Expression of CD6 in Aggressive NK/T-cell Neoplasms and Assessment as a Potential Therapeutic Target: A Bone Marrow Pathology Group Study.

BACKGROUND: Aggressive NK/T-Cell neoplasms are rare hematological malignancies characterized by the abnormal proliferation of NK or NK-like T (NK/T) cells. CD6 is a transmembrane signal transducing receptor involved in lymphocyte activation and differentiation. This study aimed to investigate the CD6 expression in these malignancies and explore the potential of targeting CD6 in these diseases. MATERIALS AND METHODS: We conducted a retrospective study with totally 41 cases to investigate the expression of CD6 by immunohistochemistry, including aggressive NK-cell leukemia/lymphoma (ANKLL: N = 10) and extranodal NK/T-cell lymphoma (ENKTL: N = 31). A novel ANKLL model was applied for proof-of-concept functional studies of a CD6 antibody-drug-conjugate (CD6-ADC) both in vitro and in animal trial. RESULTS: CD6 was expressed in 68.3% (28/41) of cases (70% (7/10) of ANKLL and 67.7% (21/31) of ENKTL). The median overall survival (OS) for ANKLL and ENTKL cases was 1 and 12 months, respectively, with no significant difference in OS based on CD6 expression (p > 0.05, Kaplan-Meier with log-rank test). In vitro exposure of the CCANKL cell line, derived from an ANKL patient, to an anti-CD6ADC resulted in dose dependent induction of apoptosis. Furthermore, CCANKL engraftment in NSG mice could be blocked by treatment with the anti-CD6 ADC. CONCLUSION: To date, this is the first report to explore the expression of CD6 in ANKLL and ENKTL and confirms its expression in the majority of cases. The in vitro and in vivo data support further investigation of CD6 as a potential therapeutic target in these aggressive NK/T-cell malignancies.

Soluble CD72, is a T-cell activator probably via binding to CD6 in homeostasis and autoimmunity.

Background: CD72 is a highly required regulatory molecule in B cells. Its sufficient expression is crucial for maintaining self-tolerance. In contrast, soluble CD72 (sCD72) is reported to be increased in the serum of autoimmune diseases such as systemic lupus erythematosus and primary Sjogren's syndrome (pSS). Objective: We wanted to assess the biological effect of sCD72 on CD4+T cells. Methods: We performed mass spectrometry and co-immunoprecipitation experiments to look for a sCD72 receptor on activated CD4+T cells. Afterward, to explore the biological functions of sCD72, we used flow cytometry for the cytokine secretion profile, a phosphorylation assay for the signaling pathway, and a CFSE dye-based assay for cell proliferation. Results: We found and validated the sCD72 and CD6 interaction as a possible ligand-receptor interaction. We also demonstrated that sCD72 significantly increases the expression of pro-inflammatory cytokines, namely IL-17A and IFN-γ, in activated CD4+T cells and increases the proliferation of CD4+T cells, possibly through its activation of the SLP-76-AKT-mTOR pathway. Conclusion: The sCD72-CD6 axis on activated CD4+T cells is probably a new signaling pathway in the induction of immune-mediated diseases. Therefore, targeting sCD72 may become a valuable therapeutic tool in some autoimmune disorders.

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.

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.

Polymorphisms in the CD6-ALCAM axis may modulate psoriasis risk and outcomes.

The fact that CD6, along with its ligand - ALCAM, plays a role in regulating T cell activation makes the genes encoding these molecules promising candidates for research in T cell-mediated diseases such as psoriasis vulgaris (PsV). Our study aimed to determine whether CD6 (rs17824933C>G, rs11230563C>T and rs12360861G>A) and ALCAM (rs6437585C>T, rs11559013G>A) polymorphisms may affect psoriasis susceptibility and severity (assessed by Psoriasis Area and Severity Index (PASI)). Moreover, the presence of HLA-C*06:02, the strongest psoriasis risk factor in the Caucasian population, was also investigated. 273 patients diagnosed with psoriasis vulgaris and 256 blood donors with no history of PsV or other dermatoses were included in this study. Genotyping of the investigated polymorphisms was carried out using the allelic discrimination method with the application of TaqMan SNP Genotyping Assays. We observed the association of rs17824933G allele with a higher psoriasis risk in HLA-C*06:02(+) individuals (CG + GG vs CC, OR = 1.87, CI95% = 1.03; 3.37, p = 0.0350). Furthermore, we found a difference in average PASI score among groups of patients divided according to the number of CD6 and ALCAM polymorphic sites with minor alleles (F2,173 = 6.159, p = 0.0026). Collectively, our findings suggest that polymorphisms of CD6-ALCAM axis genes may modulate psoriasis risk and outcomes.

Recombinant CD5 and CD6 Ectodomains Induce Antiparasitic and Immunomodulatory Effects in Secondary Cystic Echinococcosis.

Scavenger receptors participate in a wide range of biological functions after binding to multiple non-self or altered self-ligands. Among them, CD5 and CD6 are lymphocyte scavenger receptors known to interact with different microbial-associated molecular patterns, and the administration of the recombinant soluble ectodomains of human CD5 (rshCD5) and/or CD6 (rshCD6) has shown therapeutic/prophylactic potential in experimental models of fungal, bacterial and echinococcal infections. The latter is a zoonosis caused by the larval stage of the cestode parasite Echinococcus granulosus sensu lato, which in humans can induce secondary cystic echinococcosis (CE) after the spillage of protoscoleces contained within fertile cysts, either spontaneously or during surgical removal of primary hydatid cysts. Herein, we have analysed the mechanisms behind the significant protection observed in the mouse model of secondary CE following prophylactic administration of rshCD5 or rshCD6. Our results show that both molecules exhibit intrinsic antiparasitic activities in vitro, as well as immunomodulatory functions during early secondary CE, mainly through Th1/Th17 cytokine bias and promotion of peritoneal polyreactive antibodies. These data support the relevance of the parasite components bound by rshCD5 and rshCD6, as well as the potential of their prophylactic administration as a useful strategy to reduce secondary CE in patients.

Activation of cytotoxic lymphocytes through CD6 enhances killing of cancer cells.

Immune checkpoint inhibitors (ICIs) have demonstrated efficacy and improved survival in a growing number of cancers. Despite their success, ICIs are associated with immune-related adverse events that can interfere with their use. Therefore, safer approaches are needed. CD6, expressed by T-lymphocytes and human NK cells, engages in cell-cell interactions by binding to its ligands CD166 (ALCAM) and CD318 (CDCP1). CD6 is a target protein for regulating immune responses and is required for the development of several mouse models of autoimmunity. Interestingly, CD6 is exclusively expressed on immune cells while CD318 is strongly expressed on most cancers. Here we demonstrate that disrupting the CD6-CD318 axis with UMCD6, an anti-CD6 monoclonal antibody, prolongs survival of mice in xenograft mouse models of human breast and prostate cancer, treated with infusions of human lymphocytes. Analysis of tumor-infiltrating immune cells showed that augmentation of lymphocyte cytotoxicity by UMCD6 is due to effects of this antibody on NK, NKT and CD8 + T cells. In particular, tumor-infiltrating cytotoxic lymphocytes from UMCD6-treated mice expressed higher levels of perforin and were found in higher proportions than those from IgG-treated mice. Moreover, RNA-seq analysis of human NK-92 cells treated with UMCD6 revealed that UMCD6 up-regulates the NKG2D-DAP10 receptor complex, important in NK cell activation, as well as its downstream target PI3K. Our results now describe the phenotypic changes that occur on immune cells upon treatment with UMCD6 and further confirm that the CD6-CD318 axis can regulate the activation state of cytotoxic lymphocytes and their positioning within the tumor microenvironment.

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-1ß 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.

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.

Activation of Cytotoxic Lymphocytes Through CD6 Enhances Killing of Cancer Cells.

Immune checkpoint inhibitors (ICIs) have demonstrated efficacy and improved survival in a growing number of cancers. Despite their success, ICIs are associated with immune-related adverse events that can interfere with their use. Therefore, safer approaches are needed. CD6, expressed by T-lymphocytes and human NK cells, engages in cell-cell interactions by binding to its ligands CD166 (ALCAM) and CD318 (CDCP1). CD6 is a target protein for regulating immune responses and is required for the development of several mouse models of autoimmunity. Interestingly, CD6 is exclusively expressed on immune cells while CD318 is strongly expressed on most cancers. Here we demonstrate that disrupting the CD6-CD318 axis with UMCD6, an anti-CD6 monoclonal antibody, prolongs survival of mice in xenograft models of human breast and prostate cancer, treated with infusions of human lymphocytes. Analysis of tumor-infiltrating immune cells showed that augmentation of lymphocyte cytotoxicity by UMCD6 is due to effects of this antibody on NK, NKT and CD8+ T cells. Tumor-infiltrating cytotoxic lymphocytes were found in higher proportions and were activated in UMCD6-treated mice compared to controls. Similar changes in gene expression were observed by RNA-seq analysis of NK cells treated with UMCD6. Particularly, UMCD6 up-regulated the NKG2D-DAP10 complex and activated PI3K. Thus, the CD6-CD318 axis can regulate the activation state of cytotoxic lymphocytes and their positioning within the tumor microenvironment.

REcovery and SURvival of patients with moderate to severe acute REspiratory distress syndrome (ARDS) due to COVID-19: a multicenter, single-arm, Phase IV itolizumab Trial: RESURRECT.

BACKGROUND: Itolizumab, an anti-CD6 monoclonal antibody, down-regulates COVID-19-mediated inflammation and the acute effects of cytokine release syndrome. This study aimed to evaluate the safety and efficacy of itolizumab in hospitalized COVID-19 patients with PaO2/FiO2 ratio (PFR) ≤200 requiring oxygen therapy. RESEARCH DESIGN AND METHODS: This multicenter, single-arm, Phase 4 study enrolled 300 hospitalized adults with SARS-CoV-2 infection, PFR ≤200, oxygen saturation ≤94%, and ≥1 elevated inflammatory markers from 17 COVID-19 specific tertiary Indian hospitals. Patients received 1.6 mg/kg of itolizumab infusion, were assessed for 1 month, and followed-up to Day 90. Primary outcome measures included incidence of severe acute infusion-related reactions (IRRs) (≥Grade-3) and mortality rate at 1 month. RESULTS: Incidence of severe acute IRRs was 1.3% and mortality rate at 1 month was 6.7% (n = 20/300). Mortality rate at Day 90 was 8.0% (n = 24/300). By Day 7, most patients had stable/improved SpO2 without increasing FiO2 and by Day 30, 91.7% patients were off oxygen therapy. Overall, 63 and 10 patients, respectively, reported 123 and 11 treatment-emergent adverse events up to Days 30 and 90. No deaths were attributable to itolizumab. Patient-reported outcomes showed gradual and significant improvement for all five dimensions on EQ-5D-5L. CONCLUSION: Itolizumab demonstrated acceptable safety with a favorable prognosis in hospitalized COVID-19 patients. CLINICAL TRIAL REGISTRATION: CTRI/2020/09/027941 (Clinical Trials Registry of India).

Keratinocyte-induced costimulation of human T cells through CD6 - but not CD2 - activates mTOR and prevents oxidative stress.

In psoriasis and other inflammatory skin diseases, keratinocytes (KCs) secrete chemokines that attract T cells, which, in turn, cause epidermal hyperplasia by secreting proinflammatory cytokines. To date, it remains unclear whether skin-homing T cells, particularly memory T cells, can also be activated by direct cell contact with KCs. In this study, we demonstrated the ability of primary human KCs to activate human memory T cells directly by transmitting costimulatory signals through the CD6/CD166/CD318 axis. Interestingly, despite being negative for CD80/CD86, KCs initiate a metabolic shift within T cells. Blockade of the CD6/CD166/CD318 axis prevents mammalian target of rapamycin activation and T cell proliferation but promotes oxidative stress and aerobic glycolysis. In addition, it diminishes formation of central memory T cells. Importantly, although KC-mediated costimulation by CD2/CD58 also activates T cells, it cannot compensate for the lack of CD6 costimulation. Therefore, KCs likely differentially regulate T cell functions in the skin through two distinct costimulatory receptors: CD6 and CD2. This may at least in part explain the divergent effects observed when treating inflammatory skin diseases with antibodies to CD6 versus CD2. Moreover, our findings may provide a molecular basis for selective interference with either CD6/CD166/CD318, or CD2/CD58, or both to specifically treat different types of inflammatory skin diseases.

The dual role of CD6 as a therapeutic target in cancer and autoimmune disease.

Autoimmune disease involves loss of tolerance to self-antigen, while progression of cancer reflects insufficient recognition and response of the immune system to malignant cells. Patients with immune compromised conditions tend to be more susceptible to cancer development. On the other hand, cancer treatments, especially checkpoint inhibitor therapies, can induce severe autoimmune syndromes. There is recent evidence that autoimmunity and cancer share molecular targets and pathways that may be dysregulated in both types of diseases. Therefore, there has been an increased focus on understanding these biological pathways that link cancer and its treatment with the appearance of autoimmunity. In this review, we hope to consolidate our understanding of current and emerging molecular targets used to treat both cancer and autoimmunity, with a special focus on Cluster of Differentiation (CD) 6.

Experimental and genetic evidence for the impact of CD5 and CD6 expression and variation in inflammatory bowel disease.

Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBD) resulting from the interaction of multiple environmental, genetic and immunological factors. CD5 and CD6 are paralogs encoding lymphocyte co-receptors involved in fine-tuning intracellular signals delivered upon antigen-specific recognition, microbial pattern recognition and cell adhesion. While CD5 and CD6 expression and variation is known to influence some immune-mediated inflammatory disorders, their role in IBD remains unclear. To this end, Cd5- and Cd6-deficient mice were subjected to dextran sulfate sodium (DSS)-induced colitis, the most widely used experimental animal model of IBD. The two mouse lines showed opposite results regarding body weight loss and disease activity index (DAI) changes following DSS-induced colitis, thus supporting Cd5 and Cd6 expression involvement in the pathophysiology of this experimental IBD model. Furthermore, DNA samples from IBD patients of the ENEIDA registry were used to test association of CD5 (rs2241002 and rs2229177) and CD6 (rs17824933, rs11230563, and rs12360861) single nucleotide polymorphisms with susceptibility and clinical parameters of CD (n=1352) and UC (n=1013). Generalized linear regression analyses showed association of CD5 variation with CD ileal location (rs2241002CC) and requirement of biological therapies (rs2241002C-rs2229177T haplotype), and with poor UC prognosis (rs2241002T-rs2229177T haplotype). Regarding CD6, association was observed with CD ileal location (rs17824933G) and poor prognosis (rs12360861G), and with left-sided or extensive UC, and absence of ankylosing spondylitis in IBD (rs17824933G). The present experimental and genetic evidence support a role for CD5 and CD6 expression and variation in IBD's clinical manifestations and therapeutic requirements, providing insight into its pathophysiology and broadening the relevance of both immunomodulatory receptors in immune-mediated disorders.

Intrahepatic activated leukocyte cell adhesion molecule induces CD6highCD4+ T cell infiltration in autoimmune hepatitis.

Background and objectives: Autoimmune hepatitis (AIH) is characterized by the expansion and accumulation of pathogenic T cells in liver. Although CD6 and its ligand activated leukocyte cell adhesion molecule (ALCAM) are involved in the evolution of multiple inflammatory diseases, their roles in the pathogenesis of AIH remain unknown. Herein, we aimed to investigate ALCAM-CD6 axis in AIH development. Methods: Immunohistochemistry was performed to examine hepatic expression of CD6 and ALCAM. The concentration of serum ALCAM was evaluated by ELISA. The phenotypes of liver infiltrating T cells were determined by flow cytometry. Primary human CD4+ T cells were used for functional studies. Results: Our data showed that patients with AIH exhibited significantly higher expression of CD6 in the liver as compared to primary biliary cholangitis (PBC), chronic hepatitis B (CHB), non-alcoholic liver disease (NAFLD), and healthy controls (HC). In addition, hepatic CD6 expression was strongly correlated with disease severity of AIH. CD6 was mainly expressed on CD4+ T cells in the liver and intrahepatic CD6highCD4+ T cells demonstrated stronger proinflammatory response and proliferation features than CD6low counterparts in both AIH and HC. ALCAM, the ligand of CD6, was highly expressed in the hepatocytes of AIH and serum ALCAM was strongly associated with clinical indices of AIH. Interestingly, close spatial location between CD6+CD4+ T cells and ALCAM+ hepatocytes was observed. Finally, we found that CD6highCD4+ T cells showed enhanced capacity of trans-endothelial migration in vitro, which could be promoted by recombinant ALCAM. Conclusions: Our study found that ALCAM-CD6 axis was upregulated in the AIH liver, suggesting a potential target for alleviating AIH.

Gene variation impact on prostate cancer progression: Lymphocyte modulator, activation, and cell adhesion gene variant contribution.

BACKGROUND: The view of prostate cancer (PCa) progression as a result of the interaction of epithelial cancer cells with the host's immune system is supported by the presence of tumor infiltrating lymphocytes (TILs). TILs fate and interaction with the tumor microenvironment is mediated by accessory molecules such as CD5 and CD6, two signal-transducing coreceptors involved in fine-tuning of T cell responses. While the nature of the CD5 ligand is still controversial, CD6 binds CD166/ALCAM, a cell adhesion molecule involved in progression and dissemination of epithelial cancers, including PCa. The purpose of the present study was to determine the role of CD5, CD6, and CD166/ALCAM gene variants in PCa. METHODS: Functionally relevant CD5 (rs2241002 and rs2229177), CD6 (rs17824933, rs11230563, and rs12360861) and CD166/ALCAM (rs6437585, rs579565, rs1044243, and rs35271455) single nucleotide polymorphisms (SNPs) were genotyped in germline DNA samples from 376 PCa patients. Their association with PCa prognostic factors, namely biochemical recurrence (BCR) and International Society of Urological Pathology (ISUP) grade was analyzed by generalized linear models and survival analyses. RESULT: Proportional hazards regression showed that the minor CD6 rs12360861AA and CD166/ALCAM rs579565AA genotypes were associated with earlier BCR, with hazard ratios of 2.65 (95% CI: 1.39-5.05, p = 0.003) and 1.86, (95% CI: 1.02-3.39, p = 0.043), respectively. Individually, none of the analyzed SNPs was significantly associated with ISUP grade, but haplotype analyses revealed association of the CD5 rs2241002C -rs2229177T haplotype with ISUP grade ≥2, with odds ratio of 1.52 (95% CI: 1.05-2.21, p = 0.026). CONCLUSION: The results show the impact on PCa aggressiveness and recurrence brought about by gene variants involved in modulation of lymphocyte activation (CD5, CD6) and immune-epithelial cell adhesion (CD166/ALCAM) in PCa aggressiveness and recurrence, thus supporting a role for host immune response in PCa pathophysiology.

Blocking FSTL1 boosts NK immunity in treatment of osteosarcoma.

Osteosarcoma (OS) is the most common primary bone malignancy. Many patients develop relapse and metastasis after treatments, and more effective treatments are needed for improving the clinical outcome. FSTL1 overexpression has been reported in murine and human OS, while the functional roles of FSTL1 remain unclear. Here, we elucidated tumor biological and immunological mechanisms underlying the refractory OS using mouse and human OS cell lines, mouse OS models, and clinical specimens. FSTL1 knockout in OS cells significantly suppressed cellular functions, including proliferation, invasion, sphere colony formation, and ALCAM expression. The FSTL1-ablated tumor cells were completely rejected due to generation of potent NK cells in the in vivo setting. Indeed, FSTL1 stimulation suppressed NK activity partly via apoptosis induction, but blocking FSTL1 or CD6, a receptor for ALCAM, significantly restored NK activity. Anti-FSTL1 therapy significantly suppressed tumor growth and metastasis in mouse OS models, and synergized with anti-CD6 therapy in providing significantly better prognosis. These suggest that blocking FSTL1 is a promising strategy for successfully treating OS. This study demonstrates a rationale of targeting the FSTL1-ALCAM axis in the treatment of OS in clinical settings.

Gene Variation at Immunomodulatory and Cell Adhesion Molecules Loci Impacts Primary Sjögren's Syndrome.

Primary Sjögren's syndrome (pSS) is an autoimmune disease triggered by a combination of environmental and host genetic factors, which results in the focal lymphocytic infiltration of exocrine glands causing eye and mouth dryness. Glandular infiltrates include T and B cell subsets positive for CD5 and/or CD6, two surface scavenger receptors involved in the fine-tuning of intracellular signals mediated by the antigen-specific receptor complex of T (TCR) and B (BCR) cells. Moreover, the epithelial cells of inflamed glands overexpress CD166/ALCAM, a CD6 ligand involved in homo and heterotypic cell adhesion interactions. All this, together with the reported association of functionally relevant single nucleotide polymorphisms (SNPs) of CD5, CD6, and CD166/ALCAM with the risk or prognosis of some immune-mediated inflammatory disorders, led us to investigate similar associations in a local cohort of patients with pSS. The logistic regression analyses of individual SNPs showed the association of CD5 rs2241002T with anti-Ro/La positivity, CD6 rs17824933C with neutropenia, and CD6 rs11230563T with increased leukopenia and neutropenia but decreased peripheral nervous system EULAR Sjögren's syndrome disease activity index (ESSDAI). Further analyses showed the association of haplotypes from CD5 (rs2241002T-rs2229177C) with anemia and thrombocytopenia, CD6 (rs17824933G-rs11230563C-rs12360861G) with cutaneous ESSDAI, and CD166/ALCAM (rs6437585C-rs579565A-rs1044243C and rs6437585C-rs579565G-rs1044243T) with disease susceptibility and several analytical parameters (anti-nuclear antibodies, neurological ESSDAI, and hematologic cytopenias). These results support the relevance of gene variation at loci coding for cell surface receptors involved in the modulation of T and B lymphocyte activation (CD5, CD6) and epithelial-immune cell adhesion (CD166/ALCAM) in modulating the clinical and analytical outcomes in patients with pSS.

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.