Abstract 4474: Turning up the heat: nanoimmunotherapy transforming outcomes in breast cancer treatment

Immune checkpoint blockade reaches remarkable clinical responses. However, even in the most favorable cases, half of these patients do not benefit from these therapies in the long term. This work hypothesized that the activation of host immunity by co-delivering peptide antigens, adjuvants, and regulators of the transforming growth factor (TGF)-β expression using a polyoxazoline (POx)-poly(lactic-co-glycolic) acid (PLGA) nanovaccine, while modulating the tumor-associated macrophages (TAM) function within the tumor microenvironment (TME) and blocking the anti-programmed cell death protein 1 (PD-1) can constitute an alternative approach for cancer immunotherapy. Nanoparticles (NP) prepared by the double emulsion solvent evaporation method were modified with mannose to target the mannose receptor (CD206) expressed at the dendritic cells (DC) surface, thus promoting receptor-ligand interaction and subsequently improving payload delivery. NP physicochemical properties were characterized, and the loading of antigens, adjuvants, immune modulators was quantified by fluorescence. The synergistic immunotherapeutic potential of our multifunctional nanovaccine, isolated and in combination with the TGF-β downregulation and Pexidartinib (colony-stimulating factor 1 receptor (CSF-1R) inhibitor that modulates TAM), was assessed in the immune-competent MC38 colorectal (CRC) mouse model. The added value of combining the immune checkpoint inhibitor anti-PD-1 monoclonal antibody to control the CRC (MC38 and CT26) and the highly aggressive melanoma (B16F10) growth and survival was also evaluated.NP presented a mean diameter close to 200 nm, low polydispersity index, neutral surface charge, homogenous spherical shape, and high loadings for antigens, immune adjuvants, and modulators. POx-Mannose (Man) nanovaccines generated stronger antigen-specific T-cell responses, which led to significant tumor growth inhibition when compared with poly(ethylene glycol) (PEG)-Man nanovaccines. This anti-tumor effect induced by the POx-Man nanovaccines is mediated by a CD8+-T cell-dependent mechanism, in contrast to the PEG-Man nanovaccines. POx-Man nanovaccine combined with Pexidartinib restricted the MC38 tumor growth and synergized with PD-1 blockade, controlling MC38 and CT26 tumor growth and survival. This data was further validated in B16F10-bearing mice, a highly aggressive and poorly immunogenic melanoma mouse model for immunotherapy studies.This innovative approach discloses the synergy among the targeted cancer nanovaccine and immune modulatory and checkpoint therapies (αCSF-1R and αPD-1) within the immunosuppressive TME, which overall outcome may constitute a promising nanotechnology-enhanced immunotherapy for solid cancer patients. Citation Format: Ana I. Matos, Bárbara Carreira, Liane I. F. Moura, Rita C. Acúrcio, Ronit Satchi-Fainaro, Helena F. Florindo. Turning up the heat: nanoimmunotherapy transforming outcomes in breast cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4474.