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BackgroundWe previously demonstrated potent antitumor activity against human breast cancer xenografts using photodynamic therapy (PDT) targeting a novel tumor-specific photosensitizer (HS201), which binds heat shock protein 90 (HS201-PDT). However, induction of systemic antitumor immunity by HS201-PDT alone or by the combination strategy with immune checkpoint blockade has yet to be determined.MethodsUsing unilateral and bilateral implantation models of syngeneic breast tumors (E0771, MM3MG-HER2, and JC-HER3) in mice, we assessed whether HS201-PDT could induce local and systemic antitumor immunity. In an attempt to achieve a stronger abscopal effect for distant tumors, the combination strategy with anti-PD-L1 antibody was tested. Tumor-infiltrating leukocytes were analyzed by single cell RNA-sequencing and receptor-ligand interactome analysis to characterize in more detailed the mechanisms of action of the treatment and key signaling pathways involved.ResultsHS201-PDT demonstrated greater tumor control and survival in immune competent mice than in immunocompromised mice, suggesting the role of induced antitumor immunity; however, survival was modest and an abscopal effect on distant implanted tumor was weak. A combination of HS201-PDT with anti-PD-L1 antibody demonstrated the greatest antigen-specific immune response, tumor growth suppression, prolonged mouse survival time and abscopal effect. The most significant increase of intratumoral, activated CD8+T cells and decrease of exhausted CD8+T cells occurred following combination treatment compared with HS201-PDT monotherapy. Receptor-ligand interactome analysis showed marked enhancement of several pathways, such as CXCL, GALECTIN, GITRL, PECAM1 and NOTCH, associated with CD8+T cell activation in the combination group. Notably, the expression of the CXCR3 gene signature was the highest in the combination group, possibly explaining the enhanced tumor infiltration by T cells.ConclusionsThe increased antitumor activity and upregulated CXCR3 gene signature induced by the combination of anti-PD-L1 antibody with HS201-PDT warrants the clinical testing of HS201-PDT combined with PD-1/PD-L1 blockade in patients with breast cancer, and the use of the CXCR3 gene signature as a biomarker.

Background: T-DXd is a new antibody-drug conjugate targeting HER2 that has demonstrated superior clinical efficacy over previous HER2-targeting agent Trastuzumab emtansine (T-DM1) in patients with advanced-stage HER2+ breast cancer (BC). T-Dxd consists of the anti-HER2 antibody Trastuzumab conjugated to Dxd (a topoisomerase-I inhibitor). While the HER2-mediated internalization of Dxd leads to direct and bystander tumor cell killing, it is unclear whether T-Dxd retains Fc-mediated induction of immunity and how these responses may interact with Dxd-mediated tumor cell killing. Therefore, in this study we investigated tumor-specific innate and adaptive immune responses elicited upon T-Dxd treatment versus other HER2-targeting agents. Method: We first compared immune responses of T-Dxd versus T-DM1 or Trastuzumab on macrophage activation after co-culture with HER2+ BC cells. We next utilized JEDI T cells to model tumor-antigen presentation by those macrophages. We also investigated the therapeutic effect of T-Dxd in an endogenous HER2 transgenic mouse model, and measured HER2-specific adaptive immune responses, in combination with immune checkpoint blockades. Results: We found that T-Dxd retains the capability to engage with FCGRs and promote ADCP of HER2+ BC cells by macrophages, with comparable efficacy to Trastuzumab. Interestingly, T-Dxd mediated ADCP combined with Dxd-mediated immunogenic cell death promoted superior macrophage activation over Trastuzumab and T-DM1, resulting in increased expression of antigen presentation genes, chemokines, and interferon-stimulated genes. In co-culture experiments with JEDI T cells, macrophages that have phagocytosed eGFP-expressing tumor cells after T-Dxd treatment showed superior activation of antigen-specific effector T cells. In vivo, T-Dxd demonstrated exceptional tumor growth inhibition over Trastuzumab, accompanied by increased HER2-specific adaptive T cell responses. Lastly, T-Dxd therapy showed synergistic antitumor activity when combined with immune checkpoint blockade of the CD47/SIRPA axis. Conclusion: T-Dxd retains antibody-mediated antitumor mechanisms of Trastuzumab such as FCGR activation and ADCP of HER2+ tumor cells. Importantly, this is synergized with T-Dxd induced immunogenic tumor cell death, which results in enhanced macrophage activation upon tumor cell phagocytosis. This result in enhanced tumor antigen presentation and activation of adaptive immunity in vitro and in preclinical mouse models, which may illustrate T-Dxd’s superior and long-lasting clinical efficacy in HER2+ BC patients. Combination therapy of T-Dxd with CD47/SIRPA checkpoint blockade resulted in synergistic therapeutic benefits in our mouse model studies, and further clinical research with this combination is warranted. Citation Format: Li-Chung Tsao, Zachary Conrad Hartman. Trastuzumab-deruxtecan (T-Dxd) induces superior macrophage/DC activation, antigen-presentation and anti-tumor adaptive immune responses, which can be augmented by CD47/SIRPA blockade [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 2944.

BackgroundThe majority of colorectal carcinomas (CRCs) are insensitive to programmed death protein-1/programmed death-ligand 1 (anti-PD-1/PD-L1) immune checkpoint inhibitor (ICI) antibodies. While there are many causes for ICI insensitivity, recent studies suggest that suppression of innate immune gene expression in tumor cells could be a root cause of this insensitivity and an important factor in the evolution of tumor immunosuppression.MethodsWe first assessed the reduction of mitochondrial antiviral signaling gene (MAVS) and related RIG-I pathway gene expression in several patient RNA expression datasets. We then engineered MAVS expressing tumor cells and tested their ability to elicit innate and adaptive anti-tumor immunity using both in vitro and in vivo approaches, which we then confirmed using MAVS expressing viral vectors. Finally, we observed that MAVS stimulated PD-L1 expression in multiple cell types and then assessed the combination of PD-L1 ICI antibodies with MAVS tumor expression in vivo.ResultsMAVS was significantly downregulated in CRCs, but its re-expression could stimulate broad cellular interferon-related responses, in both murine and patient-derived CRCs. In vivo, local MAVS expression elicited significant anti-tumor responses in both immune-sensitive and insensitive CRC models, through the stimulation of an interferon responsive axis that provoked tumor antigen-specific adaptive immunity. Critically, we found that tumor-intrinsic MAVS expression triggered systemic adaptive immune responses that enabled abscopal CD8 +T cell cytotoxicity against distant CRCs. As MAVS also induced PD-L1 expression, we further found synergistic anti-tumor responses in combination with anti-PD-L1 ICIs.ConclusionThese data demonstrate that intratumoral MAVS expression results in local and systemic tumor antigen-specific T cell responses, which could be combined with PD-L1 ICI to permit effective anti-tumor immunotherapy in ICI resistant cancers.