title: In situ prior proliferation of CD4+ CCR6+ regulatory T cells facilitated by TGF-β secreting DCs is crucial for their enrichment and suppression in tumor immunity.
abstract: BACKGROUND
  CD4(+)CD25(+) regulatory T cells (Tregs), a heterogeneous population, were enrichment in tumor mass and played an important role in modulating anti-tumor immunity. Recently, we reported a Treg subset, CCR6(+) Tregs but not CCR6(-)Tregs, were enriched in tumor mass and closely related to poor prognosis of breast cancer patients. However, the underlying mechanism remains elusive. Here, we carefully evaluate the enrichment of CCR6(+)Tregs in tumor mass during progression of breast cancer and explore its possible mechanism.
  
  
  RESULTS
  The frequency of CCR6(+)Tregs in tumor infiltrating lymphocytes (TILs ) was analyzed at early stage and at late stage of tumor in a murine breast cancer model by FACS respectively. The expansion of CCR6(+)Tregs and their CCR6(-) counterpart in tumor mass were determined by BrdU incorporation assay. The effect and its possible mechanism of tumor-resident antigen presenting cells (APCs) on the proliferation of CCR6(+)Tregs also were evaluated. The role of local expansion of CCR6(+)Tregs in their enrichment and suppression in vivo also was evaluated in adoptive cell transfer assay. We found that the prior enrichment of CCR6(+)Tregs but not CCR6(-)Tregs in tumor mass during progression of murine breast cancer, which was dependent on the dominant proliferation of CCR6(+) Tregs in situ. Further study demonstrated that tumor-resident DCs triggered the proliferation of CCR6(+)Treg cells in TGF-β dependent manner. Adoptive transfer of CCR6(+)Tregs was found to potently inhibit the function of CD8(+)T cells in vivo, which was dependent on their proliferation and subsequently enrichment in tumor mass.
  
  
  CONCLUSIONS
  Our finding suggested that CCR6(+) Tregs, a distinct subset of Tregs, exert its predominant suppressive role in tumor immunity through prior in situ expansion, which might ultimately provide helpful thoughts for the designing of Treg-based immunotherapy for tumor in the future.
authors.affiliation: Institute for Immunobiology and Department of Immunology, Shanghai Medical College of Fudan University, Shanghai, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Xu
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.forename: Zhenke
authors.initials: Z
authors.lastname: Wen
authors.forename: Sidong
authors.initials: S
authors.lastname: Xiong
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D054414:Chemokine CCL17 / Q000494:pharmacology; D054418:Chemokine CCL20 / Q000494:pharmacology; D054422:Chemokine CCL22 / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D054399:Receptors, CCR6 / Q000235:genetics / Q000378:metabolism*; D050378:T-Lymphocytes, Regulatory / Q000166:cytology* / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: C498126:CCR6 protein, mouse; D054414:Chemokine CCL17; D054418:Chemokine CCL20; D054422:Chemokine CCL22; D054399:Receptors, CCR6; D016212:Transforming Growth Factor beta