MAP4K1 (Mitogen-activated protein kinase kinase kinase kinase 1): MAP4K1 is a signalling protein, also known as HPK1 (Hematopoietic progenitor kinase 1), and a member of the STE20 kinase family. It plays an important role in immune cell signalling, where it regulates T-cell activation and differentiation by acting upstream in the MAP kinase pathway. Through its role in modulating the immune response, MAP4K1 is considered a potential target for immunotherapy, particularly in autoimmune diseases and cancer.