Impaired antigen‐specific lymphocyte priming in mice after Toll‐like receptor 4 activation via induction of monocytic myeloid‐derived suppressor cells

Abstract

In sepsis, the pathology involves a shift from a proinflammatory state toward an immunosuppressive phase. We previously showed that an agonistic anti‐TLR4 antibody induced long‐term endotoxin tolerance and suppressed antigen‐specific secondary IgG production when primed prior to immunization with antigen. These findings led us to speculate that TLR4‐induced innate tolerance due to primary infection causes an immunosuppressive pathology in sepsis. Therefore, the mechanism underlying impaired antigen‐specific humoral immunity by the TLR4 antibody was investigated. We showed, in a mouse model, that primary antigen‐specific IgG responses were impaired in TLR4 antibody‐induced tolerized mice, which was the result of reduced numbers of antigen‐specific GC B cells and plasma cells. Ovalbumin‐specific CD4 and CD8 T‐cell responses were impaired in TLR4 antibody‐injected OT‐I and ‐II transgenic mice ex vivo. Adoptive transfer studies demonstrated suppression of OVA‐specific CD4 and CD8 T‐cell responses by the TLR4 antibody in vivo. The TLR4 antibody induced Gr1+CD11b+ myeloid‐derived suppressor cell (MDSC) expansion with suppression of T‐cell activation. Monocytic MDSCs were more suppressive and exhibited higher expression of PD‐L1 and inducible nitric oxidase compared with granulocytic MDSCs. In conclusion, immune tolerance conferred by TLR4 activation induces the expansion of monocytic MDSCs, which impairs antigen‐specific T‐cell priming and IgG production.

An agonistic anti‐Toll‐like receptor 4 monoclonal antibody as an effective adjuvant for cancer immunotherapy

“…5,12,13,51 Such poorly immunogenic tumours could be targets of tumour vaccine therapy using an anti-TLR4 mAb. 32 Therefore, the efficacy of combinations of an anti-TLR4 mAb and checkpoint inhibitors, particularly an anti-PD-1 or -PD-L1 mAb, is of interest. Recently, we showed that administration of an anti-TLR4 mAb to mice in the Figure 7.…”

“…The mouse anti-mouse TLR4/MD-2 agonistic mAb (UT12) 38,39 was purified from conditioned serum-free medium (Hybridoma-SFM; Thermo Fisher Scientific, Waltham, MA) used to culture hybridomas. 32 Rat antimouse CD4 (GK1Á5), CD8 (YTS 169Á4Á2Á1) and PD-1 (RMP1-14) mAbs were purified from ascitic fluid of mice with severe combined immunodeficiency by caprylic acid precipitation followed by diethylaminomethyl ion-exchange chromatography. 26 Pam3CSK4 and low-molecular-weight poly(I:C) were from InvivoGen (San Diego, CA).…”

“…40,41 An OT-II mouse strain congenic for Ly5Á1 was generated in our laboratory. 32 The mice were bred and maintained under specific pathogen-free conditions according to the Guidelines for Animal Experimentation of Tohoku University. The study protocol was approved by the Institutional Animal Care and Use Committee of Tohoku University.…”

“…25,26 Upon binding of LPS, TLR4-in conjunction with the accessory molecules MD-2, CD14 and LPS-binding protein-activates NF-jB, leading to the production of proinflammatory cytokines, interferons and lipid mediators. 22,24,32,33 Therefore, the efficacy of LPS derivatives as adjuvants in vaccines against infectious diseases and various types of cancer has been evaluated. 22,24,32,33 Therefore, the efficacy of LPS derivatives as adjuvants in vaccines against infectious diseases and various types of cancer has been evaluated.…”

“…[27][28][29][30][31] Activation of TLR4 in dendritic cells enhances Ag-specific priming of lymphocytes due to upregulation of MHC and co-stimulatory molecules. 22,24,32,33 Therefore, the efficacy of LPS derivatives as adjuvants in vaccines against infectious diseases and various types of cancer has been evaluated. 21,34 However, the clinical application of LPS is hampered by its potent proinflammatory activity; this problem can be overcome by the development of detoxified LPS derivatives.…”