CD3 (Cluster of differentiation 3), originally known as T3, is one of the first groups of human T lymphocyte surface antigens recognized by monoclonal antibodies. It has been reported that antibodies against CD3 could either stimulate T cells to divide or inhibit the progress of effector functions according to the conditions used. It plays an important role in T cell and the CD3 T-cell co-receptor helps to activate the cytotoxic T-Cell and T helper cells. The CD3 molecule is composed of a protein complex and consists of four distinct chains. The complex of mammals contains a CD3γ chain, a CD3δ chain, and two CD3ε chains. All these chains associate with T-cell receptor and the ζ-chain to generate an activation signal in T lymphocytes. The EPCAM gene provides an instruction for the protein named epithelial cellular adhesion molecule. It is a type I membrane protein of 314 amino acids in humans, which consists of a large extracellular domain (N-terminal) of 242 amino acids, a short cytoplasmic domain of 26 amino acids (C-terminal) and a single-spanning transmembrane domain of 23 amino acids. The encoded EPCAM gene is located on the chromosome 2p21 and estimated with a size of 14 kb. This transmembrane glycoprotein with approximately 35kDa mediates Ca2+-independent homotypic cell-cell adhesion in epithelial cells and responses to cell surface interactions at the vascular wall. Diseases linked to EPCAM include congenital and colorectal cancer, with tufting enteropathy, and so on. It is used as a target for immunotherapy treatments of human cancer.