• Iulia Popescu, Mark E Snyder, Carlo J Iasella, Stefanie J Hannan, Ritchie Koshy, Robin Burke, Antu Das, Mark J Brown, Emily J Lyons, Sophia C Lieber, Xiaoping Chen, John C Sembrat, Payal Bhatt, Evan Deng, Xiaojing An, Kelsey Linstrum, Georgios Kitsios, Ioannis Konstantinidis, Melissa Saul, Daniel J Kass, Jonathan K Alder, Bill B Chen, Elizabeth A Lendermon, Silpa Kilaru, Bruce Johnson, Joseph M Pilewski, Joseph E Kiss, Alan H Wells, Alison Morris, Bryan J McVerry, Deborah K McMahon, Darrell J Triulzi, Kong Chen, Pablo G Sanchez, and John F McDyer.
• Division of Pulmonary, Allergy, and Critical Care Medicine.
• Am. J. Respir. Crit. Care Med. 2022 Jun 15; 205 (12): 140314181403-1418.

AbstractRationale: 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-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 (n = 76; R = -0.797; P < 0.0001). In vitro 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 (P < 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. Conclusions: 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.

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