A platform incorporating trimeric antigens into self-assembling nanoparticles reveals SARS-CoV-2-spike nanoparticles to elicit substantially higher neutralizing responses than spike alone

Abstract

Antigens displayed on self-assembling nanoparticles can stimulate strong immune responses and have been playing an increasingly prominent role in structure-based vaccines. However, the development of such immunogens is often complicated by inefficiencies in their production. To alleviate this issue, we developed a plug-and-play platform using the spontaneous isopeptide-bond formation of the SpyTag:SpyCatcher system to display trimeric antigens on self-assembling nanoparticles, including the 60-subunit Aquifex aeolicus lumazine synthase (LuS) and the 24-subunit Helicobacter pylori ferritin. LuS and ferritin coupled to SpyTag expressed well in a mammalian expression system when an N-linked glycan was added to the nanoparticle surface. The respiratory syncytial virus fusion (F) glycoprotein trimer—stabilized in the prefusion conformation and fused with SpyCatcher—could be efficiently conjugated to LuS-SpyTag or ferritin-SpyTag, enabling multivalent display of F trimers with prefusion antigenicity. Similarly, F-glycoprotein trimers from human parainfluenza virus-type 3 and spike-glycoprotein trimers from SARS-CoV-2 could be displayed on LuS nanoparticles with decent yield and antigenicity. Notably, murine vaccination with 0.08 µg of SARS-CoV-2 spike-LuS nanoparticle elicited similar neutralizing responses as 2.0 µg of spike, which was ~ 25-fold higher on a weight-per-weight basis. The versatile platform described here thus allows for multivalent plug-and-play presentation on self-assembling nanoparticles of trimeric viral antigens, with SARS-CoV-2 spike-LuS nanoparticles inducing particularly potent neutralizing responses.

A Single Immunization with Spike-Functionalized Ferritin Vaccines Elicits Neutralizing Antibody Responses against SARS-CoV-2 in Mice

“… 31 , 32 A comparison of neutralizing antibody titers observed in these other studies reveals that, despite the use of different adjuvants, the spike ferritin nanoparticles we present here elicit similar levels of neutralizing antibodies following one or two doses. 31 , 32 …”

Mosaic nanoparticles elicit cross-reactive immune responses to zoonotic coronaviruses in mice

“…In one such approach, multiple copies of an engineered protein domain called SpyCatcher fused to subunits of a virus-like particle form spontaneous isopeptide bonds to purified antigens tagged with a 13-residue SpyTag ( 29 – 32 ). The SpyCatcher-SpyTag system was used to prepare multimerized SARS-CoV-2 RBD or S trimer that elicited high titers of neutralizing antibodies ( 33 , 34 ). Although promising for protection against SARS-CoV-2, coronavirus reservoirs in bats suggest future cross-species transmission ( 6, 7, 35 ), necessitating a vaccine that protects against emerging coronaviruses as well as SARS-CoV-2.…”

Newcastle Disease Virus-Like Particles Displaying Prefusion-Stabilized SARS-CoV-2 Spikes Elicit Potent Neutralizing Responses

“…Although multiple vaccines are proceeding through clinical trials, some of which are achieving high levels of efficacy against COVID-19 [ 3 , 4 , 5 , 6 ], it seems prudent to explore the development of second-generation vaccines for improved immunogenicity, manufacturability, and scalability to fill gaps in the global vaccine portfolio. Particularly for immunogenicity, improvements could be made in the speed, potency, and durability of neutralizing antibody responses and/or T-cell responses [ 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. The SARS-CoV-2 spike glycoprotein is the main target for neutralizing antibodies and has, therefore, been a focus of vaccine design efforts [ 16 , 17 ].…”

“…To design second-generation SARS-CoV-2 vaccines, current efforts have focused on nanoparticle-based, viral-vector-based, or virus-derived replicon RNA-based vaccine candidates and virus-like particle (VLP) versions of immunogens. Protein nanoparticles displaying spike or RBD have been shown to elicit greater than 10-fold higher neutralizing titers than non-nanoparticle immunogens [ 10 , 11 ]. Current vector-based viral particle platforms to present SARS-CoV-2 antigens include the Moloney murine leukemia virus (MLV)-vectored COVID-19 vaccine [ 28 ], Newcastle disease virus (NDV)-vectored COVID-19 vaccine [ 9 ], rabies-virus-based COVID-19 vaccine [ 7 ], vesicular stomatitis virus (VSV)-vectored COVID-19 vaccines [ 29 , 30 ], virus-derived replicon RNA-based COVID-19 vaccines [ 8 , 31 ], and recombinant adenovirus-vectored COVID-19 vaccines [ 5 , 32 , 33 ].…”