Introduction: CD4 T cells secreting IL-10 have been predominantly described as immunosuppressive and include both Tr1 cells and FOXP3+ Treg. In contrast, CD4 T cells secreting IL-17 have been mostly described as helper/effectors (TH17). Recent evidence indicates that some CD4 T cells secreting IL-17 can be of regulatory type, as human FOXP3+ Treg that secrete IL-17 ex vivo while concomitantly exerting suppressive activity have been described. CD4 T cells secreting IL-10 or IL-17 are frequent at mucosal sites where their equilibrium is important for simultaneously maintaining tolerance and immunity to the resident microbiota. Although TH17 and IL-10-secreting CD4 T cells have mostly been considered as distinct populations, the generation of which involves distinct factor, Staphylococcus Aureus specific TH17 clones that co-secrete the two cytokines have been identified (Zielinski,C.E; Nature 2012.484:514-518) underlining the close relationship between the two populations, along with their relevance in host immunity. Their mode of action, however, is as yet incompletely understood. To get insight into these questions, in this study, we addressed the prevalence, characteristics, mode of action and potential role of this type of populations.

Methods: We combined ex vivo analysis of CD4 T cells producing IL-10 or/and IL-17 isolated from PBMC of healthy donors with assessment of clonal populations isolated ex vivo using a cytokine catch assay.

Results: We found that, in average, 0.9 ± 0.3% and 3 ± 0.9% of memory CD4 T cells secreted IL-10 or IL-17, respectively. The majority of cells secreting IL-10 or IL-17 ex vivo appeared as distinct. However, a subpopulation, representing about 0.1% of the cells, co-secreted the two cytokines. The proportion of FOXP3+ cells was significantly higher among IL-10 single secreting (39 ± 8%) than IL-17 single secreting (13 ± 5%) cells and represented 58 ± 9%, in average, of the cells co-secreting the two cytokines ex vivo. The majority of FOXP3+ Treg within each of the cytokine secreting populations failed to express the transcription factor Helios, suggesting that these cells are peripherally induced (pTreg) rather than Tregs derived from thymus (tTreg). To further assess, we generated IL-10 or IL-17 single secreting and IL-10/IL-17 double secreting populations using the Miltenyi secretion/detection assay and flow cytometry cell sorting. We found that IL-10 secretion is prevalent at early time points after TCR stimulation, independent of co-stimulation and is increased in the presence of the microbial fermentation product butyrate. In contrast, IL-17 secretion is higher at distance from TCR stimulation and in the presence of co-stimulatory signals.

Conclusion: These results suggest that the capacity of modulate cytokine secretion depending on conditions might allow IL-10 and IL-17 producing CD4 T cells to maintain tolerance to microbes locally, while retaining the ability to participate in protective immune responses at distant sites.

Citation Format: Kanako Saito, Pascale Pignon, Maha Ayyoub, Danila Valmori. Modulation of cytokine secretion allows CD4 T cells secreting IL-10 and IL-17 to simultaneously participate in maintaining tolerance and immunity. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B056.