Cbl-b-IN-15 (compound 25) is an inhibitor of the RING finger E3 ligase Cbl (IC 50 : 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 EC 50 =0.41 μM.