Abstract Body: BACKGROUND: OHCA has been characterized at times as a “sepsis-like” syndrome, but the shared and distinct features of the immune response in OHCA and sepsis have not been precisely defined. We hypothesized that rigorous comparison of OHCA and sepsis at single-cell resolution would define shared immune states that form an “universal” immune response to critical illness.
METHODS: We integrated two published single-cell (sc) RNA-sequencing (seq) datasets of peripheral blood mononuclear cells (PBMCs) from patients with sepsis (at ICU admission) with our previously published scRNA-seq dataset of PBMC from patients at 6h and 48h post-OHCA. The dataset’s subpopulation structure was inferred using Latent Cellular State Analysis (LCA). Marker genes and differential gene expression were identified using the negative binomial model with independent dispersions (NBID) with batch effect inferred using surrogate variable algorithm (SVA). Validation studies were performed on PBMC from OHCA and sepsis patients: Spectral flow cytometry; flow cytometry sorting of NECTIN2+ monocytes for bulk RNA-seq analysis; and in vitro functional studies with anti-NECTIN2 blocking mAb.
RESULTS: Two CD14+ monocyte subclusters were shared by OHCA and sepsis. Monocyte cluster 3 (M3), expressing ALOX5AP, CLU, and S100A8/9, was enriched in patients 48h post-OHCA and resembled an “immunosuppressive” monocyte subtype previously identified in sepsis. The NECTIN2+ monocyte cell cluster M4 had markedly increased abundance 6h post-OHCA in patients with poor neurological outcomes. In sepsis, increased expression of the NECTIN2+ monocyte gene signature was associated with sepsis endotypes with worse mortality and immunosuppression. We validated the increased abundance of the NECTIN2+ monocyte subset in OHCA and sepsis PBMC by spectral flow cytometry and global transcriptomic profiling of NECTIN2+ monocytes (R²=0.62 between OHCA and sepsis). In interactome analysis both OHCA and sepsis NECTIN2+ monocytes interacted with NK cells via the NECTIN2-TIGIT axis; and in-vitro blockade of the immune checkpoint NECTIN2 increased inflammatory cytokine production by NK cells.
CONCLUSIONS: Two CD14+ monocyte cell states are shared in OHCA and sepsis PBMC. A NECTIN2+ monocyte subset is associated with poor clinical outcomes in both diseases and may regulate NK cells via immune checkpoints. These monocyte subsets may represent a universal immune response to critical illness.