HPK1 (Hematopoietic Progenitor Kinase 1) is a serine/threonine kinase belonging to the STE20 family. It consists of a kinase domain, a proline-rich region, and a C-terminal regulatory region, primarily located in the cytoplasm. HPK1 plays a crucial role in immune cell signaling, regulating the activation, proliferation, and differentiation of T and B cells by activating downstream kinases such as JNK and p38 MAPK. HPK1 is also involved in regulating cell apoptosis and cytoskeletal reorganization. The expression of HPK1 is specific in different cells and tissues, and mutations or dysregulation in its gene expression are associated with various diseases, including immune system disorders and cancer.