B-hHER2 MC38 plus and B-hHER2 CT26.WT cell lines demonstrate overexpression of the human HER2 protein. B-hHER2 MC38 plus and B-hHER2 CT26.WT cell lines exhibit normal tumor growth in B-hHER2 and BALB/c mice, respectively. Treatment with 10 mg/kg Trastuzumab analog-MMAE and 5 mg/kg DS8201 fully inhibited B-hHER2 MC38 plus growth in vivo. 10 mg/kg Trastuzumab analog-MMAE significantly inhibited B-hHER2 CT26.WT growth in vivo. Both HER2-humanized cell lines form syngeneic mouse tumor models ideal for in vivo HER2 ADC pharmacodynamic studies.