CD6, a Rheostat-Type Signalosome That Tunes T Cell Activation

Long-term therapy with itolizumab is safe and effective for patients with moderate to severe psoriasis: Results from an expanded-access program

Itolizumab is a humanized monoclonal antibody that selectively targets the CD6-ALCAM pathway. This article reports on the safety and efficacy of itolizumab in the treatment of moderate-to-severe plaque psoriasis in a clinical study conducted in Cuba in the setting of an expanded-access program (EAP). The study included 84 patients who had previously received conventional anti-psoriatic systemic therapies but were either intolerant, had an inadequate response, or had contraindications to these therapies. It consisted of multiple phases, including a 12-week induction phase, a 40-week maintenance phase, and a 24-week off-treatment follow-up phase, using either a 0.4 or 1.6 mg/Kg dose. The results showed that itolizumab monotherapy was safe and effective during 52 weeks of continuous treatment and the subsequent 24 follow-up weeks. Itolizumab treatment resulted in a significant improvement (PASI 75) in 80 % of patients at the end of the induction phase, and this effect was sustained till week 52 during the maintenance phase. Moreover, 24 weeks after treatment stopped nearly two-thirds of patients still showed a PASI ≥ 75. The observed effects were dose-dependent, with 1.6 mg/kg being the most convenient dose. This study further supports the strategy of targeting the CD6-ALCAM signaling pathway for the treatment of psoriasis and the use of itolizumab as a valuable asset in the armamentarium of anti-psoriasis drugs.

New and emerging therapies for systemic lupus erythematosus

Systemic Lupus Erythematosus (SLE) and lupus nephritis treatment is still based on non-specific immune suppression despite the first biological therapy for the disease having been approved more than a decade ago. Intense basic and translational research has uncovered a multitude of pathways that are actively being evaluated as treatment targets in SLE and lupus nephritis, with two new medications receiving FDA approval in the last 3 years. Herein we provide an overview of targeted therapies for SLE including medications targeting the B lymphocyte compartment, intracellular signaling, co-stimulation, and finally the interferons and other cytokines.

The CD6 interactome orchestrates ligand-independent T cell inhibitory signaling

BACKGROUND

T-cell membrane scaffold proteins are pivotal in T cell function, acting as versatile signaling hubs. While CD6 forms a large intracellular signalosome, it is distinguished from typical scaffolds like LAT or PAG by possessing a substantial ectodomain that binds CD166, a well-characterized ligand expressed on most antigen-presenting cells (APC), through the third domain (d3) of the extracellular region. Although the intact form of CD6 is the most abundant in T cells, an isoform lacking d3 (CD6∆d3) is transiently expressed on activated T cells. Still, the precise character of the signaling transduced by CD6, whether costimulatory or inhibitory, and the influence of its ectodomain on these activities are unclear.

METHODS

We expressed CD6 variants with extracellular deletions or cytosolic mutations in Jurkat cells containing eGFP reporters for NF-κB and NF-AT transcription factor activation. Cell activation was assessed by eGFP flow cytometry following Jurkat cell engagement with superantigen-presenting Raji cells. Using imaging flow cytometry, we evaluated the impact of the CD6-CD166 pair on cell adhesiveness during the antigen-dependent and -independent priming of T cells. We also examined the role of extracellular or cytosolic sequences on CD6 translocation to the immunological synapse, using immunofluorescence-based imaging.

RESULTS

Our investigation dissecting the functions of the extracellular and cytosolic regions of CD6 revealed that CD6 was trafficked to the immunological synapse and exerted tonic inhibition wholly dependent on its cytosolic tail. Surprisingly, however, translocation to the synapse occurred independently of the extracellular d3 and of engagement to CD166. On the other hand, CD6 binding to CD166 significantly increased T cell:APC adhesion. However, this activity was most evident in the absence of APC priming with superantigen, and thus, in the absence of TCR engagement.

CONCLUSIONS

Our study identifies CD6 as a novel 'on/off' scaffold-receptor capable of modulating responsiveness in two ways. Firstly, and independently of ligand binding, it establishes signaling thresholds through tonic inhibition, functioning as a membrane-bound scaffold. Secondly, CD6 has the capacity for alternative splicing-dependent variable ligand engagement, modulating its checkpoint-like activity.

The CD318/CD6 axis limits type 1 diabetes islet autoantigen-specific human T cell activation

CD6 is a glycoprotein expressed on CD4 and CD8 T cells involved in immunoregulation. CD318 has been identified as a CD6 ligand. The role of CD318 in T cell immunity is restricted as it has only been investigated in a few mice autoimmune models but not in human diseases. CD318 expression was thought to be limited to mesenchymal-epithelial cells and, therefore, contribute to CD6-mediated T cell activation in the CD318-expressing tissue rather than through interaction with antigen-presenting cells. Here, we report CD318 expression in a subpopulation of CD318+ myeloid dendritic (mDC), whereas the other peripheral blood populations were CD318 negative. However, CD318 can be induced by activation: a subset of monocytes treated with LPS and IFNγ and in vitro monocyte derived DCs were CD318+. We also showed that recombinant CD318 inhibited T cell function. Strikingly, CD318+ DCs suppressed the proliferation of autoreactive T cells specific for GAD65, a well-known targeted self-antigen in Type 1 Diabetes (T1D). Our study provides new insight into the role of the CD318/CD6 axis in the immunopathogenesis of inflammation, suggesting a novel immunoregulatory role of CD318 in T cell-mediated autoimmune diseases and identifying a potential novel immune checkpoint inhibitor as a target for intervention in T1D which is an unmet therapeutic need.

Type I interferon induces TCR-dependent and -independent antimicrobial responses in γδ intraepithelial lymphocytes

Intraepithelial lymphocytes (IEL) expressing the γδ T cell receptor (TCR) survey the intestinal epithelium to limit the invasion of microbial pathogens. The production of type I interferon (IFN) is a central component of an antiviral immune response, yet how these pro-inflammatory cytokines contribute to γδ IEL effector function remains unclear. Based on the unique activation status of IELs, and their ability to bridge innate and adaptive immunity, we investigated the extent to which type I IFN signaling modulates γδ IEL function. Using an ex vivo culture model, we find that type I IFN alone is unable to drive IFNγ production, yet low level TCR activation synergizes with type I IFN to induce IFNγ production in murine γδ IELs. Further investigation into the underlying molecular mechanisms of co-stimulation revealed that TCRγδ-mediated activation of NFAT and JNK is required for type I IFN to promote IFNγ expression in a STAT4- dependent manner. Whereas type I IFN rapidly upregulates antiviral gene expression independent of a basal TCRγδ signal, neither tonic TCR triggering nor the presence of a TCR agonist was sufficient to elicit type I IFN-induced IFNγ production in vivo . However, bypassing proximal TCR signaling events synergized with IFNAR/STAT4 activation to induce γδ IEL IFNγ production. These findings indicate that γδ IELs contribute to host defense in response to type I IFN by mounting a rapid antimicrobial response independent of TCRγδ signaling, and under permissive conditions, produce IFNγ in a TCR-dependent manner.

A CD6 homolog of Nile tilapia (Oreochromis niloticus) conserved binding bacteria involved in the regulation of Streptococcus agalactiae induced inflammation

As a lymphocyte-specific surface receptor belonging to the cysteine-rich superfamily of scavenger receptors, CD6 acts as a pattern recognition receptor for microbial components and is involved in the regulation of inflammatory responses. However, the characteristics and functions of CD6 molecules in lower vertebrates represented by teleost fish are unknown. In this study, a CD6 homolog (designated OnCD6) was characterized from Nile tilapia (Oreochromis niloticus), and establishing its role as a PRRs that participates in immune recognition. OnCD6 contains an open reading frame of 1872 bp that encodes a peptide of 623 amino acids, and contains two conserved SR domain. Multiple sequence alignment revealed that OnCD6 shares a relatively high level of identity with those of other species. Transcriptional expression analysis revealed that OnCD6 was constitutively expressed in immunes tissues such as head kidney and thymus. The expression level of OnCD6 in mainly immune tissues were found significantly upregulated after the injection of Streptococcus agalactiae (S. agalactiae). Moreover, OnCD6 protein was located in the head kidney and brain, mainly over the plasma membrane of lymphocytes in these immune tissues. In vitro experiments showed that CD6 extracellular protein bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of bacterial surface conserved components LPS and LTA etc. In vivo experiments demonstrated that overexpression OnCD6 before S. agalactiae challenge significantly improved tilapia survival, and this was concomitant with reduced bacterial load and pro-inflammatory cytokines (IL-1β and TNF-α). Taken together, our results illustrated the function of CD6 molecular pattern recognition receptors (PRRs) is conserved and plays an important role in antibacterial infection.

CD6 triggers actomyosin cytoskeleton remodeling after binding to its receptor complex

The T cell marker CD6 regulates both T cells and target cells during inflammatory responses by interacting with its receptors. However, only a few receptors binding to the extracellular domains of CD6 have been identified, and cellular events induced by CD6 engagement with its receptors in target cells remain poorly understood. In this study, we identified CD44 as a novel CD6 receptor by proximity labeling and confirmed the new CD6-CD44 interaction by biochemical and biophysical approaches. CD44 and the other 2 known CD6 receptors, CD166 and CDCP1, were distributed diffusely on resting retinal pigment epithelium (RPE) cells but clustered together to form a receptor complex upon CD6 binding. CD6 stimulation induced dramatic remodeling of the actomyosin cytoskeleton in RPE cells mediated by activation of RhoA, and Rho-associated kinase signaling, resulting in increased myosin II phosphorylation. Such actomyosin activation triggered the disassembly of tight junctions responsible for RPE barrier integrity in a process that required all components of the tripartite CD6 receptor complex. These data provided new insights into the mechanisms by which CD6 mediates T cell-driven disruption of tissue barriers during inflammation.

Cerebrospinal fluid metabolomic and proteomic characterization of neurologic post-acute sequelae of SARS-CoV-2 infection

The mechanism by which SARS-CoV-2 causes neurological post-acute sequelae of SARS-CoV-2 (neuro-PASC) remains unclear. Herein, we conducted proteomic and metabolomic analyses of cerebrospinal fluid (CSF) samples from 21 neuro-PASC patients, 45 healthy volunteers, and 26 inflammatory neurological diseases patients. Our data showed 69 differentially expressed metabolites and six differentially expressed proteins between neuro-PASC patients and healthy individuals. Elevated sphinganine and ST1A1, sphingolipid metabolism disorder, and attenuated inflammatory responses may contribute to the occurrence of neuro-PASC, whereas decreased levels of 7,8-dihydropterin and activation of steroid hormone biosynthesis may play a role in the repair process. Additionally, a biomarker cohort consisting of sphinganine, 7,8-dihydroneopterin, and ST1A1 was preliminarily demonstrated to have high value in diagnosing neuro-PASC. In summary, our study represents the first attempt to integrate the diagnostic benefits of CSF with the methodological advantages of multi-omics, thereby offering valuable insights into the pathogenesis of neuro-PASC and facilitating the work of neuroscientists in disclosing different neurological dimensions associated with COVID-19.

CD6 and Its Interacting Partners: Newcomers to the Block of Cancer Immunotherapies

Cancer management still requires more potent and safer treatments, of which immunomodulatory receptors on the lymphocyte surface have started to show promise in new cancer immunotherapies (e.g., CTLA-4 and PD-1). CD6 is a signal-transducing transmembrane receptor, mainly expressed by all T cells and some B and NK cell subsets, whose endogenous ligands (CD166/ALCAM, CD318/CDCP-1, Galectins 1 and 3) are overexpressed by malignant cells of different lineages. This places CD6 as a potential target for novel therapies against haematological and non-haematological malignancies. Recent experimental evidence for the role of CD6 in cancer immunotherapies is summarised in this review, dealing with diverse and innovative strategies from the classical use of monoclonal antibodies to soluble recombinant decoys or the adoptive transfer of immune cells engineered with chimeric antigen receptors.

Assessing the Effects of Dietary Cadmium Exposure on the Gastrointestinal Tract of Beef Cattle via Microbiota and Transcriptome Profile

Cadmium (Cd) is an environmental pollutant, widely existing in soil, and can be absorbed and accumulated by plants. Hunan Province exhibits the worst cadmium contamination of farmland in China. Ruminants possess an abundant microbial population in the rumen, which enables them to tolerate various poisonous plants. To investigate whether the rumen microbiota could respond to Cd and mitigate the toxicity of Cd-accumulated maize to ruminants, 6-month-old cattle were fed with 85.82% (fresh basis) normal whole-plant maize silage diet (CON, n = 10) or Cd-accumulated whole-plant maize silage diet (CAM, n = 10) for 107 days. When compared to the CON cattle, CAM cattle showed significantly higher gain-to-feed ratio and an increased total bacterial population in the rumen, but a decreased total bacterial population in the colon. CAM cattle had higher relative abundance of Prevotella and Lachnospiraceae ND3007 group in the rumen, and Lachnospiraceae NK4A136 group and Clostridia vadinBB60 group in the colon. Notably, microbial correlations were enhanced in all segments of CAM cattle, especially Peptostreptococcaceae in the jejunum. Transcriptome analysis revealed down-regulation of several immune-related genes in the rumen of CAM cattle, and differentially expressed genes in the rumen were mostly involved in immune regulation. These findings indicated that feeding Cd-accumulated maize diet with a Cd concentration of 6.74 mg/kg dry matter (DM) could stimulate SCFA-related bacteria in the rumen, induce hormesis to promote weight gain, and improve energy utilization of cattle.

Pre-T cell receptor localization and trafficking are independent of its signaling

Expression of the pre-T cell receptor (preTCR) is an important checkpoint during the development of T cells, an essential cell type of our adaptive immune system. The preTCR complex is only transiently expressed and rapidly internalized in developing T cells and is thought to signal in a ligand-independent manner. However, identifying a mechanistic basis for these unique features of the preTCR compared with the final TCR complex has been confounded by the concomitant signaling that is normally present. Thus, we have reconstituted preTCR expression in non-immune cells to uncouple receptor trafficking dynamics from its associated signaling. We find that all the defining features of the preTCR are intrinsic properties of the receptor itself, driven by exposure of an extracellular hydrophobic region, and are not the consequence of receptor activation. Finally, we show that transitory preTCR cell surface expression can sustain tonic signaling in the absence of ligand binding, suggesting how the preTCR can nonetheless drive αβTCR lineage commitment.

Friend or Foe - Tc17 cell generation and current evidence for their importance in human disease

The term Tc17 cells refers to interleukin 17 (IL-17)-producing CD8+ T cells. While IL-17 is an important mediator of mucosal defense, it is also centrally involved in driving the inflammatory response in immune-mediated diseases, such as psoriasis, multiple sclerosis, and inflammatory bowel disease. In this review, we aim to gather the current knowledge on the phenotypic and transcriptional profile, the in vitro and in vivo generation of Tc17 cells, and the evidence pointing towards a relevant role of Tc17 cells in human diseases such as infectious diseases, cancer, and immune-mediated diseases.

Mapping the SLP76 interactome in T cells lacking each of the GRB2-family adaptors reveals molecular plasticity of the TCR signaling pathway

The propagation and diversification of signals downstream of the T cell receptor (TCR) involve several adaptor proteins that control the assembly of multimolecular signaling complexes (signalosomes). The global characterization of changes in protein-protein interactions (PPI) following genetic perturbations is critical to understand the resulting phenotypes. Here, by combining genome editing techniques in T cells and interactomics studies based on affinity purification coupled to mass spectrometry (AP-MS) analysis, we determined and quantified the molecular reorganization of the SLP76 interactome resulting from the ablation of each of the three GRB2-family adaptors. Our data showed that the absence of GADS or GRB2 induces a major remodeling of the PPI network associated with SLP76 following TCR engagement. Unexpectedly, this PPI network rewiring minimally affects proximal molecular events of the TCR signaling pathway. Nevertheless, during prolonged TCR stimulation, GRB2- and GADS-deficient cells displayed a reduced level of activation and cytokine secretion capacity. Using the canonical SLP76 signalosome, this analysis highlights the plasticity of PPI networks and their reorganization following specific genetic perturbations.

CD6-mediated inhibition of T cell activation via modulation of Ras

BACKGROUND

CD6 is one of many cell surface receptors known to regulate signal transduction upon T cell activation. However, whether CD6 mediates costimulatory or inhibitory signals is controversial. When T cells engage with antigen presenting cells (APCs), CD6 interacts with its ligand CD166 at the cell-cell interface while the cytosolic tail assembles a complex signalosome composed of adaptors and effector enzymes, that may either trigger activating signaling cascades, or instead modulate the intensity of signaling. Except for a few cytosolic adaptors that connect different components of the CD6 signalosome, very little is known about the mechanistic effects of the cytosolic effectors that bind CD6.

METHODS

Jurkat model T cells were transfected to express wild-type (WT) CD6, or a cytoplasmic truncation, signaling-disabled mutant, CD6Δcyt. The two resulting cell lines were directly activated by superantigen (sAg)-loaded Raji cells, used as APCs, to assess the net signaling function of CD6. The Jurkat cell lines were further adapted to express a FRET-based unimolecular HRas biosensor that reported the activity of this crucial GTPase at the immunological synapse.

RESULTS

We show that deletion of the cytosolic tail of CD6 enhances T-cell responses, indicating that CD6 restrains T-cell activation. One component of the CD6-associated inhibitory apparatus was found to be the GTPase activating protein of Ras (RasGAP), that we show to associate with CD6 in a phosphorylation-dependent manner. The FRET HRas biosensor that we developed was demonstrated to be functional and reporting the activation of the T cell lines. This allowed to determine that the presence of the cytosolic tail of CD6 results in the down-regulation of HRas activity at the immunological synapse, implicating this fundamental GTPase as one of the targets inhibited by CD6.

CONCLUSIONS

This study provides the first description of a mechanistic sequence of events underlying the CD6-mediated inhibition of T-cell activation, involving the modulation of the MAPK pathway at several steps, starting with the coupling of RasGAP to the CD6 signalosome, the repression of the activity of Ras, and culminating in the reduction of ERK1/2 phosphorylation and of the expression of the T-cell activation markers CD69 and IL-2R α chain. Video abstract.

CD6 deficiency impairs early immune response to bacterial sepsis

CD6 is a lymphocyte-specific scavenger receptor expressed on adaptive (T) and innate (B1a, NK) immune cells, which is involved in both fine-tuning of lymphocyte activation/differentiation and recognition of bacterial-associated molecular patterns (i.e., lipopolysaccharide). However, evidence on CD6’s role in the physiological response to bacterial infection was missing. Our results show that induction of monobacterial and polymicrobial sepsis in Cd6^−/− mice results in lower survival rates and increased bacterial loads and pro-inflammatory cytokine levels. Steady state analyses of Cd6^−/− mice show decreased levels of natural polyreactive antibodies, concomitant with decreased cell counts of spleen B1a and marginal zone B cells. Adoptive transfer of wild-type B cells and mouse serum, as well as a polyreactive monoclonal antibody improve Cd6^−/− mouse survival rates post-sepsis. These findings support a nonredundant role for CD6 in the early response against bacterial infection, through homeostatic expansion and functionality of innate-related immune cells.

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CD6 is a nonredundant receptor in early immune response to sepsis

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Cd6−/− mice show higher susceptibility to bacterial sepsis

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Cd6−/− mice show lower B1a and MZB cell and natural polyreactive antibody levels

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B cell and serum transfer restore susceptibility of Cd6−/− mice to bacterial sepsis

Kinetic proofreading through the multi-step activation of the ZAP70 kinase underlies early T cell ligand discrimination

T cells recognize a few high-affinity antigens among a vast array of lower affinity antigens. According to the kinetic proofreading model, antigen discrimination properties could be explained by the gradual amplification of small differences in binding affinities as the signal is transduced downstream of the T cell receptor. Which early molecular events are affected by ligand affinity, and how, has not been fully resolved. Here, we used time-resolved high-throughput proteomic analyses to identify and quantify the phosphorylation events and protein-protein interactions encoding T cell ligand discrimination in antigen-experienced T cells. Although low-affinity ligands induced phosphorylation of the Cd3 chains of the T cell receptor and the interaction of Cd3 with the Zap70 kinase as strongly as high-affinity ligands, they failed to activate Zap70 to the same extent. As a result, formation of the signalosome of the Lat adaptor was severely impaired with low- compared with high-affinity ligands, whereas formation of the signalosome of the Cd6 receptor was affected only partially. Overall, this study provides a comprehensive map of molecular events associated with T cell ligand discrimination.

High-dimensional profiling reveals Tc17 cell enrichment in active Crohn's disease and identifies a potentially targetable signature

The immune-pathology in Crohn’s disease is linked to dysregulated CD4+ T cell responses biased towards pathogenic TH17 cells. However, the role of CD8+ T cells able to produce IL-17 (Tc17 cells) remains unclear. Here we characterize the peripheral blood and intestinal tissue of Crohn’s disease patients (n = 61) with flow and mass cytometry and reveal a strong increase of Tc17 cells in active disease, mainly due to induction of conventional T cells. Mass cytometry shows that Tc17 cells express a distinct immune signature (CD6^high, CD39, CD69, PD-1, CD27^low) which was validated in an independent patient cohort. This signature stratifies patients into groups with distinct flare-free survival associated with differential CD6 expression. Targeting of CD6 in vitro reduces IL-17, IFN-γ and TNF production. These results identify a distinct Tc17 cell population in Crohn’s disease with proinflammatory features linked to disease activity. The Tc17 signature informs clinical outcomes and may guide personalized treatment decisions.

The T cell compartment in patients with Crohn's disease is dysregulated. Here the authors use cytometric profiling to reveal an enrichment of distinct Tc17 cells during active Crohn's disease and may suggest CD6 as a potential target for therapeutic studies.

Th1 and Th17 cells are resistant towards T cell activation-induced downregulation of CD6

BACKGROUND

The cell surface molecule CD6 is a modulator of T cell receptor (TCR) signaling. Recently, it has been reported that CD6 is downregulated on CD4+ T cells following T cell activation. This mechanism could limit the efficacy of anti-CD6 therapeutical antibodies.

METHODS

We analyzed CD6 expression on activated and non-activated Th1 cells and Th17 cells by flow cytometry.

RESULTS

Our experiments confirmed a significant downregulation of CD6 on IFNγ- and IL17-negative CD4+ T cells from healthy individuals and from patients with rheumatoid arthritis following T cell activation with anti-CD3 and anti-CD28 antibodies. In contrast, CD6 expression remained stable on activated Th17 cells and Th1 cells.

CONCLUSIONS

Th1 and Th17 cells are resistant towards T cell activation-induced downregulation of CD6. These findings are relevant for the future development of CD6 targeting therapies and show that CD6 expression is differentially regulated in CD4+ T cell subsets.

Deconvolving clinically relevant cellular immune crosstalk from bulk gene expression using CODEFACS and LIRICS stratifies melanoma patients to anti-PD-1 therapy

The tumor microenvironment (TME) is a complex mixture of cell types whose interactions affect tumor growth and clinical outcome. To discover such interactions, we developed CODEFACS (COnfident DEconvolution For All Cell Subsets), a tool deconvolving cell-type-specific gene expression in each sample from bulk expression, and LIRICS (LIgand Receptor Interactions between Cell Subsets), a statistical framework prioritizing clinically relevant ligand-receptor interactions between cell types from the deconvolved data. We first demonstrate the superiority of CODEFACS versus the state-of-the-art deconvolution method, CIBERSORTx. Second, analyzing the TCGA, we uncover cell-type-specific ligand-receptor interactions uniquely associated with mismatch repair deficiency across different cancer types, providing additional insights into their enhanced sensitivity to anti-PD1 therapy compared to other tumors with high neoantigen burden. Finally, we identify a subset of cell-type-specific ligand-receptor interactions in the melanoma TME that stratify survival of patients receiving anti-PD1 therapy better than some recently published bulk transcriptomics-based methods.

Pre-existing chromatin accessibility and gene expression differences among naive CD4+ T cells influence effector potential

CD4+ T cells have a remarkable potential to differentiate into diverse effector lineages following activation. Here, we probe the heterogeneity present among naive CD4+ T cells before encountering their cognate antigen to ask whether their effector potential is modulated by pre-existing transcriptional and chromatin landscape differences. Single-cell RNA sequencing shows that key drivers of variability are genes involved in T cell receptor (TCR) signaling. Using CD5 expression as a readout of the strength of tonic TCR interactions with self-peptide MHC, and sorting on the ends of this self-reactivity spectrum, we find that pre-existing transcriptional differences among naive CD4+ T cells impact follicular helper T (TFH) cell versus non-TFH effector lineage choice. Moreover, our data implicate TCR signal strength during thymic development in establishing differences in naive CD4+ T cell chromatin landscapes that ultimately shape their effector potential.

Peptide Targeting of PDZ-Dependent Interactions as Pharmacological Intervention in Immune-Related Diseases

PDZ (postsynaptic density (PSD95), discs large (Dlg), and zonula occludens (ZO-1)-dependent interactions are widely distributed within different cell types and regulate a variety of cellular processes. To date, some of these interactions have been identified as targets of small molecules or peptides, mainly related to central nervous system disorders and cancer. Recently, the knowledge of PDZ proteins and their interactions has been extended to various cell types of the immune system, suggesting that their targeting by viral pathogens may constitute an immune evasion mechanism that favors viral replication and dissemination. Thus, the pharmacological modulation of these interactions, either with small molecules or peptides, could help in the control of some immune-related diseases. Deeper structural and functional knowledge of this kind of protein–protein interactions, especially in immune cells, will uncover novel pharmacological targets for a diversity of clinical conditions.

The T cell CD6 receptor operates a multitask signalosome with opposite functions in T cell activation

To determine the respective contribution of the LAT transmembrane adaptor and CD5 and CD6 transmembrane receptors to early TCR signal propagation, diversification, and termination, we describe a CRISPR/Cas9-based platform that uses primary mouse T cells and permits establishment of the composition of their LAT, CD5, and CD6 signalosomes in only 4 mo using quantitative mass spectrometry. We confirmed that positive and negative functions can be solely assigned to the LAT and CD5 signalosomes, respectively. In contrast, the TCR-inducible CD6 signalosome comprised both positive (SLP-76, ZAP70, VAV1) and negative (UBASH3A/STS-2) regulators of T cell activation. Moreover, CD6 associated independently of TCR engagement to proteins that support its implication in inflammatory pathologies necessitating T cell transendothelial migration. The multifaceted role of CD6 unveiled here accounts for past difficulties in classifying it as a coinhibitor or costimulator. Congruent with our identification of UBASH3A within the CD6 signalosome and the view that CD6 constitutes a promising target for autoimmune disease treatment, single-nucleotide polymorphisms associated with human autoimmune diseases have been found in the Cd6 and Ubash3a genes.

A Scalable Strand-Specific Protocol Enabling Full-Length Total RNA Sequencing From Single Cells

RNA sequencing (RNAseq) has been widely used to generate bulk gene expression measurements collected from pools of cells. Only relatively recently have single-cell RNAseq (scRNAseq) methods provided opportunities for gene expression analyses at the single-cell level, allowing researchers to study heterogeneous mixtures of cells at unprecedented resolution. Tumors tend to be composed of heterogeneous cellular mixtures and are frequently the subjects of such analyses. Extensive method developments have led to several protocols for scRNAseq but, owing to the small amounts of RNA in single cells, technical constraints have required compromises. For example, the majority of scRNAseq methods are limited to sequencing only the 3' or 5' termini of transcripts. Other protocols that facilitate full-length transcript profiling tend to capture only polyadenylated mRNAs and are generally limited to processing only 96 cells at a time. Here, we address these limitations and present a novel protocol that allows for the high-throughput sequencing of full-length, total RNA at single-cell resolution. We demonstrate that our method produced strand-specific sequencing data for both polyadenylated and non-polyadenylated transcripts, enabled the profiling of transcript regions beyond only transcript termini, and yielded data rich enough to allow identification of cell types from heterogeneous biological samples.

Alternative Splicing of Pre-mRNA in the Control of Immune Activity

The human immune response is a complex process that responds to numerous exogenous antigens in preventing infection by microorganisms, as well as to endogenous components in the surveillance of tumors and autoimmune diseases, and a great number of molecules are necessary to carry the functional complexity of immune activity. Alternative splicing of pre-mRNA plays an important role in immune cell development and regulation of immune activity through yielding diverse transcriptional isoforms to supplement the function of limited genes associated with the immune reaction. In addition, multiple factors have been identified as being involved in the control of alternative splicing at the cis, trans, or co-transcriptional level, and the aberrant splicing of RNA leads to the abnormal modulation of immune activity in infections, immune diseases, and tumors. In this review, we summarize the recent discoveries on the generation of immune-associated alternative splice variants, clinical disorders, and possible regulatory mechanisms. We also discuss the immune responses to the neoantigens produced by alternative splicing, and finally, we issue some alternative splicing and immunity correlated questions based on our knowledge.

Soluble CD5 and CD6: Lymphocytic Class I Scavenger Receptors as Immunotherapeutic Agents

CD5 and CD6 are closely related signal-transducing class I scavenger receptors mainly expressed on lymphocytes. Both receptors are involved in the modulation of the activation and differentiation cell processes triggered by clonotypic antigen-specific receptors present on T and B cells (TCR and BCR, respectively). To serve such a relevant immunomodulatory function, the extracellular region of CD5 and CD6 interacts with soluble and/or cell-bound endogenous counterreceptors but also microbial-associated molecular patterns (MAMPs). Evidence from genetically-modified mouse models indicates that the absence or blockade of CD5- and CD6-mediated signals results in dysregulated immune responses, which may be deleterious or advantageous in some pathological conditions, such as infection, cancer or autoimmunity. Bench to bedside translation from transgenic data is constrained by ethical concerns which can be overcome by exogenous administration of soluble proteins acting as decoy receptors and leading to transient “functional knockdown”. This review gathers information currently available on the therapeutic efficacy of soluble CD5 and CD6 receptor infusion in different experimental models of disease. The existing proof-of-concept warrants the interest of soluble CD5 and CD6 as safe and efficient immunotherapeutic agents in diverse and relevant pathological conditions.

Overexpression of CD6 and PD-1 Identifies Dysfunctional CD8+ T-Cells During Chronic SIV Infection of Rhesus Macaques

Effective CD8⁺ T-cell responses play an important role in determining the course of SIV/HIV viral infection. Here we identified a unique population of dysfunctional CD8⁺ T-cells in lymphoid tissues and bronchoalveolar lavage (BAL) of rhesus macaques with chronic SIV infection characterized by co-expression of CD6 and PD-1. The frequency of CD6 and PD-1 co-expressing CD8⁺ T-cells was significantly increased in lymphoid tissues and BAL during chronic SIV infection compared to pre-infection levels. These CD6⁺PD-1⁺CD8⁺ T-cells displayed impaired proliferation, cytokine secretion and cytotoxicity compared to their CD6^-PD-1⁺CD8⁺ T cell counterparts. The frequency of CD8⁺PD-1⁺ and CD8⁺CD6^-PD-1⁺ T-cells in the lymph node and bone marrow did not correlate with SIV viral load, whereas the frequency of CD8⁺CD6⁺PD-1⁺ T-cells positively correlated with SIV viral load in these tissues highlighting the contribution of CD6 to disease progression. CD6⁺PD-1⁺CD8⁺ T-cells expressed elevated levels of SHP2 phosphatase compared to CD6^-PD-1⁺CD8⁺ T-cells providing a potential mechanism by which CD6 may induce T-cell dysfunction during chronic SIV infection. Combined targeting of CD6 and PD-1 effectively revived the CD8⁺ T-cell proliferative response in vitro suggesting a strategy for potential therapeutic benefit.

Domain-specific CD6 monoclonal antibodies identify CD6 isoforms generated by alternative-splicing

The characterization of the architecture, structure and extracellular interactions of the CD6 glycoprotein, a transmembrane receptor expressed in medullary thymocytes and all mature T‐cell populations, has been enhanced by the existence of monoclonal antibodies (mAbs) that specifically recognize the various scavenger receptor cysteine‐rich (SRCR) domains of the ectodomain. Using engineered isoforms of CD6 including or excluding each of the three SRCR domains, either expressed at the membranes of cells or in soluble forms, we provide conclusive and definitive evidence that domain 2 of CD6, previously not identifiable, can be recognized by the CD6 mAbs OX125 and OX126, and that OX124 targets domain 3 and can block the interaction at the cell surface of CD6 with its major ligand CD166. Alternative splicing‐dependent CD6 isoforms can now be confidently identified. We confirm that following T‐cell activation there is a partial replacement of full‐length CD6 by the CD6Δd3 isoform, which lacks the CD166‐binding domain, and we find no evidence for the expression of other CD6 isoforms at the mRNA or protein levels.