With emerging supremacy, cancer immunotherapy has evolved as a promising therapeutic modality compared to conventional antitumor therapies. Cancer immunotherapy composed of biodegradable poly(lactic-co-glycolic acid) (PLGA) particles containing antigens and toll-like receptor ligands induces vigorous antitumor immune responses in vivo. Here, we demonstrate the supreme adjuvant effect of the recently developed and pharmaceutically defined double-stranded (ds)RNA adjuvant Riboxxim especially when incorporated into PLGA particles. Encapsulation of Riboxxim together with antigens potently activates murine and human dendritic cells, and elevated tumor-specific CD8+ T cell responses are superior to those obtained using classical dsRNA analogues. This PLGA particle vaccine affords primary tumor growth retardation, prevention of metastases, and prolonged survival in preclinical tumor models. Its advantageous therapeutic potency was further enhanced by immune checkpoint blockade that resulted in reinvigoration of cytotoxic T lymphocyte responses and tumor ablation. Thus, combining immune checkpoint blockade with immunotherapy based on Riboxxim-bearing PLGA particles strongly increases its efficacy.

HLA-F adjacent transcript 10 (FAT10) is a cytokine-inducible ubiquitin-like modifier that is highly expressed in the thymus and directly targets FAT10-conjugated proteins for degradation by the proteasome. High expression of FAT10 in the mouse thymus could be assigned to strongly autoimmune regulator–expressing, mature medullary thymic epithelial cells, which play a pivotal role in negative selection of T cells. Also in the human thymus, FAT10 is localized in the medulla but not the cortex. TCR Vβ-segment screening revealed a changed T cell repertoire in FAT10-deficient mice. Analysis of five MHC class I– and II–restricted TCR-transgenic mice demonstrated an altered thymic negative selection in FAT10-deficient mice. Furthermore, the repertoire of peptides eluted from MHC class I molecules was influenced by FAT10 expression. Hence, we identified FAT10 as a novel modifier of thymic Ag presentation and epitope-dependent elimination of self-reactive T cells, which may explain why the fat10 gene could recently be linked to enhanced susceptibility to virus-triggered autoimmune diabetes.

BACKGROUND. PLGA microsphere-based vaccination has been proven to be effective in immunotherapy of syngeneic model tumors in mice. The critical step for the translation to humans is the identification of immunogenic tumor antigens and potent vaccine formulations to overcome immune tolerance. METHODS. HLA-AÃ 0201 transgenic mice were immunized with eight different human prostate cancer peptide antigens co-encapsulated with TLR ligands into PLGA microspheres and analyzed for antigen-specific and functional cytotoxic T lymphocyte responses. RESULTS. Only vaccination with STEAP1 262-270 peptide encapsulated in PLGA MS could effectively crossprime CTLs in vivo. These CTLs recognized STEAP1 262-270 /HLA-A Ã 0201 complexes on human dendritic cells and prostate cancer cell lines and specifically lysed target cells in vivo. Vaccination with PLGA microspheres was much more potent than with incomplete Freund's adjuvant. CONCLUSIONS. Our data suggests that there exist great differences in the immunogenicity of human PCa peptide antigens despite comparable MHC class I binding characteristics. Immunogenic STEAP1 262-270 peptide encapsulated into PLGA microspheres however was able to induce vigorous and functional antigen-specific CTLs and therefore is a promising novel approach for immunotherapy against advanced stage prostate cancer.

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Introduction Oncolytic viruses (OVs), which selectively replicate in and destroy tumor cells, represent a highly promising class of cancer therapeutics with a strong immune stimulatory potential. VSV-GP, a chimeric Vesicular Stomatitis Virus (VSV) pseudotyped with the glycoprotein of the lymphocytic choriomeningitis virus (LCMV) is a potent tumor cell-lysing agent and capable of jump-starting α-tumor immunity. The current study explores the immune promoting properties of VSV-GP and one of its cargo-armed, next generation variants with a T-cell/DC-directed MoA. It further investigates clinically relevant combination therapies with checkpoint inhibition (α-PD-1) as well as a “second mitochondria-derived activator of caspases“ mimetic (SMACm). Experimental Procedures Immune competent mice bearing established LLC1-IFNARKO, B16-F1-OVA or CT26.CL25-IFNARKO tumors were subject to treatments comprising VSV-GP variants, α-PD-1, a SMACm or combinations of the latter. Anti-tumor effects were determined by tumor growth inhibition and/or changes in overall survival. VSV-GP´s tumor cell selective replication, resulting in immune activation as well as cargo mediated immune modulation, were assessed using FFPE based IHC staining as well as NanoString and functional in vitro assays. Data Summary Here we present data on VSV-GP and one of its improved, next generation variants, which display potent α-tumor efficacy and upon systemic delivery increase the local T-cell and dendritic cell infiltration as well as activation within the tumor microenvironment. Building on the observed therapeutic and immune-modulatory potential of VSV-GP and its cargo-armed variant, we further explored therapeutic combinations with a PD-1 blocking antibody, which resulted in a strong improvement of the VSV-GP-mediated α-tumor efficacy. Immunological memory formation in cured animals was demonstrated by a tumor rechallange experiment. We further explored the therapeutic combination of VSV-GP and its cargo-bearing variant with a SMACm, which resulted in a strongly improved therapeutic benefit as well as increased overall survival in case of VSV-GP. The VSV-GP encoded immune-stimulatory cargo further improved this therapeutic synergy. Conclusion In summary VSV-GP induces a pro-inflammatory microenvironment within infected tumors, increases immune cell infiltration, a feature, which is further improved by tumor selective expression of VSV-GP encoded therapeutic cargos, and synergizes with α-PD-1 as well as a SMACm. The strong α-tumor immunity promoting potential of the VSV-GP platform observed in preclinical disease models justifies further testing of VSV-GP variants and the respective therapeutic combinations in clinical trials. Citation Format: Philipp Mueller, Tobias Nolden, Klaus Erb, Monika Petersson, Brigit Stierstorfer, Fabian Heinemann, Valerie Laura Herrmann, Maria Antonietta Impagnatiello, Eric Borges, Knut Elbers, John Park, Guido Wollmann, Patrik Erlmann. Therapeutic potential of cargo-armed next generation variants of VSV-GP and synergy with immune modulators [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4450.