CD19 is a type I transmembrane glycoprotein of the immunoglobulin superfamily, serving as a B cell-specific marker. It is continuously expressed throughout B cell development but disappears upon terminal differentiation into plasma cells. As it lacks intrinsic kinase activity, CD19 needs to form a B cell co-receptor complex with proteins such as CD21 and CD81 to function. Acting as a co-receptor for the B cell receptor (BCR), when the BCR recognizes an antigen, CD19 cooperates to bring the antigen protein closer and strengthens binding. It then rapidly activates kinases like Lyn, which are connected to its intracellular domain, while powerfully recruiting and activating key downstream signaling molecules such as PI3K, Vav, and PLC-γ. Through this mechanism, CD19 enhances BCR-mediated signal transduction, significantly lowers the activation threshold for B cells, and makes immune responses more sensitive and efficient.

c-MET is a receptor tyrosine kinase encoded by the MET proto-oncogene. It consists of an extracellular ligand-binding domain, a transmembrane region, and an intracellular tyrosine kinase domain, and is primarily located on the cell surface. Its sole ligand is Hepatocyte Growth Factor (HGF). Under normal physiological conditions, binding with its ligand HGF activates downstream signaling pathways, regulating cell proliferation, migration, differentiation, survival, and tissue repair. This is crucial for embryonic development and maintaining tissue homeostasis in adults. However, when the MET gene undergoes mutation, amplification, overexpression, or exon 14 skipping, the c-MET signaling pathway becomes abnormally and constitutively activated. This drives tumor growth, invasion, metastasis, and angiogenesis, and is also a key mechanism of resistance to EGFR-targeted therapies.

TSLP (Thymic Stromal Lymphopoietin) is a pleiotropic cytokine primarily secreted by epithelial cells, fibroblasts, mast cells, etc. It mainly acts on various cells such as dendritic cells, T cells, and B cells, promoting their activation, differentiation, and proliferation, and inducing them to secrete Th2 cytokines. It activates signaling pathways like JAK-STAT, thereby initiating Th2-type immune responses and playing a crucial role in immune regulation, inflammatory responses, and disease development.

CD5 (Cluster of Differentiation 5) is a key transmembrane glycoprotein receptor belonging to the scavenger receptor family. Its core function is to negatively regulate signaling mediated by the T-cell receptor (TCR) and B-cell receptor (BCR), thereby maintaining immune tolerance in the body and preventing excessive lymphocyte activation. For instance, within tumor cells, CD5 promotes proliferation, survival, and inhibits apoptosis by regulating pathways such as NF-κB and PI3K/Akt. CD5 is a classic marker for T cells and is expressed on the surface of nearly all mature T cells. Additionally, it is expressed on subsets of B cells and NK cells but is not expressed on normal hematopoietic stem cells or non-hematopoietic solid tissues. This highly restricted expression profile provides an ideal foundation for developing highly specific, low off-target toxicity targeted therapies.