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 key proteins to initiate T-cell development and activation, which are essential for the adaptive immune response. Dysregulation of LCK can impair 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.