Neutralizing Efficacy of Encapsulin Nanoparticles against SARS-CoV2 Variants of Concern

Abstract

Rapid emergence of the SARS-CoV-2 variants has dampened the protective efficacy of existing authorized vaccines. Nanoparticle platforms offer a means to improve vaccine immunogenicity by presenting multiple copies of desired antigens in a repetitive manner which closely mimics natural infection. We have applied nanoparticle display combined with the SpyTag–SpyCatcher system to design encapsulin–mRBD, a nanoparticle vaccine displaying 180 copies of the monomeric SARS-CoV-2 spike receptor-binding domain (RBD). Here we show that encapsulin–mRBD is strongly antigenic and thermotolerant for long durations. After two immunizations, squalene-in-water emulsion (SWE)-adjuvanted encapsulin–mRBD in mice induces potent and comparable neutralizing antibody titers of 105 against wild-type (B.1), alpha, beta, and delta variants of concern. Sera also neutralizes the recent Omicron with appreciable neutralization titers, and significant neutralization is observed even after a single immunization.

Sortase A-Based Post-translational Modifications on Encapsulin Nanocompartments

“…2,11,12 However, direct genetic fusion or chemical conjugation of whole proteins or domain ligands to the nanoparticle's protein backbone is challenging due to potential improper protein folding and aggregation. 5,13,14 In this regard, chemical linkers have certain drawbacks, including imprecision, variability, potential steric hindrance, complex synthesis, and high cost. 15,16 Similarly, biological methods such as the SpyTag−SpyCatcher system are not without limitations.…”

“…The efficiency and specificity of binding can vary depending on the proteins involved and reaction conditions, presenting challenges in achieving high efficiency and specificity. 5,17,18 Additionally, the use of this system may increase the immunogenic effect of nanoparticles. 19 In recent years, enzymatic conjugation systems like sortase A (SrtA) have emerged as a robust approach for efficient protein conjugation and post-translational modifications.…”

Sortase A-based post-translational modifications on encapsulin nanocompartments

“…3 Encapsulin nanocompartments offer versatile applications ranging from vaccine development to targeted drug delivery. [4][5][6] Encapsulins can act as efficient nanocarriers, 7 and their inherent properties make them promising candidates in the field of nanomedicine, highlighting the potential for enhanced therapies and diagnostics. 8 In this context, Quasibacillus thermotolerans' large encapsulin compartment has garnered attention.…”

Heterologous Prime-Boost with Immunologically Orthogonal Protein Nanoparticles for Peptide Immunofocusing

“…4,[8][9] Since their discovery in the 1990s, encapsulin scaffolds have been derivatized to serve a variety of biotechnology, therapeutic, and materials functions, including as photo-switchable imaging, 10 catalysis, [11][12][13] cellular imaging, [14][15][16] targeted drug delivery, [17][18] toxin remediation, 19 and vaccination. [20][21][22][23][24] In modern immunization strategies, the selection of antigenic peptide epitopes from a given pathogen's protein repertoire is often key to developing successful antibody and T cell responses against infectious pathogens. However, vaccination with such peptides alone usually fails to promote sufficiently robust responses, [25][26] requiring the use of carrier proteins for conjugate vaccines, a role for which protein nanoparticles are well suited by virtue of their efficient lymphatic trafficking, engagement of immune cell receptors, uptake, processing, and induction of cellular signaling.…”

“…20 The former particle was administered to mice with Freund's adjuvant and the latter with the Sigma adjuvant system. Encapsulins from Myxococcus xanthus were recently engineered to display receptor binding domains form SARS-CoV-2 virus 24 or influenza hemagglutinin, 23 and were tested immunologically with a squalene-in-water emulsion adjuvant. Lastly, only one report has appeared of an encapsulin-peptide conjugate vaccine, in this case using the prototypical Ova2 peptide (SIINFEKL) antigen attached by chemical means to T. maritima encapsulins and administered with poly (I:C) adjuvant.…”