LCK (Lymphocyte-Specific Protein Tyrosine Kinase): LCK is an enzyme that plays a crucial role in the T-cell receptor (TCR) signalling pathway. It phosphorylates essential proteins to initiate T-cell development and activation, which are vital for the adaptive immune response. Dysregulation of LCK can impact immune function and is associated with autoimmune diseases and immunodeficiency. Due to its central role, LCK is a target for immunotherapy in cancer and autoimmune disorders.