In the layout of bispecific antibodies, CD3 is undoubtedly the "core target." In addition to classic pairings like CD3×CD19, CD3×CD20, and CD3×BCMA, more target combinations are under development. According to statistics from the PharmaSeek database, there are currently 417 CD3-related drugs in development, of which 409 are antibody drugs, with 378 being mult-ispecific and 333 being bispecific. As of now, there are 12 approved CD3-targeted drugs, 10 of which are bispecific antibodies.

Table 1: Summary of CD3-TCE Approved Drugs (Source: PharmaSeek)

CD3 is a polymeric protein complex consisting of four polypeptide chains: epsilon (ε), gamma (γ), delta (δ), and zeta (ζ). CD3ε, CD3δ, CD3γ, and CD3ζ are encoded by the CD3E, CD3D, CD3G, and CD247 genes, respectively. This forms three distinct subunits: CD3δε, CD3γε, and CD3ζπ dimers. The cytoplasmic tails of CD3ε, CD3δ, and CD3γ each contain an immunoreceptor tyrosine-based activation motif (ITAM), while the cytoplasmic tail of CD3ζ contains three ITAMs. As a result, a CD3 complex contains 10 ITAMs, making it highly sensitive to antigen binding.

Figure 2: Schematic Diagram of CD3 Structure

After the CD3 subunits bind to the α and β chains of the T cell receptor (TCR), they form a complete TCR–CD3 complex, which functions as a full functional unit: providing the "first signal" to initiate T cell activation and determining the specificity of the immune response. The TCR provides binding specificity, while the CD3 subunits facilitate the necessary signaling for T cell activation. The TCRαβ recognizes the pMHC complex on antigen-presenting cells at the immunological synapse, and the ITAM domains in the intracellular regions of the CD3 subunits mediate signal transduction. These domains are phosphorylated by Src family kinases. The cascade reaction ultimately leads to the production of second messengers (Ca2+, diacylglycerol (DAG), and IP3) and activation of Ras, which, through NF-κB, AP-1, and NFAT, triggers the upregulation of gene transcription and initiates T cell activation.

The transmembrane regions of all CD3 subunits and TCR chains tightly bind to each other through complementary electrostatic interactions between amino acid residues with opposite charges. This complementary electrostatic organization causes the transmembrane helices of each TCR/CD3 subunit to intertwine, anchoring the TCR/CD3 complex firmly in the cell membrane and allowing it to move as a single, independent functional unit within the lipid bilayer. As a key regulatory node in T cell immune responses, CD3 plays a critical role in modulating T cell activation and the strength of the immune response. Intervening with the CD3 target is significant in the treatment of immune diseases and cancer immunotherapy.

Figure 3: TCR Structure and T Cell Activation Pathway

Due to its unique structural functions, the CD3 target remains a key focus in antibody research and development worldwide, despite challenges such as cytokine release syndrome (CRS), low efficiency, and treatment resistance. Pharmaceutical companies are actively exploring breakthroughs, and with the extensive clinical development of CD3 drugs, there is hope that more CD3-targeted therapies will emerge as "beacons of treatment" and reach the market.

Novoprotein provides a range of CD3-targeted antigens and a variety of tumor targets, suitable for the development of bispecific and multispecific antibody drugs. Additionally, CD3-TCE has shown positive effects in autoimmune diseases such as multiple sclerosis by regulating T cell activity and immune tolerance mechanisms.

Novoprotein currently offers MOG protein, which can be used for experimental autoimmune encephalomyelitis (EAE) animal modeling, assisting in the evaluation of the efficacy of related CD3-TCE drugs.

Furthermore, Novoprotein provides reference antibodies validated by ELISA/BLI, which can be used as positive controls in antibody drug development and in basic scientific research.

CD3 Target: Data Display

Loaded Anti-Human CD3E mAb-mFc(NC079) on AMC Biosensor, can bind Human CD3E-Fc-6His&C-Fc-Flag(CY33) with an affinity constant of 0.6 nM as determined in BLI assay.

Loaded Anti-Human/Monkey CD3E mAb-Fc(NC006) on Protein A Biosensor, can bind Human CD3D&CD3E Heterodimer-His(C01S) with an affinity constant of 1.13 nM as determined in BLI assay.