Table 1.
In vitro models of SARS-CoV-2 infection
| Format | Description | Duration (days) | Primary outcome | Quantification methods | Target outcome | Refs |
|---|---|---|---|---|---|---|
| ACE2–RBD inhibition assays | SARS-CoV-2 spike RBD incubated with soluble hACE2 and Ab at various concentrations | 1 | RBD binding to hACE2 | Binding can be measured by ELISA, FRET, SPR or BLI | Ab concentration required to inhibit RBD and ACE2 binding by 50% | 8,9 |
| Pseudovirus (single cycle) |
VSV lacking G protein is pseudotyped with SARS-CoV-2 spike (usually lacking 18–21 amino-terminal residues) HIV-1 or MLV lacking envelope is pseudotyped with SARS-CoV-2 spike and cultured in susceptible cell lines after the addition of Ab at various concentrations |
1 | Viral entry | Viral entry can be quantified using fluorescent or luciferase reporters | Ab required to reduce viral entry after a single cycle by 50% | 1,10,12,55–57 |
| Chimeric virus (replicating) | VSV with the G gene replaced by SARS-CoV-2 spike (usually lacking 18–21 amino-terminal residues) and cultured in susceptible cell lines after the addition of Ab at various concentrations | 1–2 | Viral entry, viral replication | Infection read-out using GFP or FRNT | Ab required to reduce the viral entry or viral load at the assay end point by 50% | 1,15,58 |
| Live SARS-CoV-2 — quantitative | Live SARS-CoV-2 is cultured in susceptible cell lines after incubation with Ab at various concentrations | 1–4 | Viral replication | Viral antigens (generally N protein) or cell death (measured using LDH) detected by ELISA or microscopy | Ab required to reduce the viral load at the assay end point by 50% | 1,21 |
| Live SARS-CoV-2 — limiting dilution | SARS-CoV-2 (often 100 TCID50) and various concentrations of Ab are co-incubated before addition to susceptible cell lines | 3–5 | Fraction of replicate wells positive for virus | Cytopathic effect or viral antigens (generally N protein) detected by ELISA or microscopy, or fluorescence or luminescence with labelled SARS-CoV-2 | Ab required to inhibit ~99% of inoculum | 22,59–61 |
| PRNT or FRNT | SARS-CoV-2 and Ab (at various concentrations) are co-incubated before addition to a cell monolayer | 3 | Reduction in plaque number | Plaques can be quantified by visual examination aided by colorimetric or fluorescent reporters | Ab required to reduce the number of plaques by 50% (or 90% for PRNT90) | 62 |
Ab, antibody; BLI, biolayer interferometry; ELISA, enzyme-linked immunosorbent assay; FRET, fluorescence resonance energy transfer; FRNT, focus reduction neutralization titre; GFP, green fluorescent protein; hACE2, human angiotensin-converting enzyme 2; LDH, lactate dehydrogenase; MLV, murine leukaemia virus; PRNT, plaque reduction neutralization titre; RBD, receptor binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; SPR, surface plasmon resonance; TCID50, 50% tissue culture infectious dose; VSV, vesicular stomatitis virus.