Intranasal virus-particle mimicking vaccine enhances SARS-CoV-2 clearance in the Syrian hamster model (preprint)

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a pandemic and multiple vaccines have been developed and authorized for human use. While these vaccines reduce disease severity, they do not prevent infection allowing SARS-CoV-2 to continue to spread and evolve. To confer protection against infection and limit transmission, vaccines must be developed that induce mucosal immunity in the respiratory tract. Therefore, we performed proof-of-principle pre-clinical vaccine and challenge studies with a virus-particle mimicking intranasal vaccine against SARS-CoV-2. The vaccine candidate consisted of the self-assembling 60-subunit I3-01 protein scaffold covalently decorated with the SARS-CoV-2 receptor binding domain (RBD) using the SpyCatcher-SpyTag system. We verified the intended antigen display features by reconstructing the I3-01 scaffold to 3.4A using cryo-EM, and established RBD decoration through both SDS-PAGE and negative stain TEM. Using this RBD grafted SpyCage scaffold (RBD+SpyCage), we performed two vaccination studies in Syrian hamsters using an intranasal prime and boost vaccine regiment followed by SARS-CoV-2 challenge. The initial study focused on assessing the immunogenicity of RBD+SpyCage, which indicated that vaccination of hamsters induced a non-neutralizing antibody response that enhanced viral clearance but did not prevent infection. In an expanded study, we demonstrated that covalent bonding of RBD to the scaffold was required to induce an antibody response. Consistent with the initial study, animals vaccinated with RBD+SpyCage more rapidly cleared SARS-CoV-2 from both the upper and lower respiratory tract, whereas admixtures of SpyCage and RBD, or either component alone did not. These findings demonstrate the intranasal SpyCage vaccine platform can induce protection against SARS-CoV-2 and, with additional modifications to improve immunogenicity, is a versatile and adaptable system for the development of intranasal vaccines targeting respiratory pathogens.

Limited window for donation of convalescent plasma with high live-virus neutralizing antibodies for COVID-19 immunotherapy (preprint)

The optimal timeframe for donating convalescent plasma to be used for COVID-19 immunotherapy is unknown. To address this important knowledge deficit, we determined in vitro live-virus neutralizing capacity and persistence of IgM and IgG antibody responses against the receptor-binding domain and S1 ectodomain of the SARS-CoV-2 spike glycoprotein in 540 convalescent plasma samples obtained from 175 COVID-19 plasma donors for up to 142 days post-symptom onset. Robust IgM, IgG, and viral neutralization responses to SARS-CoV-2 persist, in the aggregate, for at least 100 days post-symptom onset. However, a notable acceleration in decline in virus neutralization titers [≥]160, a value suitable for convalescent plasma therapy, was observed starting 60 days after first symptom onset. Together, these findings better define the optimal window for donating convalescent plasma useful for immunotherapy of COVID-19 patients and reveal important predictors of an ideal plasma donor, including age and COVID-19 disease severity score. One Sentence SummaryEvaluation of SARS-CoV-2 anti-spike protein IgM, IgG, and live-virus neutralizing titer profiles reveals that the optimal window for donating convalescent plasma for use in immunotherapy is within the first 60 days of symptom onset.