Characterization of therapeutic antibody efficacy against multiple SARS-CoV-2 variants in the hamster model.

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and onset of the coronavirus disease-19 (COVID-19) pandemic led to an immediate need for therapeutic treatment options. Therapeutic antibodies were developed to fill a gap when traditional antivirals were not available. In late 2020, the United States Government undertook an effort to compare candidate therapeutic antibodies in virus neutralization assays and in the hamster model of SARS-CoV-2 infection. With the emergence of SARS-CoV-2 variants, the effort expanded to evaluate the efficacy of nearly 50 products against major variants. A subset of products was further evaluated for therapeutic efficacy in hamsters. Here we report results of the hamster studies, including pathogenicity with multiple variants, neutralization capacity of products, and efficacy testing of products against Delta and Omicron variants. These studies demonstrate the loss of efficacy of early products with variant emergence and support the use of the hamster model for evaluating therapeutics.

RBD design increases the functional antibody titers elicited by SARS-CoV-2 spike vaccination.

Most COVID-19 vaccines contain the SARS-CoV-2 spike protein as an antigen, but they lose efficacy as neutralizing antibody titers wane and escape variants emerge. Modifying the spike antigen to increase neutralizing antibody titers would help counteract this decrease in titer. We previously used a structure-based computational design method to identify nine amino acid changes in the receptor-binding domain (RBD) of spike that stabilize the RBD and increase the neutralizing antibody titers elicited by vaccination. Here, we introduce those enhancing amino acid changes into a full-length spike (FL-S-2P) ectodomain representative of most approved vaccine antigens. These amino acid changes can be incorporated into the FL-S-2P protein without negatively effecting expression or stability. Furthermore, the amino acid changes improved functional antibody titers in both mice and monkeys following vaccination. These amino acid changes could increase the duration of protection conferred by most COVID-19 vaccines.

Antigenic cartography using hamster sera identifies SARS-CoV-2 JN.1 evasion seen in human XBB.1.5 booster sera.

Antigenic assessments of SARS-CoV-2 variants inform decisions to update COVID-19 vaccines. Primary infection sera are often used for assessments, but such sera are rare due to population immunity from SARS-CoV-2 infections and COVID-19 vaccinations. Here, we show that neutralization titers and breadth of matched human and hamster pre-Omicron variant primary infection sera correlate well and generate similar antigenic maps. The hamster antigenic map shows modest antigenic drift among XBB sub-lineage variants, with JN.1 and BA.4/BA.5 variants within the XBB cluster, but with five to six-fold antigenic differences between these variants and XBB.1.5. Compared to sera following only ancestral or bivalent COVID-19 vaccinations, or with post-vaccination infections, XBB.1.5 booster sera had the broadest neutralization against XBB sub-lineage variants, although a five-fold titer difference was still observed between JN.1 and XBB.1.5 variants. These findings suggest that antibody coverage of antigenically divergent JN.1 could be improved with a matched vaccine antigen.