SARS‐CoV‐2 mutations: A strain on efficacy of neutralizing monoclonal antibodies?

The novel Severe Acute Respiratory Syndrome Virus 2 (SARS-CoV-2) pandemic was declared by the WHO in March 2020, with the number of new cases per day exceeding 50 000 globally. The spread of SARS-CoV-2 across the world threw the pharmaceutical industry into a race for the first COVID-19 vaccine. Since then, COVID-19 new infection rates have increased substantially with the emergence of new SARS-CoV-2 variants, notably in the United Kingdom (B.1.1.7), South Africa (S.501Y.V2), and Brazil (B.1.1.28). Despite the success in formulating several highly efficacious vaccines in such a short period of time, certain reservations remain. Public hesitancy towards vaccination is of particular concern as it undermines the strategy of herd immunity. This wide-spread hesitancy towards vaccination necessitates the availability of alternative treatment options that could be more readily accepted. More worrisome, however, is the emergence of novel SARS-CoV-2 mutations and their resulting impact on the efficiency of vaccines and spike protein directed neutralizing monoclonal antibodies (NMAb). Data presented below examines the efficacy and use of NMAbs as post-exposure prophylaxis. NMAbs function through inhibiting the viral spike protein (S-protein) which binds to host cells, and therefore, inhibition of the S-protein blocks viral entry into host cells. The S-protein consists of two subunits, S1 and S2, with the receptor binding domain (RBD) residing on the S1 subunit. The RBD binds to the transmembrane metalloprotein, angiotensin converting enzyme 2 (ACE-2), found abundantly in lung, small intestine epithelia as well as renal and arterial linings, supporting corresponding clinical presentations of COVID-19. With the consideration of public hesitancy towards vaccination, coupled with a continuous influx of newly infected COVID-19 patients, establishing a suitable therapy for post-exposure prophylaxis is essential. Countries with vaccination hesitancy rates significantly below herd immunity threshold should consider investing in options for the prompt treatment of new positive cases. Efforts have been taken to utilize the neutralization of the S-protein of SARS-CoV-2 as a method of post-exposure prophylaxis and this can occur in one of three ways: functionally mimicking ACE-2 to bind the viruses RBD and stopping the ACE-2-RBD complex (1), binding to RBD without mimicking ACE-2 (2), and binding RBD but without stopping ACE-2-RBD binding (3). When conducting a search of all clinical trials testing the efficiency of NMAbs against SARS-CoV-2 with interest placed on trial start date, phase of study, number of participants, combination therapy (Y/N), and novel SARSCoV-2 therapy (Y/N), a significant increase in the number of clinical trials testing novel NMAbs targeting SARS-CoV-2 spike protein could be demonstrated (Figure 1). The main contributors to enrolment totals initially were Regeneron's SARS-CoV-2 spike protein combination therapy REGN10933 + REGN10987 now called REGN-COV2. Since the beginning of the first novel SARS-CoV-2 NMAb trials, not only do we see initial trials progress to advanced clinical trial stages, but we also observe additional novel NMabs. This includes Astrazeneca's AZD8895, AZD1061, and Tychan's TY027 which is a fully engineered human IgG NMab stated to decrease disease severity in acutely infected COVID-19 patents. Many new NMAbs have undergone testing and some show potential. VIR-7831 is a fully humanized anti-SARS-CoV-2 NMAb characterized by S309, an antibody that is able to neutralize SARSCoV-2. Importantly, the antibody binds to a highly conserved epitope found on the spike protein, challenging mutational escape. VIR-7831 was developed from S309 and has affinity for both coronaviruses. Currently, Vir Biotechnology Inc. are investigating its use in early COVID-19 infection in non-hospitalized patients. The trial is assessing key safety, tolerability, efficacy, and PK parameters, and results are expected July 2021 (NCT04545060). Similar to VIR-7831, BRII-196/198 blocks viral entry and neutralizes SARS-CoV-2 infection in vivo by binding to a highly conserved epitope on the spike protein. Specifically, BRII-198 binds to a different site on the spike protein, and its combination with BRII-196 resulted in synergistic effects. It is now expected to continue into phase II/III clinical trials as part of the NIH's Accelerating COVID-19 Therapeutic Interventions and Vaccines program (ACTIV). Here, it will be evaluated for safety and efficacy in people with mild to moderate COVID-19 severity who are at risk of disease progression (NCT04501978). Previous ACTIV trials included Eli Lilly's LY-CoV555 (bamlanivimab) which is currently authorized for use in mild-to-moderate COVID-19 and has recently received additional authorization for its use in combination with etesevimab. NMAbs have shown to be effective in reducing viral load in both animal and human trials. However, the impact on clinical outcomes has not been described in detail. Specifically, Regeneron's REGNCOV2 reported a response in sero-negative patients with high viral load in their interim analysis, with similar safety outcomes compared to placebo group. Fuelled with preclinical success, the combination therapy NMAb had high hopes for translating the reduction of viral load into clinical impact. In a recent publication, Regeneron presented descriptive data on the impact of REGN-COV2's ability to remove post treatment healthcare visits. While the NMAb did decrease the Received: 19 January 2021 Revised: 14 March 2021 Accepted: 22 March 2021