TIM3 on natural killer cells regulates antibody-dependent cellular cytotoxicity in HER2-positive gastric cancer

Therapies targeting HER2 are the standard treatment for HER2-positive gastric cancer (GC). Trastuzumab, a monoclonal antibody against HER2, exerts anti-tumor activity through cell growth regulation and antibody-dependent cellular cytotoxicity (ADCC). ADCC is induced by the binding of trastuzumab to Fcγ receptor III (CD16) in natural killer (NK) cells. However, the relationship between immune checkpoint (IC) molecules of NK cells and trastuzumab-induced ADCC is poorly understood. We performed single-cell RNA sequencing (scRNA-seq) and immunohistochemistry to identify IC molecules associated with CD16 expression in NK cells of GC patients. Additionally, we conducted in vitro assays with HER2-transfected GC cells and in vivo experiments using a mouse HER2-positive GC model to assess expression changes in IC molecules in NK cells and their ligands during trastuzumab treatment. In GC patients, the expression of TIM3, an IC molecule, was strongly correlated with that of CD16 in NK cells. In vitro assays showed that ADCC with trastuzumab increased TIM3 expression in NK cells. scRNA-seq analysis revealed that TIM3 expression of cytotoxic NK cells was elevated in HER2-positive GC patients treated with trastuzumab. HMGB1, a TIM3 ligand, was expressed at higher levels in HER2-transfected GC cells than in controls. Furthermore, HMGB1 expression was higher in HER2-positive GC patients treated with trastuzumab compared to untreated HER2-positive GC patients. In the mouse HER2-positive GC model, anti-TIM3 antibodies and trastuzumab demonstrated synergistic anti-tumor effects without toxicity. This study suggests the combined anti-TIM3 antibody and trastuzumab therapy may have potential as a new treatment strategy for HER2-positive GC.