Development of cell-based models for the evaluation of immune responses in COVID-19

Promoters

Prof. Jonathan DOUXFILS, UNamur, Department of pharmacy, Research Unit in Clinical Pharmacology and Toxicology (URPC) - promoter

Prof. Jean-Michel DOGNE, UNamur, Department of pharmacy, Research Unit in Clinical Pharmacology and Toxicology (URPC) - co-promoter

Jury

• Prof. Jonathan Douxfils, UNamur
• Prof. Jean-Michel Dogné, UNamur
• Benoît Muylkens, UNamur
• Prof. François Mullier, UCLouvain
• Prof. Christophe Beauloye, UCLouvain
• Prof. Paolo Palma, UAntwerpen

Summary

SARS-CoV-2 first emerged in Wuhan, China, in December 2019, spreading worldwide and leading the World Health Organization to declare a pandemic in March 2020. As of December 2024, over 777 million cases and 7.1 million deaths have been reported globally.

This thesis primarily examines the humoral immune response to COVID-19, investigating both infection- and vaccine-induced antibody production. A pseudovirus neutralization test (pVNT) was developed to measure neutralizing antibodies (NAbs), and multiple binding assays—targeting nucleocapsid (NCP), spike protein (S), and receptor-binding domain (RBD)—were used to evaluate overall antibody levels. NAbs have proven to be strong correlates of protection (CoP) against SARS-CoV-2.

The CRO-VAX HCP study recruited healthcare professionals who received up to four doses of the BNT162b2 mRNA vaccine, with periodic blood sampling revealing a gradual decrease in vaccine efficacy (VE). Booster doses, including a bivalent version targeting emerging variants, were introduced to counter waning VE and the rise of breakthrough infections. While antibody titers declined substantially over time, T-cell responses—as measured by an interferon gamma (IFNγ) release assay (IGRA)—remained largely stable. This suggests that cellular immunity may continue to protect against severe disease despite lower antibody levels. Nonetheless, whether T-cell responses provide a better CoP for severe cases than NAbs remains an open question.

The second part of this thesis investigates the excessive inflammatory response observed in acute COVID-19 infections. Early clinical findings indicated a spectrum of respiratory complications, from mild symptoms to acute respiratory distress syndrome (ARDS), often accompanied by thromboses and multi-organ failure. This severe clinical presentation has been linked to a “cytokine storm,” with neutrophils playing a pivotal role through the formation of neutrophil extracellular traps (NETs) in a process known as NETosis. In this work, an in vitro NETosis model was established to qualitatively and quantitatively examine NET formation. This model helped identify potential inducers and inhibitors of NETosis; notably, serum from patients who experienced septic shock proved a potent inducer, likely due to its high cytokine content.