The present invention relates to a TCR KO—or TCR KO and dCK KO—engineered immune cells expressing a Chimeric Antigen Receptors (CAR) specific for CD123 that is a recombinant chimeric protein able to redirect immune cell specificity and reactivity toward CD123-expressing cells, and more particularly in which extracellular ligand binding is a scFV derived from a CD123 monoclonal antibody, conferring specific immunity against CD123 positive cells. The engineered immune cells endowed with such CD123 CARs are particularly suited for treating relapse refractory AML and blastic plasmacytoid dendritic cell neoplasm and for use as a treatment before bone marrow transplantation.