Our data demonstrated that the trifunctional fusion protein QP34563457 have higher biological activity than single anti-HER2 antibody T-mab or P-mab and their combination, suggesting a more effective HER2 (+) cancer treatment potential. In combination with a dosing matching IL-15 activity, QP34563457 is expected to engage immune cells in a HER2 (+) tumor targeted manner and exhibit synergistic effects by bispecific targeting on HER2 (+) tumors as well. The yield and physiochemical properties of QP34563457 is up to the industrial production standard.