Regulatory NK cells: IL-18-elicited NK cells with immunosuppressive functions

Cancer-induced tolerance mostly involves myeloid suppressor cells, regulatory T cells and immunosuppressive cytokines, which all subvert adaptive immune responses against tumor cells. Here, we show that a subset of innate effectors, c-kit expressing NK cells (Kit+ NK), can participate in tumor-induced tolerance by compromising the NK cell arm of tumor immunosurveillance. IL-18 produced by tumor cells can convert Kit- into Kit+ NK cells that overexpress B7-H1/PD-L1 molecules. Upon tumor inoculation, Kit+ NK cells rapidly develop in lymphoid organs in a IL-18R/MyD88 dependent manner and directly kill Kit- NK cells in a B7-H1/PD-1-dependent manner, thereby promoting the progression of NK-controlled cancers. Our data suggest that, in a tumoral context, IL-18 subverts antitumor NK cell functions. Systemic neutralization of IL-18 by IL-18-binding protein may improve the NK-mediated immunosurveillance. Keywords: cell type comparison Treatment Protocol: Two subpopulations of NK cells are sorted from mouse spleens with a FACS Vantage instrument (BD Bioscience). NK kit+ are defined as CD3-NK1.1+CD117+ cells and NK kit- as CD3-NK1.1+CD117- cells. Splenocytes from C57Bl/6 mice were sorted in two steps. First, they were enriched in NK cells (NK1.1+/CD3-) by a magnetic separation using NK cell Isolation Kit (Miltenyi Biotec). Second, enriched NK cells were stained with FITC-conjugated anti-CD117 (c-kit) and PE-conjugated anti-NK1.1 monoclonal antibodies to allow a sorting of NK kit+ and NK kit- cells. Antibodies were purchased from Pharmingen, San Diego, CA or eBioscience, San Diego, CA. The purity of NK cells was around 98% after cell sorting. Characteristics: CD3-NK1.1+CD117+ NK cells are compared to CD3-NK1.1+CD117- NK cells from spleen. Cell sorts and comparison are performed three times. Strain: C57Bl/6. Gender: female. Age: 7 weeks. C57Bl/6 mice were obtained from C.River Laboratories (L’Arbresle, France) and the Centre d’Elevage Janvier (Le Genest-st-Isle, France). Biomaterial provided: Material provided from laboratory of Prof. Laurence Zitvogel, Immunology, INSERM U805, Instiut Gustave Roussy, Villejuif, France.