Immunosuppressive CD29+ Treg accumulation in the liver in mice upon checkpoint inhibitor therapy

We report that anti-PD1 treatment expands regulatory T cells (Tregs) in the liver of tumor-bearing mice and this contributes to the resistance mechanism of metastatic liver cancer to immunotherapy. Using FoxP3-GFP strain, Tregs after anti-PD1 treatment were sorted and Tregs from the liver and spleen were sequenced. CD29 positive cluster expanded in PD1-treated mouse liver. CD29-positive Tregs had also a suppression function in vitro validation study. And we identified CD29-positive Tregs in the public database of human liver cancer. We propose that CD29+ Tregs constitute a unique subpopulation of hepatic Tregs that are primed to respond to ICI agents and mediate resistance. Overall design: Intrahepatic MC38 tumors were established in FoxP3-GFP mice (JAX:006772). Seven days following establishment, 200 µg of either IgG2b isotype or aPD-1 were delivered intraperitoneally. Three days following treatment, tumor-bearing livers and spleens were harvested and processed. CD3+CD4+GFP+ cells were lysed and partitioned. Single-cell barcoding of reverse transcribed mRNA was performed on the Chromium controller. 3' immune cell profiling chemistry v1.0 and v1.1 (10x Genomics, USA) was used. Single-cell cDNA amplification, and library preparation was proceeded via the manufacturer guidelines. Expression libraries were sequenced on a NextSeq 550 (Illumina).