Human CD2 is also referred as LFA-2 (leukocyte function-associated antigen-2), which belongs to the immunoglobulin supergene family. CD2 is a monomeric transmembrane glycoprotein with a weight of 45–50 kDa and binds CD58, CD48, or CD59. It consists of two extracellular Ig-like domains (one V-like and one C-like) and a proline-rich cytoplasmic tail. CD2 is commonly expressed on most mature peripheral T cells, NK-cells, and a subset of thymic B-cells during human thymocyte development. CD2 is crucial in T-cell activation, T- or NK-mediated cytolysis, apoptosis in activated peripheral T-cells, and the production of cytokines by T-cells. CD2 is an excellent pan-T-cell marker. The low expression level of CD2 is thought to associated with some of the T-lymphoid malignancies, particularly peripheral T-cell lymphomas. TCR (T-cell receptor) is a molecule originally found on the surface of T cells or T lymphocytes. From beginning, it is clearly described as a pair of clone-specific and heterodimeric polypeptide chains composed of both constant and variable regions. In humans, the majority of T cells (95%) express the TCR with alpha (α) and beta (β) chains, and only a smaller proportion express a TCR with gamma (γ) and delta (δ) chains. This receptor can recognize small fragments of proteins that are exhibited on the surface of foreign antigen-presenting cells and then convey the message to the nucleus inducing an immune response. And TCR endows T cells with the ability to identify and respond to "non self" material, through its complementarity-determining regions (CDRs).