Maingot, B. | bioRxiv Science

bioRxiv2025

Identification of protective human monoclonal antibodies using a K18 hACE2 transgenic mouse SARS-CoV-2 challenge model

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), uses human angiotensin converting enzyme 2 (hACE2) as its obligate receptor for cell entry. The K18 hACE2 transgenic mouse line, which expresses hACE2 under control of the human keratin 18 (K18) promoter, is used as an animal model for the study of COVID-19 pathogenesis. Here, we evaluate this model in the screening of human monoclonal antibody (hmAb) therapies against SARS-CoV-2. We included 206 hmAbs from the Coronavirus Immunotherapeutic Consortium Database (CoVIC-DB) and identified many that protected against a lethal challenge with the virus. Our data showed that mouse weight change from day 5 onward highly correlated with survival. Many of the protective hmAb candidates we identified also showed strong viral neutralization and spike protein (SP) binding when measured in vitro; however, in many cases, in vitro assays failed to identify protective hmAbs, suggesting that the mouse model may capture characteristics of the hmAbs that other methods cannot. Our findings demonstrate the relevance of including in vivo models for the characterization of therapeutics against SARS-CoV-2, as these improve both accuracy and expediency in the screening process.

immunology↗

bioRxiv2025

Single dose alum adjuvanted RBD protein vaccine provides protection against homologous challenge with SARS-CoV-2 Washington strain and heterologous rechallenge with Delta and Omicron BA.5 variants in K18 hACE2 mouse model

Most COVID-19 vaccination strategies require at least two doses-a primary vaccine followed by a booster dose with the updated variant-specific vaccine. However, vaccine and booster dose hesitancy make it challenging to administer multiple doses of vaccines in the unvaccinated and vaccinated populations, respectively. Thus, it is important to determine if vaccinated individuals exposed to SARS-CoV-2 infection develop immune responses that may protect them against emerging variants of concern (VoCs). We have developed mouse models to understand the protective efficacy of an RBD-based vaccine against challenge and rechallenge with SARS-CoV-2 VoCs. Mice were vaccinated with RBD protein vaccine formulated in 2% Alhydrogel (alum) adjuvant by subcutaneous route. To determine the efficacy of RBD vaccine, mice were challenged approximately 4 weeks post-vaccination with SARS-CoV-2 variants by intranasal route. To determine the efficacy of RBD vaccine against SARS-CoV-2 rechallenge, mice were rechallenged with SARS-CoV-2 Delta and Omicron BA.5 variants at day 14 post SARS-CoV-2 Washington (WA) strain challenge. Our data suggest that single dose alum adjuvanted RBD protein from Wuhan strain provides protection against homologous challenge with SARS-CoV-2 WA strain but failed to provide protection against heterologous challenge with Delta and Omicron BA.5 variants. Interestingly, vaccinated mice that survived homologous challenge with the WA strain showed protection against heterologous rechallenge with Delta and omicron BA.5 variants. Furthermore, infectious viral loads of Delta and Omicron BA.5 were not detected in the lung tissues collected from the rechallenged mice at 3 days post-rechallenge. The data suggest that a single dose RBD vaccine from the ancestral Wuhan strain together with survival from WA strain challenge induces protective immune responses against Delta and Omicron BA.5 variants rechallenge. These mouse models will be useful to determine the immune responses that correlate with protection against challenge and rechallenge with SARS-CoV-2 VoCs.

microbiology↗