HPK1-IN-57 (Compound 10c) is an inhibitor of hematopoietic progenitor kinase 1 (HPK1) with an IC50 of 0.09 nM. It suppresses the activity of HPK1 kinase, inhibits the phosphorylation of downstream adaptor protein SLP76 (IC50 of 33.74 nM), and effectively induces the secretion of the T cell activation marker IL-2 (EC50 of 84.24 nM). HPK1-IN-57 holds promise for research in tumor immunotherapy.