CD4⁺ T-Cell Dysfunction in Severe COVID-19 Disease Is Tumor Necrosis Factor-α/Tumor Necrosis Factor Receptor 1-Dependent.

Abstract

<b>Rationale:</b> Lymphopenia is common in severe coronavirus disease (COVID-19), yet the immune mechanisms are poorly understood. As inflammatory cytokines are increased in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we hypothesized a role in contributing to reduced T-cell numbers. <b>Objectives:</b> We sought to characterize the functional SARS-CoV-2 T-cell responses in patients with severe versus recovered, mild COVID-19 to determine whether differences were detectable. <b>Methods:</b> Using flow cytometry and single-cell RNA sequence analyses, we assessed SARS-CoV-2-specific responses in our cohort. <b>Measurements and Main Results:</b> In 148 patients with severe COVID-19, we found lymphopenia was associated with worse survival. CD4⁺ lymphopenia predominated, with lower CD4⁺/CD8⁺ ratios in severe COVID-19 compared with patients with mild disease (<i>P</i> < 0.0001). In severe disease, immunodominant CD4⁺ T-cell responses to Spike-1 (S1) produced increased <i>in vitro</i> TNF-α (tumor necrosis factor-α) but demonstrated impaired S1-specific proliferation and increased susceptibility to activation-induced cell death after antigen exposure. CD4⁺TNF-α⁺ T-cell responses inversely correlated with absolute CD4⁺ counts from patients with severe COVID-19 (<i>n</i> = 76; <i>R</i> = -0.797; <i>P</i> < 0.0001). <i>In vitro</i> TNF-α blockade, including infliximab or anti-TNF receptor 1 antibodies, strikingly rescued S1-specific CD4⁺ T-cell proliferation and abrogated S1-specific activation-induced cell death in peripheral blood mononuclear cells from patients with severe COVID-19 (<i>P</i> < 0.001). Single-cell RNA sequencing demonstrated marked downregulation of type-1 cytokines and NFκB signaling in S1-stimulated CD4⁺ cells with infliximab treatment. We also evaluated BAL and lung explant CD4⁺ T cells recovered from patients with severe COVID-19 and observed that lung T cells produced higher TNF-α compared with peripheral blood mononuclear cells. <b>Conclusions:</b> Together, our findings show CD4⁺ dysfunction in severe COVID-19 is TNF-α/TNF receptor 1-dependent through immune mechanisms that may contribute to lymphopenia. TNF-α blockade may be beneficial in severe COVID-19.