Blockade of TNF-alpha and IFN-gamma induced PD-L1 alleviates lymphopenia by SARS-CoV-2

Patients with severe COVID-19 often suffer from lymphopenia, which is linked to T cell sequestration, cytokine storm and mortality. However, it remains largely unknown how SARS-CoV-2 induces lymphopenia. Here, we studied the transcriptomic profile and epigenomic alterations involved in cytokine production by SARS-CoV-2-infected cells. We adopted a reverse time-order gene coexpression network (TO-GCN) approach to analyze time-series RNA-sequencing data, revealing epigenetic modifications at the late stage of viral egress. Furthermore, we identified SARS-CoV-2-activated TNF-a/NF-kB and IFN-a/IRF1pathways contributing to viral infection and COVID-19 severity through epigenetic analysis of H3K4me3 ChIP-sequencing. Cross-referencing of our transcriptomic and epigenomic datasets revealed that coupling of TNF-a/NF-kB and IFN-gamma/IRF1 pathways mediate PD-L1 immunosuppressive programs. Interestingly, we observed higher PD-L1 expression in Omicron-infected cells than SARS-CoV-2 infected cells. Blocking PD-L1 at an early stage of virally-infected AAV-hACE2 mice significantly recovered lymphocyte counts and lowered inflammatory cytokine levels. Our findings indicate that targeting the SARS-CoV-2-mediated TNF-a and IFN-gamma-PD-L1 axis may represent an alternative strategy to reduce COVID-19 severity.