These nonclinical studies demonstrated that ADG138, a novel double masked HER2×CD3 POWERbody TCE, exhibited an impressively high therapeutic index relative to its parental non-masked TCE in HER2 high and low expressing solid tumors. This provides strong support for advancing the ADG138 prodrug into clinical development for treating HER2-expressing solid tumors as a single agent and in combination with other immune stimulatory agents.