Yongbin Choi^1,2, Jake N. Lichterman³, Laura A. Coughlin¹, Nicole Poulides¹, Wenling Li¹, Priscilla Del Valle^1,4, Suzette N. Palmer^1,5,6, Shuheng Gan⁵, Jiwoong Kim⁵, Xiaowei Zhan⁵, Yajing Gao², Bret M. Evers⁷, Lora V. Hooper^2,8, Chandrashekhar Pasare^9,10, Andrew Y. Koh^1,11,12*

¹Division of Hematology/Oncology, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas,TX 75390, USA.
²Department of Immunology, University of Texas Southwestern Medical Center,Dallas,TX 75390,USA.
³Divisionof Hematology/Oncology, Department of Internal Medicine,University of Texas South western Medical Center, Dallas, TX 75390, USA.
⁴Department of Cell and Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
⁵Department of Population and Data Sciences,University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
⁶Department of Biomedical Engineering, University of Texas Southwestern Medical Center, Dallas, TX75390, USA.
⁷Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
⁸Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX75390, USA.
⁹Division of Immunobiology and Center for Inflammation and Tolerance, Cincinnati Children’s Hospital Medical Center Cincinnati, Cincinnati, OH 45229, USA.
¹⁰Department of Pediatrics, University of Cincinnati, College of Medicine, Cincinnati, OH 45220, USA.
¹¹Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
¹²Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

*Correspondingauthor : Andrew Y. Koh

Gut microbiota, specifically gut bacteria, are critical for effective immune checkpoint blockade therapy (ICT) for cancer. The mechanisms by which gut microbiota augment extraintestinal anticancer immune responses, however, are largely unknown. Here, we find that ICT induces the translocation of specific endogenous gut bacteria into secondary lymphoid organs and subcutaneous melanoma tumors. Mechanistically, ICT induces lymph node remodeling and dendritic cell (DC) activation, which facilitates the translocation of a selective subset of gut bacteria to extraintestinal tissues to promote optimal antitumor T cell responses in both the tumor-draining lymph nodes (TDLNs) and the primary tumor. Antibiotic treatment results in decreased gut microbiota translocation into mesenteric lymph nodes (MLNs) and TDLNs, diminished DC and effector CD8⁺ T cell responses, and attenuated responses to ICT. Our findings illuminate a key mechanism by which gut microbiota promote extraintestinal anticancer immunity.