Regulatory T cells induce CD4− NKT cell anergy and suppress NKT cell cytotoxic function
Due to the strong tumoricidal activities of activated natural killer T (NKT) cells, invariant NKT cell-based immunotherapy has shown promising clinical efficacy. However, suppressive factors, such as regulatory T cells (Tregs), may be obstacles in the use of NKT cell-based cancer immunotherapy for advanced cancer patients. Here, we investigated the suppressive effects of Tregs on NKT cells and the underlying mechanisms with the aim to improve the antitumor activities of NKT cells.
Peripheral blood samples were obtained from healthy donors, patients with benign tumors, and patients with head and neck squamous cell carcinoma (HNSCC). NKT cells, induced with α-galactosylceramide (α-GalCer), and monocyte-derived dendritic cells (DCs) were co-cultured with naïve CD4+ T cell-derived Tregs to investigate the mechanism of the Treg suppressive effect on NKT cell cytotoxic function. The functions and phenotypes of NKT cells were evaluated with flow cytometry and cytometric bead array.
Treg suppression on NKT cell function required cell-to-cell contact and was mediated via impaired DC maturation. NKT cells cultured under Treg-enriched conditions showed a decrease in CD4− NKT cell frequency, which exert strong tumoricidal responsiveness upon α-GalCer stimulation. The same results were observed in HNSCC patients with significantly increased effector Tregs.
Tregs exert suppressive effects on NKT cell tumoricidal function by inducing more CD4− NKT cell anergy and less CD4+ NKT cell anergy. Both Treg depletion and NKT cell recovery from the anergy state may be important for improving the clinical efficacy of NKT cell-based immunotherapy in patients with advanced cancers.
KeywordsHead and neck cancer Regulatory T cell Immune suppression NKT cell Anergy
Carboxyfluorescein succinimidyl ester
Cytotoxic T-lymphocyte-associated antigen
Head and neck squamous cell carcinoma
- NKT cells
Invariant natural killer T cells
Mean fluorescence intensity
Non-small cell lung cancer
Peripheral blood mononuclear cells
Programmed cell death ligand 1
Regulatory T cells
We thank Saori Tagi for her excellent technical assistance and thank Katie Oakley, PhD, from Edanz Group (http://www.edanzediting.com/ac) for editing a draft of this paper.
FI, DS, SM and YO designed the study. FI, DS, MT, TK performed experiments. FI, DS, MK, TK, NK, KY, TI, TN, SM and YO discussed the experimental design. MT and TK contributed to analysis and interpretation. NK, KY and TI contributed to collecting the samples and analyzing the data. FI and DS analyzed the data and wrote the manuscript. TN, SM and YO critically revised the manuscript. All authors reviewed the manuscript.
This study was funded by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) KAKENHI (Grant numbers 15K10799 and 17K16892).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical approval and ethical standards
Blood samples from all healthy donors and patients were collected only after obtaining written informed consent. All procedures involving human participants were approved on August 2, 2013 by the institutional review board of Chiba University Hospital and were conducted in accordance with the Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study. All participants consented to providing their peripheral blood and the use of their specimens and data for research and for publication.
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