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

Rationale: 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. Objectives: 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. Methods: Using flow cytometry and single-cell RNA sequence analyses, we assessed SARS-CoV-2-specific responses in our cohort. Measurements and Main Results: 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 (P < 0.0001). In severe disease, immunodominant CD4(+) T-cell responses to Spike-1 (S1) produced increased in vitro TNF-alpha (tumor necrosis factor-alpha) but demonstrated impaired S1-specific proliferation and increased susceptibility to activation-induced cell death after antigen exposure. CD4(+) TNF-alpha(+) T-cell responses inversely correlated with absolute CD4(+) counts from patients with severe COVID-19 (n = 76; R = - 0.797; P < 0.0001). In vitro TNF-alpha 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 (P < 0.001). Single-cell RNA sequencing demonstrated marked downregulation of type-1 cytokines and NFKB 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-alpha compared with peripheral blood mononuclear cells. Conclusions: Together, our findings show CD4(+) dysfunction in severe COVID-19 is TNF-alpha/TNF receptor 1-dependent through immune mechanisms that may contribute to lymphopenia. TNF-alpha blockade may be beneficial in severe COVID-19.

Automated summary

This study found lymphopenia, especially CD4(+) lymphopenia, in severe COVID-19 patients, which is associated with TNF-alpha/TNF receptor 1-dependent immune mechanisms. In severe cases, CD4(+) T-cell response to Spike-1 (S1) is impaired, leading to increased susceptibility to activation-induced cell death. TNF-alpha blockade may be beneficial in severe COVID-19.