Cancer immunotherapy with 4-1BB agonists has limited further clinical development because of dose-limiting toxicity. Here, we developed a bispecific antibody (bsAb; B7-H3×4-1BB), targeting human B7-H3 (hB7-H3) and mouse or human 4-1BB, to restrict the 4-1BB stimulation in tumors. B7-H3×m4-1BB elicited a 4-1BB–dependent antitumor response in hB7-H3–overexpressing tumor models without systemic toxicity. BsAb primarily targets CD8 T cells in the tumor and increases their proliferation and cytokine production. Among the CD8 T cell population in the tumor, 4-1BB is solely expressed on PD-1⁺Tim-3⁺ “terminally differentiated” subset, and bsAb potentiates these cells for eliminating the tumor. Furthermore, the combination of bsAb and PD-1 blockade synergistically inhibits tumor growth accompanied by further increasing terminally differentiated CD8 T cells. B7-H3×h4-1BB also shows antitumor activity in h4-1BB–expressing mice. Our data suggest that B7-H3×4-1BB is an effective and safe therapeutic agent against B7-H3–positive cancers as monotherapy and combination therapy with PD-1 blockade.

由于剂量限制性毒性，4-1BB 激动剂的癌症免疫疗法限制了进一步的临床开发。在这里，我们开发了一种针对人 B7-H3 (hB7-H3) 和小鼠或人 4-1BB 的双特异性抗体 (bsAb; B7-H3×4-1BB)，以限制 4-1BB 对肿瘤的刺激。B7-H3×m4-1BB 在没有全身毒性的 hB7-H3 过表达肿瘤模型中引发了 4-1BB 依赖性抗肿瘤反应。BsAb 主要靶向肿瘤中的 CD8 T 细胞并增加它们的增殖和细胞因子的产生。在肿瘤中的 CD8 T 细胞群中，4-1BB 仅在 PD-1 ⁺ Tim-3 ^+上表达“终末分化”亚群，bsAb 增强这些细胞以消除肿瘤。此外，bsAb 和 PD-1 阻断剂的组合协同抑制肿瘤生长，同时进一步增加终末分化的 CD8 T 细胞。B7-H3×h4-1BB 在表达 h4-1BB 的小鼠中也显示出抗肿瘤活性。我们的数据表明，B7-H3×4-1BB 作为单一疗法和与 PD-1 阻断的联合疗法，是一种有效且安全的针对 B7-H3 阳性癌症的治疗剂。