CD19/CD3/PD-L1/4-1BB Antibodies

Target Information

CD19 is an immunoglobulin superfamily protein with two Ig-like domains and is expressed on B cells at nearly all developmental stages except plasma cells. It is also found on follicular dendritic cells and some myeloid leukemia cells. As the earliest and most broadly expressed B cell marker, CD19 is present in all B cell precursor leukemias. CD19 forms a signaling complex with CD21, CD81, Leu13, MHC class II, and the B cell receptor (BCR). It acts as a key BCR co-receptor, amplifying signals and lowering the activation threshold, enabling sensitive responses even to low-affinity antigens. CD19 signaling induces tyrosine phosphorylation, calcium flux, and B cell proliferation, and can also function independently as a central signaling regulator. It is essential for normal and malignant B cell growth. Mutations can cause hypogammaglobulinemia, while overexpression may result in B cell hyperactivity. CD19 is expressed on virtually all peripheral B cells.

CD137 ligand (CD137L/4-1BBL) is a TNF superfamily member expressed on activated antigen-presenting cells. Its receptor, CD137 (4-1BB), is induced on activated T cells and other cells. Their interaction enhances T cell proliferation, survival, IL-2 production, and cytotoxicity. CD137L is expressed in many B cell lymphomas and some carcinomas and may contribute to tumor-immune interactions. CD137 signaling supports T cell expansion and memory formation, while soluble CD137 may regulate immune responses.

The CD3 complex (gamma, delta, epsilon, zeta) is essential for T cell receptor (TCR) assembly and signaling. Expressed on thymocytes and mature T cells, CD3 transduces antigen-recognition signals through tyrosine-based motifs in its cytoplasmic tails, leading to T cell activation, proliferation, survival, or growth arrest. CD3 defects cause immunodeficiency.

PD-L1 (B7-H1) binds PD-1 to inhibit TCR signaling, reducing T cell proliferation and cytokine production. It is widely expressed on many cancers and can be upregulated by IFN-gamma, contributing to tumor immune evasion.