Identification of an Immunogenic Mimic of a Conserved Epitope on the Plasmodium falciparum Blood Stage Antigen AMA1 Using Virus-Like Particle (VLP) Peptide Display

Abstract

We have developed a peptide display platform based on VLPs of the RNA bacteriophage MS2 that combines the high immunogenicity of VLP display with affinity selection capabilities. Random peptides can be displayed on the VLP surface by genetically inserting sequences into a surface-exposed loop of the viral coat protein. VLP-displayed peptides can then be isolated by selection using antibodies, and the VLP selectants can then be used directly as immunogens. Here, we investigated the ability of this platform to identify mimotopes of a highly conserved conformational epitope present on the Plasmodium falciparum blood-stage protein AMA1. Using 4G2, a monoclonal antibody that binds to this epitope and is a potent inhibitor of erythrocyte invasion, we screened three different VLP-peptide libraries and identified specific VLPs that bound strongly to the selecting mAb. We then tested the ability of a handful of selected VLPs to elicit anti-AMA1 antibody responses in mice. Most of the selected VLPs failed to reliably elicit AMA1 specific antibodies. However, one VLP consistently induced antibodies that cross-reacted with AMA1. Surprisingly, this VLP bound to 4G2 more weakly than the other selectants we identified. Taken together, these data demonstrate that VLP-peptide display can identify immunogenic mimics of a complex conformational epitope and illustrate the promise and challenges of this approach.

Engineering virus-like particles as vaccine platforms

“…Bacteriophage MS2 and PP7 VLPs have been adapted to allow affinity selection against monoclonal antibodies of interest as well a patient serum and have yielded vaccine candidates [14,45,49–54]. RNA bacteriophage VLPs are particularly well-suited to be used in vaccine discovery efforts due to their simple structures made from a single coat protein, ability to encapsidate their own coding RNA (i.e.…”

“…For instance, the MS2 and PP7 VLP vaccine discovery platforms are limited to relatively short peptide inserts (<10 aa is ideal). Recent efforts have attempted to couple the affinity selection features of MS2 VLP platform with computational structural modeling approaches to further enhance its vaccine discovery capabilities [45]. We used the predictive structural modeling tool Phyre2 [55] to generate models of VLPs displaying foreign peptides and then tried to identify conformational mimics of an antigen of interest [45].…”

“…Recent efforts have attempted to couple the affinity selection features of MS2 VLP platform with computational structural modeling approaches to further enhance its vaccine discovery capabilities [45]. We used the predictive structural modeling tool Phyre2 [55] to generate models of VLPs displaying foreign peptides and then tried to identify conformational mimics of an antigen of interest [45]. As described by Joshi et al, first “building” a VLP computationally is another way to improve vaccine discovery efforts, and can provide a much needed rational approach that can increase the number of VLP vaccine candidate successes, save money and time, and ultimately provide the tools needed to make VLPs much more versatile and adaptable going forward [44].…”

The True Story and Advantages of RNA Phage Capsids as Nanotools

“…A review on HPV vaccine candidates, including RNA phage VLP-based vaccines, was recently published [212]. A malaria vaccine based on MS2 VLPs has also been reported as very promising [213,214]. As to the selection of optimal VLP carriers for such purposes, AP205 VLPs have demonstrated a high capacity and tolerance to foreign insertions [67].…”

Enabling Vaccine Delivery Platforms and Adjuvants for Malaria

“…For example, a VLP mimotope to reticulocyte-binding protein homologue 5 (RH5) found through affinity selection of MS2 libraries using a monoclonal antibody able to block parasite invasion of erythrocytes (in vitro via growth inhibition assay) was shown to elicit inhibitory antibodies when administered to mice as an immunogen [42]. In addition, MS2 VLP library affinity selection has also been performed with two anti-AMA-1 monoclonal antibodies [42,43]. Of note is that Agilvax LLC (a startup that was spun out of the Science & Technology Corporation at the University of New Mexico) holds an exclusive license to commercialize this technology for vaccines and immunotherapies based on the MS2 and AP205 VLP platforms.…”