Long-term engagement of CD6 and ALCAM is essential for T-cell proliferation induced by dendritic cells

DNA methylation changes following narrative exposure therapy in a randomized controlled trial with female former child soldiers

The aftermath of traumatization lives on in the neural and epigenetic traces creating a momentum of affliction in the psychological and social realm. Can psychotherapy reorganise these memories through changes in DNA methylation signatures? Using a randomised controlled parallel group design, we examined methylome-wide changes in saliva samples of 84 female former child soldiers from Eastern DR Congo before and six months after Narrative Exposure Therapy. Treatment predicted differentially methylated positions (DMPs) related to ALCAM, RIPOR2, AFAP1 and MOCOS. In addition, treatment associations overlapped at gene level with baseline clinical and social outcomes. Treatment related DMPs are involved in memory formation-the key agent in trauma focused treatments-and enriched for molecular pathways commonly affected by trauma related disorders. Results were partially replicated in an independent sample of 53 female former child soldiers from Northern Uganda. Our results suggest a molecular impact of psychological treatment in women with war-related childhood trauma.Trial registration: Addressing Heightened Levels of Aggression in Traumatized Offenders With Psychotherapeutic Means (ClinicalTrials.gov Identifier: NCT02992561, 14/12/2016).

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.

Inflammatory Environment Promotes the Adhesion of Tumor Cells to Brain Microvascular Endothelial Cells

Cancer patients usually suffer from unfavorable prognosis, particularly with the occurrence of brain metastasis of lung cancer. The key incident of brain metastasis initiation is crossing of blood-brain barrier (BBB) by cancer cells. Although preventing brain metastasis is a principal goal of cancer therapy, the cellular mechanisms and molecular regulators controlling the transmigration of cancer cells into the brain are still not clearly illustrated. We analyzed the mRNA expression profiles of metastatic brain tissues and TNF-α treated cancer cells to understand the changes in adhesion molecule expression during the tumor phase. To imitate the tumor microenvironment, an in vitro model was developed and the low or high metastatic potential lung tumor cells (A549 or H358) were cultured with the human brain microvascular endothelial cells (hBMECs) under TNF-α treatment. The analysis of online database indicated an altered expression for adhesion molecules and enrichment of their associated signaling pathways. TNF-α treatment activated hBMECs via up-regulating several adhesion molecules, including ICAM1, CD112, CD47, and JAM-C. Meanwhile, TNF-α induced an increased expression of adhesion molecule ligands such as ALCAM and CD6 in both A549 and H358. Moreover, the expression of adhesion molecules and the ligands were also increased both in A549- or H358-hBMECs mixed culture system, which promoted tumor cells adhesion to endothelial cells. These results suggested that the enhanced interaction between tumor cells and brain microvascular endothelium might facilitate the incidence of metastatic brain tumors and further offer a better comprehension of brain metastasis prevention and treatment.

Compromised levels of CD6 and reduced T cell activation in the aged immune system

The CD6 molecule, a cell surface marker, is involved in immunological synapse formation between T cell and antigen-presenting cell and T lymphocyte activation for adequate immune response. Geriatric individuals fail to mount a satisfactory immunological response against pathogens thus, insights into the functionality of CD6 may provide information for competence building in elderly immune cells. However, limited information is available regarding the status of CD6 in geriatric individuals. In this study, various isoforms of CD6 were analysed in aged mononuclear cells (MNCs) and compared with young individuals. In geriatric individuals, protein and mRNA expressions of CD6 molecule/isoforms were found to be decreased compared to their young counterparts. Furthermore, geriatric MNCs failed to show any change in CD6 levels and its isoforms upon polyclonal activation compared to young MNCs, marked by reduced Ca⁺⁺ release and IL-2 expression. We suggest an overall decrease in CD6 levels in geriatric MNCs and T cells with suboptimal T cell activation in aged individuals.

Identification of SARS-CoV-2-specific immune alterations in acutely ill patients

Dysregulated immune profiles have been described in symptomatic patients infected with SARS-CoV-2. Whether the reported immune alterations are specific to SARS-CoV-2 infection or also triggered by other acute illnesses remains unclear. We performed flow cytometry analysis on fresh peripheral blood from a consecutive cohort of (a) patients hospitalized with acute SARS-CoV-2 infection, (b) patients of comparable age and sex hospitalized for another acute disease (SARS-CoV-2 negative), and (c) healthy controls. Using both data-driven and hypothesis-driven analyses, we found several dysregulations in immune cell subsets (e.g., decreased proportion of T cells) that were similarly associated with acute SARS-CoV-2 infection and non-COVID-19-related acute illnesses. In contrast, we identified specific differences in myeloid and lymphocyte subsets that were associated with SARS-CoV-2 status (e.g., elevated proportion of ICAM-1+ mature/activated neutrophils, ALCAM+ monocytes, and CD38+CD8+ T cells). A subset of SARS-CoV-2-specific immune alterations correlated with disease severity, disease outcome at 30 days, and mortality. Our data provide an understanding of the immune dysregulation specifically associated with SARS-CoV-2 infection among acute care hospitalized patients. Our study lays the foundation for the development of specific biomarkers to stratify SARS-CoV-2-positive patients at risk of unfavorable outcomes and to uncover candidate molecules to investigate from a therapeutic perspective.

CD6 is a target for cancer immunotherapy

Limitations of checkpoint inhibitor cancer immunotherapy include induction of autoimmune syndromes and resistance of many cancers. Since CD318, a novel CD6 ligand, is associated with the aggressiveness and metastatic potential of human cancers, we tested the effect of an anti-CD6 monoclonal antibody, UMCD6, on killing of cancer cells by human lymphocytes. UMCD6 augmented killing of breast, lung, and prostate cancer cells through direct effects on both CD8+ T cells and NK cells, increasing cancer cell death and lowering cancer cell survival in vitro more robustly than monoclonal antibody checkpoint inhibitors that interrupt the programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) axis. UMCD6 also augmented in vivo killing by human peripheral blood lymphocytes of a human breast cancer line xenotransplanted into immunodeficient mice. Mechanistically, UMCD6 upregulated the expression of the activating receptor NKG2D and downregulated expression of the inhibitory receptor NKG2A on both NK cells and CD8+ T cells, with concurrent increases in perforin and granzyme B production. The combined capability of an anti-CD6 monoclonal antibody to control autoimmunity through effects on CD4+ lymphocyte differentiation while enhancing killing of cancer cells through distinct effects on CD8+ and NK cells opens a potential new approach to cancer immunotherapy that would suppress rather than instigate autoimmunity.

ALCAM and VCAM-1 as urine biomarkers of activity and long-term renal outcome in systemic lupus erythematosus

OBJECTIVES

We investigated the cell adhesion molecules (CAMs) Vascular CAM 1 (VCAM-1) and Activated Leucocyte CAM (ALCAM) as urinary biomarkers in SLE patients with and without renal involvement.

METHODS

Female SLE patients (n = 111) and non-SLE population-based controls (n = 99) were enrolled. We measured renal activity using the renal domain of the BILAG index and urine (U) and plasma (P) concentrations of soluble (s)VCAM 1 and U-sALCAM using ELISA. U-sCAM levels were next corrected by U-creatinine.

RESULTS

U-sVCAM-1/creatinine and U-sALCAM/creatinine ratios were higher in SLE patients vs non-SLE controls (P < 0.001 for both), as well as in patients with active/low-active (BILAG A-C; n = 11) vs quiescent (BILAG D; n = 19) LN (P = 0.023 and P = 0.001, respectively). U-sALCAM/creatinine but not U-sVCAM-1/creatinine ratios were higher in patients with nephritis history (BILAG A-D; n = 30) vs non-renal SLE (BILAG E; n = 79) (P = 0.014). Patients with baseline U-sVCAM-1/creatinine ratios ≥75th percentile showed a 23-fold increased risk of a deterioration in estimated glomerular filtration rate by ≥25% during a 10-year follow-up (odds ratio: 22.9; 95% CI: 2.8, 189.2; P = 0.004); this association remained significant after adjustments for age, disease duration and organ damage. Traditional markers including anti-dsDNA antibodies did not predict this outcome.

CONCLUSION

While high U-sVCAM-1 levels appear to reflect SLE disease activity, sALCAM might have particular importance in renal SLE. Both U-sVCAM-1 and U-sALCAM showed ability to distinguish SLE patients with active renal involvement from patients with quiescent or no prior nephritis. High U-sVCAM-1 levels may indicate patients at increased risk for long-term renal function loss.

An anti-CD6 antibody for the treatment of COVID-19 patients with cytokine-release syndrome: report of three cases

In COVID-19, the inflammatory cytokine-release syndrome is associated with the progression of the disease. Itolizumab is a monoclonal antibody that recognizes human CD6 expressed in activated T cells. The antibody has shown to be safe and efficacious in the treatment of moderate to severe psoriasis. Its effect is associated with the reduction of pro-inflammatory cytokines release, including IFN-γ, IL-6 and TNF-α. Here, we report the outcome of three severe and critically ill COVID-19 patients treated with itolizumab as part of an expanded access protocol. Itolizumab was able to reduce IL-6 concentrations in all the patients. Two of the three patients showed respiratory and radiological improvement and were fully recovered. We hypothesize this anti-inflammatory therapy in addition to antiviral and anticoagulant therapy could reduce COVID-19 associated morbidity and mortality.

Multifaceted effects of soluble human CD6 in experimental cancer models

Background

CD6 is a lymphocyte surface co-receptor physically associated with the T-cell receptor (TCR)/CD3 complex at the center of the immunological synapse. There, CD6 assists in cell-to-cell contact stabilization and modulation of activation/differentiation events through interaction with CD166/ALCAM (activated leukocyte cell adhesion molecule), its main reported ligand. While accumulating evidence is attracting new interest on targeting CD6 for therapeutic purposes in autoimmune disorders, little is known on its potential in cancer. In an attempt to elucidate the in vivo relevance of blocking CD6-mediated interactions in health and disease, we explored the consequences of expressing high circulating levels of a soluble form CD6 (sCD6) as a decoy receptor.

Methods

High sCD6 serum levels were achieved by using transgenic C57BL/6 mice expressing human sCD6 under the control of lymphoid-specific transcriptional elements (shCD6LckEμTg) or wild type either transduced with hepatotropic adeno-associated virus coding for mouse sCD6 or undergoing repeated infusions of recombinant human sCD6 protein. Characterization of sCD6-induced changes was performed by ex vivo flow cytometry and functional analyses of mouse lymphoid organ cells. The in vivo relevance of those changes was explored by challenging mice with subcutaneous or metastatic tumors induced by syngeneic cancer cells of different lineage origins.

Results

Through a combination of in vitro and in vivo studies, we show that circulating sCD6 expression induces defective regulatory T cell (Treg) generation and function, decreased CD166/ALCAM-mediated tumor cell proliferation/migration and impaired galectin-induced T-cell apoptosis, supporting the fact that sCD6 modulates antitumor lymphocyte effector function and tumorigenesis. Accordingly, sCD6 expression in vivo resulted in delayed subcutaneous tumor growth and/or reduced metastasis on challenge of mice with syngeneic cancer cells.

Conclusions

Evidence is provided for the disruption of CD6 receptor–ligand interactions as a feasible immunomodulatory approach in cancer.

Proteomic assessment of serum biomarkers of longevity in older men

The biological bases of longevity are not well understood, and there are limited biomarkers for the prediction of long life. We used a high-throughput, discovery-based proteomics approach to identify serum peptides and proteins that were associated with the attainment of longevity in a longitudinal study of community-dwelling men age ≥65 years. Baseline serum in 1196 men were analyzed using liquid chromatography-ion mobility-mass spectrometry, and lifespan was determined during ~12 years of follow-up. Men who achieved longevity (≥90% expected survival) were compared to those who died earlier. Rigorous statistical methods that controlled for false positivity were utilized to identify 25 proteins that were associated with longevity. All these proteins were in lower abundance in long-lived men and included a variety involved in inflammation or complement activation. Lower levels of longevity-associated proteins were also associated with better health status, but as time to death shortened, levels of these proteins increased. Pathway analyses implicated a number of compounds as important upstream regulators of the proteins and implicated shared networks that underlie the observed associations with longevity. Overall, these results suggest that complex pathways, prominently including inflammation, are linked to the likelihood of attaining longevity. This work may serve to identify novel biomarkers for longevity and to understand the biology underlying lifespan.

Proteomic Characterization of Host-Pathogen Interactions during Bovine Trophoblast Cell Line Infection by Neospora caninum

Despite the importance of bovine neosporosis, relevant knowledge gaps remain concerning the pathogenic mechanisms of Neospora caninum. Infection of the placenta is a crucial event in the pathogenesis of the disease; however, very little is known about the relation of the parasite with this target organ. Recent studies have shown that isolates with important variations in virulence also show different interactions with the bovine trophoblast cell line F3 in terms of proliferative capacity and transcriptome host cell modulation. Herein, we used the same model of infection to study the interaction of Neospora with these target cells at the proteomic level using LC-MS/MS over the course of the parasite lytic cycle. We also analysed the proteome differences between high- (Nc-Spain7) and low-virulence (Nc-Spain1H) isolates. The results showed that mitochondrial processes and metabolism were the main points of Neospora-host interactions. Interestingly, Nc-Spain1H infection showed a higher level of influence on the host cell proteome than Nc-Spain7 infection.

Activated leukocyte cell adhesion molecule as a biomarker for disease severity and efficacy of sublingual immunotherapy in allergic rhinitis

BACKGROUND

Activated leukocyte cell adhesion molecule (ALCAM) plays an important role in T cell activation and immune response, but the role of ALCAM in allergic rhinitis (AR) remains unclear. The objective of the current study was to validate serum ALCAM as a biomarker in assessing disease severity and predicting the efficacy of sublingual immunotherapy (SLIT) in AR patients.

METHODS

We recruited 40 healthy controls (HC group), 38 mild AR patients (MAR group) and 80 moderate-severe AR patients (MSAR group) in this study. Serum levels of ALCAM were determined by ELISA, and the association between ALCAM levels and disease severity was evaluated. In the MSAR group, 68 patients underwent and finished 3-years of SLIT, and were divided into effective group and ineffective group, the relationship between ALCAM levels and efficacy of SLIT was exampled.

RESULTS

ALCAM levels were elevated in the serum of AR patients in comparison with HC. Moreover, serum ALCAM concentrations were higher in MSAR group than in MAR group and HC group, and levels of ALCAM significantly correlated with AR total nasal symptom score (TNSS) (r = 0.330, P < 0.001), visual analogue scale (VAS) (r = 0.387, P < 0.001) and serum total IgE levels (r = 0.442, P < 0.001). In the effective group, the ALCAM levels were significantly lower than in the ineffective group. Receiver operating characteristic (ROC) curve exhibited good accuracy for predicting clinical efficacy of SLIT (area under the curve = 0.805, P < 0.001).

CONCLUSIONS

The serum ALCAM maybe a novel biomarker for assessing disease severity and predicting clinical efficacy of SLIT in AR patients.

Activated leukocyte cell adhesion molecule regulates B lymphocyte migration across central nervous system barriers

The presence of B lymphocyte-associated oligoclonal immunoglobulins in the cerebrospinal fluid is a classic hallmark of multiple sclerosis (MS). The clinical efficacy of anti-CD20 therapies supports a major role for B lymphocytes in MS development. Although activated oligoclonal populations of pathogenic B lymphocytes are able to traffic between the peripheral circulation and the central nervous system (CNS) in patients with MS, molecular players involved in this migration have not yet been elucidated. In this study, we demonstrated that activated leukocyte cell adhesion molecule (ALCAM/CD166) identifies subsets of proinflammatory B lymphocytes and drives their transmigration across different CNS barriers in mouse and human. We also showcased that blocking ALCAM alleviated disease severity in animals affected by a B cell-dependent form of experimental autoimmune encephalomyelitis. Last, we determined that the proportion of ALCAM⁺ B lymphocytes was increased in the peripheral blood and within brain lesions of patients with MS. Our findings indicate that restricting access to the CNS by targeting ALCAM on pathogenic B lymphocytes might represent a promising strategy for the development of next-generation B lymphocyte-targeting therapies for the treatment of MS.

Metabolite Patterns in Human Myeloid Hematopoiesis Result from Lineage-Dependent Active Metabolic Pathways

Assessment of hematotoxicity from environmental or xenobiotic compounds is of notable interest and is frequently assessed via the colony forming unit (CFU) assay. Identification of the mode of action of single compounds is of further interest, as this often enables transfer of results across different tissues and compounds. Metabolomics displays one promising approach for such identification, nevertheless, suitability with current protocols is restricted. Here, we combined a hematopoietic stem and progenitor cell (HSPC) expansion approach with distinct lineage differentiations, resulting in formation of erythrocytes, dendritic cells and neutrophils. We examined the unique combination of pathway activity in glycolysis, glutaminolysis, polyamine synthesis, fatty acid oxidation and synthesis, as well as glycerophospholipid and sphingolipid metabolism. We further assessed their interconnections and essentialness for each lineage formation. By this, we provide further insights into active metabolic pathways during the differentiation of HSPC into different lineages, enabling profound understanding of possible metabolic changes in each lineage caused by exogenous compounds.

Species-Specificity of Transcriptional Regulation and the Response to Lipopolysaccharide in Mammalian Macrophages

Mammalian macrophages differ in their basal gene expression profiles and response to the toll-like receptor 4 (TLR4) agonist, lipopolysaccharide (LPS). In human macrophages, LPS elicits a temporal cascade of transient gene expression including feed forward activators and feedback regulators that limit the response. Here we present a transcriptional network analysis of the response of sheep bone marrow-derived macrophages (BMDM) to LPS based upon RNA-seq at 0, 2, 4, 7, and 24 h post-stimulation. The analysis reveals a conserved transcription factor network with humans, and rapid induction of feedback regulators that constrain the response at every level. The gene expression profiles of sheep BMDM at 0 and 7 h post LPS addition were compared to similar data obtained from goat, cow, water buffalo, horse, pig, mouse and rat BMDM. This comparison was based upon identification of 8,200 genes annotated in all species and detected at >10TPM in at least one sample. Analysis of expression of transcription factors revealed a conserved transcriptional millieu associated with macrophage differentiation and LPS response. The largest co-expression clusters, including genes encoding cell surface receptors, endosome-lysosome components and secretory activity, were also expressed in all species and the combined dataset defines a macrophage functional transcriptome. All of the large animals differed from rodents in lacking inducible expression of genes involved in arginine metabolism and nitric oxide production. Instead, they expressed inducible transporters and enzymes of tryptophan and kynurenine metabolism. BMDM from all species expressed high levels of transcripts encoding transporters and enzymes involved in glutamine metabolism suggesting that glutamine is a major metabolic fuel. We identify and discuss transcripts that were uniquely expressed or regulated in rodents compared to large animals including ACOD1, CXC and CC chemokines, CD163, CLEC4E, CPM, CSF1, CSF2, CTSK, MARCO, MMP9, SLC2A3, SLC7A7, and SUCNR1. Conversely, the data confirm the conserved regulation of multiple transcripts for which there is limited functional data from mouse models and knockouts. The data provide a resource for functional annotation and interpretation of loci involved in susceptibility to infectious and inflammatory disease in humans and large animal species.

Genetic variations in the host dependency factors ALCAM and TPST2 impact HIV-1 disease progression

OBJECTIVES

Recently, the activated leukocyte cell adhesion molecule (ALCAM) and tyrosylprotein sulfotransferase 2 (TPST2) have been identified as important host dependency factors (HDFs) for in-vitro HIV-1 replication. To determine whether these genes play a role in HIV-1 pathogenesis, we analysed whether naturally occurring genetic variations were associated with the clinical course of infection.

DESIGN/METHODS

Single nucleotide polymorphisms (SNPs) in ALCAM and TPST2 were analysed in a cohort of 304 HIV-1-infected men who have sex with men and survival analysis was used to determine their effect on the outcome of untreated HIV-1 infection. Flowcytometry was used to determine the effect of SNPs on CD4 T-cell activation prior to HIV-1 infection and 1 and 5 years after infection. In-vitro HIV-1 infections were performed to analyse the effect of the SNPs on HIV-1 replication.

RESULTS

We observed that the minor allele of rs1344861 in ALCAM was associated with accelerated disease progression, whereas the minor allele of rs9613199 in TPST2 was associated with delayed disease progression. In-vitro infection assays did not demonstrate any differences in HIV-1 replication associated with rs9613199. However, the increase in CD4 T-cell immune activation levels during HIV-1 infection was less pronounced in infected individuals homozygous for rs9613199, which is in agreement with delayed disease progression.

CONCLUSION

Our data demonstrate that ALCAM and TPST2 play a role in HIV-1 pathogenesis. SNPs in these genes, without known functional implications, had a major effect on disease progression, and therefore, these HDFs may be attractive and effective targets for new treatment strategies.

Negatively charged amino acids in the stalk region of membrane proteins reduce ectodomain shedding

Ectodomain shedding is a post-translational modification mechanism by which the entire extracellular domain of membrane proteins is liberated through juxtamembrane processing. Because shedding rapidly and irreversibly alters the characteristics of cells, this process is properly regulated. However, the molecular mechanisms governing the propensity of membrane proteins to shedding are largely unknown. Here, we present evidence that negatively charged amino acids within the stalk region, an unstructured juxtamembrane region at which shedding occurs, contribute to shedding susceptibility. We show that two activated leukocyte cell adhesion molecule (ALCAM) protein variants produced by alternative splicing have different susceptibilities to ADAM metallopeptidase domain 17 (ADAM17)-mediated shedding. Of note, the inclusion of a stalk region encoded by a 39-bp-long alternative exon conferred shedding resistance. We found that this alternative exon encodes a large proportion of negatively charged amino acids, which we demonstrate are indispensable for conferring the shedding resistance. We also show that the introduction of negatively charged amino acids into the stalk region of shedding-susceptible ALCAM variant protein attenuates its shedding. Furthermore, we observed that negatively charged amino acids residing in the stalk region of Erb-B2 receptor tyrosine kinase 4 (ERBB4) are indispensable for its shedding resistance. Collectively, our results indicate that negatively charged amino acids within the stalk region interfere with the shedding of multiple membrane proteins. We conclude that the composition of the stalk region determines the shedding susceptibility of membrane proteins.

Urinary activated leukocyte cell adhesion molecule as a novel biomarker of lupus nephritis histology

Background

Lupus nephritis (LN) is one of the most severe complications of SLE patients. We aim to validate urinary ALCAM as a biomarker in predicting renal disease histpathology in a Chinese lupus cohort.

Methods

In this cross-sectional study, a total of 256 patients and controls were recruited. Urinary levels of ALCAM were determined by ELISA. Renal histopathology was reviewed by an experienced renal pathologist.

Results

Urinary ALCAM levels were significantly increased in active LN patients when compared to active SLE patients without renal involvement (p < 0.001), inactive LN patients (p = 0.023), inactive SLE patients without renal involvement (p < 0.001), and healthy controls (p < 0.001). Correlation analysis revealed a positive correlation between urinary ALCAM and general disease activity—SLEDAI score (r = 0.487, p < 0.001), as well as renal disease activity—rSLEDAI (r = 0.552, p < 0.001) and SLICC RAS (r = 0.584, p < 0.001). Urinary ALCAM also correlated with lab parameters including 24-h urine protein, hemoglobin, and complement 3. Moreover, urinary ALCAM levels were significantly increased in class III and IV (proliferative) LN as compared to those in class V (membranous) LN. It outperformed conventional biomarkers (anti-dsDNA antibody, C3, C4, proteinuria) in discriminating the two groups of LN. On renal histopathology, urinary ALCAM levels correlated positively with activity index (r = 0.405, p < 0.001) but not chronicity index (r = 0.079, p = 0.448).

Conclusion

Urinary ALCAM is a potential biomarker for predicting renal pathology activity in LN and may serve as a valuable surrogate marker of renal histopathology.

Endophilin-A3 and Galectin-8 control the clathrin-independent endocytosis of CD166

While several clathrin-independent endocytic processes have been described so far, their biological relevance often remains elusive, especially in pathophysiological contexts such as cancer. In this study, we find that the tumor marker CD166/ALCAM (Activated Leukocyte Cell Adhesion Molecule) is a clathrin-independent cargo. We show that endophilin-A3—but neither A1 nor A2 isoforms—functionally associates with CD166-containing early endocytic carriers and physically interacts with the cargo. Our data further demonstrates that the three endophilin-A isoforms control the uptake of distinct subsets of cargoes. In addition, we provide strong evidence that the construction of endocytic sites from which CD166 is taken up in an endophilin-A3-dependent manner is driven by extracellular galectin-8. Taken together, our data reveal the existence of a previously uncharacterized clathrin-independent endocytic modality, that modulates the abundance of CD166 at the cell surface, and regulates adhesive and migratory properties of cancer cells.

How and which cell surface molecules are taken up by clathrin-independent endocytosis is an ongoing area of research. Here, the authors show that the tumor marker CD166 is a clathrin-independent cargo that is taken up by endophilin-A3 and galectin-8, which regulates cancer cell migration.

Transcriptome Analysis Identifies ALCAM Overexpression as a Prognosis Biomarker in Laryngeal Squamous Cell Carcinoma

BACKGROUND

Laryngeal squamous cell carcinoma (LSCC) is one of the most incident tumors in the world, especially in developing countries, such as Brazil. Different from other tumors, LSCC prognosis did not improve during the past four decades. Therefore, the objective of this study was to develop biomarkers that can predict LSCC patient's prognosis.

RESULTS

Transcriptome analysis pointed out 287 overexpressed genes in LSCC in comparison to adjacent mucosa. Among these, a gene-pattern signature was created with 24 genes associated with prognosis. The Bayesian clustering of both Brazil and The Cancer Genome Atlas (TCGA) data pointed out clusters of samples possessing significative differences in the prognosis, and the expression panel of three genes (ALCAM, GBP6, and ME1) was capable to distinguish patients with worse prognosis with an accuracy of 97%. Survival analyses with TCGA data highlighted ALCAM gene expression as an independent prognostic factor for LSCC. This was further confirmed through immunohistochemistry, using a validation set of Brazilian patients. ALCAM expression was not associated with prognosis for other head and neck tumor sites.

CONCLUSION

ALCAM overexpression seems to be an independent prognosis biomarker for LSCC patients.

Modulation of CD4 T cell function via CD6-targeting

In recent years molecules involved on the immune synapse became successful targets for therapeutic immune modulation. CD6 has been extensively studied, yet, results regarding CD6 biology have been controversial, in spite of the ubiquitous presence of this molecule on virtually all CD4 T cells. We investigated the outcome of murine and human antibodies targeting CD6 domain 1. We found that CD6-targeting had a major impact on the functional specialization of CD4 cells, both human and murine. Differentiation of CD4 T cells towards a Foxp3+ Treg fate was prevented with increasing doses of anti-CD6, while Th1 polarization was favoured. No impact was observed on Th2 or Th17 specialization. These in vitro results provided an explanation for the dose-dependent outcome of in vivo anti-CD6 administration where the anti-inflammatory action is lost at the highest doses. Our data show that therapeutic targeting of the immune synapse may lead to paradoxical dose-dependent effects due to modification of T cell fate.

Activated Leukocyte Cell Adhesion Molecule Stimulates the T-Cell Response in Allergic Asthma

RATIONALE

The activated leukocyte cell adhesion molecule (ALCAM) is a cluster of differentiation 6 ligand that is important for stabilizing the immunological synapse and inducing T-cell activation and proliferation.

OBJECTIVES

In this study, we investigated the role of ALCAM in the development of inflammation in allergic asthma.

METHODS

An ovalbumin (OVA)-induced allergic asthma model was established in wild-type (WT) and ALCAM-deficient (ALCAM^-/-) mice. T-cell proliferation was evaluated in cocultures with dendritic cells (DCs). Bone marrow-derived dendritic cells (BMDCs) from WT and ALCAM^-/- mice were cultured and adoptively transferred to OT-II mice for either OVA sensitization or challenge. An anti-ALCAM antibody was administered to assess its therapeutic potential. ALCAM concentrations in the sputum and serum of children with asthma were quantified by ELISA.

MEASUREMENTS AND MAIN RESULTS

Inflammatory responses were lower in ALCAM^-/- mice than in WT mice, and T cells cocultured with DCs from ALCAM^-/- mice showed reduced proliferation relative to those cocultured with DCs from WT mice. A decreased inflammatory response was observed upon adoptive transfer of BMDCs from ALCAM^-/- mice as compared with that observed after transfer of BMDCs from WT mice. In addition, anti-ALCAM antibody-treated mice showed a reduced inflammatory response, and sputum and serum ALCAM concentrations were higher in children with asthma than in control subjects.

CONCLUSIONS

ALCAM contributes to OVA-induced allergic asthma by stimulating T-cell activation and proliferation, suggesting it as a potential therapeutic target for allergic asthma.

ALCAM Mediates DC Migration Through Afferent Lymphatics and Promotes Allospecific Immune Reactions

Activated leukocyte cell adhesion molecule (ALCAM, CD166) is a cell adhesion molecule of the immunoglobulin superfamily and has been implicated in diverse pathophysiological processes including T cell activation, leukocyte trafficking, and (lymph)angiogenesis. However, exploring the therapeutic potential of ALCAM blockade in immune-mediated inflammatory disorders has been difficult due to the lack of antibodies with blocking activity toward murine ALCAM. In this study, we identified and characterized a monoclonal antibody with high affinity and specificity for murine ALCAM. This antibody reduced in vitro T cell activation induced by antigen-presenting dendritic cells (DCs) as well as (trans)migration of murine DCs across lymphatic endothelial monolayers. Moreover, it reduced emigration of DCs from in vitro-cultured human skin biopsies. Similarly, antibody-based blockade of ALCAM reduced (lymph)angiogenic processes in vitro and decreased developmental lymphangiogenesis in vivo to levels observed in ALCAM-deficient mice. Since corneal allograft rejection is an important medical condition that also involves (lymph)angiogenesis, DC migration and T cell activation, we investigated the therapeutic potential of ALCAM blockade in murine corneal disease. Blocking ALCAM lead to DC retention in corneas and effectively prevented corneal allograft rejection. Considering that we also detected ALCAM expression in human corneal DCs and lymphatics, our findings identify ALCAM as a potential novel therapeutic target in human corneal allograft rejection.

Critical Role of CD6highCD4+ T Cells in Driving Th1/Th17 Cell Immune Responses and Mucosal Inflammation in IBD

BACKGROUND AND AIMS

CD6 is a crucial regulator of T cell activation and is implicated in the pathogenesis of multiple autoimmune diseases. ALCAM is the first identified endogenous ligand of CD6. We sought to investigate potential roles of CD6 in regulating intestinal mucosal inflammation in inflammatory bowel disease [IBD].

METHODS

We analysed the expression of CD6 and ALCAM in the inflamed mucosa of IBD patients using qRT-PCR and immunohistochemistry. Phenotypic properties of CD6low/- and CD6highCD4+ T cells were determined by flow cytometry, qRT-PCR, and ELISA. ALCAM Fc chimeric protein was used to evaluate the role of CD6-ALCAM engagement in regulating IBD CD4+ T cell activation and differentiation.

RESULTS

Expression of CD6 and its ligand ALCAM was markedly increased in the inflamed mucosa of IBD patients compared with that in normal controls, and was significantly correlated with disease activity indices of IBD patients. Interestingly, CD6highCD4+ T cells of IBD patients exhibited significantly higher pathogenicity compared with CD6low/-CD4+ T cells, characterized by enhanced T cell activation and preferential Th1 and Th17 cell phenotypes, but a markedly decreased proportion of nTreg [CD25highFoxp3+, CD25highCD127low] cells. Importantly, inclusion of ALCAM Fc chimeric protein significantly facilitated IBD CD4+ T cell, especially CD6highCD4+ T cell, differentiation into Th1/Th17 cells compared with hIgG1 Fc-treated controls.

CONCLUSIONS

These data indicate that overexpression of CD6 and ALCAM in the inflamed mucosa of IBD patients accelerates intestinal mucosal immune responses via promoting CD4+ T cell proliferation and differentiation into Th1/Th17 cells. Thus, CD6 may serve as a novel therapeutic target for treatment of IBD.

Modulation of cell adhesion and migration through regulation of the immunoglobulin superfamily member ALCAM/CD166

In epithelial-derived cancers, altered regulation of cell-cell adhesion facilitates the disruption of tissue cohesion that is central to the progression to malignant disease. Although numerous intercellular adhesion molecules participate in epithelial adhesion, the immunoglobulin superfamily (IgSF) member activated leukocyte cell adhesion molecule (ALCAM), has emerged from multiple independent studies as a central contributor to tumor progression. ALCAM is an archetypal member of the IgSF with conventional organization of five Ig-like domains involved in homo- and heterotypic adhesions. Like many IgSF members, ALCAM is broadly expressed and involved in cellular adhesion across many cellular processes. While the redundancy of intercellular adhesion molecules (CAMs) could diminish the impact of any single CAM, consistent correlation between ALCAM expression and patient outcome for multiple cancers underscores its role in tumor progression. Unlike most oncogenes and tumor suppressors, ALCAM is neither mutated nor amplified or deleted. Experimental disruption of ALCAM-mediated adhesions implies that this IgSF member contributes to tumor progression through dynamic turnover of the protein at the cell surface. Since ALCAM is not frequently altered at the gene level, it appears to promote malignant behavior through regulation of its availability rather than its specific activity. These observations help explain its heterogeneous expression within malignant disease and the drastic changes in protein levels across tumor progression. To reveal how ALCAM contributes to tumor progression, we review regulation of its gene expression, alternative splicing, targeted proteolysis, binding partners, and surface shedding within the context of cancer. Studying ALCAM regulation has led to a novel understanding of the fine-tuning of cell adhesive state through the utilization of otherwise normal regulatory processes, which thereby enable tumor cell invasion and metastasis.

Activated Leukocyte Cell Adhesion Molecule Modulates Th2 Immune Response in Atopic Dermatitis

PURPOSE

Activated leukocyte cell adhesion molecule (ALCAM), a member of the immunoglobulin superfamily, is highly expressed on dendritic cells. ALCAM and its receptor CD6 are co-stimulatory molecules in the immunological synapse; their interaction is required for T cell activation. While atopic dermatitis (AD) is recognized as a T helper 2 (Th2)-mediated allergic disease, the role of ALCAM in its pathogenesis is unclear.

METHODS

ALCAM levels were measured in the serum of AD patients and AD-induced murine model by ovalbumin treatment. We next investigated transepidermal water loss, clinical score, Th2-immune responses, skin barrier gene expression and T-cell activation using wild-type (WT) and ALCAM deficiency mice. An oxazolone-induced AD-like model was also established and analyzed using WT- and ALCAM-deficient mice.

RESULTS

We found that serum ALCAM levels were elevated in pediatric AD patients as well as WT AD mice, whereas Th2-type cytokine production and AD symptoms were suppressed in ALCAM-deficient mice. In addition, CD4⁺ effector T-cell counts in murine skin and skin-draining lymph nodes were lower in ALCAM-deficient mice than in their WT counterparts. ALCAM deficiency was also linked to higher expression of skin barrier genes and number of lamellar bodies.

CONCLUSIONS

These findings indicate that ALCAM may contribute to AD pathogenesis by meditating a Th2-dominant immune response and disrupting the barrier function of the skin.

A sequence conserved between CD5 and CD6 binds an FERM domain and exerts a restraint on T-cell activation

CD5 and CD6 are related surface receptors that limit and promote T‐cell responses. Co‐stimulatory effects of CD6 depend on binding a cell surface ligand, CD166, and recruitment of the intracellular adaptor proteins GADS and SLP‐76 by C‐terminal phosphotyrosines. We have continued to identify interactions of CD5 and CD6 to understand their roles in T‐cell activation. In a screen to identify binding partners for peptides containing a cytoplasmic sequence, SDSDY conserved between CD5 and CD6, we identified ezrin radixin moesin (ERM) proteins, which link plasma membrane proteins to actin. Purified radixin FERM domain bound directly to CD5 and CD6 SDSDY peptides in a phosphorylation‐dependent manner (K_D = 0·5‐2 μm) at 37°. In human T‐cell blasts, mutation of the CD6 SDSDY sequence enhanced CD69 expression in response to CD3 monoclonal antibody. In this proximal readout, interactions of the SDSDY sequence were dominant compared with the C‐terminal tyrosines of CD6. In contrast, in a more downstream readout, interleukin‐2 expression, in response to immobilized CD3 and CD6 monoclonal antibodies, the C‐terminal tyrosines were dominant. The data suggest that varying functional effects of CD6 and potentially CD5 depend on interactions of different cytoplasmic regions with the cytoskeleton and alter depending on the stimuli.

Addition of the C-terminus of CD6 to a chimeric antigen receptor enhances cytotoxicity and does not compromise expression

T cells expressing chimeric antigen receptors (CARs) are a promising new cancer immunotherapy that has now reached the clinic. CARs are synthetic receptors that redirect T cells towards a tumour‐associated antigen and activate them through various fused signalling regions, for example derived from CD3ζ, 4‐1BB or CD28. Analysis of the optimal combination of CAR components including signalling domains is not yet comprehensive and may vary with the particular application. The C‐terminus of the T‐cell surface receptor CD6 is critical for its co‐stimulatory effects and signals through two phospho‐tyrosine motifs that bind to the intracellular adaptor proteins GADS and SLP‐76. Addition of the C terminus of CD6 did not compromise CAR expression, showing it was a stable moiety that can be used independently of the native receptor. A third‐generation CAR containing 4‐1BB, CD3ζ and the C terminus of CD6 (4‐1BBz‐CD6) enhanced interferon‐γ release and cytotoxicity when compared with the second‐generation 4‐1BB CD3ζ (4‐1BBz) CAR. The CD6 C terminus is a valuable addition to potential components for modular design of CARs to improve effector function, particularly cytotoxicity.

Biophysical Characterization of CD6-TCR/CD3 Interplay in T Cells

Activation of the T cell receptor (TCR) on the T cell through ligation with antigen-MHC complex of an antigen-presenting cell (APC) is an essential process in the activation of T cells and induction of the subsequent adaptive immune response. Upon activation, the TCR, together with its associated co-receptor CD3 complex, assembles in signaling microclusters that are transported to the center of the organizational structure at the T cell-APC interface termed the immunological synapse (IS). During IS formation, local cell surface receptors and associated intracellular molecules are reorganized, ultimately creating the typical bull's eye-shaped pattern of the IS. CD6 is a surface glycoprotein receptor, which has been previously shown to associate with CD3 and co-localize to the center of the IS in static conditions or stable T cell-APC contacts. In this study, we report the use of different experimental set-ups analyzed with microscopy techniques to study the dynamics and stability of CD6-TCR/CD3 interaction dynamics and stability during IS formation in more detail. We exploited antibody spots, created with microcontact printing, and antibody-coated beads, and could demonstrate that CD6 and the TCR/CD3 complex co-localize and are recruited into a stimulatory cluster on the cell surface of T cells. Furthermore, we demonstrate, for the first time, that CD6 forms microclusters co-localizing with TCR/CD3 microclusters during IS formation on supported lipid bilayers. These co-localizing CD6 and TCR/CD3 microclusters are both radially transported toward the center of the IS formed in T cells, in an actin polymerization-dependent manner. Overall, our findings further substantiate the role of CD6 during IS formation and provide novel insight into the dynamic properties of this CD6-TCR/CD3 complex interplay. From a methodological point of view, the biophysical approaches used to characterize these receptors are complementary and amenable for investigation of the dynamic interactions of other membrane receptors.

CD6 monoclonal antibodies differ in epitope, kinetics and mechanism of action

CD6 is a type I T-cell surface receptor that modulates antigen receptor signalling. Its activity is regulated by binding of its membrane proximal domain (domain 3) to a cell surface ligand, CD166. CD6 monoclonal antibodies (mAbs) specific for the membrane distal domain (domain 1) perturb CD6 function including itolizumab (Alzumab™), which has reached the clinic for treatment of autoimmune disease. We characterized molecular and functional properties of several CD6 mAbs including itolizumab to define potential mechanisms of action. Epitope mapping using the crystal structure of CD6 to design mutants identified two distinct binding sites on different faces of domain 1, one containing residue R77, crucial for MT605 and T12.1 binding and the other, E63, which is crucial for itolizumab and MEM98. Analysis of binding kinetics revealed that itolizumab has a lower affinity compared with other CD6 domain 1 mAbs. We compared potential agonistic (triggering) and antagonistic (blocking) properties of CD6 mAbs in assays where the mechanism of action was well defined. CD6 domain 1 and 3 mAbs were equally effective in triggering interleukin-2 production by a cell line expressing a chimeric antigen receptor containing the extracellular region of CD6. CD6 domain 1 mAbs hindered binding of multivalent immobilized CD166 but were inferior compared with blocking by soluble CD166 or a CD6 domain 3 mAb. Characterization of CD6 mAbs provides an insight into how their functional effects in vivo may be interpreted and their therapeutic use optimized.

Tetraspanin CD9: A Key Regulator of Cell Adhesion in the Immune System

The tetraspanin CD9 is expressed by all the major subsets of leukocytes (B cells, CD4⁺ T cells, CD8⁺ T cells, natural killer cells, granulocytes, monocytes and macrophages, and immature and mature dendritic cells) and also at a high level by endothelial cells. As a typical member of the tetraspanin superfamily, a prominent feature of CD9 is its propensity to engage in a multitude of interactions with other tetraspanins as well as with different transmembrane and intracellular proteins within the context of defined membranal domains termed tetraspanin-enriched microdomains (TEMs). Through these associations, CD9 influences many cellular activities in the different subtypes of leukocytes and in endothelial cells, including intracellular signaling, proliferation, activation, survival, migration, invasion, adhesion, and diapedesis. Several excellent reviews have already covered the topic of how tetraspanins, including CD9, regulate these cellular processes in the different cells of the immune system. In this mini-review, however, we will focus particularly on describing and discussing the regulatory effects exerted by CD9 on different adhesion molecules that play pivotal roles in the physiology of leukocytes and endothelial cells, with a particular emphasis in the regulation of adhesion molecules of the integrin and immunoglobulin superfamilies.

Activated leucocyte cell adhesion molecule (ALCAM/CD166) regulates T cell responses in a murine model of food allergy

Food allergy is a major public health problem. Studies have shown that long-term interactions between activated leucocyte cell adhesion molecule (ALCAM/CD166) on the surface of antigen-presenting cells, and CD6, a co-stimulatory molecule, influence immune responses. However, there are currently no studies on the functions of ALCAM in food allergy. Therefore, we aimed to identify the functions of ALCAM in ovalbumin (OVA)-induced food allergy using ALCAM-deficient mice. Wild-type (WT) and ALCAM-deficient (ALCAM^-/- ) mice were sensitized intraperitoneally and with orally fed OVA. The mice were killed, and parameters related to food allergy and T helper type 2 (Th2) immune responses were analysed. ALCAM serum levels increased and mRNA expression decreased in OVA-challenged WT mice. Serum immunoglobulin (Ig)E levels, Th2 cytokine mRNA and histological injuries were higher in OVA-challenged WT mice than in control mice, and these were attenuated in ALCAM^-/- mice. T cell proliferation of total cells, CD3⁺ CD4⁺ T cells and activated T cells in immune tissues were diminished in OVA-challenged ALCAM^-/- mice. Proliferation of co-cultured T cells and dendritic cells (DCs) was decreased by the anti-CD6 antibody. In addition, WT mice sensitized by adoptive transfer of OVA-pulsed ALCAM^-/- BM-derived DCs showed reduced immune responses. Lastly, serum ALCAM levels were higher in children with food allergy than in control subjects. In this study, serum levels of ALCAM were elevated in food allergy-induced WT mice and children with food allergy. Moreover, immune responses and T cell activation were attenuated in OVA-challenged ALCAM^-/- mice. These results indicate that ALCAM regulates food allergy by affecting T cell activation.

Alternative splicing of ALCAM enables tunable regulation of cell-cell adhesion through differential proteolysis

While many adhesion receptors are known to influence tumor progression, the mechanisms by which they dynamically regulate cell-cell adhesion remain elusive. We previously identified Activated Leukocyte Cell Adhesion Molecule (ALCAM) as a clinically relevant driver of metastasis and hypothesized that a tunable mechanism of ectodomain shedding regulates its contribution to dissemination. To test this hypothesis, we examined an under-explored ALCAM splice variant (ALCAM-Iso2) and demonstrated that loss of the membrane-proximal region of ALCAM (exon 13) increased metastasis four-fold. Mechanistic studies identified a novel MMP14-dependent membrane distal cleavage site in ALCAM-Iso2, which mediated a ten-fold increase in shedding, thereby decreasing cellular cohesion. Importantly, the loss of cohesion is not limited to the cell capable of shedding because the released extracellular domain diminished cohesion of non-shedding cells through disruption of ALCAM-ALCAM interactions. ALCAM-Iso2-dominated expression in bladder cancer tissue, compared to normal bladder, further emphasizes that ALCAM alternative splicing may contribute to clinical disease progression. The requirement for both the loss of exon 13 and the gain of metalloprotease activity suggests that ALCAM shedding and concomitant regulation of tumor cell adhesion is a locally tunable process.

Prognostic Significance of Activated Leukocyte Cell Adhesion Molecule (ALCAM) in Association with Promoter Methylation of the ALCAM Gene in Breast Cancer

Activated leukocyte cell adhesion molecule (ALCAM) has been implicated in tumorigenesis. In this study, we studied DNA methylation status of the ALCAM gene using pyrosequencing in breast cancer tissues. We analyzed the association between the methylation status of the ALCAM gene and its expression. Also, the effects of inflammation on the ALCAM gene methylation and its expression were investigated. The ALCAM gene methylation was associated with the ALCAM transcripts in tumor tissues. The methylation status of the ALCAM gene was not significantly different between tumor and normal tissues. The level of ALCAM transcripts was associated with the expression of TNFα, NF-κB p50, IL-4, and intratumoral inflammation. The IHC expression of ALCAM was associated with histologic grade, HER2 overexpression and molecular subtype. The expression of TNFα, NF-κB p50, and IL-4 showed significant association with the clinicopathologic characteristics. In conclusion, the ALCAM gene methylation was related to the level of ALCAM transcripts. Also, the level of ALCAM transcripts was associated with the inflammatory markers in breast cancer. Our results suggest that the methylation of the ALCAM gene contributes to the decreased expression of ALCAM. Also, ALCAM is linked to the inflammatory response in breast cancer.

Stromal Expression of Activated Leukocyte Cell Adhesion Molecule Promotes Lung Tumor Growth and Metastasis

Activated leukocyte cell adhesion molecule (ALCAM) is expressed on various cell types, including leukocytes, endothelial cells, and certain tumor cells. Although ALCAM expression on tumor cells has been linked to tumor invasion and metastatic spread, the contribution of ALCAM expressed in cells forming the tumor stroma to cancer progression has not been investigated. In this study, ALCAM-deficient (ALCAM^-/-) mice were used to evaluate the role of ALCAM in lung tumor growth and metastasis. ALCAM^-/- mice displayed an altered blood vascular network in the lung and the diaphragm, indicative of an angiogenetic defect. The absence of ALCAM expression in cells forming the stromal tumor microenvironment profoundly affected lung tumor growth in three different i.v. metastasis models. In the case of Lewis lung carcinoma (LLC), an additional defect in tumor cell homing to the lungs and a resulting reduction in the number of lung tumor nodules were observed. Similarly, when LLC cells were implanted subcutaneously for the study of spontaneous tumor cell metastasis, the rate of LLC metastasis to the lungs was profoundly reduced in ALCAM^-/- mice. Taken together, our work demonstrates for the first time the in vivo contribution of ALCAM to angiogenesis and reveals a novel role of stromally expressed ALCAM in supporting tumor growth and metastatic spread.

Expression of ALCAM (CD166) and PD-L1 (CD274) independently predicts shorter survival in malignant pleural mesothelioma

Diffuse malignant mesothelioma of the pleura is a highly aggressive tumor typically associated with short survival. ALCAM (CD166), a type I transmembrane protein, is a member of the immunoglobulin superfamily. In normal cells, ALCAM regulates physiological processes such as angiogenesis and immune response. In cancer, it is associated with neoplastic progression, including invasion, migration, and metastasis. Furthermore, ALCAM is considered one of the cancer stem cell markers such as ALDH1 (ALDH1A1) and SALL4. The PD-L1 (CD274)/PD-1 (PDCD1, CD279) pathway is crucial for the modulation of immune responses in normal cells. Nevertheless, pathologic activation of the PD-L1/PD-1 pathway participates in immune evasion by tumor cells. Many PD-L1-expressing tumor cells have been identified in different types of cancer, including malignant mesothelioma. In this study, 175 well-characterized primary diffuse pleural mesotheliomas, including the epithelioid (n = 148), biphasic (n = 15), and sarcomatoid (n = 12) histotypes, were evaluated immunohistochemically for cancer stem cell markers (ALCAM, ALDH1, and SALL4) and PD-L1 expression. Twenty-five percent of the mesotheliomas (43/175) expressed ALCAM, whereas ALDH1 and SALL4 positivity was seen in 1% to 2% of cases. Thirty-three percent of the analyzed tumors (57/175) contained PD-L1-positive cells. Overall survival was significantly decreased in the cohort of patients with ALCAM- or PD-L1-positive tumors (both P < .01). Furthermore, the multivariate Cox hazards regression analysis identified ALCAM and PD-L1 (both P < 0.01) as potential independent risk factors. Thus, a combination of these 2 markers might be useful for prognostication and planning the treatment of patients with malignant pleural mesothelioma.

CD318 is a ligand for CD6

It has been proposed that CD6, an important regulator of T cells, functions by interacting with its currently identified ligand, CD166, but studies performed during the treatment of autoimmune conditions suggest that the CD6-CD166 interaction might not account for important functions of CD6 in autoimmune diseases. The antigen recognized by mAb 3A11 has been proposed as a new CD6 ligand distinct from CD166, yet the identity of it is hitherto unknown. We have identified this CD6 ligand as CD318, a cell surface protein previously found to be present on various epithelial cells and many tumor cells. We found that, like CD6 knockout (KO) mice, CD318 KO mice are also protected in experimental autoimmune encephalomyelitis. In humans, we found that CD318 is highly expressed in synovial tissues and participates in CD6-dependent adhesion of T cells to synovial fibroblasts. In addition, soluble CD318 is chemoattractive to T cells and levels of soluble CD318 are selectively and significantly elevated in the synovial fluid from patients with rheumatoid arthritis and juvenile inflammatory arthritis. These results establish CD318 as a ligand of CD6 and a potential target for the diagnosis and treatment of autoimmune diseases such as multiple sclerosis and inflammatory arthritis.

SK, Montero E, Pai HV, Palanivelu DV, Melarkode R, Nair P. T cell activation and differentiation is modulated by a CD6 domain 1 antibody Itolizumab

CD6 is associated with T-cell modulation and is implicated in several autoimmune diseases. We previously demonstrated that Itolizumab, a CD6 domain 1 (CD6D1) specific humanized monoclonal antibody, inhibited the proliferation and cytokine production by T lymphocytes stimulated with anti-CD3 antibody or when co-stimulated with ALCAM. Aberrant IL-17 producing CD4+ helper T-cells (Th17) have been identified as pivotal for the pathogenesis of certain inflammatory autoimmune disorders, including psoriasis. Itolizumab has demonstrated efficacy in human diseases known to have an IL-17 driven pathogenesis. Here, in in vitro experiments we show that by day 3 of human PBMC activation using anti-CD3 and anti-CD28 co-stimulation in a Th17 polarizing milieu, 15-35% of CD4+ T-cells overexpress CD6 and there is an establishment of differentiated Th17 cells. Addition of Itolizumab reduces the activation and differentiation of T cells to Th17 cells and decreases production of IL-17. These effects are associated with the reduction of key transcription factors pSTAT3 and RORγT. Further, transcription analysis studies in these conditions indicate that Itolizumab suppressed T cell activation by primarily reducing cell cycle, DNA transcription and translation associated genes. To understand the mechanism of this inhibition, we evaluated the effect of this anti-human CD6D1 mAb on ALCAM-CD6 as well as TCR-mediated T cell activation. We show that Itolizumab but not its F(ab')2 fragment directly inhibits CD6 receptor hyper-phosphorylation and leads to subsequent decrease in associated ZAP70 kinase and docking protein SLP76. Since Itolizumab binds to CD6 expressed only on human and chimpanzee, we developed an antibody binding specifically to mouse CD6D1. This antibody successfully ameliorated the incidence of experimental autoimmune encephalitis in the mice model. These results position CD6 as a key molecule in sustaining the activation and differentiation of T cells and an important target for modulating autoimmune diseases.

Human CD6 Down-Modulation following T-Cell Activation Compromises Lymphocyte Survival and Proliferative Responses

Available evidence indicates that the CD6 lymphocyte surface receptor is involved in T-cell developmental and activation processes, by facilitating cell-to-cell adhesive contacts with antigen-presenting cells and likely modulating T-cell receptor (TCR) signaling. Here, we show that in vitro activation of human T cells under different TCR-ligation conditions leads to surface downregulation of CD6 expression. This phenomenon was (i) concomitant to increased levels of soluble CD6 (sCD6) in culture supernatants, (ii) partially reverted by protease inhibitors, (iii) not associated to CD6 mRNA down-regulation, and (iv) reversible by stimulus removal. CD6 down-modulation inversely correlated with the upregulation of CD25 in both FoxP3⁻ (T_act) and FoxP3⁺ (T_reg) T-cell subsets. Furthermore, ex vivo analysis of peripheral CD4⁺ and CD8⁺ T cells with activated (CD25⁺) or effector memory (effector memory T cell, CD45RA⁻CCR7⁻) phenotype present lower CD6 levels than their naïve or central memory (central memory T cell, CD45RA⁻CCR7⁺) counterparts. CD6^lo/− T cells resulting from in vitro T-cell activation show higher apoptosis and lower proliferation levels than CD6^hi T cells, supporting the relevance of CD6 in the induction of proper T-cell proliferative responses and resistance to apoptosis. Accordingly, CD6 transfectants also showed higher viability when exposed to TCR-independent apoptosis-inducing conditions in comparison with untransfected cells. Taken together, these results provide insight into the origin of sCD6 and the previously reported circulating CD6-negative T-cell subset in humans, as well as into the functional consequences of CD6 down-modulation on ongoing T-cell responses, which includes sensitization to apoptotic events and attenuation of T-cell proliferative responses.

ALCAM a novel biomarker in patients with type 2 diabetes mellitus complicated with diabetic nephropathy

BACKGROUND & AIM

Activated leukocyte cell adhesion molecule (ALCAM/CD166) functions analogue to the receptor of advanced glycation end products, which has been implicated in the development of diabetic nephropathy (DN). We investigated the expression of ALCAM and its ligand S100B in patients with DN.

METHODS

A total of 34 non-diabetic patients, 29 patients with type 2 diabetes and normal albuminuria and 107 patients with type 2 diabetes complicated with DN were assessed for serum concentration of soluble ALCAM (sALCAM) by ELISA. Expression of ALCAM and S100B in kidney histology from patients with DN was determined by immunohistochemistry. Cell expression of ALCAM and S100B was analyzed through confocal immunofluorescence microscopy.

RESULTS

Serum concentration of sALCAM was increased in diabetic patients with DN compared to non-diabetic (59.85±14.99ng/ml vs. 126.88±66.45ng/ml, P<0.0001). Moreover sALCAM correlated positively with HbA1c (R=0.31, P<0.0001), as well as with the stages of chronic kidney disease and negatively correlated with eGFR (R=-0.20, P<0.05). In diabetic patients with normal albuminuria sALCAM was increased compared to patients with DN (126.88±66.45ng/ml vs. 197.50±37.17ng/ml, P<0.0001). In diabetic patients, ALCAM expression was significantly upregulated in both the glomeruli and tubules (P<0.001). ALCAM expression in the glomeruli correlated with presence of sclerosis (R=0.25, P<0.001) and localized mainly in the podocytes supporting the hypothesis that membrane bound ALCAM drives diabetic nephropathy and thus explaining sALCAM decrease in diabetic patients with DN. The expression of S100B was increased significantly in the glomeruli of diabetic patients (P<0.001), but not in the tubules. S100B was as well localized in the podocytes.

CONCLUSIONS

This study identifies for the first time ALCAM as a potential mediator in the late complications of diabetes in the kidney.

Relevance of CD6-Mediated Interactions in the Regulation of Peripheral T-Cell Responses and Tolerance

The CD6 lymphocyte receptor has been involved in the pathophysiology of different autoimmune disorders and is now considered a feasible target for their treatment. In vitro data show the relevance of CD6 in the stabilization of adhesive contacts between T-cell and antigen-presenting cells, and the modulation of T-cell receptor signals. However, the in vivo consequences of such a function are yet undisclosed due to the lack of suitable genetically modified animal models. Here, the in vitro and in vivo challenge of CD6-deficient (CD6^-/-) cells with allogeneic cells was used as an approach to explore the role of CD6 in immune responses under relative physiological stimulatory conditions. Mixed lymphocyte reaction (MLR) assays showed lower proliferative responses of splenocytes from CD6^-/- mice together with higher induction of regulatory T cells (T_reg, CD4⁺CD25⁺FoxP3⁺) with low suppressive activity on T and B-cell proliferation. In line with these results, CD6^-/- mice undergoing a lupus-like disorder induced by chronic graft-versus-host disease (cGvHD) showed higher serum titers of anti-double-stranded DNA and nucleosome autoantibodies. This occurred together with reduced splenomegaly, which was associated with lower in vivo bromodesoxyuridine incorporation of spleen cells and with increased percentages of spleen follicular B cells (B2, CD21⁺CD23^hi) and T_reg cells. Interestingly, functional analysis of in vivo-generated CD6^-/- T_reg cells exhibited defective suppressive activity. In conclusion, the data from MLR and cGvHD-induced lupus-like models in CD6^-/- mice illustrate the relevance of CD6 in T (and B) cell proliferative responses and, even more importantly, T_reg induction and suppressive function in the in vivo maintenance of peripheral tolerance.

T Cell Costimulation by CD6 Is Dependent on Bivalent Binding of a GADS/SLP-76 Complex

The cell surface receptor CD6 regulates T cell activation in both activating and inhibitory manners. The adaptor protein SLP-76 is recruited to the phosphorylated CD6 cytoplasmic Y662 residue during T cell activation, providing an activating signal to T cells. In this study, a biochemical approach identified the SH2 domain-containing adaptor protein GADS as the dominant interaction partner for the CD6 cytoplasmic Y629 residue. Functional experiments in human Jurkat and primary T cells showed that both mutations Y629F and Y662F abolished costimulation by CD6. In addition, a restraint on T cell activation by CD6 was revealed in primary T cells expressing CD6 mutated at Y629 and Y662. These data are consistent with a model in which bivalent recruitment of a GADS/SLP-76 complex is required for costimulation by CD6.

A Proteomic Analysis of the Malignant Mesothelioma Secretome Using iTRAQ

Backgound/Aim: Malignant mesothelioma (MM) is an aggressive and fatal pleural cancer. The cell secretome offers information allowing insight into the pathogenesis of MM while offering the possibility to identify potential therapeutic targets and biomarkers. In the present study the secretome protein profile of MM cell lines was compared to normal mesothelial cells.

MATERIALS AND METHODS

Six MM cell lines were compared against three primary mesothelial cell culture preparations using iTRAQ® mass spectrometry.

RESULTS

MM cell lines more abundantly secreted exosome-associated proteins than mesothelial cells. MM cell secretomes were enriched in proteins that are involved in response to stress, carbon metabolism, biosynthesis of amino acids, antigen processing and presentation and protein processing in the endoplasmic reticulum.

CONCLUSION

The MM cell secretome is enriched in proteins that are likely to enhance its growth and response to stress and help it inhibit an adaptive immune response. These are potential targets for therapeutic and biomarker discovery.

Serum CD166: A novel biomarker for predicting nasopharyngeal carcinoma response to radiotherapy

The present study aimed to identify whether CD166 can be used as a biomarker for predicting the response of nasopharyngeal carcinoma (NPC) to radiotherapy. The serum concentration of CD166 in patients with NPC were detected by enzyme-linked immunosorbent assay. The secreted level of CD166 with radioresistant NPC was significantly higher than that with radiosensitive NPC. In vitro, the CD166 positive rate in the CNE2 cell membrane was significantly lower than that in the CNE2R cell membrane. The magnetic-activated cell sorting technology was used to obtain CNE-2R-CD166(+) and CNE-2R-CD166(−) cell lines. Then radiosensitivity, cell proliferation, and apoptosis were assessed using colony formation assay, cell counting kit 8 assay (CCK-8), and flow cytometry, respectively. The radiation sensitivity ratio was 1.28, indicating that the CNE2R-CD166(−) cells had a stronger radiation sensitivity. The result of CCK-8 assay indicated that the survival fraction of CNE2R-CD166(+) cells was significantly higher than that of CNE2R-CD166(−) cells. The apoptotic rate of CNE2R-CD166(+) cells was significantly lower than that of CNE2R-CD166(−) cells. Our data demonstrate that the secreted protein CD166 may be can used as a biomarker for predicting the response of NPC to radiotherapy.

Dual role of ALCAM in neuroinflammation and blood-brain barrier homeostasis

Activated leukocyte cell adhesion molecule (ALCAM) is a cell adhesion molecule found on blood-brain barrier endothelial cells (BBB-ECs) that was previously shown to be involved in leukocyte transmigration across the endothelium. In the present study, we found that ALCAM knockout (KO) mice developed a more severe myelin oligodendrocyte glycoprotein (MOG)_35-55-induced experimental autoimmune encephalomyelitis (EAE). The exacerbated disease was associated with a significant increase in the number of CNS-infiltrating proinflammatory leukocytes compared with WT controls. Passive EAE transfer experiments suggested that the pathophysiology observed in active EAE was linked to the absence of ALCAM on BBB-ECs. In addition, phenotypic characterization of unimmunized ALCAM KO mice revealed a reduced expression of BBB junctional proteins. Further in vivo, in vitro, and molecular analysis confirmed that ALCAM is associated with tight junction molecule assembly at the BBB, explaining the increased permeability of CNS blood vessels in ALCAM KO animals. Collectively, our data point to a biologically important function of ALCAM in maintaining BBB integrity.

CD6 Receptor Regulates Intestinal Ischemia/Reperfusion-induced Injury by Modulating Natural IgM-producing B1a Cell Self-renewal

Intestinal ischemia/reperfusion (I/R) injury is a relatively common pathological condition that can lead to multi-organ failure and mortality. Regulatory mechanism for this disease is poorly understood, although it is established that circulating pathogenic natural IgM, which is primarily produced by B1a cells outside of the peritoneal cavity, are integrally involved. CD6 was originally identified as a marker for T cells and was later found to be present on some subsets of B cells in humans; however, whether CD6 plays any role in intestinal I/R-induced injury and, if so, the underlying mechanisms, remain unknown. Here we report that CD6^-/- mice were significantly protected from intestinal inflammation and mucosal damage compared with WT mice in a model of intestinal I/R-induced injury. Mechanistically, we found that CD6 was selectively expressed on B1 cells outside of the bone marrow and peritoneal cavity and that pathogenic natural IgM titers were reduced in the CD6^-/- mice in association with significantly decreased B1a cell population. Our results reveal an unexpected role of CD6 in the pathogenesis of intestinal IR-induced injury by regulating the self-renewal of B1a cells.

Transcriptional and functional characterization of CD137L-dendritic cells identifies a novel dendritic cell phenotype

The importance of monocyte-derived dendritic cells (DCs) is evidenced by the fact that they are essential for the elimination of pathogens. Although in vitro DCs can be generated by treatment of monocytes with GM-CSF and IL-4, it is unknown what stimuli induce differentiation of DCs in vivo. CD137L-DCs are human monocyte-derived DC that are generated by CD137 ligand (CD137L) signaling. We demonstrate that the gene signature of in vitro generated CD137L-DCs is most similar to those of GM-CSF and IL-4-generated immature DCs and of macrophages. This is reminiscent of in vivo inflammatory DC which also have been reported to share gene signatures with monocyte-derived DCs and macrophages. Performing direct comparison of deposited human gene expression data with a CD137L-DC dataset revealed a significant enrichment of CD137L-DC signature genes in inflammatory in vivo DCs. In addition, surface marker expression and cytokine secretion by CD137L-DCs resemble closely those of inflammatory DCs. Further, CD137L-DCs express high levels of adhesion molecules, display strong attachment, and employ the adhesion molecule ALCAM to stimulate T cell proliferation. This study characterizes the gene expression profile of CD137L-DCs, and identifies significant similarities of CD137L-DCs with in vivo inflammatory monocyte-derived DCs and macrophages.

CD6 modulates thymocyte selection and peripheral T cell homeostasis

Orta-Mascaró, Lozano, and collaborators provide the first analysis of CD6-deficient mice, showing that this molecule modulates T cell receptor signaling and the threshold for thymocyte and peripheral T cell subset selection.

The CD6 glycoprotein is a lymphocyte surface receptor putatively involved in T cell development and activation. CD6 facilitates adhesion between T cells and antigen-presenting cells through its interaction with CD166/ALCAM (activated leukocyte cell adhesion molecule), and physically associates with the T cell receptor (TCR) at the center of the immunological synapse. However, its precise role during thymocyte development and peripheral T cell immune responses remains to be defined. Here, we analyze the in vivo consequences of CD6 deficiency. CD6^−/− thymi showed a reduction in both CD4⁺ and CD8⁺ single-positive subsets, and double-positive thymocytes exhibited increased Ca²⁺ mobilization to TCR cross-linking in vitro. Bone marrow chimera experiments revealed a T cell–autonomous selective disadvantage of CD6^−/− T cells during development. The analysis of TCR-transgenic mice (OT-I and Marilyn) confirmed that abnormal T cell selection events occur in the absence of CD6. CD6^−/− mice displayed increased frequencies of antigen-experienced peripheral T cells generated under certain levels of TCR signal strength or co-stimulation, such as effector/memory (CD4⁺T_EM and CD8⁺T_CM) and regulatory (T reg) T cells. The suppressive activity of CD6^−/− T reg cells was diminished, and CD6^−/− mice presented an exacerbated autoimmune response to collagen. Collectively, these data indicate that CD6 modulates the threshold for thymocyte selection and the generation and/or function of several peripheral T cell subpopulations, including T reg cells.