Abstract 2740: Safe and effective delivery of antibody fragments to the solid tumor microenvironment

Abstract Promising immunotherapeutics, particularly agonists, have shown limited clinical benefit, in part because of dose-limiting toxicities, caused by potent immune activation in systemic compartments, with limited evidence of activity in the tumor microenvironment (TME). The Tumor Specific Immunogene (T-SIGn) platform is designed to generate vectors that can express combinations of transgenes producing immunotherapeutics selectively within the tumor microenvironment. T-SIGn is clinically validated for intravenous delivery, enabling the vectors to reach primary and metastatic sites to replicate and produce their therapeutic transgene payloads specifically in malignant epithelial cells. Transgene (TG) cassettes of T-SIGn vectors can be up to approximately 3.5Kb, allowing the expression of multiple distinct TGs. NG-350A is a clinical stage T-SIGn vector, with an established safety/tolerability profile, that expresses a full-length agonist CD40 antibody, and shows evidence of target engagement and adaptive immune activation in patients with different epithelial solid tumors via prolonged, dose-dependent increases in IL-12p70, IFNγ and IL-17A detected in the circulation of patients about 2 weeks after the initiation of the day 1, 3, 5 dosing regimen. NG-350A is currently being evaluated in phase I clinical studies in combination with Pembrolizumab or Ipilimumab. We have been characterizing numerous smaller fragment antibody formats that enable us to combine their expression with other antibody fragments or immunomodulatory molecules as a T-SIGn vector. An ScFv anti-CD40 fragment antibody design was identified as a potent immunotherapeutic to induce the secretion of IL-12p70 cytokine following stimulation of human monocyte-derived dendritic cells, as well as an enhanced antigen-specific T-cell activation and macrophage conversion to a more pro-inflammatory phenotype. When encoded together with CXCL9 and other immunostimulatory cytokines, the anti-CD40 ScFv has been selected as a potential follow-up to NG-350A that synergistically drives enhanced in vitro T-cell priming, activation and migration. Other checkpoint inhibitor and coactivator antibodies, as both ScFv and camelid VHH formats, have also been encoded individually, in combination with the anti-CD40 antibody fragment or other fragment antibodies to create a set of viral vectors that are being evaluated preclinically as future T-SIGn vector candidates. Data from these studies with initial vectors encoding combinations of functionally active antibody fragments will be presented. Collectively, these clinical and preclinical datasets demonstrate the broad utility of the T-SIGn platform for expressing rationally-designed combinations of antibodies and other natural and synthetic agents within tumors and thus enabling the development of new and potent immunotherapies for patients with solid epithelial cancers. Citation Format: Rachel Bergin, Amandine Pelletier, Manuela Zonca, Alice Muntzer, Meg Snowden, Samuel Hardy, Carla Cerqueira, Tae Hyun-Jang, Rochelle Lear, Masumi Fujinobu, Maria Stella Sasso, Samantha Bucktrout, Brian R. Champion. Safe and effective delivery of antibody fragments to the solid tumor microenvironment [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 2740.