Before COVID-19
- Interferons are among the earliest cytokines produced during a viral infection2 and generate a cascade that culminates in controlling viral replication and inducing an adaptive immune response.3
- Type 1 interferons (IFN-1) have frequently been studied against coronaviruses, having the most antiviral properties.
- They can be subdivided in α, β, ε, ω and κ subtypes;
- They are secreted by various cell types, especially plasmacytoid dendritic cells, upon recognition of viral constituents by pattern recognition receptors (PRRs)2;
- Once produced, interferons are recognized cells and activate the JAK-STAT pathway. This then leads to the phosphorylation of transcriptional factors STAT1 and STAT2, and together with a third transcription factor, IRF9, they form the Interferon Stimulated Gene Factor 3 (ISGF3) complex. The complex is then relocalized to the nucleus so that it can activate the transcription of interferon stimulated genes (ISG);1,2,3
- ISGs produce proteins can interfere with viral replication by mechanisms such as slowing of cell metabolism and secretion of cytokines promoting adaptive immunity.2
- SARS-CoV-2 is closely similar to MERS-CoV and SARS-CoV coronaviruses, against which IFN-1 treatments have been studied in vitro and in vivo, combined or not with other medications.
- Though some potential benefit has been demonstrated, a lack of significant improvement was possibly explained by the mechanisms of suppression of the IFN signaling pathway used by SARS-CoV and MERS-CoV.2, 3
- The Orf6 and Orf3 protein of SARS-CoV plays major role in inhibiting IFN type 1 response, thus decreasing STAT1 phosphorylation2.
- This delayed IFN type 1 can potentially lead to a pro-inflammatory cytokines response3.
- Though some potential benefit has been demonstrated, a lack of significant improvement was possibly explained by the mechanisms of suppression of the IFN signaling pathway used by SARS-CoV and MERS-CoV.2, 3
During COVID-19 outbreak
- The Orf3 and Orf6 proteins of SARS-CoV-2 are truncated and have therefore potentially lost their anti-IFN function.2
- In vitro study showed that SARS-CoV-2 is unable to completely inhibit IFN-1 response compared to SARS-CoV1.
- Significant reduction in viral replication at 24 and 48 hours was seen
- Infected cells were capable of inducing STAT1 phosphorylation by 48 hours post-infection;
- Augmented levels of ISGs were produced.
- As opposed to SARS-CoV, SARS-CoV-2 could be more sensitive to recombinant IFN-1α pretreatment in vitro, lacking the capacity to restrain a type 1 interferon response.1-2
This data comes from a study conducted at the University of Texas Medical Branch in Galveston, Texas, with firstly, VeroE6 cells that were incubated with 1000 units/mL of recombinant type 1 IFN alpha 18 hours prior to infection with SARS-CoV-2 and that were compared with cells free of IFN-1. Secondly, IFN competent Calu3 2B4 cells were infected with SARS-CoV-2. Multiple outcomes were examined for both cell types, such as titers of viral and host proteins, viral replication and ISG expression.
Clinical trials for Interferons are currently underway
Sources:
- Lokugamage, K.G., Hage, A., Schindewolf, C., et al (April 9, 2020). SARS-CoV-2 is sensitive to type I interferon pretreatment. bioRxiv. https://doi.org/10.1101/2020.03.07.982264
- Sallard, E., Lescure, F., Yazdanpanah, Y., et al (April 7, 2020). Type 1 interferons as a potential treatment against COVID-19. Antiviral Research. https://doi.org/10.1016/j.antiviral.2020.104791
- Prompetchara E., Ketloy C., Palaga T. (March 2020). Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic. Asian Pacific Journal of Allergy and Immunology. https://doi.org/10.12932/AP-200220-0772