Biology subjects

Keegan, J.

Publications and source records attributed to Keegan, J..

5 recordsLinked to original sources

bioRxiv2026

Functional inactivation of the telomerase chaperone TCAB1 primes cells for the activation of ALT in osteosarcoma

Activation of the alternative lengthening of telomeres (ALT) pathway accounts for cellular immortalization in 75% of pediatric osteosarcoma. ALT does not rely on a single enzyme but instead, catalyzes telomere elongation via homologous recombination. There has been steady progress in defining the mechanisms that regulate the ALT pathway. However, the spectrum of genetic mutations that underlie activation of ALT remains unclear. Osteosarcomas, like many cancers, frequently harbor inactivating mutations in the tumor suppressor gene TP53. However, instead of single nucleotide variants that lead to expression of mutant TP53 protein, osteosarcoma tumors often acquire unique structural variations within the first intron of the TP53 gene leading to complete gene inactivation. TP53 is located on chromosome 17p13.1 in a head-to-head orientation and partially overlapping with the gene WRAP53 (WD repeat containing antisense to TP53). WRAP53, also known as TCAB1, is an RNA chaperone that is an essential component of the telomerase holoenzyme. TCAB1 functions to facilitate trafficking of the telomerase RNA (hTR) within the nucleus to ensure assembly and localization of the telomerase enzyme to telomere ends to promote telomere elongation. Loss of TCAB1 function abolishes telomerase activity, driving progressive telomere attrition. Here, using whole-genome sequencing of osteosarcoma samples we identified SVs within the TP53 gene that not only compromise TP53, but also inactivate TCAB1. These TCAB1 SVs were prevalent in approximately 40% of ALT positive osteosarcoma tumors suggesting that functional inactivation of the telomerase holoenzyme may be an early and previously unrecognized event contributing to the activation of the ALT pathway.

cancer biology↗

bioRxiv2024

Blood immunophenotyping identifies distinct kidney histopathology and outcomes in patients with lupus nephritis

Lupus nephritis (LN) is a frequent manifestation of systemic lupus erythematosus, and fewer than half of patients achieve complete renal response with standard immunosuppressants. Identifying non-invasive, blood-based pathologic immune alterations associated with renal injury could aid therapeutic decisions. Here, we used mass cytometry immunophenotyping of peripheral blood mononuclear cells in 145 patients with biopsy-proven LN and 40 healthy controls to evaluate the heterogeneity of immune activation in patients with LN and to identify correlates of renal parameters and treatment response. Unbiased analysis identified 3 immunologically distinct groups of patients with LN that were associated with different patterns of histopathology, renal cell infiltrates, urine proteomic profiles, and treatment response at one year. Patients with enriched circulating granzyme B+ T cells at baseline showed more severe disease and increased numbers of activated CD8 T cells in the kidney, yet they had the highest likelihood of treatment response. A second group characterized primarily by a high type I interferon signature had a lower likelihood of response to therapy, while a third group appeared immunologically inactive by immunophenotyping at enrollment but with chronic renal injuries. Main immune profiles could be distilled down to 5 simple cytometric parameters that recapitulate several of the associations, highlighting the potential for blood immune profiling to translate to clinically useful non-invasive metrics to assess immune-mediated disease in LN.

immunology↗

bioRxiv2023

Deep immunophenotyping reveals circulating activated lymphocytes in individuals at risk for rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease with currently no universally highly effective prevention strategies. Identifying pathogenic immune phenotypes in At-Risk populations prior to clinical disease onset is crucial to establishing effective prevention strategies. Here, we applied mass cytometry to deeply characterize the immunophenotypes in blood from At-Risk individuals identified through the presence of serum antibodies to citrullinated protein antigens (ACPA) and/or first-degree relative (FDR) status (n=52), as compared to established RA (n=67), and healthy controls (n=48). We identified significant cell expansions in At-Risk individuals compared with controls, including CCR2+CD4+ T cells, T peripheral helper (Tph) cells, type 1 T helper cells, and CXCR5+CD8+ T cells. We also found that CD15+ classical monocytes were specifically expanded in ACPA-negative FDRs, and an activated PAX5low naive B cell population was expanded in ACPA-positive FDRs. Further, we developed an "RA immunophenotype score" classification method based on the degree of enrichment of cell states relevant to established RA patients. This score significantly distinguished At-Risk individuals from controls. In all, we systematically identified activated lymphocyte phenotypes in At-Risk individuals, along with immunophenotypic differences among both ACPA+ and ACPA-FDR At-Risk subpopulations. Our classification model provides a promising approach for understanding RA pathogenesis with the goal to further improve prevention strategies and identify novel therapeutic targets.

genomics↗

bioRxiv2021

Longitudinal immune cell profiling in early systemic lupus erythematosus

ObjectiveTo investigate the immune cell profiling and their longitudinal changes in systemic lupus erythematosus (SLE). MethodsWe employed mass cytometry with three different 38-39 marker panels (Immunophenotyping, T cell/monocyte, and B cell) in cryopreserved peripheral blood mononuclear cells (PBMCs) from nine patients with early SLE, 15 patients with established SLE, and 14 non-inflammatory controls. We used machine learning-driven clustering, FlowSOM (Flow Self-Organizing Maps) and dimensional reduction with tSNE (t-distributed Stochastic Neighbor Embedding) to identify unique cell populations in early and established SLE. For the nine early SLE patients, longitudinal mass cytometry analysis was applied to PBMCs at three time points (at enrollment, six months post-enrollment, and one year post-enrollment). Serum samples were also assayed for 65 cytokines by Luminex multiplex assay, and associations between cell types and cytokines/chemokines assessed. ResultsT peripheral helper cells (Tph cells), T follicular helper cells (Tfh cells) and several Ki67+ proliferating subsets (ICOS+ Ki67+ CD8 T cells, Ki67+ regulatory T cells, CD19int Ki67hi plasmablasts, and Ki67hi PU.1hi monocytes) were increased in early SLE. Longitudinal mass cytometry and multiplex serum cytokine assays of samples from early SLE patients revealed that Tfh cells and CXCL10 decreased at one year post-enrollment. CXCL13 correlated positively with several of the expanded cell populations in early SLE. ConclusionsTwo major helper T cell subsets and unique Ki67+ proliferating immune cell subsets were expanded in the early phase of SLE, and the immunologic features characteristic of early SLE evolved over time.

immunology↗

bioRxiv2018

High dimensional analyses of cells dissociated from cryopreserved synovial tissue

BackgroundDetailed molecular analyses of cells from rheumatoid arthritis (RA) synovium hold promise in identifying cellular phenotypes that drive tissue pathology and joint damage. The Accelerating Medicines Partnership (AMP) RA/SLE network aims to deconstruct autoimmune pathology by examining cells within target tissues through multiple high-dimensional assays. Robust standardized protocols need to be developed before cellular phenotypes at a single cell level can be effectively compared across patient samples.\n\nMethodsMultiple clinical sites collected cryopreserved synovial tissue fragments from arthroplasty and synovial biopsy in a 10%-DMSO solution. Mechanical and enzymatic dissociation parameters were optimized for viable cell extraction and surface protein preservation for cell sorting and mass cytometry, as well as for reproducibility in RNA sequencing (RNA-seq). Cryopreserved synovial samples were collectively analyzed at a central processing site by a custom-designed and validated 35-marker mass cytometry panel. In parallel, each sample was flow sorted into fibroblast, T cell, B cell, and macrophage suspensions for bulk population RNA-seq and plate-based single cell CEL-Seq2 RNA-seq.\n\nResultsUpon dissociation, cryopreserved synovial tissue fragments yielded a high frequency of viable cells, comparable to samples undergoing immediate processing. Optimization of synovial tissue dissociation across six clinical collection sites with [~]30 arthroplasty and [~]20 biopsy samples yielded a consensus digestion protocol using 100{micro}g/mL of Liberase TL enzyme. This protocol yielded immune and stromal cell lineages with preserved surface markers and minimized variability across replicate RNA-seq transcriptomes. Mass cytometry analysis of cells from cryopreserved synovium distinguished: 1) diverse fibroblast phenotypes, 2) distinct populations of memory B cells and antibody-secreting cells, and 3) multiple CD4+ and CD8+ T cell activation states. Bulk RNA sequencing of sorted cell populations demonstrated robust separation of synovial lymphocytes, fibroblasts, and macrophages. Single cell RNA-seq produced transcriptomes of over 1000 genes/cell, including transcripts encoding characteristic lineage markers identified.\n\nConclusionWe have established a robust protocol to acquire viable cells from cryopreserved synovial tissue with intact transcriptomes and cell surface phenotypes. A centralized pipeline to generate multiple high-dimensional analyses of synovial tissue samples collected across a collaborative network was developed. Integrated analysis of such datasets from large patient cohorts may help define molecular heterogeneity within RA pathology and identify new therapeutic targets and biomarkers.

immunology↗