Fc-Independent Protection from SARS-CoV-2 Infection by Recombinant Human Monoclonal Antibodies

Abstract

The use of passively-administered neutralizing antibodies is a promising approach for the prevention and treatment of SARS-CoV-2 infection. Antibody-mediated protection may involve immune system recruitment through Fc-dependent activation of effector cells and the complement system. However, the role of Fc-mediated functions in the efficacious in-vivo neutralization of SARS-CoV-2 is not yet clear, and it is of high importance to delineate the role this process plays in antibody-mediated protection. Toward this aim, we have chosen two highly potent SARS-CoV-2 neutralizing human monoclonal antibodies, MD65 and BLN1 that target distinct domains of the spike (RBD and NTD, respectively). The Fc of these antibodies was engineered to include the triple mutation N297G/S298G/T299A that eliminates glycosylation and the binding to FcγR and to the complement system activator C1q. As expected, the virus neutralization activity (in-vitro) of the engineered antibodies was retained. To study the role of Fc-mediated functions, the protective activity of these antibodies was tested against lethal SARS-CoV-2 infection of K18-hACE2 transgenic mice, when treatment was initiated either before or two days post-exposure. Antibody treatment with both Fc-variants similarly rescued the mice from death reduced viral load and prevented signs of morbidity. Taken together, this work provides important insight regarding the contribution of Fc-effector functions in MD65 and BLN1 antibody-mediated protection, which should aid in the future design of effective antibody-based therapies.

Fc-modified SARS-CoV-2 neutralizing antibodies with therapeutic effects in two animal models

“…In contrast, sotrovimab increases binding to FcRn by LS modification (Gupta et al, 2021). In the absence of Fc receptor binding ability, there is a report that the therapeutic effect is decreased (Chan et al, 2021) and others that it is not significantly changed (Noy-Porat et al, 2021), and a consensus has not been established. In this context, our antibodies demonstrated the therapeutic effects in hamsters and macaques at doses of at least 5 to 7 mg/kg, without increased viral uptake by ADE (Figure 7).…”

Passive Immunotherapy Against SARS-CoV-2: From Plasma-Based Therapy to Single Potent Antibodies in the Race to Stay Ahead of the Variants

“…There is an ongoing discussion concerning the importance and the potential risk of having active Fc activity in antibodies targeting SARS-CoV-2. On one hand, Fc effector functions have been reported to be essential for optimal therapeutic protection against SARS-CoV-2 [ 218 , 240 , 284 – 286 ]; on the other hand, at least in some cases, significant protection was achieved in animal models independent of Fc functionality, suggesting that antibody Fab-dependent neutralization in absence of Fc function was sufficient to eliminate the virus [ 287 ]. Additionally, Fc engagement of FcγRIIIa has been correlated with disease severity in COVID-19 patients [ 288 , 289 ] and Fc engagement of FcγRIIa/b is a potential risk of increasing viral infection via an ADE mechanism [ 221 , 288 ].…”

“…While it has been demonstrated that antibodies to SARS-CoV-2 can neutralize the virus in the absence of Fc functionality [ 287 ], it has become clear that Fc activity enhances the ability of IgGs to neutralize SARS-CoV-2. Several groups have recently demonstrated using in vitro and/or in vivo experiments that an intact Fc, which interacts with immune cells such as NK cells to promote ADCC and phagocytes to promote antibody dependent cellular phagocytosis (ADCP), is required for optimal anti-SARS-CoV-2 antiviral activity [ 218 , 284 , 291 ], just as it is with HIV [ 292 , 293 ].…”

Antibody-mediated immunity to SARS-CoV-2 spike

“…Another RBM antibody, COV2–2050 ( Zost, Gilchuk, Case, et al, 2020 ), displayed reduced protection in a mouse model of SARS-CoV-2 infection by introduction of the LALA-PG (L234A, L235A, P329G) Fc mutations which eliminate Fc ɣ R binding ( Lo et al, 2017 ; Winkler et al, 2021 ). The importance of these functions for ultra potent neutralizing RBM antibodies is unclear, however, as C144 and other ACE2-blocking antibodies can prophylactically and therapeutically protect mice from SARS-CoV-2 challenge by neutralization ( Noy-Porat et al, 2021 ; Schäfer et al, 2020 ). In general, it seems that Fc effector functions may be more important for protection by less-potently neutralizing antibodies or with delayed onset of therapy ( Chan et al, 2021 ; Winkler et al, 2021 ).…”