CD19/4-1BB Antibodies

Target Information

CD19 is a member of the immunoglobulin superfamily with two Ig-like domains. It is expressed on B cells at nearly all stages of development except terminal plasma cells. It is also found on follicular dendritic cells and some myeloid leukemia cells, especially of monocytic lineage. CD19 is the earliest and most broadly expressed B cell marker and 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). As a key BCR co-receptor, it amplifies signaling and lowers the threshold for B cell activation, allowing sensitive responses even to low-affinity antigens. CD19 signaling triggers tyrosine phosphorylation, calcium mobilization, and B cell proliferation. It can also signal independently of direct BCR engagement, serving as a central regulator that integrates multiple signaling pathways. Because of this role, CD19 is critical in both normal immune responses and malignant B cell growth. Mutations in CD19 can cause hypogammaglobulinemia (low antibody levels), while overexpression may lead to excessive B cell activity. CD19 is present on virtually all peripheral B cells expressing kappa or lambda light chains.

CD137 ligand (CD137L) is a type II membrane protein in the TNF superfamily. It acts as a co-stimulatory molecule and is expressed on activated antigen-presenting cells such as dendritic cells, monocytes/macrophages, and B cells. Its receptor, CD137 (4-1BB), is expressed on activated T cells and other cells, including inflamed endothelial cells. Interaction between CD137L and CD137 enhances T cell proliferation, IL-2 production, survival, and cytotoxic function, and supports monocyte migration into inflamed tissues. CD137L is expressed on many B cell lymphomas, including mantle cell, follicular, and diffuse large B cell lymphoma, but not on Hodgkin or T cell lymphomas. It is also found in some carcinoma cell lines and may contribute to interactions between T cells and tumor cells.