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Maximizing the potency of an anti-TLR4 monoclonal antibody by exploiting proximity to Fcγ receptors.

ABSTRACT: In order to treat Toll like receptor 4 (TLR4)-mediated diseases, we generated a potent antagonistic antibody directed against human TLR4, Hu 15C1. This antibody's potency can be modulated by engaging not only TLR4 but also Fcγ receptors (FcγR), a mechanism that is driven by avidity and not cell signaling. Here, using various formats of the antibody, we further dissect the relative contributions of the Fv and Fc portions of Hu 15C1, discovering that the relationship to potency of the different antibody arms is not linear. First, as could be anticipated, we observed that Hu 15C1 co-engages up to 3 receptors on the same plasma membrane, i.e., 2 TLR4 molecules (via its variable regions) and either FcγRI or FcγRIIA (via the Fc). The Kd of these interactions are in the nM range (3 nM of the Fv for TLR4 and 47 nM of the Fc for FcγRI). However, unexpectedly, neutralization experiments revealed that, due to the low level of cell surface TLR4 expression, the avidity afforded by engagement through 2 Fv arms was significantly limited. In contrast, the antibody's neutralization capacity increases by 3 logs when able to exploit Fc-FcγR interactions. Taken together, these results demonstrate an unforeseen level of contribution by FcγRs to an antibody's effectiveness when targeting a cell surface protein of relatively low abundance. These findings highlight an exploitable mechanism by which FcγR-bearing cells may be more powerfully targeted, envisioned to be broadly applicable to other reagents aimed at neutralizing cell surface targets on cells co-expressing FcγRs.

SUBMITTER: Loyau J

PROVIDER: S-EPMC4622919 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Previous studies have revealed that activation of the Toll‑like receptor 4 (TLR4)‑mediated proinflammatory signaling pathway plays an important role in acute inflammation, sepsis and chronic inflammatory disorders. Moreover, TLR4 significantly contributes to lipopolysaccharide (LPS)‑induced immune response. Thus, modulation of the TLR4 pathway is an important strategy to specifically target these pathologies. The aim of the present study was to develop a complete human anti‑TLR4 IgG2 antibody by screening human TLR4 Fab from a phage‑display library and integrating it with constant regions of the heavy chain of human IgG2 via antibody engineering. ELISA, a BLItz system and fluorescence‑activated cell sorting were used to assess its affinity. Furthermore, mouse‑derived peritoneal macrophages were treated with human anti‑TLR4 IgG2 and induced with LPS in vitro. Reverse transcription‑quantitative PCR and western blotting were used to determine mRNA expression levels of cytokines and phosphorylation levels of signaling pathways, respectively. It was found that human anti‑TLR4 IgG2 bound to TLR4 with a high affinity of 8.713x10‑10 M, and that preincubation with anti‑TLR4 IgG2 inhibited the LPS‑induced production of tumor necrosis factor‑α, interferon‑β and interleukin‑6 mRNA expression levels in mouse peritoneal macrophages. It was also demonstrated that human anti‑TLR4 IgG2 inhibited LPS‑induced TLR4 signaling by reducing the phosphorylation of the NF‑κB, mitogen‑activated protein kinase and interferon regulatory factor 3 signaling pathways. In addition, human anti‑TLR4 IgG2 protected mice from LPS challenge with a survival rate of 40% and also significantly increased the survival time in the cecal ligation and puncture model. Therefore, it was speculated that human anti‑TLR4 IgG2 plays a protective role against sepsis‑associated injury and is potentially applicable for the treatment of infection‑associated immune dysfunction.

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Maximizing the potency of an anti-TLR4 monoclonal antibody by exploiting proximity to Fcγ receptors.

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