CTLA4 and Autoimmunity: Antibodies targeting cytotoxic T lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and its ligand PD-L1 aim to disrupt these negative regulatory signals, which under physiological conditions protect the host from autoimmunity and chronic inflammation, to disrupt the ability of tumour cells to evade the host immune response.