Poster CC13 - Intratumoral Injectable Immune Niche Improves the Abscopal Effect in Radio-Immunotherapy

Introduction: Cancer immunotherapy has emerged as a potent strategy for leveraging a patient’s immune system against cancer, offering long-term immunosurveillance. Breakthroughs in immune checkpoint inhibitors have extended survival for patients. However, a complete therapeutic response from the immune checkpoint therapy remains limited in metastatic cancer patients. An immune-mediated abscopal effect, a phenomenon in which local treatment not only shrinks the treated tumor but also leads to the shrinkage of untreated tumor(s), was observed in a number of patients who received an immune checkpoint blockade and X-ray radiotherapy (XRT). Due to the rarity of the abscopal effect, there is a significant interest in developing treatments to augment its frequency and efficacy. In this study, we report the development of an intratumoral (i.t.) injectable nanofiber (NF)-based tumor immune niche that converts radiotherapy-treated tumors into an in situ cancer vaccine, eliciting robust systemic antitumor immunity. This NF-based immune niche incorporates redox-degradable α-CTLA-4 nanogels (NGs) and IL-2 NGs for controlled release in hypoxic irradiated tumors, reversing the immunosuppressive tumor microenvironment into a pro-inflammatory microenvironment and expanding the tumor-infiltrating CD8+ T cell population. Additionally, it is functionalized with polyinosinic-polycytidylic acid (poly(I:C)) to promote antigen-presenting cell maturation and prime neoantigen-specific CD8+ T cells.

Materials and

Methods: Nanofiber-based immune niche was constructed from dibenzocyclooctyne (DBCO)-functionalized diblock copolymer NFs, redox-degradable azide (N3)-functionalized IL-2 NGs and α-CTLA-4 NGs, and poly(I:C). The NGs were prepared by chemically crosslinking IL-2 FcIg and α-CTLA-4 with a primary amine-reactive 3,3′-dithiobis(sulfosuccinimidyl propionate) (DTSSP) crosslinker, in the presence of an azide- and primary amine-functionalized statistical copolymer stabilizer. The NGs were conjugated to the DBCO-functionalized NFs through strain-promoted azide-alkyne cycloaddition. Poly(I:C) was ionically adsorbed onto the amine-rich steric stabilizer on the NF-conjugated NGs. The control release behaviors of the fluorescently-labeled IL-2 FcIg, α-CTLA-4 and poly(I:C) at different hypoxic conditions were evaluated through fluorescence assay. The abilities of the immune niche to expand naïve CD8+ T cells and mature antigen-presenting cells were evaluated through FACS-based assay. The ability of the immune niche to enhance antigen-specific cell killing was further evaluated in OT-1 assay in vitro. The ability for the i.t.-administrated immune niche to inhibit treated primary tumor growth and induce systemic anticancer activity was first evaluated in bilateral B16OVA tumor model. Further anticancer efficacies and mechanistic studies were performed in bilateral B16F10, CT26, and MC38 tumor models to demonstrate that the i.t. immune niche effectively convert X-ray irradiated tumor into an in situ vaccine to improve the abscopal effect.

Results, Conclusions, and Discussions: In this study, we successfully developed an i.t. injectable immune niche that transforms XRT-treated tumors into an in situ cancer vaccine. In this proof-of-concept study, this immune niche was engineered with redox-degradable IL-2 NGs, α-CTLA-4 NGs, and poly(I:C), facilitating the controlled release of active immune activators (IL-2 FcIg and poly(I:C)) and an immune checkpoint inhibitor (α-CTLA-4) within the hypoxic, irradiated tumor microenvironment. The released poly(I:C) and IL-2 FcIg, facilitated the maturation of tumor-infiltrating DCs and promoted the development of neoantigen-specific CD8+ T cells. Concurrently, α-CTLA-4 release prevented the inhibitory immune checkpoint ligands CD86 and CD80, overexpressed on mature tumor-infiltrating DCs, from inducing CD8+ T cell exhaustion. We also determined that this tumor immune niche combined with XRT at the primary tumor site, induced robust systemic anticancer activity in both bilateral melanoma and colorectal cancer mouse models. However, this result was not replicated by the i.t. administration of free IL-2 FcIg, α-CTLA-4, and poly(I:C) alone. Mechanistic studies confirmed that the locoregional treatment expanded neoantigen-specific memory CD8+ T cells in the primary tumor. Unlike traditional systemic immunotherapy, this locoregional treatment effectively mitigated immune-related adverse events associated with IL-2 and poly(I:C), overcoming significant barriers to clinical translation.

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