RIG-I-induced innate antiviral immunity protects mice from lethal SARS-CoV-2 infection

Abstract

The SARS-CoV-2 pandemic has underscored the need for rapidly employable prophylactic and antiviral treatments against emerging viruses. Targeted stimulation of antiviral innate immune receptors can trigger a broad antiviral response that also acts against new, unknown viruses. Here, we utilized the K18-hACE2 mouse model of COVID-19 to examine whether activation of the antiviral RNA receptor RIG-I protects mice from lethal SARS-CoV-2 infection and reduces disease severity. We found that prophylactic, systemic treatment of mice with the specific RIG-I ligand 3pRNA, but not type-I interferon, one to seven days before viral challenge, improved survival of mice by up to 50 %. Survival was also improved with therapeutic 3pRNA treatment starting one day after viral challenge. This improved outcome was associated with lower viral load in oropharyngeal swabs and in the lungs and brain of 3pRNA-treated mice. Moreover, 3pRNA-treated mice exhibited reduced lung inflammation and developed a SARS-CoV-2-specific neutralizing antibody response. These results demonstrate that systemic RIG-I activation by therapeutic RNA oligonucleotide agonists is a promising strategy to convey effective, short-term antiviral protection against SARS-CoV-2 infection, as well as its potential as a broad-spectrum approach to constrain the spread of newly emerging viruses until virus-specific therapies and vaccines become available.

Intranasal Delivery of RIG-I Agonist Drives Pulmonary Myeloid Cell Activation in Mice

“…Due to its robust transient ISG response within the first three days, one intranasal administration of 3p10LA9 alone without HA significantly reduced the viral burden in the lungs of influenza-infected mice. Consistent with our data, recent publications demonstrated similar efficacy in prophylactic short-term antiviral immunity not only against influenza ( 25 ) but also against SARS-CoV-2 ( 17 , 41 ). Intravenously injected RIG-I agonists, when injected within 24 h before SARS-CoV-2 challenge, prevented viral infection of the lower respiratory tract in a type I IFN dependent-manner and the protection was independent of adaptive immune responses ( 17 ).…”

Expression of a Functional Mx1 Protein Is Essential for the Ability of RIG-I Agonist Prophylaxis to Provide Potent and Long-Lasting Protection in a Mouse Model of Influenza A Virus Infection

“…Moreover, i.v. and intraperitoneal injections were used to demonstrate 3pRNA-mediated protection against SARS-CoV-2 [ 12 , 13 ] and CHIKV [ 7 ], respectively. Given that IAV is a respiratory virus, our initial studies in mice compared the effectiveness of a single intranasal (i.n).…”

“…3pRNA was prepared as previously described [ 11 ]. CA21-mer oligonucleotide (5′-CACACACACACACACACACAC-3′) was used as control RNA as previously described [ 13 ]. For in vitro studies, Lipofectamine 2000 (Invitrogen) was used to transfect mammalian cells with 3pRNA (100 ng/mL) or ctrl RNA (100 ng/mL) in OptiMEM (Gibco-BRL) according to manufacturer’s instructions.…”

“…For example, pre-treatment of human A549 cells [ 8 , 9 , 10 ] or monocyte-derived dendritic cells [ 9 ] with RIG-I agonists resulted in reduced intracellular expression of IAV proteins and/or reduced titres of infectious virus following subsequent IAV infection. Several studies have also used mouse models to demonstrate the prophylactic and/or therapeutic effects of RIG-I agonists in vivo against a smaller subset of viruses, namely IAV [ 8 , 9 , 10 , 11 ], CHIKV [ 7 ] and SARS-CoV-2 [ 12 , 13 ].…”

RIG-I activation primes and trains innate antiviral immune memory

“…As several recent studies on SARS-CoV-2 have demonstrated(Cheemarla et al , 2021; Decker, 2021; Lopez et al , 2021), the speed of the innate immune response is critical to an effective host defense, particularly since SARS-CoV-2 and many other viruses code for proteins that delay ISG induction(Shemesh, 2021; Fung et al , 2022). Given that SARS-CoV-2 and IAV both activate RIG-I like receptors(Rehwinkel et al , 2010), these findings may also explain why RIG-I is a particularly effective prophylaxis against these two viruses(Marx et al , 2022; Mao et al , 2021b; Coch et al , 2017b).…”