The SARS-CoV-2 Y453F mink variant displays a striking increase in ACE-2 affinity but does not challenge antibody neutralization (preprint)

SARS-CoV-2 transmission from humans to animals has been reported for many domesticated species, including cats, dogs and minks. Identification of novel spike gene mutations appearing in minks has raised major concerns about potential immune evasion and challenges for the global vaccine strategy. The genetic variant, known as cluster-five, arose among farmed minks in Denmark and resulted in a complete shutdown of the worlds largest mink production. However, the functional properties of this new variant are not established. Here we present functional data on the Y453F cluster-five receptor-binding domain (RBD) and show that it does not decrease established humoral immunity or affect the neutralizing response in a vaccine model based on wild-type RBD or spike. However, it binds the human ACE-2 receptor with a four-fold higher affinity suggesting an enhanced transmission capacity and a possible challenge for viral control.

Vaccine monitoring shows that focused immunization with SARS-CoV-2 receptor-binding domain provides a better neutralizing antibody response than full-length spike protein (preprint)

Effective tools to monitor SARS-CoV-2 transmission and humoral immune responses are highly needed. Protective humoral immunity involves neutralizing antibodies and will be a hallmark for the evaluation of a vaccine response efficacy. Here we present a sensitive, fast and simple neutralization ELISA method to determine the levels of antibody-mediated virus neutralization. We can show that it is strongly correlated with the more elaborate plaque reduction neutralization test (PRNT) (ρ = 0.9231, p < 0.0001). Furthermore, we present pre-clinical vaccine models using recombinant receptor binding domain (RBD) and full-length spike antigen as immunogens showing a profound antibody neutralization capacity that exceeds the highest neutralization titers from convalescent individuals. Using a panel of novel high-affinity murine monoclonal antibodies (mAbs) we also show that majority of the RBD-raised mAbs have inhibitory properties while only a few of the spike-raised mAbs do. In conclusion, the ELISA-based viral neutralization test offers a time- and cost-effective alternative to the PRNT. The immunization results indicate that vaccine strategies focused only on the RBD region may have major advantages over those based on the full spike sequence.

SARS-CoV-2 antibody responses determine disease severity in COVID-19 infected individuals (preprint)

Globally, the COVID-19 pandemic has had extreme consequences for the healthcare system and calls for diagnostic tools to monitor and understand the transmission, pathogenesis and epidemiology, as well as to evaluate future vaccination strategies. Here we have developed novel flexible ELISA-based assays for specific detection of SARS-CoV-2 antibodies against the receptor-binding domain (RBD): An antigen sandwich-ELISA relevant for large population screening and three isotype-specific assays for in-depth diagnostics. Their performance was evaluated in a cohort of 350 convalescent participants with previous COVID-19 infection, ranging from asymptomatic to critical cases. We mapped the antibody responses to different areas on protein N and S and showed that the IgM, A and G antibody responses against RBD are significantly correlated to the disease severity. These assays-and the data generated from them-are highly relevant for diagnostics and prognostics and contribute to the understanding of long-term COVID-19 immunity.