Work

840 Cleavable albumin-hitchhiking STING agonists for innate immune activation and combination with adoptive cell therapy in solid tumors

Year: 2026

Type: conference-paper

Abstract: Background Solid tumors resist immunotherapy in part through an immunosuppressive tumor microenvironment (TME) that disables effector T cells. Agonists of the stimulator of interferon genes (STING) pathway trigger type I interferon responses that reprogram the TME, recruit and activate innate effectors, and license antitumor T cell immunity. 1 However, systemic delivery of agonists such as diamidobenzimidazole (diABZI) is limited by poor pharmacokinetics and dose-limiting toxicity.2 We developed an albumin-hitchhiking nanobody-diABZI conjugate (nAlb-diABZI) that extends agonist half-life and tumor accumulation.3 Here, we assess the immunological activity of nAlb-diABZI as monotherapy and in combination with adoptive cell therapy (ACT) and develop a tumor-protease-activated conjugate designed to concentrate STING signaling within the TME.Methods We characterized nAlb-diABZI ( figure 1A-B) for STING bioactivity (interferon reporter cell assays), assessed biodistribution, and evaluated antitumor efficacy in mice with syngeneic EMT6 breast tumors, with immune activation in the TME profiled by flow cytometry and tumor qPCR. We tested ACT combination in MC38-SIINFEKL and B16F10-SIINFEKL tumors treated with OVA-specific CD8+ OT-I T cells with/without nAlb-diABZI. As a strategy to localize agonist release to the TME, we used a self-assembling coiled-coil conjugation approach4 to append cathepsin B-cleavable linkers (VC and GGFG) to diABZI (figure 1E-G), overcoming the hydrophobicity that has precluded conventional cleavable conjugation of diABZI.Results nAlb-diABZI retains STING agonism comparable to free diABZI and accumulates in tumors ( figure 1C), where flow cytometry shows uptake by tumor cells and macrophages, and tumor qPCR confirms induction of interferon-stimulated genes (figure 1D). As monotherapy, nAlb-diABZI reduces tumor burden and prolongs survival in EMT6. Critically, combining nAlb-diABZI with OT-I ACT markedly improves tumor control over OT-I alone with a single dose in MC38-SIINFEKL (n = 7-8, p <0.001) and a triple dose in B16F10-SIINFEKL (n = 10-13, study ongoing), indicating that innate immune activation enhances ACT efficacy (figure 2A-D). Consistent with its immune mechanism, nAlb-diABZI distributes to healthy organs, motivating tumor-restricted delivery; a stable coiled-coil conjugate reproduces the biodistribution of nAlb-diABZI, and cleavable variants that have been made and characterized are being evaluated to localize STING signaling and widen the therapeutic window.Conclusions Albumin-hitchhiking STING agonists reprogram the TME and potentiate adoptive cell therapy across two antigen-matched solid-tumor models, positioning innate STING activation as a tractable partner for cellular immunotherapy. Tumor-protease-activated conjugates now in testing aim to concentrate this immune activation within the tumor and reduce systemic exposure. Studies dissecting transferred T cell phenotype and TME remodeling under combination therapy are underway.Acknowledgements The authors acknowledge funding from NIH R01CA274675 (JTW) and the Vanderbilt Medical Scientist Training Program T32 GM007347.References Corrales L, Glickman LH, McWhirter SM, et al. Direct activation of STING in the tumor microenvironment leads to potent and systemic tumor regression and immunity. Cell Rep. 2015;11(7):1018–1030.Ramanjulu JM, Pesiridis GS, Yang J, et al. Design of amidobenzimidazole STING receptor agonists with systemic activity. Nature 2018;564(7736):439-443.Kimmel BR, Arora K, Chada NC, et al. Potentiating cancer immunotherapies with modular albumin-hitchhiking nanobody-STING agonist conjugates. Nat Biomed Eng. 2025;9(10):1719–1739.Ringaci A, Shih T-Y, Grinstaff MW. Supramolecular coiled-coil peptide platform for site-specific antibody-drug conjugate engineering. Nat Commun. 2026;17:3603.Ethics Approval All animal studies were approved by the Vanderbilt University Institutional Animal Care and Use Committee (IACUC); protocol number M2200026.Abstract 840 Figure 1Engineering and characterization of albumin-hitchhiking STING agonist conjugates. diABZI is conjugated to an anti-albumin nanobody via sortase/click chemistry. The stable payload is characterized for biodistribution and antitumor gene activation, followed by cathepsin B-cleavable payloads and a self-assembling coiled-coil platformAbstract 840 Figure 2nAlb-diABZI combined with adoptive OT-I T cell therapy is tested in two syngeneic tumor models. In MC38-SIINFEKL colorectal tumors, the combination significantly prolongs survival over OT-I alone; in B16F10-SIINFEKL melanoma, a similar trend is emerging

Source: Journal for ImmunoTherapy of Cancer

DOI: 10.1136/jitc-2026-sitc2026.0840