MS40 is a WDR5 PROTAC that selectively degrades WDR5 and serves as a novel degrader for immune-modulating compounds (IMiDs), including the new substrates CRBN and Ikaros zinc finger (IKZF) transcription factors IKZF1 and IKZF3. MS40 facilitates the degradation of WDR5, resulting in the dissociation of the MLL/KMT2A complex from chromatin, thereby reducing H3K4me2 levels. In vitro, MS40 inhibits the growth of primary leukemia patient cells, and in vivo, it suppresses the expansion of patient-derived xenografts.