Ontorpacept (TTI-621) is a soluble fusion protein comprising the N-terminal (1-118) of human SIRPα fused to the Fc region of human IgG1. This N-terminal (1-118) segment serves as the binding domain for CD47, an inhibitor of macrophage-mediated phagocytosis. As a checkpoint inhibitor that blocks CD47, ontorpacept exhibits antitumor activity [1].

Ontorpacept（0.001-1000 nmol/L；2小时）能够在急性髓性白血病、骨髓增生不良综合症、多发性骨髓瘤、B细胞急性淋巴细胞白血病以及T细胞急性淋巴细胞白血病患者的肿瘤细胞样本中，剂量依赖性提高巨噬细胞的吞噬功能，其平均EC50值为10 nmol/L[1]。

Ontorpacept (8 mg/kg；腹腔注射，每周三次，连续四周) 对SCID小鼠急性髓性白血病异种移植模型显示出显著的抗肿瘤效应[1]。