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ObjectiveThe anti-α4β7 integrin antibody vedolizumab is administered at a fixed dose for the treatment of IBDs. This leads to a wide range of serum concentrations in patients and previous studies had suggested that highest exposure levels are associated with suboptimal clinical response. We aimed to determine the mechanisms underlying these non-linear exposure-efficacy characteristics of vedolizumab.DesignWe characterised over 500 samples from more than 300 subjects. We studied the binding of vedolizumab to T cells and investigated the functional consequences for dynamic adhesion, transmigration, gut homing and free binding sites in vivo. Employing single-cell RNA sequencing, we characterised α4β7 integrin-expressing T cell populations ‘resistant’ to vedolizumab and validated our findings in vitro and in samples from vedolizumab-treated patients with IBD. We also correlated our findings with a post-hoc analysis of the Gemini II and III studies.ResultsRegulatory T (TReg) cells exhibited a right-shifted vedolizumab binding profile compared with effector T (TEff) cells. Consistently, in a certain concentration range, the residual adhesion, transmigration, homing of and availability of functional α4β7 on TReg cells in vivo was higher than that of/on TEff cells. We identified a vedolizumab-‘resistant’ α4β7-expressing β1+PI16+ TReg cell subset with pronounced regulatory properties as the substrate for this effect. Our observations correlated with exposure-efficacy data from Gemini II and III trials.ConclusionCompletely blocking TEff cell trafficking with vedolizumab, while simultaneously permitting residual homing of powerful TReg cells in an optimal ‘therapeutic window’ based on target exposure levels might be a strategy to optimise treatment outcomes in patients with IBD.

Theresa Steeb,1,2 Anja Wessely,1,2 Heike Merkl,3 Caroline Voskens,1,2 Michael Erdmann,1,2 Lucie Heinzerling,1,2 Carola Berking,1,2 Markus V Heppt1,2 1Department of Dermatology, University Hospital Erlangen, Friedrich-Alexander-University (FAU) Erlangen-Nuremberg, Erlangen 91054, Germany; 2Comprehensive Cancer Center Erlangen, European Metropolitan Region of Nuremberg, Erlangen, Germany; 3University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nuremberg (FAU), Erlangen 91054, GermanyCorrespondence: Markus V HepptDepartment of Dermatology, University Hospital Erlangen, Friedrich-Alexander-University (FAU) Erlangen-Nuremberg, Ulmenweg 18, Erlangen 91054, GermanyTel +49-9131-85-35747Email markus.heppt@uk-erlangen.dePurpose: An important measure of hospital quality is the satisfaction of the patients receiving in-patient care. This cross-sectional study aimed to assess skin cancer patients’ experiences in a university hospital setting as a measure of quality of cancer care.Patients and Methods: Questionnaires were mailed to patients with skin cancer after receiving in-patient overnight treatment in the dermatological unit of the university hospital Erlangen (Germany) from 1 September to 30 November 2017. Patients were asked to evaluate their overall experience of this episode of care and to complete the Picker Inpatient Survey questionnaire on specific aspects of their care, such as patient satisfaction regarding contact with staff, need for information, recommendation of the hospital as well as tumor-specific questions. The results were re-coded as problems and reported as frequencies and their percentage.Results: A total of 103 of 159 questionnaires were returned (64.8%). All patients rated the treatment and care they had received to be good or very good. Additionally, all patients would recommend our in-patient clinic to their families or friends. The patients most commonly criticized inconsistency of care delivered by the same physician (29.7%, 30/101) and feeling of insufficient involvement in the decision-making processes (21.1%, 20/95). Besides this, 19.0% (11/58) and 34.6% (18/52) of patients were not satisfied with physicians and nurses, respectively, appropriately addressing their fears or anxieties. In the cancer-specific questionnaire, the majority of patients were dissatisfied with further support regarding professional and social rehabilitation possibilities (85.7%, 30/35) and psycho-oncology (56.3%, 18/32).Conclusion: Overall, the majority of patients were satisfied with the in-patient skin cancer treatment. However, physicians and nurses can enhance patient satisfaction by addressing patients’ fears and anxieties regarding their disease and treatment. Besides, our results highlight the importance of psycho-oncological support.Keywords: patient satisfaction, quality improvement, dermatology, hospital evaluation, in-patient experiences, skin cancer

Natural killer (NK) cells, members of the innate immune system, play an important role in the rejection of HLA class I negative tumor cells. Hence, a therapeutic vaccine, which can activate NK cells in addition to cells of the adaptive immune system might induce a more comprehensive cellular response, which could lead to increased tumor elimination. Dendritic cells (DCs) are capable of activating and expanding NK cells, especially when the NFκB pathway is activated in the DCs thereby leading to the secretion of the cytokine IL-12. Another prominent NK cell activator is IL-15, which can be bound by the IL-15 receptor alpha-chain (IL-15Rα) to be transpresented to the NK cells. However, monocyte-derived DCs do neither secrete IL-15, nor express the IL-15Rα. Hence, we designed a chimeric protein consisting of IL-15 and the IL-15Rα. Upon mRNA electroporation, the fusion protein was detectable on the surface of the DCs, and increased the potential of NFκB-activated, IL-12-producing DC to activate NK cells in an autologous cell culture system with ex vivo-generated cells from healthy donors. These data show that a chimeric IL-15/IL-15Rα molecule can be expressed by monocyte-derived DCs, is trafficked to the cell surface, and is functional regarding the activation of NK cells. These data represent an initial proof-of-concept for an additional possibility of further improving cellular DC-based immunotherapies of cancer.

Natural killer (NK) cells are important effector cells in the immune response to cancer. Clinical trials on adoptively transferred NK cells in patients with solid tumors, however, have thus far been unsuccessful. As NK cells need to pass stringent safety evaluation for clinical use, the cells are cryopreserved to bridge the necessary evaluation time. While a degranulation assay confirms the ability of cryopreserved NK cells to kill target cells, we find a significant decrease of cytotoxicity after cryopreservation in a chromium release assay. We complement these standard assays with measurements of NK cell motility and cytotoxicity in 3-dimensional (3-D) collagen gels that serve as a substitute for connective tissue. We find a 5.6 fold decrease of cytotoxicity after cryopreservation and establish that this is mainly caused by a 6-fold decrease in the fraction of motile NK cells. These findings may explain the persistent failure of NK cell therapy in patients with solid tumors and highlight the crucial role of a 3-D environment for testing NK cell function.SynopsisCryopreservation of natural killer (NK) cells dramatically impairs their motility and cytotoxicity in tissue. This finding may explain the persistent failure of clinical trials in which NK cell therapy is used for treating solid tumors.

IntroductionAccumulating evidence suggests that the adoptive transfer of ex vivo expanded regulatory T cells (Treg) may overcome colitogenic immune responses in patients with inflammatory bowel diseases. The objective of the ER-TREG 01 trial is to assess safety and tolerability of a single infusion of autologous ex vivo expanded Treg in adults with ulcerative colitis.Methods and analysisThe study is designed as a single-arm, fast-track dose-escalation trial. The study will include 10 patients with ulcerative colitis. The study intervention consists of (1) a baseline visit; (2) a second visit that includes a leukapheresis to generate the investigational medicinal product, (3) a third visit to infuse the investigational medicinal product and (4) five subsequent follow-up visits within the next 26 weeks to assess safety and tolerability. Patients will intravenously receive a single dose of 0.5×106, 1×106, 2×106, 5×106 or 10×106autologous Treg/kg body weight. The primary objective is to define the maximum tolerable dose of a single infusion of autologous ex vivo expanded Treg. Secondary objectives include the evaluation of safety of one single infusion of autologous ex vivo expanded Treg, efficacy assessment and accompanying immunomonitoring to measure Treg function in the peripheral blood and intestinal mucosa.Ethics and disseminationThe study protocol was approved by the Ethics Committee of the Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany (number 417_19 Az). In addition, the study was approved by the Paul-Ehrlich Institute, Federal Institute for Vaccines and Biomedicines, Langen, Germany (number 3652/01). The study is funded by the German Research Foundation (DFG, KFO 257 project 08 and SFB/TransRegio 241 project C04). The trial will be conducted in compliance with this study protocol, the Declaration of Helsinki, Good Clinical Practice and Good Manufacturing Practice. The results will be published in peer-reviewed scientific journals and disseminated in scientific conferences and media.Trial registration numberNCT04691232.

In recent years, the exploration of regulatory T cell (Treg)-based cellular therapy has become an attractive strategy to ameliorate inflammation and autoimmunity in various clinical settings. The main obstacle to the clinical application of Treg in human is their low number circulating in peripheral blood. Therefore, ex vivo expansion is inevitable. Moreover, isolation of Treg bears the risk of concurrent isolation of unwanted effector cells, which may trigger or deteriorate inflammation upon adoptive Treg transfer. Here we present a protocol for the GMP-compliant production, lot-release and validation of ex vivo expanded regulatory T cells for treatment of patients with autoimmune and inflammatory disorders. In the presented production protocol, large numbers of Treg, previously enriched from a leukapheresis product by using the CliniMACS® system, are ex vivo expanded in the presence of anti CD3/anti-CD28 expander beads, exogenous IL-2 and rapamycin during 21 days. The expanded Treg drug product passed pre-defined lot release criteria. These criteria include (i) sterility testing, (ii) assessment of Treg phenotype, (iii) assessment of non-Treg cellular impurities, (iv) confirmation of successful anti-CD3/anti-CD28 expander bead removal after expansion, and (v) confirmation of the biological function of the Treg product. Furthermore, the Treg drug product was shown to retain its stability and suppressive function for at least one year after freezing and thawing. Also, dilution of the Treg drug product in 0.9% physiological saline did not affect Treg phenotype and Treg function for up to 90 minutes. These data indicate that these cells are ready to use in a clinical setting in which a cell infusion time of up to 90 minutes can be expected. The presented production process has recently undergone on site GMP-conform evaluation and received GMP certification from the Bavarian authorities in Germany. This protocol can now be used for Treg-based therapy of various inflammatory and autoimmune disorders.

Background A local imbalance between regulatory (Treg) and effector T cells is believed to play a major role in gut-specific inflammation, including ulcerative colitis (UC). Restoration of this balance through an adoptive Treg transfer is an attractive new treatment approach in patients who are refractory to current standard therapies. It was our goal to develop a Good Manufacturing Practices (GMP)-conform protocol for expansion of UC Treg cells as a rational backbone for future studies on Treg therapy in UC. Methods CD25 blood T cells derived from patients with UC were ex vivo expanded in the presence of IL-2, rapamycin, and anti-CD3/anti-CD28 expander beads using a GMP-conform protocol. Cells were subsequently assessed for stability and function. Results Patient-derived ex vivo rapamycin-expanded GMP-ready CD25 cells were polyclonal, hypomethylated at intron 1 of the FoxP3 locus, and suppressive in carboxyfluorescein succinimidyl ester-dilution assays against autologous peripheral blood-derived and allogeneic colon-derived responder cells. Function was mediated by soluble factors, including toxic granules. In addition to CD4 T cells, suppressive hypermethylated CD8 T-cell subsets were also induced during the expansion process. Conclusions Patient-derived rapamycin-expanded CD25 cells are stable and functional, and as such, ready to serve in a phase I dose-escalation safety study in UC.

Objective Gut homing of lymphocytes via adhesion molecules has recently emerged as new target for therapy in IBDs. We aimed to analyse the in vivo homing of effector (Teff) and regulatory (Treg) T cells to the inflamed gut via α4β7 and G protein receptor GPR15. Design We assessed the expression of homing receptors on T cells in peripheral blood and inflamed mucosa. We studied the migration pattern and homing of Teff and Treg cells to the inflamed gut using intravital confocal microscopy and FACS in a humanised mouse model in dextran sodium sulfate-treated NSG (NOD.Cg -Prkdcscid-Il2rgtm1Wjl /SzJ) mice. Results Expression of GPR15 and α4β7 was significantly increased on Treg rather than Teff cells in peripheral blood of patients with UC as compared with Crohn’s disease and controls. In vivo analysis in a humanised mouse model showed augmented gut homing of UC Treg cells as compared with controls. Moreover, suppression of UC (but not control) Teff and Treg cell homing was noted upon treatment with the α4β7 antibody vedolizumab. In contrast, siRNA blockade of GPR15 had only effects on homing of Teff cells but did not affect Treg homing in UC. Clinical vedolizumab treatment was associated with marked expansion of UC Treg cells in peripheral blood. Conclusions α4β7 rather than GPR15 is crucial for increased colonic homing of UC Treg cells in vivo, while both receptors control UC Teff cell homing. Vedolizumab treatment impairs homing of UC Treg cells leading to their accumulation in peripheral blood with subsequent suppression of systemic Teff cell expansion.

Background. We performed a pilot study using Trojan vaccines in patients with advanced squamous cell carcinoma of the head and neck (SCCHN). These vaccines are composed of HLA-I and HLA-II restricted melanoma antigen E (MAGE)-A3 or human papillomavirus (HPV)-16 derived peptides, joined by furin-cleavable linkers, and linked to a "penetrin'' peptide sequence derived from HIV- TAT. Thirty-one patients with SCCHN were screened for the trial and 5 were enrolled. Methods. Enrolled patients were treated with 300 lg of Trojan peptide supplemented with Montanide and granulocyte-macrophage colony- stimulating factor (GM-CSF) at 4-week intervals for up to 4 injections. Results. Following vaccination, peripheral blood mononuclear cells (PBMCs) from 4 of 5 patients recognized both the full Trojan constructs and constituent HLA-II peptides, whereas responses to HLA-I restricted peptides were less pronounced. Conclusion. This treatment regimen seems to have acceptable toxicity and elicits measurable systemic immune responses against HLA-II restricted epitopes in a subset of patients with advanced SCCHN. V C 2012 Wiley Periodicals, Inc. Head Neck 34: 1734-1746, 2012

CD137 (4-1BB)-mediated costimulation plays an important role in directing the fate of Ag-stimulated T cells and NK cells, yet the role of CD137 in mediating B cell function is unknown. We found that CD137 is expressed in vitro on anti-Ig–stimulated peripheral blood B cells and in vivo on tonsillar B cells with an activated phenotype. In vitro CD137 expression is enhanced by CD40 stimulation and IFN-γ and is inhibited by IL-4, -10, and -21. The expression of CD137 on activated human B cells is functionally relevant because engagement with its ligand at the time of activation stimulates B cell proliferation, enhances B cell survival, and induces secretion of TNF-α and -β. Our study suggests that CD137 costimulation may play a role in defining the fate of Ag-stimulated human B cells.

Antibody based manipulation of the CD137 (4-1BB) co-signaling pathway is an attractive option for the treatment of cancer and autoimmune disease. We developed a chimeric anti-human CD137 monoclonal antibody (GG) and characterized its function. As a component of planned preclinical studies, we evaluated the binding of GG to activated peripheral blood mononuclear cells (PBMCs) from cynomolgus macaque and baboon against human. Interestingly, GG only recognized human CD137, while a commercial anti-CD137 mAb (4B4-1), recognized activated PBMCs from both human and non-human primates (NHP). Subsequent analysis revealed that the amino acid sequence of CD137 is largely conserved between primate species ( approximately 95% identical), with the extracellular domain differing by only 9-10 amino acids. Based on these data, we generated mutant constructs in the extracellular domain, replacing NHP with human CD137 sequences, and identified 3 amino acids critical for GG binding. These residues are likely part of a conformational epitope, as a peptide spanning this region is unable to block mAb binding. These data demonstrate that subtle sequence variations of defined co-stimulatory molecules amongst primate species can be employed as a strategy for mapping residues necessary for antibody binding to conformational epitopes.

CD137 (4-1BB) is a costimulatory mol-ecule that can be manipulated for the treatment of cancer and autoimmune disease. Although it is known that agonistic antibodies (mAbs) against CD137 enhance the rejection of murine tumors in a natural killer (NK) cell– and T cell–dependent fashion, the mechanism for NK dependence is poorly understood. In this study, we evaluated the ability of 2 different glycoforms of a chimerized antihuman CD137 mAb, an aglycosylated (GA) and a low fucose form (GG), to react with human NK cells. Both mAbs bound similarly to CD137 and partially blocked the interaction between CD137 and CD137 ligand. However, unlike GA mAb, immobilized GG mAb activated NK cells and enhanced CD137 expression. These effects were seemingly dependent on Fc interaction with putative Fc receptors on the NK-cell surface, as only the immobilized Fc-fragment of GG was required for CD137 expression. Furthermore, CD137 expression could be enhanced with antibodies directed against non-CD137 epitopes, and the expression levels directly correlated with patterns of Fc-glycosylation recognized to improve Fc interaction with Fcγ receptors. Our data suggest that CD137 can be enhanced on NK cells in an Fc-dependent fashion and that expression correlates with phenotypic and functional parameters of activation.

Background: Ipilimumab, a cytotoxic T-lymphocyte antigen-4 (CTLA-4) blocking antibody, has been approved for the treatment of metastatic melanoma and induces adverse events (AE) in up to 64% of patients. Treatment algorithms for the management of common ipilimumab-induced AEs have lead to a reduction of morbidity, e.g. due to bowel perforations. However, the spectrum of less common AEs is expanding as ipilimumab is increasingly applied. Stringent recognition and management of AEs will reduce drug-induced morbidity and costs, and thus, positively impact the cost-benefit ratio of the drug. To facilitate timely identification and adequate management data on rare AEs were analyzed at 19 skin cancer centers. Methods and Findings: Patient files (n = 752) were screened for rare ipilimumab-associated AEs. A total of 120 AEs, some of which were life-threatening or even fatal, were reported and summarized by organ system describing the most instructive cases in detail. Previously unreported AEs like drug rash with eosinophilia and systemic symptoms (DRESS), granulomatous inflammation of the central nervous system, and aseptic meningitis, were documented. Obstacles included patientś delay in reporting symptoms and the differentiation of steroid-induced from ipilimumab-induced AEs under steroid treatment. Importantly, response rate was high in this patient population with tumor regression in 30.9% and a tumor control rate of 61.8% in stage IV melanoma patients despite the fact that some patients received only two of four recommended ipilimumab infusions. This suggests that ipilimumab-induced antitumor responses can have an early onset and that severe autoimmune reactions may reflect overtreatment. Conclusion: The wide spectrum of ipilimumab-induced AEs demands doctor and patient awareness to reduce morbidity and treatment costs and true ipilimumab success is dictated by both objective tumor responses and controlling severe side effects. OA gold

Purpose Mature dendritic cells (DCs) play a crucial role in the inflammatory process within atherosclerotic lesions by stimulation of effector T cells, which can contribute to plaque instability. Interactions between DCs and regulatory T cells (Treg), which regulate immune response by attenuating acute inflammation, are postulated to be involved in the pathogenesis of autoimmune diseases. We investigated a possible correlation between infiltrated DCs and Treg in human atherosclerotic plaques. Methods Cross-sections of 40 human carotid endarterectomy specimens were classified into groups of stable and vulnerable plaques using Trichrome staining. Immunohistochemical staining of plaques was used to detect infiltrated total (S100) and mature DCs (fascin, DC-LAMP, CD83), Treg (CD3, Foxp3), and to analyze the inflammatory state of the plaques (CD3, COX-2, CD68). In addition, RNA was isolated from plaque specimens and quantitative real-time PCR was performed to analyze transcription rates of DC markers (CD11c, CD209, HLA-DR), maturation markers (CD80, CD83, CD86), Treg-associated genes (CTLA-4, Foxp3) and of pro- and anti-inflammatory cytokines (TGFβ-family, IL-10, IFN-γ, IL-17α, IL-6). Migration assays and adhesion experiments were performed, to investigate the effects of Treg on mature DCs in vitro . Results As compared with stable plaques, vulnerable lesions were characterized by increased numbers of COX-2-expressing cells and T lymphocytes, indicating an enhanced inflammatory process. In vulnerable plaques, numbers of total and mature DCs were significantly higher in the inflammatory plaque shoulder, whereas the numbers of Treg were decreased compared to stable plaques. This inverse correlation and the association of the observed infiltration rates with plaque stability, were confirmed by PCR analyses, showing increased transcription levels of DC-specific markers, decreased mRNA expression of Treg-associated genes and decreased anti-inflammatory cytokines in vulnerable atherosclerotic plaques. In vitro , pre-incubation of mature DCs with Treg resulted in decreased DC migration and inhibited the adhesion of DCs to endothelial cells under non-uniform shear stress. Conclusions The results of our study provide novel insights in the direct interaction of mature DCs and Treg in plaque inflammation and stability.

Background The possibility that autologous NK cells could serve as an effective treatment modality for solid tumors has long been considered. However, implementation is hampered by (i) the small number of NK cells in peripheral blood, (ii) the difficulties associated with large-scale production of GMP compliant cytolytic NK cells, (iii) the need to activate the NK cells in order to induce NK cell mediated killing and (iv) the constraints imposed by autologous inhibitory receptor-ligand interactions. To address these issues, we determined (i) if large numbers of NK cells could be expanded from PBMC and GMP compliant cell fractions derived by elutriation, (ii) their ability to kill allogeneic and autologous tumor targets by direct cytotoxitiy and by antibody-mediated cellular cytotoxicity and (iii) defined NK cell specific receptor-ligand interactions that mediate tumor target cell killing. Methods Human NK cells were expanded during 14 days. Expansion efficiency, NK receptor repertoire before and after expansion, expression of NK specific ligands, cytolytic activity against allogeneic and autologous tumor targets, with and without the addition of chimeric EGFR monoclonal antibody, were investigated. Results Cell expansion shifted the NK cell receptor repertoire towards activation and resulted in cytotoxicity against various allogeneic tumor cell lines and autologous gastric cancer cells, while sparing normal PBMC. Blocking studies confirmed that autologous cytotoxicity is established through multiple activating receptor-ligand interactions. Importantly, expanded NK cells also mediated ADCC in an autologous and allogeneic setting by antibodies that are currently being used to treat patients with select solid tumors. Conclusion These data demonstrate that large numbers of cytolytic NK cells can be generated from PBMC and lymphocyte-enriched fractions obtained by GMP compliant counter current elutriation from PBMC, establishing the preclinical evidence necessary to support clinical trials utilizing autologous expanded NK cells, both directly and in combination with monoclonal antibodies in future cell-based immunotherapy in select solid tumors.

In the vast majority of studies conducted to date, activation of cancer-specific T cell immunity through peptide-based immunization has failed to induce objective tumor regression. This failure is particularly troublesome given that these vaccines often stimulate T cell responses. In this review, we attempt to understand the relative failure of peptide cancer vaccines to achieve clinically meaningful responses. In the first part of the review, we discuss specific hurdles to successful application of synthetic peptide-based vaccines including patient variability and epitope selection. In the second part of this review, we summarize the importance of CD4+ T cell help in peptide-based vaccine strategies and offer a potential strategy to improve peptide-based vaccines through the generation of both HLA class I and class II vaccine specific-immune responses.

The interaction of Fc fragments of antibodies with the Fcgamma receptors is an essential checkpoint in antibody-dependent cellular cytotoxicity (ADCC). Specific polymorphisms at position 158 enhance FcgammaRIIIa affinity for IgG1 and are associated with improved clinical outcome in lymphoma patients treated with IgG1 anti-CD20 antibody. The role of ADCC in the therapeutic effects of the alpha-epidermal growth factor receptor (EGFR) mAb, cetuximab, in patients with squamous cell carcinoma of the head and neck (SCCHN) is poorly defined. We employed three SCCHN cell lines to test two hypotheses: (1) SCCHN is susceptible to cetuximab-mediated ADCC, (2) efficacy of ADCC is associated with polymorphisms at position 158 of FcgammaRIIIa.FcgammaRIIIa-158 polymorphisms were determined for healthy donors, and their purified NK cells were used as effector cells against three SCCHN cell lines in ADCC assays. Cytotoxicity levels were compared for each polymorphism class. Proliferation and cell cycle assays were done to examine the direct effects of cetuximab.Our results indicate that SCCHN is susceptible to cetuximab-mediated ADCC in vitro. NK cytotoxic efficiency correlates with donor 158-polymorphisms in FcgammaRIIIa. Overall cytotoxicity was greatest for individuals having a single V allele when compared to homozygous F/F individuals; the cumulative percent cytotoxicity for each polymorphism among the cell lines was 58.2% V/V, 50.6% V/F, and 26.1% F/F (P0.001). Additionally, the presence of a V allele correlated with superior natural cytotoxicity against NK sensitive targets.These data have both prognostic and therapeutic relevance and support the design of a prospective trial to determine the influence of FcgammaRIIIa polymorphisms on the clinical outcome of patients with SCCHN treated with alpha-EGFR mAbs.

CD137 (4-1BB) mediated co-stimulation plays an important role in directing the fate of antigen stimulated T cells and NK cells, yet its role on B cell function is currently unknown. The goal of our study was first to evaluate which external signals regulate CD137 expression on human B cells and second to define the biological effect of CD137-mediated co-stimulation on human B cells. Flow cytometric analysis was used to evaluate cell surface expression of CD137. Cell proliferation was assessed by 3H-TdR incorporation and CFSE dilution assay. Cell apoptosis was determined by Annexin V and 7-AAD staining. Here we report that CD137 is expressed on human B cells stimulated with anti-Ig. CD137 expression is enhanced by CD40 ligation and IFN-γ, and is inhibited by IL-4 and IL-10. The expression of CD137 on activated human B cells is functionally relevant, as engagement with its ligand at the time of activation stimulates B cell proliferation. Furthermore, CD137 stimulation enhances B cell survival which is associated with expression of the anti-apoptotic proteins Bcl-xl and Mcl-1. Our study demonstrates a direct role for CD137-mediated co-stimulation in defining the fate of antigen-stimulated human B cells.