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Mutations in GUCY2D, the gene encoding retinal guanylate cyclase-1 (retGC1), are the leading cause of autosomal dominant cone-rod dystrophy (CORD6). Significant progress toward clinical application of gene replacement therapy for Leber congenital amaurosis (LCA) due to recessive mutations in GUCY2D (LCA1) has been made, but a different approach is needed to treat CORD6 where gain of function mutations cause dysfunction and dystrophy. The CRISPR/Cas9 gene editing system efficiently disrupts genes at desired loci, enabling complete gene knockout or homology directed repair. Here, adeno-associated virus (AAV)-delivered CRISPR/Cas9 was used specifically to edit/disrupt this gene's early coding sequence in mouse and macaque photoreceptors in vivo, thereby knocking out retGC1 expression and demonstrably altering retinal function and structure. Neither preexisting nor induced Cas9-specific T-cell responses resulted in ocular inflammation in macaques, nor did it limit GUCY2D editing. The results show, for the first time, the ability to perform somatic gene editing in primates using AAV-CRISPR/Cas9 and demonstrate the viability this approach for treating inherited retinal diseases in general and CORD6 in particular.

Leber congenital amaurosis type 10 is a severe retinal dystrophy caused by mutations in the CEP290 gene1,2. We developed EDIT-101, a candidate genome-editing therapeutic, to remove the aberrant splice donor created by the IVS26 mutation in the CEP290 gene and restore normal CEP290 expression. Key to this therapeutic, we identified a pair of Staphylococcus aureus Cas9 guide RNAs that were highly active and specific to the human CEP290 target sequence. In vitro experiments in human cells and retinal explants demonstrated the molecular mechanism of action and nuclease specificity. Subretinal delivery of EDIT-101 in humanized CEP290 mice showed rapid and sustained CEP290 gene editing. A comparable surrogate non-human primate (NHP) vector also achieved productive editing of the NHP CEP290 gene at levels that met the target therapeutic threshold, and demonstrated the ability of CRISPR/Cas9 to edit somatic primate cells in vivo. These results support further development of EDIT-101 for LCA10 and additional CRISPR-based medicines for other inherited retinal disorders. In human cells, a humanized mouse model and non-human primates, CRISPR/Cas9 corrects the splicing defect in a gene associated with congenital blindness.

BackgroundT-cell lymphomas and leukemias are a class of diseases lacking durable effective therapies, where median survival for patients suffering from relapsed/refractory disease is often measured in months. Translation of B-cell targeting CAR-T therapeutic success to T-cell malignancies comes with significant challenges. Notably, the shared expression of target antigens on malignant T-cells and in the T-cell product itself results in CAR-T activation and fratricide during manufacturing. To overcome the challenges associated with creating CD5-targeting CAR-Ts, we developed a process to simultaneously base edit five target genes, including CD5 and PD1, to produce potency-enhanced allogeneic anti-CD5 CAR T-cells for use as an off-the-shelf treatment for T-cell malignancies.MethodsAnti-CD5 CAR-Ts were produced in a GMP-compatible process using T-cells isolated from healthy human donors. T-cells were modified using base editing technology to simultaneously knock-out five target genes in a single electroporation step. Edited T-cells were transduced with a lentivirus encoding a second-generation anti-CD5 CAR. Knockout frequencies were evaluated by flow cytometry and next-generation sequencing. Anti-CD5 CAR-Ts were then characterized for their specificity in vitro and potency in in vivo xenograft tumor models.ResultsSimultaneous base editing at five genomic loci resulted in anti-CD5 CAR-Ts edited with 94–98% efficiency at each target gene, greatly diminishing the likelihood of GvHD, CAR-T rejection, fratricide, and checkpoint inhibitor activation. In addition, CD5 has an established role as a negative regulator of TCR signaling, and T cells lacking CD5 have enhanced proliferative capacity.1 Anti-CD5 CAR T-cells with or without CD5 KO demonstrated equally potent cytotoxicity and cytokine production in vitro against CD5 expressing tumor lines. However, CD5 KO greatly improved in vivo efficacy of anti-CD5 CAR-Ts in a murine model of T-ALL against established tumor xenografts. Mice previously cleared of tumor underwent a second tumor challenge to assess the persistence of anti-CD5 CAR-T cells and were cleared of tumor a second time, indicating extended persistence of functional anti-CD5 CAR-T cells in vivo.ConclusionsOur approach addresses current technological limitations in developing and applying CAR-Ts that target T-cell malignancies and demonstrates that simultaneous multiplex base editing of up to five targets can create universally compatible, fratricide-resistant, therapeutically active anti-CD5 CAR-Ts. We further demonstrate that CD5 knockout produces CAR-T cells with enhanced potency capable of clearing multiple tumor challenges in vivo. We are progressing this CD5-targeting CAR-T cell product towards potential clinical development for the treatment of T cell malignancies and other CD5+ hematological tumors.ReferenceGuillaume V, Peredo G, Romain R. CD5, an Undercover Regulator of TCR Signaling. Frontiers in Immunology 2018;9:2900.Ethics ApprovalAll animal studies were performed according to the guidelines and approval of the Institutional Animal Care and Use Committee.

Systemic sclerosis (SSc), systemic lupus erythematosus (SLE) and primary Sjogrens syndrome (pSS) are clinically distinct systemic autoimmune diseases (SADs) that share molecular pathways. We quantified the frequency of circulating immune-cells in 169 patients with these SADs and 44 healty controls (HC) using mass-cytometry and assessed the diagnostic value of these results. Alterations in the frequency of immune-cell subsets were present in all SADs compared to HC. Most alterations, including a decrease of CD56hi NK-cells in SSc and IgM+ Bcells in pSS, were disease specific; only a reduced frequency of plasmacytoid dendritic cells was common between all SADs Strikingly, hierarchical clustering of SSc patients identified 4 clusters associated with different clinical phenotypes, and 9 of the 12 cell subset-alterations in SSc were also present during the preclinical-phase of the disease. Additionally, we found a strong association between the use of prednisone and alterations in B-cell subsets. Although differences in immune-cell frequencies between these SADs are apparent, the discriminative value thereof is too low for diagnostic purposes. Within each disease, mass cytometry analyses revealed distinct patterns between endophenotypes. Given the lack of tools enabling early diagnosis of SSc, our results justify further research into the value of cellular phenotyping as a diagnostic aid.

While there are several small molecule, gene therapy, and gene editing approaches for treating sickle cell disease (SCD), these strategies do not result in the direct elimination of the causative sickle β-globin (HbS) variant itself. The reduction or complete removal of this pathologic globin variant and expression of normal β-hemoglobin (HbB) or other non-polymerizing β-globin variant may increase the likelihood of beneficial outcomes for SCD patients. Adenine base editors (ABEs) can precisely convert the mutant A-T base pair responsible for SCD to a G-C base pair, thus generating the hemoglobin variant, Hb G-Makassar, a naturally occurring β-globin variant that is not associated with human disease. Our studies have identified ABEs that can achieve highly efficient Makassar editing (>70%) of the sickle mutation in both sickle trait (HbAS) and homozygous sickle (HbSS) patient CD34+ cells with high cell viability and recovery and without perturbation of immunophenotypic hematopoietic stem and progenitor cell (HSPC) frequencies after ex vivo delivery of guide RNA and mRNA encoding the ABE. Furthermore, Makassar editing was retained throughout erythropoiesis in bulk in vitro erythroid differentiated cells (IVED) derived from edited CD34+ cells. To gain an understanding of allelic editing at a single clone resolution, we assessed editing frequencies of clones from both single cell expansion in erythroid differentiation media, as well as from single BFU-E colonies. We found that we could achieve >70% of colonies with bi-allelic Makassar editing and approximately 20% of colonies with mono-allelic Makassar editing, while Previously, conventional hemoglobin capillary electrophoresis and high-performance liquid chromatography (HPLC) were unable to distinguish between HbS and HbG-Makassar. Here, we developed an ultra-high-performance liquid chromatography (UPLC) method that resolves sickle globin (HbS) from Hb G-Makassar globin in IVED cells. The Makassar globin variant was further confirmed by liquid chromatography mass spectrometry (LC-MS). By developing this new method to resolve these two β-globin variants in edited HbSS cells, we were able to detect, in bulk IVED cultures, >80% abundance Hb G-Makassar of total β-globins, which corresponded to a concomitant reduction of HbS levels to 70% of cells that had bi-allelic Makassar editing. Moreover, in the approximately 20% of colonies that were found to be mono-allelically edited for the Makassar variant, there was a 60:40 ratio of Hb G-Makassar:HbS globin abundance in individual clones, at levels remarkably similar to the HbA(wildtype HbB):HbS levels found in HbAS individuals, with minimal observable in vitro sickling when exposed to hypoxia. Thus, with our ABEs, we were able to reduce HbS to 90% of IVED cells and found that in vitro sickling under hypoxia inversely correlated with the level of Hb G-Makassar globin variant installation and corresponding reduction in HbS levels. By converting HbS to Hb G-Makassar, our direct and precise editing strategy replaces a pathogenic β-globin with one that has been shown to have normal hematologic parameters. Coupled with autologous stem cell transplant, this next generation gene editing strategy presents a promising new modality for treating patients with SCD. Disclosures Chu: Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Lam:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Packer:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Olins:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Liquori:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Marshall:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Lee:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Yan:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Decker:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Gantzer:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Haskett:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Bohnuud:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Born:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Barrera:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Slaymaker:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Gaudelli:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Hartigan:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company. Ciaramella:Beam Therapeutics: Current Employment, Current equity holder in publicly-traded company.

Mutations in GUCY2D, the gene encoding retinal guanylate cyclase-1 (retGC1), are the leading cause of autosomal dominant cone–rod dystrophy (CORD6). Significant progress toward clinical application of gene replacement therapy for Leber congenital amaurosis (LCA) due to recessive mutations in GUCY2D (LCA1) has been made, but a different approach is needed to treat CORD6 where gain of function mutations cause dysfunction and dystrophy. The CRISPR/Cas9 gene editing system efficiently disrupts genes at desired loci, enabling complete gene knockout or homology directed repair. Here, adeno-associated virus (AAV)-delivered CRISPR/Cas9 was used specifically to edit/disrupt this gene's early coding sequence in mouse and macaque photoreceptors in vivo, thereby knocking out retGC1 expression and demonstrably altering retinal function and structure. Neither preexisting nor induced Cas9-specific T-cell responses resulted in ocular inflammation in macaques, nor did it limit GUCY2D editing. The results show, for the first time, the ability to perform somatic gene editing in primates using AAV-CRISPR/Cas9 and demonstrate the viability this approach for treating inherited retinal diseases in general and CORD6 in particular.

The purpose of the present studies was to use CyTOF and RNA-Seq technologies to identify cells and genes involved in lacrimal gland repair that could be targeted to treat diseases of lacrimal gland dysfunction. Lacrimal glands of female BALB/c mice were experimentally injured by intra-glandular injection of interleukin 1 alpha (IL-1α). The lacrimal glands were harvested at various time points following injury (1 to 14 days) and used to either prepare single cell suspensions for CyTOF immuno-phenotyping analyses or to extract RNA for gene expression studies using RNA-Seq. CyTOF immuno-phenotyping identified monocytes and neutrophils as the major infiltrating populations 1 and 2 days post injury. Clustering of significantly differentially expressed genes identified 13 distinct molecular signatures: 3 associated with immune/inflammatory processes included genes up-regulated at days 1-2 and 3 associated with reparative processes with genes up-regulated primarily between days 4 and 5. Finally, clustering identified 65 genes which were specifically up-regulated 2 days post injury which was enriched for muscle specific genes. The expression of select muscle-related proteins was confirmed by immunohistochemistry which identified a subset of cells expressing these proteins. Double staining experiments showed that these cells are distinct from the myoepithelial cells. We conclude that experimentally induced injury to the lacrimal gland leads to massive infiltration by neutrophils and monocytes which resolved after 3 days. RNAseq and immunohistochemistry identified a group of cells, other than myoepithelial cells, that express muscle-related proteins that could play an important role in lacrimal gland repair.

B-cell activating factor (BAFF) levels are increased in rheumatoid arthritis, lupus and primary Sjogren's syndrome (pSS). However, BAFF contribution to pathogenesis is not completely understood. In pSS, immune infiltration of the salivary and lacrimal glands leads to xerostomia and xerophtalmia. Glandular B cell hyperactivation, differentiation into germinal center (GC)-like structures and plasma cell accumulation are histopathological hallmarks that were attributed to increased BAFF. Here, we experimentally tested this hypothesis by overexpressing BAFF in a mouse model of pSS. BAFF overexpression enhanced lymphocytic infiltration and MHCII expression on B cells. Increased BAFF also induced B cell differentiation into GC B cells within the autoimmune target tissue. However, even in these conditions, GC B cells only accounted for

Beta hemoglobinopathies resulting from dysfunctional or deficient adult beta-globin expression are some of the most prevalent inherited blood disorders in the world. Upregulation of developmentally-silenced fetal gamma-globin would replace adult beta-globin to ameliorate disease symptoms. One of the approaches to reactivate fetal globin expression in erythroid cells is through gene editing by zinc finger or CRISPR-Cas9 nucleases to disrupt the expression of a transcription factor BCL11A, which mediates fetal globin silencing. As BCL11A-deficiency leads to hematopoietic stem cells (HSCs) defects, the current editing approaches target the BCL11A erythroid-enhancer region located in intron 2 of the BCL11A gene to selectively reduce BCL11A expression in erythroid cells. Instead of targeting BCL11A, we sought to identify novel cis-regulatory elements at the beta-globin locus for targeted gene editing to achieve fetal globin reactivation. From a lenti-CRISPR mediated saturated mutagenesis screen covering the beta-globin locus using Human Umbilical Cord Blood-Derived Erythroid Progenitor (HUDEP)-2 cells, multiple fetal hemoglobin (HbF)-inducing genomic domains were identified. Most of the hits were concentrated at the gamma-globin (HBG1/2) promoters, clustered at known hereditary persistence of fetal hemoglobin (HPFH) mutation hotspots. In-depth genotype to phenotype analysis further defined the indels responsible for HbF induction in these subdomains. We interrogated multiple families of nucleases and guide RNA (gRNA) combinations with or without single-stranded oligodeoxynucleotides (ssODN) to guide editing outcome. gRNAs were selected based on their HbF induction potential (up to 40%) when introduced into mobilized peripheral blood (mPB) CD34+ hematopoietic stem and progenitor cells (HSPCs) as ribonucleoprotein (RNP) complexes. HSPCs transfected with RNPs targeting either the BCL11A erythroid-enhancer or the HBG1/2 proximal regions were then injected into NBSGW mice to study the editing in SCID-repopulating cells (SRC) and their multilineage reconstitution potential. All groups achieved high levels of human chimerism (>70% hCD45+/hCD45+mCD45) and comparable monocytes, granulocytes, B lymphocytes, and hCD34+ HSPCs reconstitution. However, BCL11A-edited cells showed selective reduction in erythroid lineage (CD235a+) output, up to 4-fold lower than untreated or HBG1/2 promoter-edited HSPCs. Sequencing analysis from lineage-specific sorted cells further revealed reduced editing levels at BCL11A erythroid-specific enhancer in the erythroid compartment compared to unfractionated bone marrow (BM) or other human lineages (70% in erythroid vs. 90% in all other lineages). Furthermore, the nonproductive fraction of indels that did not disrupt the BCL11A GATAA motif was significantly enriched in erythroid cells (22% in erythroid vs. 8% in other lineages). Ex vivo erythroid cultures suggests BCL11A erythroid-enhancer editing may lead to slightly increased apoptosis during erythroid differentiation. In contrast, HBG1/2 promoter-edited cells had similar editing levels and indel patterns across all lineages with no significant lineage skewing. When chimeric BM from HBG1/2 promoter-edited groups were cultured in erythroid conditions, ex vivo-derived erythroid cells had significantly elevated levels of HbF compared to controls. When CD235a+ cells were sorted without further culture from chimeric BM of mice engrafted with HBG1/2 promoter-edited cells, significantly increased levels of HbF were detected by UPLC (up to 30%) compared to controls (~6%). Thus, long-term HSCs have been edited productively at the HBG1/2 promoters. These cells were able to generate erythroid progenitors that harbor HbF-inducing indels, which in turn, gave rise to erythroid cells in vivo with a clinically-relevant levels of HbF in a xenotransplantation model. Together, our data suggest that BCL11A-edited cells have an erythroid differentiation defect or survival disadvantage in NBSGW mouse model that warrants further investigation. In contrast, editing of the HBG1/2 promoters in mPB CD34+ cells achieved sustained HbF expression in erythroid lineage while maintaining multilineage differentiation potential. Targeting of the HBG1/2 promoters in HSPCs may be an attractive strategy for the development of potential gene editing medicines for beta hemoglobinopathies. Disclosures Chang: Editas Medicine Inc.: Employment, Equity Ownership. Sanchez:Editas Medicine Inc.: Employment, Equity Ownership. Heath:Editas Medicine Inc.: Employment, Equity Ownership. deDreuzy:Editas Medicine Inc.: Employment, Equity Ownership. Haskett:Editas Medicine Inc.: Employment, Equity Ownership. Vogelaar:Editas Medicine Inc.: Employment. Gogi:Editas Medicine Inc.: Employment, Equity Ownership. Da Silva:Editas Medicine Inc.: Employment, Equity Ownership. Wang:Editas Medicine Inc.: Employment, Equity Ownership. Sadowski:Editas Medicine Inc.: Employment, Equity Ownership. Gotta:Editas Medicine Inc.: Employment, Equity Ownership. Siwak:Editas Medicine Inc.: Employment, Equity Ownership. Viswanathan:Editas Medicine Inc.: Employment, Equity Ownership. Loveluck:Editas Medicine Inc.: Employment, Equity Ownership. Chao:Editas Medicine Inc.: Employment, Equity Ownership. Tillotson:Editas Medicine Inc.: Employment, Equity Ownership. Chalishazar:Editas Medicine Inc.: Employment, Equity Ownership. Dass:Editas Medicine Inc.: Employment, Equity Ownership. Ta:Editas Medicine Inc.: Employment, Equity Ownership. Brennan:Editas Medicine Inc.: Employment, Equity Ownership. Tabbaa:Editas Medicine Inc.: Employment, Equity Ownership. Marco:Editas Medicine Inc.: Employment, Equity Ownership. Zuris:Editas Medicine Inc.: Employment, Equity Ownership. Reyon:Editas Medicine Inc.: Employment, Equity Ownership. Isik:Editas Medicine Inc.: Employment, Equity Ownership. Friedland:Editas Medicine Inc.: Employment, Equity Ownership. Ta:Editas Medicine Inc.: Employment, Equity Ownership. Harbinski:Editas Medicine Inc.: Employment, Equity Ownership. Giannoukos:Editas Medicine Inc.: Employment, Equity Ownership. Teixeira:Editas Medicine Inc.: Employment, Equity Ownership. Wilson:Editas Medicine Inc.: Employment, Equity Ownership. Albright:Editas Medicine Inc.: Employment, Equity Ownership. Jiang:Editas Medicine Inc.: Employment, Equity Ownership.

Naïve anti-viral CD8+ T cells (TCD8+) are activated by the presence of peptide-MHC Class I complexes (pMHC-I) on the surface of professional antigen presenting cells (pAPC). Increasing the number of pMHC-I in vivo can increase the number of responding TCD8+. Antigen can be presented directly or indirectly (cross presentation) from virus-infected and uninfected cells, respectively. Here we determined the relative importance of these two antigen presenting pathways in mousepox, a natural disease of the mouse caused by the poxvirus, ectromelia (ECTV). We demonstrated that ECTV infected several pAPC types (macrophages, B cells, and dendritic cells (DC), including DC subsets), which directly presented pMHC-I to naïve TCD8+ with similar efficiencies in vitro. We also provided evidence that these same cell-types presented antigen in vivo, as they form contacts with antigen-specific TCD8+. Importantly, the number of pMHC-I on infected pAPC (direct presentation) vastly outnumbered those on uninfected cells (cross presentation), where presentation only occurred in a specialized subset of DC. In addition, prior maturation of DC failed to enhance antigen presentation, but markedly inhibited ECTV infection of DC. These results suggest that direct antigen presentation is the dominant pathway in mice during mousepox. In a broader context, these findings indicate that if a virus infects a pAPC then the presentation by that cell is likely to dominate over cross presentation as the most effective mode of generating large quantities of pMHC-I is on the surface of pAPC that endogenously express antigens. Recent trends in vaccine design have focused upon the introduction of exogenous antigens into the MHC Class I processing pathway (cross presentation) in specific pAPC populations. However, use of a pantropic viral vector that targets pAPC to express antigen endogenously likely represents a more effective vaccine strategy than the targeting of exogenous antigen to a limiting pAPC subpopulation., Author Summary To induce a protective cell type (CD8+ T cells) following virus infection, it is necessary to present degraded fragments of viral protein in complex with self molecules on the surface of so-called antigen presenting cells (APC). This process can occur in infected or uninfected APC and has been studied and quantified extensively in experimental setups in the lab. However, the extent to which presentation by infected or uninfected cells contribute to the induction of a protective CD8+ T cell response has not been studied extensively during a natural infection in a mouse model. Here we use a natural mouse virus to examine importantly, quantify, the contribution of presentation of the fragments of viral protein by infected or uninfected cells. We find that the presentation by infected cells dwarfs that seen by uninfected cells. The importance of this work lies in the fact that, if infected cells present way more antigen than uninfected cells, successful vaccine design should utilize this observation to make a vaccine where infected cells expressing virus proteins are the prevalent mode of induction of CD8+ T cells.

Background Mass cytometry has recently emerged as a promising tool for clinical research. However, few studies have demonstrated its benefit for patient stratification and biomarker identification. Primary Sjogren's syndrome (pSS) is a prototype of chronic autoimmune disease, the pathogenesis of which remains unclear and for which treatment does not exist. Objective This observational case-control study was designed to discover new cellular biomarkers and therapeutic targets in patients with pSS. Methods Forty-nine patients with pSS and 45 control subjects were enrolled for clinical evaluation and mass cytometry quantification of 34 protein markers in blood. For a third of these subjects, matched labial salivary gland biopsy specimens were also analyzed by mass cytometry and immunohistochemistry. Results In salivary gland biopsy specimens from patients with pSS, we identified a high number of activated CD8 + T cells, terminally differentiated plasma cells, and activated epithelial cells, pointing to new pathogenic mechanisms for future clinical intervention. In blood, we identified a 6-cell disease signature defined by decreased numbers of CD4 and memory B lymphocytes, decreased plasmacytoid dendritic cell numbers, and increased representation of activated CD4 and CD8 T cells and plasmablasts. These blood cellular components correlated with clinical parameters and, when taken together, clustered patients into subsets with distinct disease activity and glandular inflammation. Conclusion This first application of mass cytometry to a well-stratified clinical cohort and small biopsy tissues establishes the benefits of such an approach for the discovery of new biomarkers and therapeutic targets. Similar high-dimensional immunophenotyping strategies could be implemented in longitudinal and interventional clinical settings in this and other disease areas.

Background The cellular characterization of the immune infiltrate in exocrine glands from patients with primary Sjogren9s syndrome (pSS) has relied so far on methods with low dimensionality. As a result, our knowledge of cellular events taking place in the exocrine glands of these patients is limited. Objectives In order to quantify cellular variations associated with pathogenesis, we used here highly multiparametric cytometry by time-of-flight (CyTOF) to analyze diagnostic biopsies from patients with pSS and non-pSS sicca controls. Methods The CyTOF instrument combines single cell analysis used in flow cytometry with mass spectrometry detection of metal-conjugated antibodies. Using a panel of 36 antibodies, cell populations present in heterogeneous cell suspensions were characterized and correlated with clinical parameters. In parallel, paired formalin-fixed, paraffin embedded sections of labial glands from 15 individuals from this cohort were used to examine anatomic relationships between cell subsets identified by CyTOF. Results We studied 16 pSS patients and 13 non-pSS sicca controls, among which 81% were anti-SSA+, 44% were anti-SSB+, and 63% had a focus score of 1 or more. In addition to confirming the well-characterized presence of CD4 + T cells and B cells in Sjogren9s biopsies, this experimental approach revealed several additional pathologic features, among which are: (a) a dramatic accumulation of CD38 ++ CD27 + HLA-DR low cells (up to 50% of glandular B cells); (b) an unexpected abundance of CD8 + T cells showing marks of activation; (c) the upregulation of HLA-DR on epithelial cells in pSS patients with grades ≥3, which constitutes the first direct evidence of a potential pathological contribution of the epithelium using un-manipulated, ex vivo , primary human cells. Conclusions The CyTOF instrument is a new tool allowing precise determination of salivary gland subsets, which may generate new mechanistic hypotheses on pathogenesis of the disease. Disclosure of Interest None declared