An engineered natural killer (NK) cell engager comprised of an anti-receptor tyrosine kinase-like orphan receptor 1 (ROR1) antibody, with an increased binding affinity to CD16 Fc receptor, with potential immunostimulating and antineoplastic activities. Upon administration, CD16-based ROR1-targeted NK cell engager PBA-0405 targets and binds to ROR1 expressed on tumor cells and simultaneously binds to the activating CD16 Fc receptor expressed on NK cells, thereby bringing ROR1-expressing tumor cells and NK cells together. This stimulates the NK cells, and results in the selective NK cell-mediated tumor cell lysis of ROR1-expressing tumor cells and antibody-dependent cellular cytotoxicity (ADCC). CD16, also known as Fc-gamma receptor III, is normally expressed on the surface of NK cells, neutrophils, monocytes and macrophages, and plays a key role in initiating ADCC. It is often downregulated in certain cancers, thereby inhibiting the anti-tumor immune response. ROR1, also known as neurotrophic tyrosine kinase, receptor-related 1 (NTRKR1), is expressed during embryogenesis and in various hematological and solid malignancies. It plays key roles in tumor cell proliferation and survival.