FcγR-mediated antibody-dependent enhancement of SARS-CoV-2 infection in human monocyte-derived macrophages

Abstract

Macrophages play a central role in innate immunity but can also facilitate viral dissemination through antibody dependent mechanisms, and, in turn drive the severity of the clinical symptomatology. Although macrophages are generally considered non permissive to SARS-CoV-2, anti-Spike antibodies may mediate virus cell interactions via Fc gamma receptors’ (FcγRs) binding, potentially enabling antibody-dependent enhancement (ADE) of infection. Whether anti-Spike antibodies in vivo can mediate FcγRs dependent SARS-CoV-2 infection in macrophages remains to be fully understood. Here we explored the capacity of SARS-CoV-2 Spike directed antibodies to mediate enhancement of viral infection in human monocyte derived macrophages (hMDMs) using an experimental system capable of discriminating between productive infection and passive viral uptake. SARS-CoV-2 entry and replication were assessed in hMDMs using Spike pseudotyped lentiviral vectors and infectious recombinant SARS-CoV-2 USA-WA1/2020 expressing enhanced green fluorescent protein (eGFP) or NanoLuc luciferase (nLuc). ADE was assessed in hMDMs using three human IgG1 anti-Spike monoclonal antibodies (mAbs): DH1047 and COVA1-16, neutralizing class 1 antibodies targeting the receptor binding domain (RBD), and DH1052, a non-neutralizing mAb targeting the N-terminal domain (NTD) as well as sera from five patients with severe COVID-19. An ACE2 negative FcγRII expressing B16-F10 cell line was used to confirm FcγR dependent infection and to screen a larger panel of patients’ sera. Viral entry and replication were quantified by luciferase activity, GFP fluorescence, nucleocapsid immunostaining, and infectivity assays of released virions. Spike pseudotyped lentiviral particles were efficiently internalized by hMDMs but failed to establish infection, instead undergoing endo-lysosomal degradation. The infectious recombinant SARS-CoV-2 similarly failed to replicate in hMDMs unless preincubated with mAb DH1047, that mediated FcγR dependent infection in both hMDMs and FcγRII expressing B16-F10 cells. Sera from patients with severe COVID-19 did not promote ADE in hMDMs or FcγRII expressing cells at the experimental condition here used, and instead, dose dependently inhibited DH1047 mediated enhancement. While hMDMs are intrinsically resistant to SARS-CoV-2 infection, productive replication can occur via FcγR mediated ADE in the presence of specific mAb and defined antibody to virus ratios. However, polyclonal antibody responses in patient sera suppress this mechanism, providing a potential explanation for the lack of convincing clinical evidence of ADE of infection in COVID-19 patients.