Cowpea Mosaic Virus Nanoparticle Vaccine Candidates Displaying Peptide Epitopes Can Neutralize the Severe Acute Respiratory Syndrome Coronavirus

Abstract

The development of vaccines against coronaviruses has focused on the spike (S) protein, which is required for the recognition of host-cell receptors and thus elicits neutralizing antibodies. Targeting conserved epitopes on the S protein offers the potential for pan-beta-coronavirus vaccines that could prevent future pandemics. We displayed five B-cell epitopes, originally identified in the convalescent sera from recovered severe acute respiratory syndrome (SARS) patients, on the surface of the cowpea mosaic virus (CPMV) and evaluated these formulations as vaccines. Prime-boost immunization of mice with three of these candidate vaccines, CPMV-988, CPMV-1173, and CPMV-1209, elicited high antibody titers that neutralized the severe acute respiratory syndrome coronavirus (SARS-CoV) in vitro and showed an early Th1-biased profile (2–4 weeks) transitioning to a slightly Th2-biased profile just after the second boost (6 weeks). A pentavalent slow-release implant comprising all five peptides displayed on the CPMV elicited anti-S protein and epitope-specific antibody titers, albeit at a lower magnitude compared to the soluble formulations. While the CPMV remained intact when released from the PLGA implants, processing results in loss of RNA, which acts as an adjuvant. Loss of RNA may be a reason for the lower efficacy of the implants. Finally, although the three epitopes (988, 1173, and 1209) that were found to be neutralizing the SARS-CoV were 100% identical to the SARS-CoV-2, none of the vaccine candidates neutralized the SARS-CoV-2 in vitro suggesting differences in the natural epitope perhaps caused by conformational changes or the presence of N -linked glycans. While a cross-protective vaccine candidate was not developed, a multivalent SARS vaccine was developed. The technology discussed here is a versatile vaccination platform that can be pivoted toward other diseases and applications that are not limited to infectious diseases.

Injectable Slow-Release Hydrogel Formulation of a Plant Virus-Based COVID-19 Vaccine Candidate

“…CPMV-based vaccines were previously shown to induce Th1-biased responses against cancers, 41 , 79 , 80 but Th2-biased responses at later time points have been reported for other shared epitopes from SARS-CoV and the SARS-CoV-2 S protein, reflecting a shift from Th1 typically after the second boost injection. 43 The Th1/2 response was deemed to be dependent on the SARS-CoV2 S protein epitope. 39 , 43 With regard to epitope 826, we and others 39 observed only Th1-biased responses for soluble 826-CPMV administered using the prime-boost schedule, which implies that the observed shifting bias in the F3 group from Th1 to Th2 is possibly due to the immune-enhancing adjuvant capability of chitosan 53 − 55 , 81 and/or the slow-release characteristics of the hydrogel F3.…”

“… 48 It also serves as a delivery platform and multiple copies of the SARS-CoV-2 peptide epitopes can be displayed via chemical bioconjugation. 43 When tested as soluble prime-boost formulations, microneedle patches, or slow-release poly(lactic- co -glycolic acid) (PLGA) implants, the CPMV- and Qβ-based COVID-19 vaccine candidate formulations elicited neutralizing antibodies against SARS-CoV-2, and the soluble prime-boost vaccine (CPMV conjugated to the epitope sequence 809–826) elicited a neutralization titer comparable to Moderna’s mRNA-1273 vaccine. 39 The Qβ formulation maintained efficacy when formulated as a PLGA implant, but in a previous study with a similar approach against SARS-CoV, the efficacy of CPMV-based vaccines declined significantly in this format when administered as a single dose.…”

“… 39 The Qβ formulation maintained efficacy when formulated as a PLGA implant, but in a previous study with a similar approach against SARS-CoV, the efficacy of CPMV-based vaccines declined significantly in this format when administered as a single dose. 43 This reflected the lower immunostimulatory response caused by the loss of CPMV RNA during freeze-drying, as required for implant formulation. 49 The efficacy of a CPMV-based vaccine displaying the 809–826 epitope sequence (826-CPMV) could perhaps be improved by investigating alternative single-dose formulations, such as those based on the natural biopolymer chitosan.…”

Production and characterization of chimeric SARS-CoV-2 antigens based on the capsid protein of cowpea chlorotic mottle virus

“…The ability of plant viruses such as CCMV and brome mosaic virus (BMV) [29] to self-assemble in the presence and absence of nucleic acid as well as in different shapes can become an advantage to produce chimeric proteins that present multiple copies of the antigen of interest, which could decrease the need of using adjuvants. Furthermore, an important consideration is that plant virus nanotechnologies offer high thermal stability [30] ; CCMV VLPs can be stable at temperatures between −80 and 50 °C, thus overcoming the need for cold-chain storage and distribution [31] . This is a clear advantage over the vaccine platforms already approved today mRNA vaccines.…”

Production of Potyvirus-Derived Nanoparticles Decorated with a Nanobody in Biofactory Plants

“…Research in this area has focused on the development of plant viruses carrying antigenic epitopes from human or animal pathogens, with the aim of developing novel recombinant vaccines or diagnostic reagents ( González-Gamboa et al, 2017 ; Chung et al, 2021 ; Peyret et al, 2021 ; Stander et al, 2021 ). The most widely used plant viruses for nanotechnology approaches are cowpea mosaic virus (CPMV) ( Sainsbury et al, 2010 ; Beatty and Lewis, 2019 ; Ortega-Rivera et al, 2021 ), tobacco mosaic virus (TMV) ( Röder et al, 2017 ; Lomonossoff and Wege, 2018 ), and potato virus X (PVX) ( Lico et al, 2015 ; Le et al, 2019 ; Röder et al, 2019 ; Shukla et al, 2020b ).…”