PDCD1 and neoplasm: Normal gut microbiota is a huge but relatively unexplored treasure trove.11 Although some specific bacteria have been associated with increased anti-tumor immunity, the research about single gut bacteria in immunotherapy is still far from experimentally clarified.12 Furthermore, the exact molecular mechanisms through which these gut microbes swayed immunotherapy has rarely been studied.13 In this study, we found that Lactobacillus was significantly associated with good response to anti-PD-1 in the tumor models of CRC.