Cbl-b-IN-15 (compound 25) is an inhibitor of the RING finger E3 ligase Cbl (IC50: 15 nM) . Cbl-b refers to Casitas B-lineage lymphoma proto-oncogene-b, which inhibits T-cell, natural killer (NK) cell, and B-cell activation. Cbl-b-IN-15 activates T cell function with EC50=0.41 μM[1].