Cluster of differentiation 3 (CD3) is a multimeric protein complex that is essential for T cell activation and antigen recognition. It consists of five different polypeptide chains (γ, δ, ε, ζ, and η) that are noncovalently associated with the T cell receptor (TCR). The TCR is responsible for recognizing antigens presented by antigen-presenting cells (APCs), while CD3 transduces the activation signal into the T cell and activates helper T-cells and cytotoxic T-cells ^[1-2]. The CD3-TCR complex is expressed on the surface of all mature T cells, and its assembly is required for T cell development and function. CD3 plays a crucial role in stabilizing the TCR and facilitating its interaction with antigens. It also recruits signaling molecules to the TCR, which initiates a cascade of events that leads to T cell activation. CD3 is a highly specific T cell marker, and its expression is increased upon T cell activation. This makes it a valuable tool for identifying and characterizing T cells in tissues and blood samples. CD3 staining is also used to diagnose T-cell lymphomas and leukemias. Due to its essential role in T cell activation, CD3 is a promising target for immunosuppressive therapy. Several anti-CD3 monoclonal antibodies have been developed and are being tested in clinical trials for the treatment of autoimmune diseases, such as type 1 diabetes and rheumatoid arthritis ^[3]. The DLL3 (Delta-like canonical Notch ligand 3) gene encodes a transmembrane protein belonging to the Delta/Serrate/Lag-2 (DSL) family of ligands. Functioning within the highly conserved Notch signaling pathway, DLL3 exhibits a unique, inhibitory role, contrasting with the canonical activating function of other Notch ligands. It is believed to antagonize Notch signaling by preventing ligand-receptor interactions or by promoting receptor degradation, a mechanism critical for establishing proper cell fate decisions during development ^[4]. This is particularly evident in the formation of somites, where DLL3's function is essential for the rhythmic segmentation of the presomitic mesoderm ^[5]. While its expression is largely restricted to fetal tissues and progenitor cells in healthy adults, DLL3 is ectopically and highly expressed in a number of neuroendocrine tumors, including small cell lung cancer (SCLC), making it a promising therapeutic target. Pathogenic variants in the DLL3 gene are directly linked to Spondylocostal dysostosis type 1, a congenital disorder of vertebral segmentation ^[6]. The B6-huCD3/huDLL3 mouse is a dual-gene humanized model obtained by mating B6-huCD3 mice (catalog number: C001325) with B6-huDLL3 mice (catalog number: C001854). This model can be used for studying the pathological mechanisms and treatment methods of tumors and autoimmune diseases, as well as for the development of CD3/DLL3-targeted drugs.