Single-cell atlas of healthy human blood unveils age-related loss of NKG2C+GZMB-CD8+ memory T cells and accumulation of type 2 memory T cells.

Extensive, large-scale single-cell profiling of healthy human blood at different ages is one of the critical pending tasks required to establish a framework for the systematic understanding of human aging. Here, using single-cell RNA/T cell receptor (TCR)/BCR-seq with protein feature barcoding, we profiled 317 samples from 166 healthy individuals aged 25-85 years old. From this, we generated a dataset from ∼2 million cells that described 55 subpopulations of blood immune cells. Twelve subpopulations changed with age, including the accumulation of GZMK+CD8+ T cells and HLA-DR+CD4+ T cells. In contrast to other T cell memory subsets, transcriptionally distinct NKG2C+GZMB-CD8+ T cells counterintuitively decreased with age. Furthermore, we found a concerted age-associated increase in type 2/interleukin (IL)4-expressing memory subpopulations across CD4+ and CD8+ T cell compartments (CCR4+CD8+ Tcm and Th2 CD4+ Tmem), suggesting a systematic functional shift in immune homeostasis with age. Our work provides novel insights into healthy human aging and a comprehensive annotated resource.

Reduced antibody activity against SARS-CoV-2 B.1.617.2 delta virus in serum of mRNA-vaccinated individuals receiving tumor necrosis factor-α inhibitors.

BACKGROUND: Although vaccines effectively prevent coronavirus disease 2019 (COVID-19) in healthy individuals, they appear to be less immunogenic in individuals with chronic inflammatory disease (CID) or receiving chronic immunosuppression therapy. METHODS: Here we assessed a cohort of 77 individuals with CID treated as monotherapy with chronic immunosuppressive drugs for antibody responses in serum against historical and variant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viruses after immunization with the BNT162b2 mRNA vaccine. FINDINGS: Longitudinal analysis showed the greatest reductions in neutralizing antibodies and Fc effector function capacity in individuals treated with tumor necrosis factor alpha (TNF-α) inhibitors (TNFi), and this pattern appeared to be worse against the B.1.617.2 delta virus. Within 5 months of vaccination, serum neutralizing titers of all TNFi-treated individuals tested fell below the presumed threshold correlate for antibody-mediated protection. However, TNFi-treated individuals receiving a third mRNA vaccine dose boosted their serum neutralizing antibody titers by more than 16-fold. CONCLUSIONS: Vaccine boosting or administration of long-acting prophylaxis (e.g., monoclonal antibodies) will likely be required to prevent SARS-CoV-2 infection in this susceptible population. FUNDING: This study was supported by grants and contracts from the NIH (R01 AI157155, R01AI151178, and HHSN75N93019C00074; NIAID Centers of Excellence for Influenza Research and Response (CEIRR) contracts HHSN272201400008C and 75N93021C00014; and Collaborative Influenza Vaccine Innovation Centers [CIVIC] contract 75N93019C00051).

Itaconate confers tolerance to late NLRP3 inflammasome activation.

Itaconate is a unique regulatory metabolite that is induced upon Toll-like receptor (TLR) stimulation in myeloid cells. Here, we demonstrate major inflammatory tolerance and cell death phenotypes associated with itaconate production in activated macrophages. We show that endogenous itaconate is a key regulator of the signal 2 of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation after long lipopolysaccharide (LPS) priming, which establishes tolerance to late NLRP3 inflammasome activation. We show that itaconate acts synergistically with inducible nitric oxide synthase (iNOS) and that the ability of various TLR ligands to establish NLRP3 inflammasome tolerance depends on the pattern of co-expression of IRG1 and iNOS. Mechanistically, itaconate accumulation upon prolonged inflammatory stimulation prevents full caspase-1 activation and processing of gasdermin D, which we demonstrate to be post-translationally modified by endogenous itaconate. Altogether, our data demonstrate that metabolic rewiring in inflammatory macrophages establishes tolerance to NLRP3 inflammasome activation that, if uncontrolled, can result in pyroptotic cell death and tissue damage.

Cellular and plasma proteomic determinants of COVID-19 and non-COVID-19 pulmonary diseases relative to healthy aging.

We examine the cellular and soluble determinants of coronavirus disease 2019 (COVID-19) relative to aging by performing mass cytometry in parallel with clinical blood testing and plasma proteomic profiling of ~4,700 proteins from 71 individuals with pulmonary disease and 148 healthy donors (25-80 years old). Distinct cell populations were associated with age (GZMK+CD8+ T cells and CD25low CD4+ T cells) and with COVID-19 (TBET-EOMES- CD4+ T cells, HLA-DR+CD38+ CD8+ T cells and CD27+CD38+ B cells). A unique population of TBET+EOMES+ CD4+ T cells was associated with individuals with COVID-19 who experienced moderate, rather than severe or lethal, disease. Disease severity correlated with blood creatinine and urea nitrogen levels. Proteomics revealed a major impact of age on the disease-associated plasma signatures and highlighted the divergent contribution of hepatocyte and muscle secretomes to COVID-19 plasma proteins. Aging plasma was enriched in matrisome proteins and heart/aorta smooth muscle cell-specific proteins. These findings reveal age-specific and disease-specific changes associated with COVID-19, and potential soluble mediators of the physiological impact of COVID-19.

Comprehensive Profiling of an Aging Immune System Reveals Clonal GZMK+ CD8+ T Cells as Conserved Hallmark of Inflammaging.

Systematic understanding of immune aging on a whole-body scale is currently lacking. We characterized age-associated alterations in immune cells across multiple mouse organs using single-cell RNA and antigen receptor sequencing and flow cytometry-based validation. We defined organ-specific and common immune alterations and identified a subpopulation of age-associated granzyme K (GZMK)-expressing CD8+ T (Taa) cells that are distinct from T effector memory (Tem) cells. Taa cells were highly clonal, had specific epigenetic and transcriptional signatures, developed in response to an aged host environment, and expressed markers of exhaustion and tissue homing. Activated Taa cells were the primary source of GZMK, which enhanced inflammatory functions of non-immune cells. In humans, proportions of the circulating GZMK+CD8+ T cell population that shares transcriptional and epigenetic signatures with mouse Taa cells increased during healthy aging. These results identify GZMK+ Taa cells as a potential target to address age-associated dysfunctions of the immune system.

Complement activation on neutrophils initiates endothelial adhesion and extravasation.

Neutrophils are essential to the pathogenesis of many inflammatory diseases. In the autoantibody-mediated K/BxN model of inflammatory arthritis, the alternative pathway (AP) of complement and Fc gamma receptors (FcγRs) are required for disease development while the classical pathway is dispensable. The reason for this differential requirement is unknown. We show that within minutes of K/BxN serum injection complement activation (CA) is detected on circulating neutrophils, as evidenced by cell surface C3 fragment deposition. CA requires the AP factor B and FcγRs but not C4, implying that engagement of FcγRs by autoantibody or immune complexes directly triggers AP C3 convertase assembly. The absence of C5 does not prevent CA on neutrophils but diminishes the upregulation of adhesion molecules. In vivo two-photon microscopy reveals that CA on neutrophils is critical for neutrophil extravasation and generation of C5a at the site of inflammation. C5a stimulates the release of neutrophil proteases, which contribute to the degradation of VE-cadherin, an adherens junction protein that regulates endothelial barrier integrity. C5a receptor antagonism blocks the extracellular release of neutrophil proteases, suppressing VE-cadherin degradation and neutrophil transendothelial migration in vivo. These results elucidate the AP-dependent intravascular neutrophil-endothelial interactions that initiate the inflammatory cascade in this disease model but may be generalizable to neutrophil extravasation in other inflammatory processes.