An engineered molecule based on tri-specific natural killer (NK) cell engager therapies (TriNKET) that is directed against human epidermal growth factor receptor 2 (EGFR2; HER2; ErbB2), with potential immunostimulating and antineoplastic activities. Upon administration, HER2 tri-specific NK cell engager DF1001 targets and binds to HER2 on tumor cells and simultaneously binds to NK cells, thereby bringing HER2-expressing tumor cells and NK cells together, which stimulates the NK cells and results in the selective NK cell-mediated tumor cell lysis of HER2-expressing tumor cells. The binding of HER2-expressing tumor cells and NK cells may also lead to the activation of T-cells and B-cells, potentiating the immune response against HER2-expressing tumor cells. HER2, a receptor tyrosine kinase (RTK) mutated or overexpressed in many tumor cell types, plays a key role in tumor cell proliferation and tumor vascularization.