地塞米松通过调节中性粒细胞和巨噬细胞向肿瘤的浸润增强减毒鼠伤寒沙门菌介导的肿瘤免疫治疗的抗肿瘤效果

Dexamethasone augments the efficacy of attenuated Salmonella typhimurium-based cancer immunotherapy by modulating the infiltration of neutrophils and macrophages in the tumor microenvironment

摘要:

细菌介导的肿瘤免疫治疗(bacterium-mediated cancer immunotherapy, BCI)在癌症治疗中具有诸多优势，但地塞米松(dexamethasone, DEX)联合BCI治疗肿瘤的免疫反应机制仍不清晰。【目的】探究DEX联合减毒鼠伤寒沙门氏菌St.ΔppGpp介导的BCI肿瘤治疗效果及机制。【方法】通过鼠源结直肠癌小鼠模型，测定St.ΔppGpp+DEX联合治疗的肿瘤抑制效果。使用活体成像测定St.ΔppGpp的肿瘤靶向性与定殖时间。通过伊红(hematoxylin and eosin, H&E)染色，测试St.ΔppGpp+DEX联合治疗的器官毒性。基于流式细胞术和免疫荧光切片，测定巨噬细胞极化、中性粒细胞的募集和T细胞反应。通过qRT-PCR，检测肿瘤微环境中的炎症因子变化。通过人源结直肠癌症小鼠模型，验证T细胞缺失对St.ΔppGpp+DEX联合治疗的影响。【结果】St.ΔppGpp+DEX联合治疗可显著降低肿瘤大小，并提高小鼠生存率。DEX可延长St.ΔppGpp在肿瘤细胞的定殖。St.ΔppGpp+DEX联合治疗不会损伤重要免疫器官，并可促进M2向M1型巨噬细胞极化，同时抑制中性粒细胞的募集。T细胞缺失不会影响St.ΔppGpp+DEX联合治疗效果。【结论】DEX通过抑制中性粒细胞募集，增加肿瘤微环境中的M1型巨噬细胞比例，进而提高减毒鼠伤寒沙门氏菌St.ΔppGpp的抗肿瘤疗效。

Abstract:

Bacterium-mediated cancer immunotherapy (BCI) presents numerous advantages in cancer treatment, while the immune response mechanism of dexamethasone (DEX) combined with BCI for tumor treatment remains unclear. [Objective] To investigate the therapeutic efficacy and mechanism of dexamethasone in combination with attenuated Salmonella typhimurium St.ΔppGpp-mediated BCI. [Methods] The inhibitory effects of St.ΔppGpp+DEX on cancer were evaluated in a murine model of colorectal cancer. In vivo imaging was utilized to determine the tumor targeting and colonization duration of St.ΔppGpp. Organ toxicity resulted from St.ΔppGpp+DEX treatment was assessed by hematoxylin and eosin (H&E) staining. Macrophage polarization, neutrophil recruitment, and T-cell responses were analyzed by flow cytometry and immunofluorescence assay of sections. The changes in inflammatory cytokines in the tumor microenvironment were examined via qRT-PCR. A mouse model transplanted with human colorectal cancer was employed to confirm the effect of T cell depletion on the therapeutic efficacy of St.ΔppGpp+DEX. [Results] The combined treatment St.ΔppGpp+DEX significantly decreased tumor size and enhanced the survival rate of mice. DEX extended the colonization of St.ΔppGpp in tumor cells. Furthermore, St.ΔppGpp+DEX did not induce damage to vital immune organs, and it facilitated the polarization of macrophages from M2 to M1 phenotype while suppressing neutrophil recruitment. T cell depletion did not influence the efficacy of St.ΔppGpp+DEX. [Conclusion] DEX can enhance the anti-tumor effects of St.ΔppGpp by inhibiting neutrophil recruitment and increasing the proportion of M1 macrophages in the tumor microenvironment.