Wnt Signaling Downregulation Mediates T Cell Apoptosis Following <scp>OKT3</scp> ‐Induced T Cell Activation in Preclinical Models

OKT3 is a murine monoclonal antibody (mAb) directed against human CD3 expressed on T cells and is known to induce T cell activation followed by activation-induced cell death. This study investigated the role of canonical Wnt signaling in OKT3-mediated T cell activation and apoptosis using preclinical models. In primary human PBMCs, OKT3 treatment downregulated the expression of canonical Wnt signaling-related genes, whereas the Wnt pathway activator CHIR99021 upregulated their expression and reversed the OKT3-induced suppression. OKT3 stimulation upregulated T cell activation markers (CD69, CD25), particularly in CD8⁺ T cells, and induced apoptosis as assessed by flow cytometry. Co-treatment with CHIR99021 attenuated OKT3-induced CD25 expression and late apoptosis, suggesting that Wnt signaling modulates T cell activation and cell death. In a humanized mouse model, OKT3 administration led to marked depletion of hCD3⁺, hCD4⁺, and hCD8⁺ T cells in the peripheral blood. Transcriptomic profiling using RNA-seq of liver-infiltrating human immune cells revealed significant upregulation of genes involved in T cell activation, apoptosis, cytokine signaling, and oxidative stress, accompanied by widespread downregulation of Wnt signaling genes (CTNNB1, LRP6, DVL1, FZD family). Therefore, these findings suggest that OKT3 induces T cell responses characterized by activation and subsequent apoptosis, in association with Wnt signaling. This study provides mechanistic insight into OKT3-mediated immunomodulation and supports preclinical evaluation of T cell-targeting monoclonal antibodies.