Cmar_a_330637 6977..6987

1Sheng Yushou Center of Cell Biology and Immunology, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, People’s Republic of China; 2Joint International Research Laboratory of Metabolic & Developmental Sciences, Shanghai Jiao Tong University, Shanghai, 200240, People’s Republic of China Background: Co-stimulatory receptor agonist antibodies have shown promising antitumor efficacy in preclinical models. However, their clinical development lags due to systemic or local adverse effects of non-specific T cell activation. Utilization of a bispecific antibody format to reduce off-tumor immune activation is a focus of co-stimulatory receptor agonist antibody design. Methods: In this study, a bispecific antibody with anti-CLDN18.2 and anti-CD28 moieties was produced. Its T cell costimulation ability was evaluated in T cell coculture assay in vitro. Its safety and anti-tumor efficacy were explored in mouse tumor models. Results: Anti-CLDN18.2-anti-CD28 bispecific antibody could co-stimulate T cells and increase the expression of effector cytokines in a CLDN18.2-dependent manner. Treatment of anti-CLDN18.2-anti-CD28 could reduce tumor burden and increase tumor-infiltrated T cells. Immunosuppressive cells including tumor-associated macrophages and myeloidderived suppressor cells were also reduced without systemic adverse effects. Conclusion: This work provided proof-of-concept evidence for a new strategy to develop a bispecific co-stimulatory activator for treating CLDN18.2 tumors.