CD3 (immunology)

Phosphorylation of the ITAM on CD3 renders the CD3 chain capable of binding an enzyme called ZAP70 (zeta associated protein), a kinase that is important in the signaling cascade of the T cell.

Because CD3 is required for T-cell activation, drugs (often monoclonal antibodies) that target it are being investigated as immunosuppressant therapies (e.g., otelixizumab, teplizumab) for type 1 diabetes and other autoimmune diseases.

Cancers that possess the B7-H3 immunoregulatory checkpoint receptor on the tumor cell have been one such target in clinical trials.

This high specificity, combined with the presence of CD3 at all stages of T-cell development, makes it a useful immunohistochemical marker for T cells in tissue sections.

The antigen remains present in almost all T-cell lymphomas and leukaemias, and can therefore be used to distinguish them from superficially similar B-cell and myeloid neoplasms.