Phagocytosis of Bafilomycin A1-treated Apoptotic Neuroblastoma Cells by Bone Marrow–derived Dendritic Cells Initiates a CD8α+ Lymphocyte Response to Neuroblastoma

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This study aimed to determine whether bafilomycin A1 (Baf-A1), a vacuolar H+-ATPase inhibitor, could promote an immune response after the induction of apoptosis in mouse neuroblastoma cells. Mouse neuro-2a cells were cultured in a medium containing Baf-A1, and apoptosis was evaluated by flow cytometry. To examine the influence in the phagocytic cell, CD11b+ spleen cells or bone marrow–derived dendritic cells (BM-DCs) were cocultured with Baf-A1-treated neuro-2a. Interferon-γ (IFN-γ) production was used as an index of the immune response, and CDDP was used as the negative control. When CD8α+ cells were cocultured with CD11b+ cells and Baf-A1-treated neuro-2a cells in the presence of CpG-oligodeoxynucleotide (CpG-ODN) (a toll-like receptor 9 [TLR-9] agonist), CD8α+ lymphocyte proliferation and secretion of IFN-γ were observed. Phagocytosis of apoptotic cells by BM-DCs was maximal after simultaneous stimulation with CpG-ODN and lipopolysaccharide (LPS; a TLR-4 agonist). IFN-γ secretion was maximal when Baf-A1-treated neuro-2a cells and CD8α+ lymphocytes were cocultured with BM-DCs and stimulated with CpG-ODN. In contrast, IFN-γ production was not increased when the cells were cultured with LPS. When cells were stimulated with both CpG-ODN and LPS, promotion of IFN-γ production by CpG-ODN was suppressed. Induction of apoptosis by Baf-A1 could possibly enhance antitumor immunity in patients receiving chemotherapy for neuroblastoma. Stimulation of BM-DCs with a TLR-9 agonist could promote antitumor activity after Baf-A1 treatment.

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