Cysteine supplementation reverses immune dysfunction in cancer patients with severe COVID-19

Severe COVID-19 infection in patients with cancer is characterized by a unique pattern of immunologic dysfunction including muted adaptive immune responses. The molecular drivers of immune dysfunction in cancer patients with severe COVID-19 remain unclear, and therapeutic strategies to overcome immune dysfunction in this setting have not been identified. We performed integrated proteomic and metabolomic profiling of matched cohorts of cancer and non-cancer patients with or without COVID-19 and identified dysfunctional cysteine metabolism as uniquely associated with severe COVID-19 in cancer patients. Treatment of patients with cancer and steroid-refractory COVID-19 with N-acetylcysteine in a prospective clinical trial (NCT04374461) improved clinical outcomes compared with disease severity-matched hospitalized patients during the period immediately preceding clinical trial initiation. N-AC treatment reduced circulating markers of innate inflammation, decreased severe disease-associated MHC-II low monocytes, and increased circulating CD8+ T cell abundance, activation, and effector differentiation. Mechanistically, N-AC reduced prostaglandin E2-driven interactions between suppressive monocytes and T cells, which we confirmed was sufficient to limit T cell expansion and effector differentiation in a dose- and avidity-dependent fashion. Moreover, N-AC reduced the activity of inhibitory, redox sensitive transcription factors such as KLF6, enabling clonal expansion and effector T cell differentiation. We confirmed these observations in two murine models of severe respiratory viral infection, in which N-AC treatment significantly enhanced lung-infiltrating CD8+ T cell abundance. These findings establish cysteine supplementation as a viable therapeutic strategy to reverse redox-driven immune dysregulation in severe respiratory viral infection, particularly in the high-risk cancer population.