Oncolytic viruses induce antitumor immunity following direct viral oncolysis. However, their therapeutic effects are limited in distant untreated tumors because their antitumor function depends on indirect antitumor immunity. Here, we generated a novel fusogenic oncolytic vaccinia virus (FUVAC) and compared its antitumor activity with that of its parental non-fusogenic virus. Compared with the parent, FUVAC exerted the cytopathic effect and induced immunogenic cell death in human and murine cancer cells more efficiently. In a bilateral tumor-bearing syngeneic mouse model, FUVAC administration significantly inhibited tumor growth in both treated and untreated tumors. However, its antitumor effects were completely suppressed by CD8⁺ T cell depletion. Notably, FUVAC reduced the number of tumor-associated immune-suppressive cells in treated tumors, but not in untreated tumors. Mice treated with FUVAC before an immune checkpoint inhibitor (ICI) treatment achieved complete response (CR) in both treated and untreated tumors, whereas ICI alone did not show antitumor activity. Mice achieving CR rejected rechallenge with the same tumor cells, suggesting establishment of a long-term tumor-specific immune memory. Thus, FUVAC improves the tumor immune microenvironment and enhances systemic antitumor immunity, suggesting that, alone and in combination with ICI, it is a novel immune modulator for overcoming oncolytic virus-resistant tumors.

溶瘤病毒在直接病毒溶瘤后诱导抗肿瘤免疫。然而，它们的治疗效果在远处未治疗的肿瘤中是有限的，因为它们的抗肿瘤功能依赖于间接的抗肿瘤免疫。在这里，我们产生了一种新型融合溶瘤痘苗病毒 (FUVAC)，并将其抗肿瘤活性与其亲本非融合病毒的抗肿瘤活性进行了比较。与亲本相比，FUVAC 在人和鼠癌细胞中发挥细胞病变作用并诱导免疫原性细胞死亡的效率更高。在双侧荷瘤同基因小鼠模型中，FUVAC 给药显着抑制治疗和未治疗肿瘤的肿瘤生长。然而，其抗肿瘤作用完全被 CD8 ^+抑制T细胞耗竭。值得注意的是，FUVAC 减少了治疗肿瘤中与肿瘤相关的免疫抑制细胞的数量，但未治疗的肿瘤没有。在免疫检查点抑制剂 (ICI) 治疗之前用 FUVAC 治疗的小鼠在治疗和未治疗的肿瘤中均达到完全缓解 (CR)，而单独的 ICI 没有显示出抗肿瘤活性。达到 CR 的小鼠拒绝再次攻击相同的肿瘤细胞，这表明建立了长期的肿瘤特异性免疫记忆。因此，FUVAC改善了肿瘤免疫微环境并增强了全身抗肿瘤免疫，这表明它单独或与ICI联合使用是一种克服溶瘤病毒抗性肿瘤的新型免疫调节剂。