Abstract 1651: Generation of humanized TLR8 mice for the evaluation of human TLR8 agonists

Abstract Toll-like receptor 8 (TLR8) is encoded by the TLR8 gene and belongs to the family of toll-like receptors (TLRs). TLR8 is predominantly expressed in lung and peripheral blood leukocytes. Close to the TLR8 gene locus, another TLR family member, TLR7, is also located on chromosome X and potentially can be manipulated by TLR8. TLR8 is an endosomal receptor that recognizes single-stranded RNA (ssRNA) viruses. After exogenous ssRNA infection, TLR8 will recruit MyD88 and activate downstream signaling. Similarly, miRNAs secreted from tumor cells also can activate TLR8 and lead to activation of the transcription factor NF-κB. Therefore, TLR8 also has been recognized as a potential therapeutic target. TLR8 agonists (e.g. VTX-2337) are undergoing clinical trials as immune stimulants in combination therapy for some cancers. Immune-stimulating antibody conjugates (ISACs) were developed by Bolt therapeutics, comprising a TLR7/8 dual agonist conjugated to tumor-targeting antibodies. ISACs can drive tumor killing by TLR mediated activation of myeloid cells and subsequent T-cell-mediated antitumor immunity, resulting in tumor clearance and immunological memory. Although human TLR8 arises as a promising target, emerging therapeutic candidates are lacking suitable mouse models on the market for preclinical in vivo screening and efficacy evaluation. Biocytogen has developed a novel TLR8 humanized mouse model (B-hTLR8 mice). Exon 3 of the mouse TLR8 gene, which encodes the extracellular domain, was replaced by human TLR8 counterparts. Human TLR8 protein and mRNA were detected in lung tissue from homozygous B-hTLR8 mice with the absence of mouse TLR8. Additionally, human TLR8 was detectable via flow cytometry in the dendritic cells and monocytes. To further validate the model, we have examined the model in vivo with a benchmark TLR8 agonist GS-9688. We observed TNFα secretion in B-hTLR8 mice but not in wild-type mice. Therefore, B-hTLR8 mouse model is a promising model for preclinical in vivo studies to evaluate TLR8 agonists and antibody-conjugated TLR8 agonists. Citation Format: Yuelei Shen, Yanan Guo, Lingqi Kong, Yang Bai Bai, Jiawei Yao, Chengzhang Shang, Jingwen Huang. Generation of humanized TLR8 mice for the evaluation of human TLR8 agonists [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1651.