Development of Equine Polyclonal Antibodies as a Broad-Spectrum Therapy Against SARS-CoV-2 Variants

Abstract

The Coronavirus disease 19 (COVID-19) pandemic has accumulated over 550 million confirmed cases and more than 6.34 million deaths worldwide. Although vaccinations has largely protected the population through the last two years, the effect of vaccination has been increasingly challenged by the emerging SARS-CoV-2 variants. Although several therapeutics including both monoclonal antibodies and small molecule drugs have been used clinically, high cost, viral escape mutations, and potential side effects have reduced their efficacy. There is an urgent need to develop a low cost treatment with wide-spectrum effect against the novel variants of SARS-CoV-2. Here we report a product of equine polyclonal antibodies that showed potential broad spectrum neutralization effect against the major variants of SARS-CoV-2. The equine polyclonal antibodies were generated by horse immunization with the receptor binding domain (RBD) of SARS-CoV-2 spike protein and purified from equine serum. A high binding affinity between the generated equine antibodies and the RBD was observed. Although designed against the RBD of the early wild type strain sequenced in 2020, the equine antibodies also showed a highly efficient neutralization capacity against the major variants of SARS-CoV-2, including the recent BA.2 Omicron variant (IC50 =1.867μg/ml) in viral neutralization assay in Vero E6 cells using live virus cultured. The broad-spectrum neutralization capacity of the equine antibodies was further confirmed using pseudovirus neutralization assay covering the major SARS-CoV-2 variants including wild type, alpha, beta, delta, and omicron, showing effective neutralization against all the tested strains. Ex vivo reconstructed human respiratory organoids representing nasal, bronchial, and lung epitheliums were employed to test the treatment efficacy of the equine antibodies. Antibody treatment protected the human nasal, bronchial, and lung epithelial organoids against infection of the novel SARS-CoV-2 variants challenging public health, the Delta and Omicron BA.2 isolates, by reducing >95% of the viral load. The equine antibodies were further tested for potential side effects in a mouse model by inhalation and no significant pathological feature was observed. Equine antibodies, as a mature medical product, have been widely applied in the treatment of infectious diseases for more than a century, which limits the potential side effects and are capable of large scale production at a low cost. A cost-effective, wide-spectrum equine antibody therapy effective against the major SARS-CoV-2 variants can contribute as an affordable therapy to cover a large portion of the world population, and thus potentially reduce the transmission and mutation of SARS-CoV-2.