Proteomic Analyses in COVID-19-Associated Secondary Hemophagocytic Lymphohistiocytosis.

Context: COVID-19 has been associated with features of a cytokine storm syndrome with some patients sharing features with the hyperinflammatory disorder, secondary hemophagocytic lymphohistiocytosis (sHLH).

Hypothesis: We hypothesized that proteins associated with sHLH from other causes will be associated with COVID-sHLH and that subjects with fatal COVID-sHLH would have defects in immune-related pathways.

Methods and models: We identified two cohorts of adult patients presenting with COVID-19 at two tertiary care hospitals in Seattle, Washington in 2020 and 2021. In this observational study, we assessed clinical laboratory values and plasma proteomics. Subjects identified as having sHLH (ferritin > 1000 plus cytopenias in two or more lineages [WBC < 5000 odds ratio [OR] ANC (absolute neutrophil count) < 1000, hemoglobin < 9 or hematocrit < 27, platelets < 100,000], and elevated transaminases [either AST (aspartate aminotransferase) or ALT (alanine aminotransferase) > 30] OR subjects with a ferritin > 3000) were compared with those with COVID-19 without sHLH. We identified 264 patients with COVID-19 of whom 24 met our sHLH definition. Eight patients who died of COVID-sHLH underwent genomic sequencing to identify variants in immune-related genes.

Results: Nine percent of enrolled COVID-19 subjects met our defined criteria for sHLH (n = 24/264). Using broad serum proteomic approaches (O-link and SomaScan), we identified three proteins increased in subjects with COVID-19-associated sHLH (soluble PD-L1 [sPD-L1], tumor necrosis factor-R1, and interleukin [IL]-18BP, p < 0.05 for O-link and false discovery rate < 0.05 for SomaScan), supporting a role for proteins previously associated with other forms of sHLH (IL-18BP and soluble tumor necrosis factor receptor 1). We also identified candidate proteins and pathways associated with COVID-sHLH, including sPD-L1 and the syntaxin pathway. We detected pathogenic variants in DOCK8 and TMPRSS15 in deceased individuals with COVID-sHLH, further suggesting that alterations in immune-related processes may contribute to hyperinflammation and fatal outcomes in COVID-19.

Interpretations and conclusions: Proteins increased in COVID-19-associated sHLH, such as sPD-L1, and pathways, such as the syntaxin pathway, suggest important roles for the immune response in driving sHLH in the context of COVID-19.