Development of SARS-CoV-2 nanoparticles through a plug-and-play approach

National Institute Of Allergy And Infectious Diseases

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Abstract

Antigens displayed on self-assembling nanoparticles can stimulate strong humoral immune responses and have been playing an increasingly prominent role in structure-based vaccines. However, the development of such immunogens may be complicated by inefficiencies in nanoparticle assembly, especially with the metastable glycosylated trimeric type 1 fusion machines that are prevalent viral vaccine targets. 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 could be expressed with sufficient yield of soluble proteins from a mammalian expression system after the addition of nanoparticle surface glycans. Respiratory syncytial virus fusion (F), F-glycoprotein trimers from human parainfluenza virus-type 3 and spike-glycoprotein trimers from SARS-CoV-2 could be displayed nanoparticles with decent yield and antigenicity. We explicitly tested the immunogenicity for the nanoparticle-formatted trimeric antigen from SARS-CoV-2 in mice. The SARS-CoV-2 spike-LuS nanoparticles elicited stronger immune responses than the corresponding trimers at low immunogen doses: at the 0.08 ug dose after two immunizations, spike nanoparticle elicited neutralization response with geometric mean neutralization titers (ID50) of 413, whereas trimeric spike elicited an equivalent neutralization titer only at the 25-fold higher dose of 2 micro gram. At 0.4 micro gram, spike nanoparticle elicited 37-fold higher ID50 than trimeric spike. However, at a high dose of 2 micro gram, spike nanoparticle-elicited neutralization response appeared to plateau at a level 5-fold higher in neutralization titer than the trimeric immunogen. Overall, multivalent presentation of trimeric antigens on nanoparticle can significantly improve their immunogenicity, allowing for elicitation of potent immune responses at a relatively low immunogen dose. The versatile platform 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.