Abstract 5164: Liposomal Delivery of an Immunostimulatory CpG Induces Robust Antitumor Immunity and Long-Term Immune Memory by Reprogramming Tumor-Associated Macrophages
Authors: Kim Yujin , Jon Sangyong 
Published: April 2023

Abstract
Background: The efficacy of current T cell-based immunotherapy is known to be limited by various factors that induce immune suppression in the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) are representative TME-comprising immune suppressive cells and influence tumor growth and progression. TAMs are considered as an attractive target for cancer immunotherapy. However, current TAMs-targeting strategies are not sufficient to induce continuous antitumor responses. Here, we suggest a new strategy that can reprogram TAMs and further bridge innate-to-adaptive immunity by utilizing immunostimulatory CpG oligodeoxynucleotides (ODNs). In this study, we investigated the new role of TLR9 agonist CpG ODN as an immunotherapeutic agent and tested whether liposomal delivery of CpG could modulate the function of TAMs and lead to remodeling of the TME.
Methods: A liposome-based nanomaterial encapsulating CpG ODN was constructed. A small lipid nanoparticle (SLNP) used as the CpG delivery platform in this study was made of a cationic cholesterol derivative and two biocompatible phospholipids. The CpG-encapsulating SLNP (SLNP@CpG) was prepared by a thin-film formation and rehydration method. In vitro studies were conducted to assess whether SLNP@CpG could reprogram macrophages. To assess antitumor therapeutic efficacy of the SLNP@CpG, two subcutaneous tumor models were established in mice and tumor growth and survival rates of mice were monitored. For tumor rechallenge experiment, mice showing complete tumor regression were rechallenged with same cancer cells and their splenocytes were analyzed to confirm the development of immune memory. To elucidate the immunological mechanism of SLNP@CpG-mediated antitumor efficacy, changes of immune cell subpopulations in treated tumors were analyzed by flow cytometry.
Results: SLNP@CpG enhanced macrophage-mediated phagocytosis of cancer cells and tumor antigen cross-presentation, and skewed the polarization state of macrophages in vitro. Intratumorally injected SLNP@CpG exerted its therapeutic efficacy in an established E.G7-OVA tumor via uptake by TAMs. SLNP@CpG treatment significantly suppressed the E.G7 tumor growth and also considerably prolonged the survival of mice, with 83.3% of mice becoming tumor-free. Local administration of SLNP@CpG resisted E.G7 tumor rechallenge by inducing immunological memory and long-term antitumor immunity. Local administration of SLNP@CpG even exerted its antitumor efficacy in an aggressive B16-F10 melanoma by remodeling TME towards immune stimulation and tumor elimination.
Conclusion: Liposomal delivery of CpG via local treatment reprogrammed TAMs by enhancing phagocytic activity and repolarizing M2 to M1 phenotype and also reshaped immunosuppressive TME, leading to antitumor immunity and long-term memory responses.
Citation Format: Yujin Kim, Sangyong Jon. Liposomal Delivery of an Immunostimulatory CpG Induces Robust Antitumor Immunity and Long-Term Immune Memory by Reprogramming Tumor-Associated Macrophages. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5164.