Isolation and Characterization of SARS-CoV-2 strains circulating in Eastern India.

Emergence of SARS-CoV-2 as a serious pandemic has altered the global socioeconomic dynamics. The wide prevalence, high death counts and rapid emergence of new variants urge for establishment of research infrastructure to facilitate rapid development of efficient therapeutic modalities and preventive measures. In agreement with this, five SARS-CoV2 strains (ILS01, ILS02, ILS03, ILS15 and ILS24) of four different clades (19A, 19B, 20A and 20B) were isolated from patient swab samples collected during the 1st COVID-19 wave in Odisha, India. The viral isolates were adapted to in-vitro cultures and further characterized to identify strain specific variations in viral growth characteristics. All the five isolates showed substantial amount of virus induced CPE however ILS03 belonging to 20A clade displayed highest level of CPE. Time kinetics experiment revealed spike protein expression was evident after 16th hours post infection in all five isolates. ILS03 induced around 90% of cytotoxicity. Further, the susceptibility of various cell lines (human hepatoma cell line (Huh-7), CaCo2 cell line, HEK-293T cells, Vero, Vero-E6, BHK-21, THP-1 cell line and RAW 264.7 cells) were assessed. Surprisingly, it was found that the human monocyte cells THP-1 and murine macrophage cell line RAW 264.7 were permissive to all the SARS-CoV-2 isolates. The neutralization susceptibility of viral isolates to vaccine-induced antibodies was determined using sera from individuals vaccinated in the Government run vaccine drive in India. The micro-neutralization assay suggested that both Covaxin and Covishield vaccines were equally effective (100% neutralization) against all of the isolates. The whole genome sequencing of culture adapted viral isolates and viral genome from patient oropharyngeal swab sample suggested that repetitive passaging of SARS-CoV2 virus in Vero-E6 cells did not lead to emergence of many mutations during the adaptation in cell culture. Phylogenetic analyses revealed that the five isolates clustered to respective clades. The major goal was to isolate and adapt SARS-CoV-2 viruses in in-vitro cell culture with minimal modification to facilitate research activities involved in understanding the molecular virology, host-virus interactions, application of these strains for drug discovery and animal challenge models development which eventually will contribute towards the development of effective and reliable therapeutics.