Potent Neutralizing Activity of Polyclonal Equine Antibodies against Omicron SARS-CoV-2

Using a polyclonal approach of equine anti-SARS-CoV-2 F(ab’)2 antibodies we have achieved a high level of neutralizing potency against all SARS-CoV-2 variants tested. Neutralization titers were in the range of 105-106 IU/mL including Omicron: 111,403 UI/mL, which is 2-3 orders of magnitude what is normally achieved in response to SARS-CoV-2 infection and/or vaccination. The presence of high titers of a repertoire of antibodies targeting conserved epitopes in different regions of the spike protein could plausibly account for this remarkable breadth of neutralization. These results warrant the clinical investigation of anti-SARS-CoV-2 equine polyclonal F(ab’)2 antibodies as a novel therapeutic strategy against COVID-19


Background
The rapid widespread of SARS-CoV-2 during the COVID-19 pandemics has caused 400 M of confirmed cases and over 5 M deaths by February 2022(1) along with significant socio-economic disruptions. This active transmission of SARS-CoV-2 has resulted in the emergence of several variants of concern (VoC) that apparently have been selected by a higher transmissibility and have challenged the public health control strategies to contain the pandemics (2).
The recent appearance of the variant Omicron, that combines an augmented transmission capability along with an evasion from neutralization by convalescent or vaccinees sera, is a further hurdle for pandemics control (3). A number of potent monoclonal antibodies (mAbs) have received emergency authorization by EMA and FDA for COVID-19 treatment in selected patients (4).
However, most of these mAbs have been rendered inefficacious by the highly mutated Omicron variant (5).
Considering the experience on the evolution of SARS-CoV-2 into a diversity of variants, a polyclonal approach in which many potential epitopes within the SARS-CoV-2 Spike protein are targeted could have great advantages in terms of breadth to neutralize current and potential future SARS-CoV-2 VoC.
On the other hand, heterologous immunoglobulins have been used for more than a century in human therapy (especially for envenomation, rabies and tetanus) (6). Specific polyclonal immunoglobulins are indeed a well-known and effective therapeutic alternative that can be used quickly to respond against major health risks such as pandemics, emerging diseases and bioterrorism.
FBR-002 is composed of purified polyclonal equine fragments F(ab')2 directed against the SARS-CoV-2 spike protein. FBR-002 represents a safe and efficient therapy candidate to treat COVID-19 hospitalized patients by i) its polyclonality that allows to target multiple epitopes of the spike protein, limiting the risk of viral escape if new strains emerge and ii) its highly purifying process and lack of Fc portion minimizing the risk of Antibody-Dependent-Enhancement (ADE), immunogenicity and overall side-effects pattern (eg serum sickness syndrome) compared to whole immunoglobulins that may be used for passive immunotherapy. Therefore, F(ab')2 polyclonal fragments show less safety concerns as compared to other related products such as plasma from recovered patients or polyclonal humanized anti-SARS-CoV2 antibodies.
In this report we described the in vitro evaluation of FBR-002, a clinical grade product of polyclonal F(ab')2 immunoglobulin fragments from Fab'entech against SARS-CoV-2 VoC.

Materials & Methods
Equine hyperimmune plasma: Three healthy French trotter horses were hyperimmunized with full SARS-CoV-2 spike protein. Horses had no detectable antibodies against SARS-CoV-2 before immunization and were strictly controlled for several viruses. Blood samples were collected regularly after immunization and plasma were prepared and stored at -20°C.

Results
Results of the neutralization assays are summarized in the table 1 and figure 1 A and B. FBR-002 achieved a very high level of neutralizing potency against all SARS-CoV-2 variants tested: Neutralization titers (IU/mL) were in the range of Although much lower, we observed FBR-002 neutralization against SARS-CoV-1 with titer of 13,232 IU/mL. There was no measurable neutralizing activity detected against MERS, EBOV or VSV.

Discussion:
The emergence of diversity along the evolution of the COVID-19 pandemics has led to the emergence of different SARS-CoV-2 variants whose adaptation These antibodies that recognize residues within the RBM are among the most common produced as response to SARS-CoV-2 infection in humans (14,15).
However, the evolution of scape mutations in the circulating VoC have rendered some of them inefficacious (16). This capability for immune evasion has been exhibited to a new limit by the recent emergence of the Omicron VoC that is resistant to neutralization by most of the clinically available monoclonal antibodies (17,18).
Using a polyclonal approach of equine neutralizing anti-SARS-CoV-2 polyclonal F(ab')2 antibodies we have achieved extraordinary neutralizing potency that is 2-3 orders of magnitude what is normally achieved in response to SARS-CoV-2 infection and/or vaccination (10). The neutralization coverage for the different variants is also remarkable, reaching >200000 IU/mL for most of VoC tested. As expected, Omicron showed the highest reduction in neutralization (5.5-fold as compared with the ancestral D614G sequence) however still was 111,403 IU/mL (Table 1, Figure 1 A and B). This neutralizing titer against Omicron is in fact two orders of magnitude higher that those obtained after booster vaccination in either naïve or COVID-19 convalescent individuals (19)