The small GTPase Rac is a key node in the signaling and cytoskeletal networks that govern cell shape and dynamic behaviors. Rac proteins are ancient and highly conserved in evolution. In the 1990s, we discovered the role of Rac in cell migration. Recently we discovered that hyperactivation of Rac causes cells to engulf and kill other cells in the Drosophila ovary and in mammalian macrophages. This behavior likely contributes to the immunodeficiency phenotypes of human patients carrying activating mutations in the hematopoietic-specific RAC2 gene. We found that hyperactivating Rac also enhances chimeric antigen receptor (CAR-)macrophage engulfment of human tumor cells and antibody-dependent cellular phagocytosis. Thus Rac-enhanced macrophages offer a general approach to improving therapeutic monoclonal antibodies.