Research Article Gastrospheres as a Model of Gastric Cancer Stem Cells Skew Th17/Treg Balance toward Antitumor Th17 Cells Alaleh Rezalotfi , 1,2 Ghasem Solgi , 1,3 and Marzieh Ebrahimi 2 1 Department of Immunology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran 2 Department of Stem Cells and Developmental Biology, Cell Science Research Center, Royan Institute for Stem Cell Biology and Technology, ACECR, Tehran, Iran 3 Psoriasis Research Center, Hamadan University of Medical Sciences, Hamadan, Iran Correspondence should be addressed to Ghasem Solgi; gh.solgi@umsha.ac.ir and Marzieh Ebrahimi; marzieh.ebrahimi@gmail.com Received 5 June 2020; Revised 5 December 2020; Accepted 14 December 2020; Published 24 December 2020 Academic Editor: Margarete D. Bagatini Copyright © 2020 Alaleh Rezalotfi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Gastrosphere, an enriched cellular population with stem-like properties believed to be responsible for an escape from immune-mediated destruction. Th17 and Treg cells play a major role in gastric cancer; however, their interaction with gastrospheres remained elusive. Method. Peripheral blood mononuclear cells were isolated from healthy donors and were cultured with conditioned media of MKN-45 (parental) cells as well as gastrospheres’ conditioned media in the context of mixed lymphocyte reaction and in the presence of anti-CD3/CD28 beads. The proliferation was evaluated using CFSE staining; the percentages of CD4 + CD25 + FoxP3 + Treg and CD4 + IL-17 + Th17 cells and IFN-γ+cells and the production of IL-17, TGF-β, and IL-10 were assessed by flow cytometry and ELISA, respectively. Finally, the cytotoxic potential of induced immune cells was measured by examining the secretion of lactate dehydrogenase from target cells. Results. The results revealed a decreased expansion of PBMCs postexposure to gastrospheres’ conditioned medium which was concomitant with an increased percentage of Th17 and an enhanced Th17 to Treg ratio. The conditioned media of gastrospheres enhanced the secretion of IL-10 and IL- 17 and decreased TGF-β. Interestingly, immune cells induced by gastrospheres showed significant cytotoxicity in terms of producing IFN-γ and death induction in target cells. All these changes were related to the upregulation of IL-6, IL-10, and IL-22 in gastrospheres compared to parental cells. Conclusion. Our study showed that the condition media of gastrospheres can potentially induce Th17 with increasing in their cytotoxic effect. Based on our knowledge, the present study is the first study that emphasizes the role of gastrospheres in the induction of antitumor Th17 cells. However, it should be confirmed with complementary studies in vivo. 1. Introduction Gastric cancer stem cells (CSCs) are considered as the key player for the initiation and development of tumors which give rise to nontumorigenic and invasive tumor cells. They are responsible for metastasis and immune escape [1] and can be isolated and enriched by different mecha- nisms including stem cell surface markers, intracellular enzyme activity, the concentration of reactive oxygen spe- cies, the identification of side population cells, resistance to cytotoxic compounds or hypoxia, invasiveness/adhesion, immunoselection, and sphere formation in nonadherent conditions [2]. Gastrosphere is an in vitro tridimensional (3D) culture model of gastric CSCs with stemness proper- ties [3]. In general, CSCs employ several mechanisms to evade the immune system such as impairment of antigen presentation to prevent cytotoxic T cell activation, downregulation of CD80 and upregulation of PDL-1 to induce T cell anergy, and induction of immunosuppressive M2 macrophages by the production of CSF, TGF-β, and MIC-1 in which in turn inhibits the induction of proinflammatory antitumor M1 macrophages. Furthermore, M2 macrophages impair the activation and proliferation of T cells through IL-10 and Hindawi Journal of Immunology Research Volume 2020, Article ID 6261814, 10 pages https://doi.org/10.1155/2020/6261814