背景和理由：减毒鼠伤寒沙门氏菌VNP20009已用于治疗荷瘤小鼠并进入I期临床试验。然而，其在临床试验中的轻微抗癌作用可能与细菌定植不足以及随着剂量增加而明显的不良反应有关。鸟苷5'-二磷酸-3'-二磷酸（ppGpp）合成缺陷的沙门氏菌是一种具有良好生物安全性和抗癌功效的减毒菌株，已在各种实体癌的临床前研究中得到广泛研究。整合这两种菌株的优点可能为溶瘤细菌治疗提供新的解决方案。方法：将ΔppGpp的特征整合到VNP20009中，通过删除relA和spoT获得HCS1菌株，然后评估其体外细胞毒性和体内抗肿瘤活性。结果：体外实验显示HCS1对癌细胞的侵袭力和细胞毒性均显着低于VNP20009。此外，当静脉注射不同剂量的HCS1时，荷瘤小鼠表现出强大的癌症抑制作用，并且小鼠的存活时间和治愈率显着增加。此外，HCS1可以增加肿瘤组织中促炎细胞因子的水平，缓解肿瘤微环境中的免疫抑制。它还可以将大量的免疫细胞招募到肿瘤组织中，从而增强免疫激活反应。结论：新改造的沙门氏菌 HCS1 菌株在癌症治疗方面表现出很高的前景，是未来临床癌症免疫治疗的一个有前途的选择。© 作者。

Background and rationale: Attenuated Salmonella typhimurium VNP20009 has been used to treat tumor-bearing mice and entered phase I clinical trials. However, its mild anticancer effect in clinical trials may be related to insufficient bacterial colonization and notable adverse effects with increasing dosages. Guanosine 5'-diphosphate-3'-diphosphate (ppGpp) synthesis-deficient Salmonella is an attenuated strain with good biosafety and anticancer efficacy that has been widely investigated in various solid cancers in preclinical studies. Integration of the advantages of these two strains may provide a new solution for oncolytic bacterial therapy. Methods: We incorporated the features of ΔppGpp into VNP20009 and obtained the HCS1 strain by deleting relA and spoT, and then assessed its cytotoxicity in vitro and antitumor activities in vivo. Results: In vitro experiments revealed that the invasiveness and cytotoxicity of HCS1 to cancer cells were significantly lower than those of the VNP20009. Additionally, tumor-bearing mice showed robust cancer suppression when treated with different doses of HCS1 intravenously, and the survival time and cured mice were dramatically increased. Furthermore, HCS1 can increase the levels of pro-inflammatory cytokines in tumor tissues and relieve the immunosuppression in the tumor microenvironments. It can also recruit abundant immune cells into tumor tissues, thereby increasing immune activation responses. Conclusion: The newly engineered Salmonella HCS1 strain manifests high prospects for cancer therapeutics and is a promising option for future clinical cancer immunotherapy.© The author(s).