TNRX-257 blocks the interaction of LAG3 with MHC-II and enhances TCR signaling with similar potency as Relatlimab. In contrast, the corresponding untargeted IL2Rγ/β Tentacle had no efficacy. Together, these data show that TNRX-257 has drug-like properties and elicits strong anti-tumor efficacy, supporting its clinical development.