Chimeric Antigen Receptors are recombinant protein molecules that cause cell activation upon encountering the target antigen. The antigen-recognition domain of a CAR is usually derived from monoclonal antibody sequences. Cell therapies being used or in development for treating cancer or autoimmune diseases use T cells or regulatory T cells (Tregs) respectively. CAR-T cells are engineered T cells and CAR-Treg cells are engineered Tregs. T cells modified with a chimeric antigen receptor (CAR), called CAR-T cells, are designed to find and kill cancer cells that carry the protein recognized by the receptor. This region interacts with tumor cell surface proteins and signaling motifs in the intracellular portion of the CAR ensure cell activation.