Abstract
Background and objectives: Mature dendritic cells (DCs) are essential inducers of anti-tumor immunity. However, the inflammatory tumor microenvironment (TME) develops tumor associated DCs (TADCs) that adopt different immunosuppressive mechanisms. T-cell immunoglobulin and mucin domain 3 receptor (TIM-3) is an immune checkpoint that suppresses anti-tumor immunity and accelerates T-cell exhaustion which is expressed on IFN-c-producing T cells, macrophages, and dendritic cells. Administering TIM-3 blockade in vivo can enhance anti-tumor immunity and inhibit tumor growth. TIM-3 expression can be induced on natural killer cells (NKs) in vitro by tumor necrosis factor alpha (TNF-alpha). Therefore, this study aims to investigate whether TNF-alpha can induce the expression of TIM-3 and its ligand galectin-9 (Gal-9) on DCs in vitro. Materials and methods: DCs were produced from peripheral blood mononuclear cells (PBMCs) of healthy donors by 800 U/ml rh IL-4 and 500 U/ml rh GM-CSF in the presence or absence of 1 lg/ml lipopolysac-charide (LPS) and/or 5 ng/ml rh TNF-alpha. Results: Phenotypic analysis showed that treating cells with LPS induced the expression of DC markers (MHC class I & II), maturation markers (CD83), costimulatory markers (CD80, CD86) and reduced mono-cyte markers (CD14). Similar results were observed in the presence of TNF-alpha alone or in combination with LPS. Interestingly, LPS-treated and TNF-alpha-treated cells lack TIM-3 expression compared to untreated cells as 90% of these untreated cells were TIM-3 positive, with no differences in the expression of Gal-9 in all treated and untreated cells. Interpretation and conclusion: These results revealed that TNF-a and LPS either alone or combined induced the maturation of DCs in vitro and that the absence of both caused DCs to maintain an immature state and induced the expression of TIM-3. This finding indicates that TNF-alpha is unable to induce TIM-3 on mature DCs in vitro. (C) 2022 The Authors. Published by Elsevier B.V. on behalf of King Saud University.