Cancer treatment has been deeply changed by immunotherapy, achieving unprecedented improvement in overall and progression-free survival in several advanced and metastatic cancers. Currently, immune checkpoint inhibitor (ICI) antibodies against cytotoxic T-lymphocyte antigen (CTLA-4) and programmed death/ligand 1 (PD-1/PD-L1) are being tested and approved for different tumors, ranging from melanoma to lung carcinoma. However, only a subgroup of patients can reach treatment benefits and long-term responses, and reliable biomarkers that can accurately predict clinical responses to immunotherapy are still unidentified.

In the last decade, accumulating evidence seems to suggest the gut microbiota as one of the modulators that can alter the efficacy and toxicity of immunotherapy drugs (as well as chemotherapeutics), mainly acting through the local and systemic immune system.

Herein, we reviewed the highly dynamic and complex microbiome-immune system interface, its bidirectional relationship with cancer immunotherapies, and explored the future possibilities and risks in manipulating the gut microbiome.

免疫疗法极大地改变了癌症治疗，在几种晚期和转移性癌症中实现了前所未有的总体和无进展生存期改善。目前，针对细胞毒性 T 淋巴细胞抗原 (CTLA-4) 和程序性死亡/配体 1 (PD-1/PD-L1) 的免疫检查点抑制剂 (ICI) 抗体正在测试和批准用于从黑色素瘤到肺癌的不同肿瘤. 然而，只有一小部分患者可以达到治疗益处和长期反应，而能够准确预测免疫治疗临床反应的可靠生物标志物仍然未知。

在过去十年中，越来越多的证据似乎表明肠道微生物群是可以改变免疫治疗药物（以及化学治疗剂）的功效和毒性的调节剂之一，主要通过局部和全身免疫系统发挥作用。

在这里，我们回顾了高度动态和复杂的微生物组-免疫系统界面，它与癌症免疫疗法的双向关系，并探讨了未来操纵肠道微生物组的可能性和风险。