Influence of antigen density and TLR ligands on preclinical efficacy of a VLP‐based vaccine against peanut allergy

Background Virus‐like particle (VLP) Peanut is a novel immunotherapeutic vaccine candidate for the treatment of peanut allergy. The active pharmaceutical ingredient represents cucumber mosaic VLPs (CuMVTT‐VLPs) that are genetically fused with one of the major peanut allergens, Ara h 2 (CuMVTT‐Ara h 2). We previously demonstrated the immunogenicity and the protective capacity of VLP Peanut‐based immunization in a murine model for peanut allergy. Moreover, a Phase I clinical trial has been initiated using VLP Peanut material manufactured following a GMP‐compliant manufacturing process. Key product characterization studies were undertaken here to understand the role and contribution of critical quality attributes that translate as predictive markers of immunogenicity and protective efficacy for clinical vaccine development. Method The role of prokaryotic RNA encapsulated within VLP Peanut on vaccine immunogenicity was assessed by producing a VLP Peanut batch with a reduced RNA content (VLP Peanut low RNA). Immunogenicity and peanut allergen challenge studies were conducted with VLP Peanut low RNA, as well as with VLP Peanut in WT and TLR 7 KO mice. Furthermore, mass spectrometry and SDS‐PAGE based methods were used to determine Ara h 2 antigen density on the surface of VLP Peanut particles. This methodology was subsequently applied to investigate the relationship between Ara h 2 antigen density and immunogenicity of VLP Peanut. Results A TLR 7 dependent formation of Ara h 2 specific high‐avidity IgG antibodies, as well as a TLR 7 dependent change in the dominant IgG subclass, was observed following VLP Peanut vaccination, while total allergen‐specific IgG remained relatively unaffected. Consistently, a missing TLR 7 signal caused only a weak decrease in allergen tolerability after vaccination. In contrast, a reduced RNA content for VLP Peanut resulted in diminished total Ara h 2 specific IgG responses, followed by a significant impairment in peanut allergen tolerability. The discrepant effect on allergen tolerance caused by an absent TLR 7 signal versus a reduced RNA content is explained by the observation that VLP Peanut‐derived RNA not only stimulates TLR 7 but also TLR 3. Additionally, a strong correlation was observed between the number of Ara h 2 antigens displayed on the surface of VLP Peanut particles and the vaccine's immunogenicity and protective capacity. Conclusions Our findings demonstrate that prokaryotic RNA encapsulated within VLP Peanut, inclu