SARS-CoV-2 ORF8 Modulates Lung Inflammation and Clinical Disease Progression

The virus severe acute respiratory syndrome coronavirus 2, SARS-CoV-2, is the causative agent of the current COVID-19 pandemic. It possesses a large 30 kilobase (kb) genome that encodes structural, non-structural, and accessory proteins. Although not necessary to cause disease, these accessory proteins are known to influence viral replication and pathogenesis. Through the synthesis of novel infectious clones of SARS-CoV-2 that lack one or more of the accessory proteins of the virus, we have found that one of these accessory proteins, ORF8, is critical for the modulation of the host inflammatory response. Mice infected with a SARS-CoV-2 virus lacking ORF8 exhibit increased weight loss and exacerbated macrophage infiltration into the lungs. Additionally, infection of mice with recombinant SARS-CoV-2 viruses encoding ORF8 mutations found in variants of concern reveal that naturally occurring mutations in this protein influence disease severity. Our studies with a virus lacking this ORF8 protein and viruses possessing naturally occurring point mutations in this protein demonstrate that this protein impacts pathogenesis. The SARS-CoV-2 genome is composed of various genes that are responsible for replication of its genome, making virions as well as aiding the virus in replicating in host cells. The virus expresses several viral proteins during infection that are also thought to modulate the host response to the virus. Identifying the role of these proteins in infection and how they affect both viral replication and host response to infection is important to understand how SARS-CoV-2 causes disease. One of these proteins, ORF8, is mutated across many variant lineages and its function is unclear. Both the role of ORF8 in pathogenesis and how these mutations could be advantageous to viral fitness are unknown. We have found that mutations in ORF8 across variants recapitulate the loss of function phenotype of an ORF8 deletion virus and affect inflammation during infection. Mutations found in variants that cause a loss of function of ORF8 increase inflammation in our animal model suggesting that these mutations may play the same role in humans. Differences in ORF8 sequences of variants may significantly impact disease severity in humans and alter transmission kinetics so that mechanistic studies of its function are important to understand as SARS-CoV-2 continues to be spread.