No abstract

No abstract

While inhibitory Siglec receptors are known to regulate myeloid cells, less is known about their expression and function in lymphocytes subsets. Here we identified Siglec-7 as a glyco-immune checkpoint expressed on non-exhausted effector memory CD8+ T cells that exhibit high functional and metabolic capacities. Seahorse analysis revealed higher basal respiration and glycolysis levels of Siglec-7+ CD8+ T cells in steady state, and particularly upon activation. Siglec-7 polarization into the T cell immune synapse was dependent on sialoglycan interactions in trans and prevented actin polarization and effective T cell responses. Siglec-7 ligands were found to be expressed on both leukemic stem cells and acute myeloid leukemia (AML) cells suggesting the occurrence of glyco-immune checkpoints for Siglec-7+ CD8+ T cells, which were found in patients’ peripheral blood and bone marrow. Our findings project Siglec-7 as a glyco-immune checkpoint and therapeutic target for T cell-driven disorders and cancer.

Variants within the gene encoding for the transcription factor Interferon Regulatory Factor 6 (IRF6) are associated with syndromic and non-syndromic Cleft Lip/Palate (CLP) cases. IRF6 plays a vital role in the regulation of the proliferation/differentiation balance in keratinocytes and is involved in wound healing and migration. Since a fraction of CLP patients undergoing corrective cleft surgery experience wound healing complications, IRF6 represents an interesting candidate gene linking the two processes. However, Irf6 function has been mainly studied in mice and knowledge on IRF6 in human cells remains sparse. Here, we aimed to elucidate the role of IRF6 in human postnatal skin- and oral mucosa-derived keratinocytes. To do so, we applied CRISPR/Cas9 to ablate IRF6 in two TERT-immortalized keratinocyte cultures, which we used as model cell lines. We show that IRF6 controls the appearance of single cells and colonies, with the latter being less cohesive in its absence. Consequently, IRF6 knockout keratinocytes often moved as single cells instead of a collective epithelial sheet migration but maintained their epithelial character. Lack of IRF6 triggered severe keratinocyte differentiation defects, which were already apparent in the stratum spinosum and extended to the stratum corneum in 3D organotypic skin cultures, while it did not alter their growth rate. Finally, proteomics revealed that most of the differentially expressed proteins in the absence of IRF6 could be associated with differentiation, cell-cell adhesion as well as immune response. Our data expand the knowledge on IRF6 in human postnatal keratinocytes, which will help to better understand IRF6-related pathologies.

Mutations in genes encoding molecular chaperones can lead to chaperonopathies, but none have so far been identified causing congenital disorders of glycosylation. Here we identified two maternal half-brothers with a novel chaperonopathy, causing impaired protein O-glycosylation. The patients have a decreased activity of T-synthase ( C1GALT1 ), an enzyme that exclusively synthesizes the T-antigen, a ubiquitous O-glycan core structure and precursor for all extended O-glycans. The T-synthase function is dependent on its specific molecular chaperone Cosmc, which is encoded by X-chromosomal C1GALT1C1 . Both patients carry the hemizygous variant c.59C>A (p.Ala20Asp; A20D-Cosmc) in C1GALT1C1 . They exhibit developmental delay, immunodeficiency, short stature, thrombocytopenia, and acute kidney injury (AKI) resembling atypical hemolytic uremic syndrome. Their heterozygous mother and maternal grandmother show an attenuated phenotype with skewed X-inactivation in blood. AKI in the male patients proved fully responsive to treatment with the complement inhibitor Eculizumab. This germline variant occurs within the transmembrane domain of Cosmc, resulting in dramatically reduced expression of the Cosmc protein. Although A20D-Cosmc is functional, its decreased expression, though in a cell or tissue-specific manner, causes a large reduction of T-synthase protein and activity, which accordingly leads to expression of varied amounts of pathological Tn-antigen (GalNAcα1-O-Ser/Thr/Tyr) on multiple glycoproteins. Transient transfection of patient lymphoblastoid cells with wild-type C1GALT1C1 partially rescued the T-synthase and glycosylation defect. Interestingly, all four affected individuals have high levels of galactose-deficient IgA1 in sera. These results demonstrate that the A20D-Cosmc mutation defines a novel O-glycan chaperonopathy and causes the altered O-glycosylation status in these patients.