and 5′- AAACTTAAGCTACTGCCTGGGCCGAGGCTCTGG -3′. alb-Flt3L DNA (10ug), Flt3L DNA (10ug) or vehicle control was injected intratumorally followed by electroporation for a total of three times in 5-day intervals. Peripheral blood mononuclear cells and tumor-infiltrated immune cells were isolated after treatment. Flow cytometry was performed for immune cell analysis.
Results: In this current study, the electroporation-mediated delivery of alb-Flt3L DNA demonstrated the ability to induce an anti-tumor immune response. This albumin fusion construct possesses more persistent bioactivity in targeted organs. Furthermore, mice receiving alb-Flt3L DNA treatment presented better tumor control and superior survival. Cellular analysis revealed that alb-Flt3L DNA administration displayed greater systemic DC population. In addition, robust cDC1 expansion, which is associated with superior antigen cross-presentation and cellular immunity against tumors, developed extensively in the tumor, lymph node, and blood. In addition, increased levels of IFN-γ-secreting CD8+ lymphocytes and tumor-infiltrated immune cells were found in correlation to greater cDC1 population.
Conclusion: Our data showcases a novel DC-based immunotherapy using electroporation to administer alb-Flt3L DNA. The treatment effect is revealed by a controlled tumor response, characterized by enhanced DC mobilization and accumulation in both the lymph nodes and TME, coupled with an increase in the expansion of cDC1 subsets and a heightened level of CD8+ T cell activation.
Citation Format: Ming-Hung Hu, Tzyy-Choou Wu, Chien-Fu Hung. Electroporation-mediated novel albumin-fused Flt3L DNA delivery promotes cDC1-associated anticancer immunity [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 2476.