Objective Tumour-infiltrating lymphocytes (TILs) favour survival in human colorectal cancer (CRC). Chemotactic factors underlying their recruitment remain undefined. We investigated chemokines attracting T cells into human CRCs, their cellular sources and microenvironmental triggers.
Design Expression of genes encoding immune cell markers, chemokines and bacterial 16S ribosomal RNA (16SrRNA) was assessed by quantitative reverse transcription-PCR in fresh CRC samples and corresponding tumour-free tissues. Chemokine receptor expression on TILs was evaluated by flow cytometry on cell suspensions from digested tissues. Chemokine production by CRC cells was evaluated in vitro and in vivo, on generation of intraperitoneal or intracecal tumour xenografts in immune-deficient mice. T cell trafficking was assessed on adoptive transfer of human TILs into tumour-bearing mice. Gut flora composition was analysed by 16SrRNA sequencing.
Results CRC infiltration by distinct T cell subsets was associated with defined chemokine gene signatures, including CCL5, CXCL9 and CXCL10 for cytotoxic T lymphocytes and T-helper (Th)1 cells; CCL17, CCL22 and CXCL12 for Th1 and regulatory T cells; CXCL13 for follicular Th cells; and CCL20 and CCL17 for interleukin (IL)-17-producing Th cells. These chemokines were expressed by tumour cells on exposure to gut bacteria in vitro and in vivo. Their expression was significantly higher in intracecal than in intraperitoneal xenografts and was dramatically reduced by antibiotic treatment of tumour-bearing mice. In clinical samples, abundance of defined bacteria correlated with high chemokine expression, enhanced T cell infiltration and improved survival.
Conclusions Gut microbiota stimulate chemokine production by CRC cells, thus favouring recruitment of beneficial T cells into tumour tissues.
- colorectal cancer
- immune response
- T lymphocytes
- bacterial translocation
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Contributors GI conceived and designed experiments, analysed and interpreted results, obtained funding and wrote the manuscript; EC designed and performed experiments, analysed and interpreted results and wrote the manuscript; FA, JFGG, VG, MGM, VM, VG-F, SK, JS-H and LMT contributed to design and conduction of experiments and to analysis and interpretation of data; DO, SRD, MB, RR, BW, and UN contributed to conception of research and data collection; GCS, NK, AE, PZ, SE-C, K-PJ and LB contributed to conception of research, design and conduction of experiments, analysis and interpretation of data and writing of the manuscript.
Funding Swiss National Science Foundation (SNF PP00P3-133699 and PP00P3-159262), University of Basel (Unibas Förderung des Akademischen Mittelbaus) and Department of Surgery, Basel University Hospital.
Competing interests None declared.
Patient consent Obtained.
Ethics approval EKBB/EKNZ (study protocol n. 2014-388), Ethics Committee of the Faculty of Medicine of the TUM (#1926/2007), Cantonal Veterinary Office Basel-Stadt (licence n. 2266), Cantonal Veterinary Office Zürich (licence n. 35/2014).
Provenance and peer review Not commissioned; externally peer reviewed.