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

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.

A nanoparticle-based COVID-19 vaccine candidate elicits broad neutralizing antibodies and protects against SARS-CoV-2 infection

“…PapMV nano was reported to accelerate germinal center formation, and to promote affinity/avidity maturation of specific IgG and isotype switching to IgG2a subclass 62 . Recently, these events were linked with the stimulation of TLR7, which is consistent with our data 61 .…”

“…The engagement of the TLR7 by the RBD-PapMV vaccine may act as a co-stimulatory signal that enhances and accelerates the antibody class switch towards the production of the IgG2a subclass and the production of higher affinity antibodies to the RBD antigen 34. , 61. .…”

Virus-like particle vaccinology, from bench to bedside

“…In addition, for some VLPs, in particular RNA virus-derived VLPs, loading the particle with RNA or CpGs (DNA oligonucleotides rich in nonmethylated CG motifs) is possible, which results in TLR7/8 or TLR9 activation, respectively, in B cells. This augments IgG2a and IgA antibody responses and enhances plasma cell formation [15] and affinity maturation [16]. The type of RNA packaged in VLPs also matters, with bacterial RNA being the most efficient B-cell enhancer [17].…”

On the role of antibody affinity in the IgE mediated allergic response

“…In addition, VLPs may package RNA from E. coli during VLP production, when assembling inside bacteria. This RNA has not only been observed to effectively drive class switching to IgG and IgA, but also to increase the affinity of the induced antibodies as well as to facilitate maintenance of a broad immunoglobulin repertoire against both VLPs as well as displayed allergens 31 . Furthermore, in a preclinical model of peanut-allergy, presence of RNA in VLPs displaying Ara h 2 proved essential for induction of protective IgG responses against peanut allergy.…”