St. Jude Children’s Research Hospital scientists have discovered a potential strategy to prevent life-threatening inflammation, lung damage and organ failure in patients with COVID-19. The research appeared online in the journal Cell.
The scientists identified the drugs after discovering that the hyperinflammatory immune response associated with COVID-19 leads to tissue damage and multi-organ failure in mice by triggering inflammatory cell death pathways. The researchers detailed how the inflammatory cell death signaling pathway worked, which led to potential therapies to disrupt the process.
The infection is marked by increased blood levels of multiple cytokines. These small proteins are secreted primarily by immune cells to ensure a rapid response to restrict the virus. Some cytokines also trigger inflammation.
The phrase cytokine storm has been used to describe the dramatically elevated cytokine levels in the blood and other immune changes that have also been observed in COVID-19, sepsis and inflammatory disorders such as hemophagocytic lymphohistiocytosis (HLH). But the specific pathways that initiate the cytokine storm and the subsequent inflammation, lung damage and organ failure in COVID-19 and the other disorders was unclear. The cellular and molecular mechanisms that comprehensively define cytokine storm was also lacking.
The team at St Jude focused on a select set of the most elevated cytokines in COVID-19 patients. The scientists showed that no single cytokine induced cell death in innate immune cells.
The St. Jude investigators then tried 28 cytokine combinations and found just one duo that, working together, induced a form of inflammatory cell death previously described by the researchers as PANoptosis. The cytokines are tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. PANoptosis is a unique type of cell death that features coordination of three different cell death pathways—pyroptosis, apoptosis and necroptosis. PANoptosis fuels inflammation through cell death, resulting in the release of more cytokines and inflammatory molecules.
The investigators showed that blocking individual cell death pathways was ineffective in stopping cell death caused by TNF-alpha and IFN-gamma. A closer look at proteins that make up the pathways identified several, including caspase-8 and STAT1, that were essential for PANoptosis in response to these cytokines. Deleting those proteins blocked PANoptosis in innate immune cells called macrophages.
Because TNF-alpha and IFN-gamma are produced during COVID-19 and cause inflammatory cell death, the investigators questioned whether these cytokines were responsible for the clinical manifestations and deadly effects of the disease. They found that the TNF-alpha and IFN-gamma combination triggered tissue damage and inflammation that mirror the symptoms of COVID-19 along with rapid death.
Neutralizing antibodies against TNF-alpha and IFN-gamma are currently used to treat inflammatory diseases in the clinic. The investigators found that treatment with these antibodies protected mice from death associated with SARS-CoV-2 infection, sepsis, HLH and cytokine shock.
Based on this fundamental research, the researchers have proposed a definition of cytokine storm that puts the cytokine-mediated inflammatory cell death via PANoptosis at the center of the process. The researchers noted that PANoptosis results in the release of more cytokines and inflammatory molecules, which intensifies systemic inflammation.
