Correlates of protection for booster doses of the SARS-CoV-2 vaccine BNT162b2.

Vaccination, especially with multiple doses, provides substantial population-level protection against COVID-19, but emerging variants of concern (VOC) and waning immunity represent significant risks at the individual level. Here we identify correlates of protection (COP) in a multicenter prospective study following 607 healthy individuals who received three doses of the Pfizer-BNT162b2 vaccine approximately six months prior to enrollment. We compared 242 individuals who received a fourth dose to 365 who did not. Within 90 days of enrollment, 239 individuals contracted COVID-19, 45% of the 3-dose group and 30% of the four-dose group. The fourth dose elicited a significant rise in antibody binding and neutralizing titers against multiple VOCs reducing the risk of symptomatic infection by 37% [95%CI, 15%-54%]. However, a group of individuals, characterized by low baseline titers of binding antibodies, remained susceptible to infection despite significantly increased neutralizing antibody titers upon boosting. A combination of reduced IgG levels to RBD mutants and reduced VOC-recognizing IgA antibodies represented the strongest COP in both the 3-dose group (HR = 6.34, p = 0.008) and four-dose group (HR = 8.14, p = 0.018). We validated our findings in an independent second cohort. In summary combination IgA and IgG baseline binding antibody levels may identify individuals most at risk from future infections.

Induction of bronchus-associated lymphoid tissue is an early life adaptation for promoting human B cell immunity.

Infants and young children are more susceptible to common respiratory pathogens than adults but can fare better against novel pathogens like severe acute respiratory syndrome coronavirus 2. The mechanisms by which infants and young children mount effective immune responses to respiratory pathogens are unknown. Through investigation of lungs and lung-associated lymph nodes from infant and pediatric organ donors aged 0-13 years, we show that bronchus-associated lymphoid tissue (BALT), containing B cell follicles, CD4+ T cells and functionally active germinal centers, develop during infancy. BALT structures are prevalent around lung airways during the first 3 years of life, and their numbers decline through childhood coincident with the accumulation of memory T cells. Single-cell profiling and repertoire analysis reveals that early life lung B cells undergo differentiation, somatic hypermutation and immunoglobulin class switching and exhibit a more activated profile than lymph node B cells. Moreover, B cells in the lung and lung-associated lymph nodes generate biased antibody responses to multiple respiratory pathogens compared to circulating antibodies, which are mostly specific for vaccine antigens in the early years of life. Together, our findings provide evidence for BALT as an early life adaptation for mobilizing localized immune protection to the diverse respiratory challenges during this formative life stage.

Set7/9 impacts COL2A1 expression through binding and repression of SirT1 histone deacetylation.

Type II collagen is a key cartilaginous extracellular protein required for normal endochondral development and cartilage homeostasis. COL2A1 gene expression is positively regulated by the NAD-dependent protein deacetylase Sirtuin 1 (SirT1), through its ability to bind chromatin regions of the COL2A1 promoter and enhancer. Although SirT1/Sox9 binding on the enhancer site of COL2A1 was previously demonstrated, little is known about its functional role on the gene promoter site. Here, we examined the mechanism by which promoter-associated SirT1 governs COL2A1 expression. Human chondrocytes were encapsulated in three-dimensional (3D) alginate beads where they exhibited upregulated COL2A1 mRNA expression and increased levels of SirT1 occupancy on the promoter and enhancer regions, when compared to monolayer controls. Chromatin immunoprecipitation (ChIP) analyses of 3D cultures showed augmented levels of the DNA-binding transcription factor SP1, and the histone methyltransferase Set7/9, on the COL2A1 promoter site. ChIP reChIP assays revealed that SirT1 and Set7/9 form a protein complex on the COL2A1 promoter region of 3D-cultured chondrocytes, which also demonstrated elevated trimethylated lysine 4 on histone 3 (3MeH3K4), a hallmark of Set7/9 methyltransferase activity. Advanced passaging of chondrocytes yielded a decrease in 3MeH3K4 and Set7/9 levels on the COL2A1 promoter and reduced COL2A1 expression, suggesting that the SirT1/Set7/9 complex is preferentially formed on the COL2A1 promoter and required for gene activation. Interestingly, despite SirT1 occupancy, its deacetylation targets (ie, H3K9/14 and H4K16) were found acetylated on the COL2A1 promoter of 3D-cultured chondrocytes. A possible explanation for this phenotype is the enrichment of the histone acetyltransferases P300 and GCN5 on the COL2A1 promoter of3 D-cultured chondrocytes. Our study indicates that Set7/9 prevents the histone deacetylase activity of SirT1, potentiating euchromatin formation on the promoter site of COL2A1 and resulting in morphology-dependent COL2A1 gene transactivation.

75-kd sirtuin 1 blocks tumor necrosis factor α-mediated apoptosis in human osteoarthritic chondrocytes.

OBJECTIVE: Sirtuin 1 (SirT1) has been implicated in the regulation of human cartilage homeostasis and chondrocyte survival. Exposing human osteoarthritic (OA) chondrocytes to tumor necrosis factor α (TNFα) generates a stable and enzymatically inactive 75-kd form of SirT1 (75SirT1) via cathepsin B-mediated cleavage. Because 75SirT1 is resistant to further degradation, we hypothesized that it has a distinct role in OA, and the present study was undertaken to identify this role. METHODS: The presence of cathepsin B and 75SirT in OA and normal human chondrocytes was analyzed. Confocal imaging of SirT1 was used to monitor its subcellular trafficking following TNFα stimulation. Coimmunofluorescence staining for cathepsin B, mitochondrial cytochrome oxidase subunit IV, and lysosome-associated membrane protein 1 together with SirT1 was performed. Human chondrocytes were tested for apoptosis by fluorescence-activated cell sorter analysis and immunoblotting for caspases 3 and 8. Human chondrocyte mitochondrial extracts were obtained and analyzed for 75SirT1-cytochrome c association. RESULTS: Confocal imaging and immunoblot analyses following TNFα challenge of human chondrocytes demonstrated that 75SirT1 was exported to the cytoplasm and colocalized with the mitochondrial membrane. Consistent with this, immunoprecipitation and immunoblot analyses revealed that 75SirT1 is enriched in mitochondrial extracts and associates with cytochrome c following TNFα stimulation. Preventing nuclear export of 75SirT1 or reducing levels of full-length SirT1 and 75SirT1 augmented chondrocyte apoptosis in the presence of TNFα. Levels of cathepsin B and 75SirT1 were elevated in OA versus normal chondrocytes. Additional analyses showed that human chondrocytes exposed to OA-derived synovial fluid generated the 75SirT1 fragment. CONCLUSION: These data suggest that 75SirT1 promotes chondrocyte survival following exposure to proinflammatory cytokines.