TLR7 Signaling Shapes and Maintains Antibody Diversity Upon Virus-Like Particle Immunization.

Xinyue Chang,Annette Oxenius,Martin F Bachmann,Monique Vogel,Pascal Krenger,Salony Roongta,Caroline C Krueger,Lisha Zha,Mona O Mohsen,Alexander Yermanos,Jiami Han

doi:10.3389/fimmu.2021.827256

Abstract

Virus-like particles (VLPs) are used in different marketed vaccines and are able to induce potent antibody responses. The innate pattern recognition receptors TLR7/8 recognize single stranded (ss) RNA naturally packaged into some VLPs and have been shown to enhance the production of IgG antibodies upon immunization. Here we demonstrate that, upon immunization with RNA-loaded bacteriophage-derived VLP Qβ, TLR7 signaling accelerates germinal center formation, promotes affinity/avidity maturation of VLP-specific IgG and isotype switching to IgG2b/2c. These findings extrapolated to antigens displayed on Qβ; as Fel d 1, the major cat allergen, chemically attached to Qβ also induced higher affinity/avidity IgG2b/2c antibodies in a TLR7-dependent fashion. Chimeric mice lacking TLR7-expression exclusively in B cells demonstrated that the enhanced IgG responses were driven by a B cell intrinsic mechanism. Importantly, deep sequencing of the BCR repertoire of antigen-specific B cells demonstrated higher diversity in mice with TLR7 signaling in B cells, suggesting that TLR7-signaling drives BCR repertoire development and diversity. Furthermore, the current data demonstrate that high levels of clonal diversity are reached early in the response and maintained by TLR7 signaling. In conclusion, TLR7 signaling enhances levels and quality of IgG antibodies, and this finding has major implications for vaccine design.

Highlights

Virus-like particles (VLPs) are known to be an excellent vaccine platform and several VLP-based vaccines have been commercially available for decades [1, 2]
We aimed to examine at the molecular level the contribution of TLR7 signaling to antibody responses against Fel d 1 displayed on RNA-loaded Qb
We first examined the effects of TLR7 signaling on germinal center (GC) reactions

Summary

Introduction

Virus-like particles (VLPs) are known to be an excellent vaccine platform and several VLP-based vaccines have been commercially available for decades [1, 2]. TLR7 Signaling Maintains Antibody Diversity of 5-10 nm between the VLP surface antigens might be beneficial for the induction of effective antiviral antibodies. As shown recently, such spacing is sometimes not present in native viruses as e.g. SARS-CoV-2 [4], but can be achieved with recombinant VLPs [5–7]. Each receptor detects a different PAMP, such as TLR4, TLR7/8 and TLR9 sensing LPS, ssRNA and DNA rich in unmethylated CpG, respectively [10]. Once they encounter the ligands, the TLRs dimerize and initiate signaling cascades, leading to production of immune effector molecules [11]. Besides the contributions of TLRs in innate immune profiles, more and more evidence shows that the B cell-intrinsic TLR signaling supports the production of antigen-specific antibody responses, providing a key link between the innate and adaptive immune system [13–16]

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