Principal Investigator Shanghai Jiao Tong University School of Medicine, Shanghai, China., Shanghai, China (People's Republic)
Introduction/Rationale: Dysregulated immune homeostasis during the acute phase of COVID-19 has been recognized as a major determinant of disease severity and long-term sequelae. Regulatory T (Treg) cells are essential for maintaining immune homeostasis, and FOXP3 serves as their lineage-defining transcription factor. Therefore, investigating the relationship between Treg cells and the inflammation driven by SARS-CoV-2 infection is essential.
Methods: We collected blood samples from COVID-19 patients for flow cytometry analysis and inflammatory markers detection. The in vivo data were secured through parallel experiments conducted in established SARS-CoV-2-infected hamster and mouse models. The mechanistic details of our proposed pathway were confirmed by a suite of molecular and biochemical experiments.
Results: Here, we demonstrated that the frequency and suppressive capacity of Treg cells were markedly reduced in COVID-19 patients, correlating strongly with elevated systemic inflammatory markers. Mechanistically, we identified the SARS-CoV-2 protein ORF8 as a virulence factor that directly interacted with FOXP3 and promoted its degradation through chaperone-mediated autophagy (CMA). Using hamster and mouse infection models, we unveiled that viral strain carrying ORF8 impaired Treg responses and exacerbated inflammation in vivo, whereas ORF8-deficient strains elicited milder immune perturbations. Furthermore, ORF8 recruited the acetyltransferase ACAT1 to acetylate FOXP3 at K416, generating a KFERQ-like motif that enabled HSC70 recognition and subsequent lysosomal degradation. Inhibition of ACAT1 effectively blocked ORF8-induced FOXP3 degradation.
Conclusion: Collectively, our findings uncover a previously unrecognized mechanism by which SARS-CoV-2 disrupts immune homeostasis through the ORF8–ACAT1–FOXP3–CMA axis, providing a potential therapeutic strategy to restore immune homeostasis and mitigate hyperinflammation in COVID-19.
