ETIDIOH - NEW

ABSTRACT In a subset of SARS-CoV-2-infected individuals treated with the antiviral nirmatrelvir -ritonavir, the virus rebounds following treatment. The mechanisms driving this rebound are not well understood. We used a mathematical model to describe the longitudinal viral load dynamics of 51 individuals treated with nirmatrelvir-ritonavir, 20 of whom rebounded. Target cell preservation , either by a robust innate immune response or initiation of N-R near the time of symptom onset, coupled with incomplete viral clearance , appears to be the main factor leading to viral rebound. Moreover, the occurrence of viral rebound is likely influenced by the time of treatment initiation relative to the progression of the infection, with earlier treatments leading to a higher chance of rebound . A comparison with an untreated cohort suggests that early treatments with nirmatrelvir-ritonavir may be associated with a delay in the onset of an adaptive immune response . Nevertheless, our model demonstra...

Abstract SARS-CoV-2 main protease, Mpro , is responsible for processing the viral polyproteins into individual proteins, including the protease itself. Mpro is a key target of anti-COVID-19 therapeutics such as nirmatrelvir (the active component of Paxlovid). Resistance mutants identified clinically and in viral passage assays contain a combination of active site mutations (e.g., E166V, E166A, L167F), which reduce inhibitor binding and enzymatic activity, and non-active site mutations (e.g., P252L, T21I, L50F), which restore the fitness of viral replication. To probe the role of the non-active site mutations in fitness rescue, here we use an Mpro triple mutant (L50F/E166A/L167F) that confers nirmatrelvir drug resistance with a viral fitness level similar to the wild-type. By comparing peptide and full-length Mpro protein as substrates, we demonstrate that the binding of Mpro substrate involves more than residues in the active site. Particularly, L50F and other non-active site mutations...