Activation-induced cell death of aggressive histology lymphomas by CD40 stimulation: induction of bax

Treg-selective IL-2 starvation synergizes with CD40 activation to sustain durable responses in lymphoma models

BACKGROUND

Roughly half of all diffuse large B-cell lymphomas (DLBCLs) are infiltrated by large numbers of regulatory T-cells (Tregs). Although the presence of 'effector' Tregs in particular is associated with an inferior prognosis in patients on standard rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) immunochemotherapy, the role of this cell type during lymphoma initiation and progression is poorly understood.

METHODS

Here, we use tissue microarrays containing prospectively collected DLBCL patient specimens, as well as data from publicly available cohorts to explore the mutational landscape of Treg-infiltrated DLBCL. We further take advantage of a model of MYC-driven lymphoma to mechanistically dissect the contribution of Tregs to lymphoma pathogenesis and to develop a strategy of Treg-selective interleukin-2 (IL-2) starvation to improve immune control of MYC-driven lymphoma.

RESULTS

We find that all genetic DLBCL subtypes, except for one characterized by co-occurring MYD88/CD79 mutations, are heavily infiltrated by Tregs. Spectral flow cytometry and scRNA-sequencing reveal the robust expression of functional and immunosuppressive markers on Tregs infiltrating MYC-driven lymphomas; notably, we find that intratumoral Tregs arise due to local conversion from naïve CD4+ precursors on tumor contact. Treg ablation in Foxp3iDTR mice, or by antibody-mediated Treg-selective blockade of IL-2 signaling, strongly reduces the lymphoma burden. We identify lymphoma B-cells as a major source of IL-2, and show that the effects of Treg depletion are reversed by the simultaneous depletion of Foxp3-negative CD4+ T-cells, but not CD8+ T-cells or natural killer (NK) cells. The inhibition of ATP hydrolyzation and adenosine production by Tregs at least partly phenocopies the effects of Treg depletion. Treg depletion further synergizes with pro-apoptotic CD40 activation to sustain durable responses.

CONCLUSION

The combined data implicate Tregs as a potential therapeutic target in DLBCL, especially in combination with other immunotherapies.

Co-Stimulatory versus Cell Death Aspects of Agonistic CD40 Monoclonal Antibody Selicrelumab in Chronic Lymphocytic Leukemia

Simple Summary

Previous observations have shown that CD40 activation of CLL cells via coculture with CD40L-expressing fibroblasts increases sensitivity to cell death by CD20 mAbs rituximab and obinutuzumab. We studied the activity of the fully human-agonistic CD40 mAb selicrelumab in primary CLL cells in relation to cell activation, induced pro-survival profile and sensitization for cell death by aCD20 mAbs. We found that the pro-survival effect of selicrelumab is minimal, while cell death by combined selicrelumab plus anti-CD20 antibody treatment is maintained. Thus, further investigation of applying selicrelumab combined with anti-CD20 mAbs in a therapeutic setting might be considered.

Abstract

Objectives: Chronic lymphocytic leukemia (CLL) is a common form of leukemia with a heterogeneous clinical course that remains incurable due to the development of therapy resistance. In lymph node proliferation centers, signals from the microenvironment such as CD40 ligation through interaction with follicular T helper cells shield CLL cells from apoptosis. Previous observations have shown that, despite CD40-induced changes in apoptotic mediators resulting in cell survival, CD40 activation also increases sensitivity to cell death by CD20 mAbs rituximab and obinutuzumab. To further investigate these observations, we here studied the activity of the fully human agonistic CD40 mAb selicrelumab in primary CLL cells in relation to cell activation, induced pro-survival profile, and sensitization for cell death by aCD20 mAbs, in vitro. Methods: CLL cells from peripheral blood were isolated by the Ficoll density method. The expression of activation markers and cytokine production following CD40 stimulation was quantified by flow cytometry and ELISA. The anti-apoptotic profile of CLL induced by stimulation was evaluated by the expression of BCL-2 proteins with Western blot, and resistance to venetoclax with flow cytometry. Cell death induced by the combination of selicrelumab and aCD20 mAbs was quantified by flow cytometry. Results: CLL cells treated with selicrelumab upregulated co-stimulatory molecules such as CD86, TNF-α and death receptor CD95/Fas. In contrast to the CD40 ligand-transfected NIH3T3 cells, induction of resistance to venetoclax by selicrelumab was very moderate. Importantly, selicrelumab stimulation positively sensitized CLL cells to CD20-induced cell death, comparable to CD40 ligand-transfected NIH3T3 cells. Conclusions: Taken together, these novel insights into selicrelumab-stimulatory effects in CLL may be considered for developing new therapeutic strategies, particularly in combination with obinutuzumab.

To respond or not to respond to CD40 agonism: That is the prediction

In the context of the clinical development of a CD40-stimulatory monoclonal antibody for the treatment of B-cell cancers, a tumor mRNA-based gene signature reflecting CD40 signaling pathway activation status was identified that could be used to predict responding and non-responding patients with diffuse large B cell lymphoma (DLBCL).

Novel targeted mtLivin nanoparticles treatment for disseminated diffuse large B-cell lymphoma

We previously showed that Livin, an inhibitor of apoptosis protein, is specifically cleaved to produce a truncated protein, tLivin, and demonstrated its paradoxical proapoptotic activity. We further demonstrated that mini-tLivin (MTV), a 70 amino acids derivative of tLivin, is a proapoptotic protein as potent as tLivin. Based on these findings, in this study we aimed to develop a venue to target MTV for the treatment of diffuse large B-cell lymphoma (DLBCL). MTV was conjugated to poly (lactide-co-glycolic acid) surface-activated nanoparticles (NPs). In order to target MTV-NPs we also conjugated CD40 ligand (CD40L) to the surface of the NPs and evaluated the efficacy of the bifunctional CD40L-MTV-NPs. In vitro, CD40L-MTV-NPs elicited significant apoptosis of DLBCL cells. In a disseminated mouse model of DLBCL, 37.5% of MTV-NPs treated mice survived at the end of the experiment. Targeting MTV-NPs using CD40L greatly improved survival and 71.4% of these mice survived. CD40L-MTV-NPs also greatly reduced CNS involvement of DLBCL. Only 20% of these mice presented infiltration of lymphoma to the brain in comparison to 77% of the MTV-NPs treated mice. In a subcutaneous mouse model, CD40L-MTV-NPs significantly reduced tumor volume in correlation with significant increased caspase-3 activity. Thus, targeted MTV-NPs suggest a novel approach to overcome apoptosis resistance in cancer.

Molecular basis and therapeutic implications of CD40/CD40L immune checkpoint

The CD40 receptor and its ligand CD40L is one of the most critical molecular pairs of the stimulatory immune checkpoints. Both CD40 and CD40L have a membrane form and a soluble form generated by proteolytic cleavage or alternative splicing. CD40 and CD40L are widely expressed in various types of cells, among which B cells and myeloid cells constitutively express high levels of CD40, and T cells and platelets express high levels of CD40L upon activation. CD40L self-assembles into functional trimers which induce CD40 trimerization and downstream signaling. The canonical CD40/CD40L signaling is mediated by recruitment of TRAFs and NF-κB activation, which is supplemented by signal pathways such as PI3K/AKT, MAPKs and JAK3/STATs. CD40/CD40L immune checkpoint leads to activation of both innate and adaptive immune cells via two-way signaling. CD40/CD40L interaction also participates in regulating thrombosis, tissue inflammation, hematopoiesis and tumor cell fate. Because of its essential role in immune activation, CD40/CD40L interaction has been regarded as an attractive immunotherapy target. In recent years, significant advance has been made in CD40/CD40L-targeted therapy. Various types of agents, including agonistic/antagonistic monoclonal antibodies, cellular vaccines, adenoviral vectors and protein antagonist, have been developed and evaluated in early-stage clinical trials for treating malignancies, autoimmune diseases and allograft rejection. In general, these agents have demonstrated favorable safety and some of them show promising clinical efficacy. The mechanisms of benefits include immune cell activation and tumor cell lysis/apoptosis in malignancies, or immune cell inactivation in autoimmune diseases and allograft rejection. This review provides a comprehensive overview of the structure, processing, cellular expression pattern, signaling and effector function of CD40/CD40L checkpoint molecules. In addition, we summarize the progress, targeted diseases and outcomes of current ongoing and completed clinical trials of CD40/CD40L-targeted therapy.

The Use of Anti-CD40 mAb in Cancer

Immunomodulatory monoclonal antibody (mAb) therapy is at the forefront of developing cancer therapeutics with numerous targeted agents proving highly effective in selective patients at stimulating protective host immunity, capable of eradicating established tumours and leading to long-term disease-free states. The cell surface marker CD40 is expressed on a range of immune cells and transformed cells in malignant states whose signalling plays a critical role in modulating adaptive immune responses. Anti-CD40 mAb therapy acts via multiple mechanisms to stimulate anti-tumour immunity across a broad range of lymphoid and solid malignancies. A wealth of preclinical research in this field has led to the successful development of multiple anti-CD40 mAb agents that have shown promise in early-phase clinical trials. Significant progress has been made to enhance the engagement of antibodies with immune effectors through their interactions with Fcγ receptors (FcγRs) by the process of Fc engineering. As more is understood about how to best optimise these agents, principally through the fine-tuning of mAb structure and choice of synergistic partnerships, our ability to generate robust, clinically beneficial anti-tumour activity will form the foundation for the next generation of cancer therapeutics.

Efficacy of cytokine-induced killer cells targeting CD40 and GITR

Since the publication of a novel protocol in 1991, cytokine-induced killer (CIK) cells have shown promising results in the treatment against neoplastic diseases. Despite ongoing preclinical and clinical studies, CIK cell treatment in the context of human monoclonal antibodies targeting tumor-necrosis factor receptors remains overlooked. The present study investigated whether a combination of CIK cells with human monoclonal antibody anti-CD40 and anti-Glucocorticoid-induced TNF-related protein (GITR) would lead to further cytotoxicity against tumor cells expressing CD40 and GITR ligand (L). Therefore, in vitro experiments with human lymphoma cell lines SU-DHL-4 and Daudi (both CD40 positive) and human breast adenocarcinoma MCF-7 (GITRL positive) were performed and the secretion of interferon (IFN)-γ was measured. Three interesting results emerged: i) a combination of CIK cells and anti-CD40 mAb is more effective than CIK cell treatment alone; ii) the use of anti-GITR mAb and CIK cells significantly enhanced the cytotoxicity of CIK cells against MCF-7 compared with single CIK cell treatment and iii) the combination of both antibodies and CIK cells abrogates the anti tumoral effect of CIK cells on all three cell lines. By performing an ELISA for IFN-γ measurement, a lower secretion was observed when anti-CD40 or anti-GITR mAb was added. This outcome indicates that further studies in vitro and in vivo may aid in understanding the synergistic molecular mechanisms of CIK cells, and anti-CD40 and anti-GITR mAb.

Expression of CD40 in Ovarian Cancer and Adenovirus-Mediated CD40 Ligand Therapy on Ovarian Cancer in Vitro

Aims and Background

To test the expression level of CD40 on ovarian cancer tissues and its correlation to clinicopathological features of patients and to evaluate the therapeutic effectiveness of adenovirus-mediated CD40 ligand on ovarian cancer in vitro.

Material and Methods

The expression of CD40 on paraffin-embedded ovarian cancer tissues (n = 58) and normal ovarian tissues (n = 15) was tested by immunohistochemistry, and CD40 expression on ovarian cancer cells derived from fresh surgical specimens was tested by flow cytometry analysis. The apoptosis-inducing effects of adenovirus-mediated CD40 ligand therapy on ovarian cancer cells derived from fresh surgical specimens were analyzed by flow cytometry analysis and TUNEL assay.

Results

CD40 expression was detected in 60.3% (35/58) of paraffin-embedded ovarian cancer tissues and 73.3% (11/15) of fresh ovarian cancer tissues, but not in normal ovarian tissues (n = 15). CD40 expression was significantly correlated with FIGO stage of ovarian cancer. Adenovirus-mediated CD40 ligand therapy induced significant apoptosis effects on ovarian cancer cells derived from fresh surgical specimens in vitro compared to null adenovirus vector and phosphate-buffered saline.

Conclusions

Our results suggested the therapeutic potential of adenovirus-mediated CD40 ligand on ovarian cancer, especially on the late stage of ovarian cancer.

RIP1 has a role in CD40-mediated apoptosis in human follicular lymphoma cells

CD40 is a cell surface receptor which belongs to tumor necrosis factor receptor (TNFR) family members. It transmits signals that regulate diverse cellular responses such as proliferation, differentiation, adhesion molecule expression and apoptosis. Unlike other TNFR family members (TRAIL-R, Fas-R and TNFR1), the CD40 cytoplasmic tail lacks death domain. However, CD40 is capable of inducing apoptosis in different types of cancer cells including lymphoma. The apoptotic effect of CD40 is linked to the involvement of Fas, TRAIL or receptor interacting protein 1 (RIP1) kinase. We have previously shown that CD40 activation has anti-apoptotic or apoptotic effect in follicular lymphoma (FL) cell lines. In this study, we investigated the mechanism by which CD40 mediates apoptosis in a follicular lymphoma cell line, HF4.9. We show here that CD40-induced apoptosis was dependent on caspase-8 activation because caspase-8 specific inhibitor, Z-IETD-FMK completely prevented apoptosis. Therefore, the involvement of TRAIL, Fas and RIP1 in caspase-8 activation was examined. The exogenous TRAIL-induced apoptosis was fully prevented by anti-TRAIL neutralizing antibody. However, the antibody had no effect on CD40-induced apoptosis indicating that CD40 did not induce the expression of endogenous TRAIL in HF4.9 cells. Moreover, the cells were not sensitive to Fas-mediated apoptosis. Interestingly, RIP1 specific inhibitor, necrostatin-1 decreased CD40-induced apoptosis, which showed that RIP1 has a role in caspase-8 activation. In conclusion, the survival or apoptotic effects of CD40-mediated signaling might be related to the differentiation stages of FL cells.

Hepatitis C virus has a genetically determined lymphotropism through co-receptor B7.2

B-cell infection by hepatitis C virus (HCV) has been a controversial topic. To examine whether HCV has a genetically determined lymphotropism through a co-receptor specific for the infection by lymphotropic HCV, we established an infectious clone and chimeric virus of hepatotropic and lymphotropic HCV strains derived from an HCV-positive B-cell lymphoma. The viral envelope and 5'-UTR sequences of the lymphotropic HCV strain were responsible for the lymphotropism. Silencing of the virus sensor, RIGI, or overexpression of microRNA-122 promoted persistent viral replication in B cells. By cDNA library screening, we identified an immune cell-specific, co-stimulatory receptor B7.2 (CD86) as a co-receptor of lymphotropic HCV. Infection of B cells by HCV inhibited the recall reaction to antigen stimulation. Together, a co-receptor B7.2 enabled lymphotropic HCV to infect memory B cells, leading to inhibition of memory B-cell function and persistent HCV infection in HCV-infected hosts.

Cancer immunotherapy: activating innate and adaptive immunity through CD40 agonists

INTRODUCTION

CD40 is a promising therapeutic target for cancer immunotherapy. In patients with advanced solid malignancies, CD40 agonists have demonstrated some anti-tumor activity and a manageable toxicity profile. A 2^nd generation of CD40 agonists has now been designed with optimized Fc receptor (FcR) binding based on preclinical evidence suggesting a critical role for FcR engagement in defining the potency of CD40 agonists in vivo. Areas covered: We provide a comprehensive review using PubMed and Google Patent databases on the current clinical status of CD40 agonists, strategies for applying CD40 agonists in cancer therapy, and the preclinical data that supports and is guiding the future development of CD40 agonists. Expert commentary: There is a wealth of preclinical data that provide rationale on several distinct approaches for using CD40 agonists in cancer immunotherapy. This data illustrates the need to strategically combine CD40 agonists with other clinically active treatment regimens in order to realize the full potential of activating CD40 in vivo. Thus, critical to the success of this class of immune-oncology drugs, which have the potential to restore both innate and adaptive immunosurveillance, will be the identification of biomarkers for monitoring and predicting responses as well as informing mechanisms of treatment resistance.

Improving Adoptive T Cell Therapy: The Particular Role of T Cell Costimulation, Cytokines, and Post-Transfer Vaccination

Adoptive cellular therapy (ACT) is a form of immunotherapy whereby antigen-specific T cells are isolated or engineered, expanded ex vivo, and transferred back to patients. Clinical benefit after ACT has been obtained in treatment of infection, various hematological malignancies, and some solid tumors; however, due to poor functionality and persistence of the transferred T cells, the efficacy of ACT in the treatment of most solid tumors is often marginal. Hence, much effort is undertaken to improve T cell function and persistence in ACT and significant progress is being made. Herein, we will review strategies to improve ACT success rates in the treatment of cancer and infection. We will deliberate on the most favorable phenotype for the tumor-specific T cells that are infused into patients and on how to obtain T cells bearing this phenotype by applying novel ex vivo culture methods. Moreover, we will discuss T cell function and persistence after transfer into patients and how these factors can be manipulated by means of providing costimulatory signals, cytokines, blocking antibodies to inhibitory molecules, and vaccination. Incorporation of these T cell stimulation strategies and combinations of the different treatment modalities are likely to improve clinical response rates further.

Multifunctional CD40L: pro- and anti-neoplastic activity

The CD40 ligand is a type I transmembrane protein that belongs to a tumor necrosis factor (TNF) superfamily. It is present not only on the surface of activated CD4+ T cells, B cells, blood platelets, monocytes, and natural killer (NK) cells but also on cancer cells. The receptor for ligand is constitutively expressed on cells, TNF family protein: CD40. The role of the CD40/CD40L pathway in the induction of body immunity, in inflammation, or in hemostasis has been well documented, whereas its involvement in neoplastic disease is still under investigation. CD40L ligand may potentiate apoptosis of tumor cells by activation of nuclear factor-κB (NF-κB), AP-1, CD95, or caspase-depended pathways and stimulate host immunity to defend against cancer. Although CD40L has a major contribution to anti-cancer activity, many reports point at its ambivalent nature. CD40L enhance release of strongly pro-angiogenic factor, vascular endothelial growth factor (VEGF), and activator of coagulation, TF, the level of which is correlated with tumor metastasis. CD40L involvement in the inhibition of tumor progression has led to the emergence of not only therapy using recombinant forms of the ligand and vaccines in the treatment of cancer but also therapy consisting of inhibiting platelets-main source of CD40L. This article is a review of studies on the ambivalent role of CD40L in neoplastic diseases.

AdCD40L--crossing the valley of death?

CD40-mediated cancer therapy has been under development since it became clear that CD40 plays a profound role in the stimulation of adaptive immune responses. Further, CD40 signaling on tumor cells may lead to growth arrest or even apoptosis that improves therapy outcome. The therapeutic window is appealing since the immune system is selective and normal cells do not apoptose upon CD40 signaling. AdCD40L is an adenoviral-based immunostimulatory gene therapy under evaluation for its efficacy to treat cancer. Because of its nature, the adenoviral backbone will stimulate TLRs while CD40L potentiates the shifts toward Th1 type of immunity. AdCD40L has shown efficacy in various murine models, and safety studies have been performed on dog patients and in human clinical trials. AdCD40L has been used for both ex vivo gene modification of tumor cell vaccines as well as for direct intratumoral injections. Lately, an oncolytic vector has been used to further increase the eradication of solid tumors that as a consequence further boosts the release of tumor antigens and creates danger signaling in the tumor micro milieu. This review discusses the currently unfolding mechanisms of action of AdCD40L gene therapy and its possibilities to reach clinical care.

CD40 blockade combines with CTLA4Ig and sirolimus to produce mixed chimerism in an MHC-defined rhesus macaque transplant model

In murine models, T-cell costimulation blockade of the CD28:B7 and CD154:CD40 pathways synergistically promotes immune tolerance after transplantation. While CD28 blockade has been successfully translated to the clinic, translation of blockade of the CD154:CD40 pathway has been less successful, in large part due to thromboembolic complications associated with anti-CD154 antibodies. Translation of CD40 blockade has also been slow, in part due to the fact that synergy between CD40 blockade and CD28 blockade had not yet been demonstrated in either primate models or humans. Here we show that a novel, nondepleting CD40 monoclonal antibody, 3A8, can combine with combined CTLA4Ig and sirolimus in a well-established primate bone marrow chimerism-induction model. Prolonged engraftment required the presence of all three agents during maintenance therapy, and resulted in graft acceptance for the duration of immunosuppressive treatment, with rejection resulting upon immunosuppression withdrawal. Flow cytometric analysis revealed that upregulation of CD95 expression on both CD4+ and CD8+ T cells correlated with rejection, suggesting that CD95 may be a robust biomarker of graft loss. These results are the first to demonstrate prolonged chimerism in primates treated with CD28/mTOR blockade and nondepletional CD40 blockade, and support further investigation of combined costimulation blockade targeting the CD28 and CD40 pathways.

CD40 pathway activation status predicts response to CD40 therapy in diffuse large B cell lymphoma

The primary function of B cells, critical components of the adaptive immune response, is to produce antibodies against foreign antigens, as well as to perform isotype class switching, which changes the heavy chain of an antibody so that it can interact with different repertoires of effector cells. CD40 is a member of the tumor necrosis factor superfamily of cell surface receptors that transmits survival signals to B cells. In contrast, in B cell cancers, stimulation of CD40 signaling results in a heterogeneous response in which cells can sometimes undergo cell death in response to treatment, depending on the system studied. We found an association between sensitivity to CD40 stimulation and mutation of the tumor suppressor p53 in a panel of non-Hodgkin's lymphoma cell lines. Consistent with p53's tumor suppressor role, we found that higher levels of intrinsic DNA damage and increased proliferation rates, as well as higher levels of BCL6, a transcriptional repressor proto-oncogene, were associated with sensitivity to CD40 stimulation. In addition, CD40 treatment-resistant cell lines were sensitized to CD40 stimulation after the introduction of DNA-damaging agents. Using gene expression analysis, we also showed that resistant cell lines exhibited a preexisting activated CD40 pathway and that an mRNA expression signature comprising CD40 target genes predicted sensitivity and resistance to CD40-activating agents in cell lines and mouse xenograft models. Finally, the gene signature predicted tumor shrinkage and progression-free survival in patients with diffuse large B cell lymphoma treated with dacetuzumab, a monoclonal antibody with partial CD40 agonist activity. These data show that CD40 pathway activation status may be useful in predicting the antitumor activity of CD40-stimulating therapeutic drugs.

Effects of environmentally-relevant levels of perfluorooctane sulfonate on clinical parameters and immunological functions in B6C3F1 mice

In the first part of a series of studies to account for perfluorooctane sulfonate (PFOS)-induced sheep red blood cell (SRBC)-specific immunoglobulin M (IgM) antibody suppression in mice, a survey of clinical and immunotoxicological endpoints was examined. Adult female B₆C₃F₁ mice were exposed orally for 28 days to a total administered dose (TAD) of 0, 0.1, 0.5, 1, or 5 mg PFOS/kg. Uterus wet weight was significantly decreased compared with control at the 5 mg/kg dose. No indications of wasting syndrome, malnutrition, alteration of thyroid homeostasis, or signs of overt toxicity were observed. Numbers of splenic CD19+/CD21⁻, CD19+/CD21+, B220+/CD40+, CD4+/CD154⁻, CD4+/CD154+, and MHC-II+ cells were not altered. Additionally, ex vivo interleukin-4 (IL-4), IL-5, and IL-6 production by in vitro anti-CD3- or phorbol myristate acetate-stimulated CD4+ T-cells was not affected. Ex vivo IL-6 production by B-cells was significantly increased by in vitro stimulation with either anti-CD40 or lipopolysaccharide. Increased IL-6 production by B-cells was the most sensitive endpoint assessed resulting in alterations at the lowest dose tested (0.1 mg/kg TAD) following anti-CD40 stimulation. Further studies are required to characterize effects on inflammatory markers such as IL-6 at environmentally relevant concentrations of PFOS and to determine the key events associated with PFOS-induced IgM suppression to address potential human health risks.

CD40 is a potential marker of favorable prognosis in patients with diffuse large B-cell lymphoma treated with immunochemotherapy

We have previously shown that expression of CD40 has a favorable prognostic impact in diffuse large B-cell lymphoma (DLBCL) after anthracycline-based chemotherapy. Here we examined the prognostic value of immunohistochemically defined CD40 expression in 95 patients with DLBCL treated with both anthracycline-based chemotherapy and rituximab. Using a 10% cut-off level, 77% of the patients had CD40-positive tumors and showed a superior overall survival (p = 0.02 log-rank, hazard ratio 0.35, 95% CI 0.14-0.88, p = 0.03 Cox regression). When adjusted for International Prognostic Index in multivariate analysis, CD40 was not an independent prognostic factor (hazard ratio 0.39, 95% CI 0.15-1.04, p = 0.06 Cox regression). However, even after the introduction of immunochemotherapy, CD40 has a potential prognostic impact in DLBCL. Additional and larger studies are necessary, regarding the immunohistochemical robustness of CD40 and the biological mechanisms that contribute to the superior prognosis in CD40-expressing DLBCL.

Fc-engineered anti-CD40 antibody enhances multiple effector functions and exhibits potent in vitro and in vivo antitumor activity against hematologic malignancies

CD40 is highly expressed on various B-lineage malignancies and represents an attractive immunotherapy target for neoplastic disease. Previous work showed that engineering the Fc domain of an antibody for increased binding to Fcγ receptors (FcγRs) significantly enhanced Fc-mediated immune effector function and antitumor activity in vitro and in vivo. We developed a humanized anti-CD40 antibody similarly Fc-engineered for increased FcγR binding (XmAbCD40) and compared its efficacy with that of an anti-CD40 native IgG1 analog and the anti-CD20 antibody rituximab. XmAbCD40 increased antibody-dependent cell-mediated cytotoxicity (ADCC) up to 150-fold relative to anti-CD40 IgG1 against B-lymphoma, leukemia, and multiple myeloma cell lines, and significantly enhanced ADCC against primary tumors. XmAbCD40 was also superior to rituximab in enhancing ADCC (both in cell lines and primary tumors) and in augmenting antibody-dependent cellular phagocytosis. XmAbCD40 significantly inhibited lymphoma growth in disseminated and established mouse xenografts and was more effective than the IgG1 analog or rituximab. An anti-CD40 antibody constructed to abrogate FcγR binding showed no reduction of tumor growth, indicating that the in vivo antitumor activity of XmAbCD40 is primarily mediated via FcγR-dependent mechanisms. These data demonstrate that XmAbCD40 displays potent antitumor efficacy and merits further evaluation for the treatment of CD40(+) malignancies.

Inhibition of proliferation and induction of apoptosis in multiple myeloma cell lines by CD137 ligand signaling

Background

Multiple myeloma (MM) is a malignancy of terminally-differentiated plasma cells, and the second most prevalent blood cancer. At present there is no cure for MM, and the average prognosis is only three to five years. Current treatments such as chemotherapy are able to prolong a patient's life but rarely prevent relapse of the disease. Even hematopoietic stem cell transplants and novel drug combinations are often not curative, underscoring the need for a continued search for novel therapeutics. CD137 and its ligand are members of the Tumor Necrosis Factor (TNF) receptor and TNF superfamilies, respectively. Since CD137 ligand cross-linking enhances proliferation and survival of healthy B cells we hypothesized that it would also act as a growth stimulus for B cell cancers.

Methodology/Principal Findings

Proliferation and survival of B cell lymphoma cell lines were not affected or slightly enhanced by CD137 ligand agonists in vitro. But surprisingly, they had the opposite effects on MM cells, where CD137 ligand signals inhibited proliferation and induced cell death by apoptosis. Furthermore, secretion of the pro-inflammatory cytokines, IL-6 and IL-8 were also enhanced in MM but not in non-MM cell lines in response to CD137 ligand agonists. The secretion of these cytokines in response to CD137 ligand signaling was consistent with the observed activation of the classical NF-κB pathway. We hypothesize that the induction of this pathway results in activation-induced cell death, and that this is the underlying mechanism of CD137-induced MM cell death and growth arrest.

Conclusions/Significance

These data point to a hitherto unrecognized role of CD137 and CD137 ligand in MM cell biology. The selective inhibition of proliferation and induction of cell death in MM cells by CD137 ligand agonists may also warrant a closer evaluation of their therapeutic potential.

Coexpression of CD40 and CD40L on B Lymphoma and Carcinoma Cells: an Autocrine Anti-Apoptotic Role

To evaluate a possible autocrine role of CD40L, the expression and functional activity of CD40L on NHL and breast carcinoma cell lines were investigated. Using flow cytometry, CD40 was consistently detectable at the surface of all 5 NHL cell lines tested. CD40L expression was detectable at the surface of DAUDI (54%, MFI 47) and BJAB (12%, MFI 32) cell lines, and marginally on the RAJI cell line (7%, MFI 30), while 4 of 5 NHL cell lines (DAUDI, RAJI, BJAB, BL70) had detectable CD40L mRNA. CD40 was expressed on T47D and BT20 breast carcinoma cell lines while CD40L was detectable on T47D (93%, MFI 137) only. Both BT20 and T47D had detectable CD40 mRNA, while CD40L mRNA was detectable only in the T47D cell line. CD40, but not CD40L, was detectable on 6 renal, 1 prostatic and 1 colon carcinoma cell lines. CD40L expressed on tumor cells was functional, as shown by its capacity to decrease drug-induced apoptosis on CD40 expressing NHL and breast carcinoma cell lines, while irradiated CD40L negative cell line (BT20) had no effect. Blocking CD40L antibody abrogated the protective effect of irradiated CD40L positive T47D cell line against drug-induced apoptosis on BL70 cell line, confirming that CD40L is functional in the DAUDI and T47D cell lines. Importantly, blocking CD40L antibody increased drug-induced apoptosis in CD40L positive cell lines but had no effect on the CD40L negative cell lines. CD40L is expressed on CD40 positive B NHL and breast carcinoma cell lines and induces an autocrine antiapoptotic signal when cells are exposed to cytotoxic agents.

Anti-CD40 monoclonal antibody

Normal, bi-directional interactions between CD 40 and its natural ligand CD 154 (CD 40 ligand) are central to the generation of both T cell-dependent, humoral immune responses and cytotoxic T-cell responses. CD 40 is expressed on a broad range of hematological and epithelial malignancies. The development of monoclonal antibodies directed against CD 40 allows effective targeting of malignant cells through multiple mechanisms that include the recruitment of immune effector mechanisms such as complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, direct anti-proliferative effects on neoplastic cells and, importantly, by the activation of tumor-targeted cellular cytotoxicity. This review provides the background to the early clinical trial data that are now beginning to emerge for this potentially exciting new treatment approach.

The Janus faces of CD40 in cancer

CD40 is a TNF receptor family member that is widely recognized for its prominent role in immune regulation and homeostasis. Expression of CD40 is not restricted to normal lymphoid cells but is also evident in the majority of haemopoietic and epithelial malignancies where it has been implicated in oncogenic events. Accumulating evidence, however, suggests that the CD40 pathway can be exploited for cancer therapy by virtue of its ability to stimulate the host anti-tumor immune response, normalize the tumor microenvironment and directly suppress the growth of CD40-positive tumors. Here, we provide an overview of the multifaceted functions of the CD40 pathway in cancer and its emerging role in the treatment of malignancy.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

CD40 activation in human pancreatic islets and ductal cells

AIMS/HYPOTHESIS

CD40 expression on non-haematopoietic cells is linked to inflammation. We previously reported that CD40 is expressed on isolated human and non-human primate islets and its activation results in secretion of IL-8, macrophage inflammatory protein 1-beta (MIP-1beta) and monocyte chemoattractant protein-1 (MCP-1) through nuclear factor-kappaB and extracellularly regulated kinases 1/2 pathways. The objective of this study was to identify the pattern of gene expression, and to study viability and functionality affected by CD40-CD40 ligand (CD40L) interaction in human islets. Furthermore, we have studied the CD40-mediated cytokine/chemokine profile in pancreatic ductal cells, as they are always present in human islet transplant preparations and express CD40 constitutively.

METHODS

CD40-CD40L gene expression modulation was studied by microarray on islet cells depleted of ductal cells. Selected genes were validated by quantitative RT-PCR. The cytokine profile in purified ductal cells was evaluated by Luminex technology, based on the use of fluorescent-coated beads, known as microspheres, and capable of multiplex detection of proteins from a single sample. Glucose-stimulated insulin secretion and islet viability were assessed by perifusion and 7-aminoactinomycin D membrane exclusion, respectively.

RESULTS

Statistical analysis of microarrays identified 30 genes exhibiting at least a 2.5-fold increase across all replicate arrays. The majority of them were related to oxidative stress/inflammation. Prominently upregulated were chemokine C-X-C motif ligand 1 (CXCL1), CXCL2 and CXCL3 belonging to the CXC family of chemokines related to IL-8. CD40-mediated CXCL1 secretion was confirmed by ELISA. The viability or in vitro function was not affected by CD40 activation. In addition to previously reported IL-8, MIP-1beta and MCP-1, CD40 stimulation in ductal cells produced IL-1beta, IFN-gamma, TNF-alpha, granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor.

CONCLUSIONS/INTERPRETATION

CD40 activation in islets and ductal cells produces cytokines/chemokines with a broad-spectrum range of biological functions.

Preclinical pharmacokinetics, pharmacodynamics, and activity of a humanized anti-CD40 antibody (SGN-40) in rodents and non-human primates

1. Cell-surface expression of CD40 in B-cell malignancies and multiple solid tumors has raised interest in its potential use as a target for antibody-based cancer therapy. SGN-40, a humanized monoclonal anti-CD40 antibody, mediates antibody-dependent cytotoxicity and inhibits B-cell tumor growth in vitro, properties of interest for the treatment of cancers, and is currently in Phase I clinical trials for B-cell malignancies. In this study, we determined in vivo activity and pharmacokinetics properties of SGN-40. 2. Effect of SGN-40 in xenograft model of CD40-expressing B-cell lymphoma in severe-combined immune deficiency mice and its in vivo pharmacokinetics properties in normal mice, rats and cynomolgus monkeys were studied. 3. Treatment with SGN-40 significantly increased the survival of mice xenografted with human B-cell lymphoma cell line. SGN-40 exhibited nearly 100% bioavailability in mice and it cleared faster when given at a low dose. In monkeys, clearance of SGN-40 was also much faster at low dose, suggesting nonlinear pharmacokinetics in these species. In rats, however, SGN-40 clearance at all tested doses was similar, suggesting that pharmacokinetics were linear in this dose range in rats. Administration of SGN-40 to monkeys also produced marked, dose-dependent, and persistent depletion of peripheral CD20(+) B lymphocytes. 4. Data presented in this report suggest that SGN-40 is active in in vivo, and based upon interspecies scaling, SGN-40 clearance in humans is predicted to be similar to observed SGN-40 clearance in monkeys. These data suggest that SGN-40 has appropriate pharmacokinetic properties that support its clinical use.

CD8+ lymphocyte-mediated injury of dorsal root ganglion neurons during lentivirus infection: CD154-dependent cell contact neurotoxicity

Neuronal damage in dorsal root ganglia (DRGs) with accompanying axonal injury is a key feature of human immunodeficiency virus (HIV)-related distal sensory polyneuropathy (DSP). In a model of HIV-related DSP, we observed numerous CD3+ T lymphocytes (p < 0.05) in DRGs from feline immunodeficiency virus (FIV)-infected animals, which also exhibited low CD4+ and high CD8+ lymphocyte levels in blood accompanied by a selective loss of small-diameter sural nerve axons (p < 0.05). FIV-infected lymphocytes cocultured with syngeneic DRGs caused neuronal damage, indicated by neurite retraction, neuronal soma atrophy, and loss (p < 0.05). In contrast, supernatants from FIV-infected or uninfected lymphocytes were minimally neurotoxic, despite high FIV virion levels. Among lymphocyte subsets cocultured with DRG cultures, CD8+ T cells from both FIV-infected and uninfected lymphocytes selectively caused DRG neuronal injury (p < 0.05). FIV-infected CD8+ T cells showed markedly increased CD154 expression (p < 0.05), whereas neurons were the predominant cells expressing CD40 in DRGs. Blocking CD154 on activated CD8+ T cells protected DRG neurons (p < 0.05). These findings indicated that CD8+ T cells were principal effectors of DRG neuronal injury after FIV infection through a CD40-CD154 interaction in a cell contact-dependent manner.

Prognostic significance of CD40 expression in malignant lymphoma developing in rheumatoid arthritis

PURPOSE

CD40, a member of tumor necrosis factor receptor superfamily, is expressed in synovial fluid B cells in rheumatoid arthritis (RA) and is postulated to contribute to RA progression. In this study, prognostic significance of CD40 expression was analyzed in B cell lymphoproliferative disorders (LPD) developing in RA.

METHOD

CD40 expression was immunohistochemically examined in 35 cases of B-cell LPD developing in RA and in 32 of sporadic B-cell LPD as control. CD40 expression at mRNA level evaluated by quantitative reverse transcription-PCR and at protein level evaluated by immunohistochemistry correlated.

RESULTS

Frequency of diffuse large B-cell lymphoma (DLBCL) in RA- and sporadic-LPD was 71.4 and 59.3%, respectively. CD40 positive rate in RA-LPD (62.9%) was significantly higher than that in sporadic LPD (37.5%) (P = 0.015). Interval between onset of RA and LPD development was shorter in CD40 positive cases than in negative cases (median 120 and 204 months, respectively) (P < 0.07). Five-year survival rate in CD40 positive DLBCL cases (75%) was significantly better than that in negative cases (25%) (P < 0.05).

CONCLUSION

RA-LPD is characterized by the higher frequency of CD40 expression compared to sporadic LPD and CD40 positive cases which showed more favorable prognosis than those without CD40 expression.

Preclinical antilymphoma activity of a humanized anti-CD40 monoclonal antibody, SGN-40

SGN-40 is a humanized IgG1 antihuman CD40 that is currently in a phase I clinical trial for the treatment of multiple myeloma. As surface CD40 expression on B-lineage cells is maintained from pro-B cells to plasma cells, SGN-40 may be applicable to treatment of other B-cell neoplasias, including non-Hodgkin's lymphoma. In this study, we examined potential in vitro and in vivo anti-B-lineage lymphoma activity of SGN-40. Recombinant SGN-40 was expressed and purified from Chinese hamster ovary cells and characterized based on binding affinity, specificity, and normal B-cell stimulation. The ability of SGN-40 to target neoplastic B cells was examined in vitro by proliferation inhibition, cytotoxicity, and antibody-dependent cell cytotoxicity assays and in vivo by human lymphoma xenograft models. Recombinant SGN-40 showed high affinity, Kd of approximately 1 nmol/L, and specific binding to CD40. Whereas SGN-40 was a weak agonist in stimulating normal B-cell proliferation in the absence of IL-4 and CD40L, it delivered potent proliferation inhibitory and apoptotic signals to, and mediated antibody-dependent cytotoxicity against, a panel of high-grade B-lymphoma lines. These in vitro antilymphoma effects were extended to disseminated and s.c. xenograft CD40 tumor models. In these xenograft models, the antitumor activity of SGN-40 was comparable with that of rituximab. The preclinical in vitro and in vivo antilymphoma activity of SGN-40 observed in this study provides a rationale for the clinical testing of SGN-40 in the treatment of CD40+ B-lineage lymphomas.

Arsenic trioxide: new clinical experience with an old medication in hematologic malignancies

Arsenic trioxide has shown great promise in the treatment of patients with relapsed or refractory acute promyelocytic leukemia (APL). In clinical trials, arsenic trioxide induces complete remission in 87% of patients and molecular remission in 83% of patients. Two-year overall and relapse-free survival estimates are 63% and 49%, respectively. Treatment with arsenic trioxide may be associated with the APL differentiation syndrome, leukocytosis, and electrocardiographic abnormalities. The expanded use of arsenic trioxide in APL for postremission therapy, in conjunction with transplantation, and in patients with newly diagnosed APL is under investigation. The multiple mechanisms of action of arsenic trioxide suggest that it may have antitumor activity in malignancies other than APL and that it may be used in combination with other agents to expand its potential use. This article reviews the clinical use of arsenic trioxide to date and discusses new therapeutic strategies evolving from its diverse biologic activities.

Modulation and function of caspase pathways in B lymphocytes

During their development, B-lineage cells are selected to mature, to die, to divide, or to survive and wait, ready to respond to external signals. The homeostatic balance between growth, death, and survival is mediated by signaling pathways through the B-cell antigen receptor (BCR) complex, cytokine and chemokine receptors or cell-cell coreceptor interactions. The BCR complex is a master regulator essential at key checkpoints during development. These checkpoints involve various processes, including negative selection (deletion), anergy, receptor editing, and positive selection. Without BCRs or downstream BCR-signaling components, B-lineage cells arrest during development. Removal of BCRs from mature B cells leads to their death. Here, we discuss signaling pathways in B cells that activate members of the caspase family of cysteine proteases. In some B-cell subsets, BCR signaling activates caspases, which in turn induce a program leading to cell death. However, in other contexts, caspases are involved in the proliferation of B cells. The outcome depends in part on the presence or absence of modifiers that affect signaling thresholds and on which caspases are activated. These mechanisms allow the coordinated regulation of proliferation and apoptosis that is essential for lymphoid homeostasis.

Outcome of treatment in adults with acute lymphoblastic leukemia: analysis of the LALA-94 trial

PURPOSE

We analyzed the benefits of a risk-adapted postremission strategy in adult lymphoblastic leukemia (ALL), and re-evaluated stem-cell transplantation (SCT) for high-risk ALL.

PATIENTS AND METHODS

A total of 922 adult patients entered onto the trial according to risk groups: standard-risk ALL (group 1), high-risk ALL (group 2), Philadelphia chromosome-positive ALL (group 3), and CNS-positive ALL (group 4). All received a standard four-drug/4-week induction course. Patients from group 1 who achieved a complete remission (CR) after one course of induction therapy were randomly assigned between intensive and less intensive postremission chemotherapy, whereas those who achieved CR after salvage therapy were then included in group 2. Patients in groups 2, 3, and 4 with an HLA-identical sibling were assigned to allogeneic SCT. In groups 3 and 4, autologous SCT was offered to all other patients, whereas in group 2 they were randomly assigned between chemotherapy and autologous SCT.

RESULTS

Overall, 771 patients achieved CR (84%). Median disease-free survival (DFS) was 17.5 months, with 3-year DFS at 37%. In group 1, the 3-year DFS rate was 41%, with no difference between arms of postremission randomization. In groups 2 and 4, the 3-year DFS rates were 38% and 44%, respectively. In group 2, autologous SCT and chemotherapy resulted in comparable median DFS. Patients with an HLA-matched sibling (groups 2 and 4) had improved DFS. Three-year DFS was 24% in group 3.

CONCLUSION

Allogeneic SCT improved DFS in high-risk ALL in the first CR. Autologous SCT did not confer a significant benefit over chemotherapy for high-risk ALL.

Tumor regression by anti-CD40 and interleukin-2: role of CD40 in hematopoietic cells and organ-specific effects

CD40 stimulation can synergize with interleukin (IL)-2 for antitumor responses against mouse metastatic renal cell carcinomas, with coincident increases in tumor-specific CD8+ T-cell responses and dendritic cell numbers in both the spleen and liver. Because CD40 is present on various hematopoietic-derived cells, endothelial cells, and some tumors themselves, this study was performed to determine whether the antitumor effects of CD40 stimulation and IL-2 were primarily mediated by CD40+ hematopoietic-derived cells. Bone marrow chimeras were created by reconstituting lethally irradiated CD40+/+ recipients with bone marrow from CD40-/- or CD40+/+ mice. Chimeric mice were then implanted orthotopically with renal cancer cells, followed by treatment with anti-CD40 agonist monoclonal antibodies and IL-2. Immune parameters of the spleen and liver were assessed after therapy and correlated with antitumor responses. The antitumor effects in the CD40-/- bone marrow transplantation chimeras were almost completely abrogated after treatment, and this shows that hematopoietically derived CD40+ cells are the principal targets for CD40 stimulation in this model. Although both spleen and liver showed reductions in CD8+ T-cell and dendritic cell expansion in the CD40-/- versus CD40+/+ chimeras after therapy, only the liver exhibited no significant increases in either CD8+ T cells or dendritic cells after treatment. CD40 cells on hematopoietic cells are the primary target for anti-CD40 and IL-2 therapy. The results also suggest that the immunologic events in the liver may be more revealing that those in lymphoid organs with regard to critical events related to responses after therapy.

Empowering targeted therapy: lessons from rituximab

Rituximab, a monoclonal antibody directed against the B cell-specific protein CD20, has revolutionized lymphoma treatment by providing a highly effective form of therapy with relatively mild toxic side effects. Effective as a single agent against some forms of B cell lymphoma, rituximab also has a chemosensitizing effect, enhancing the efficacy of chemotherapy against other forms of the disease. Although the mechanisms whereby rituximab achieves its effects remain incompletely understood, these seem to involve at least three distinct phenomena: (i) antibody-dependent cell-mediated cytotoxicity, (ii) complement-mediated cell lysis, and (iii) stimulation of apoptosis in target cells. The latter occurs through interaction of complexes of rituximab and CD20 in lipid rafts, with elements of a signaling pathway involving Src kinases. Effector molecules trigger various gene expression events, leading to sensitization of malignant cells to proapoptotic stimuli. Lessons learned from the research on rituximab may be applied to the rational development of antibody-based therapies against other forms of cancer.

Resveratrol modifies the expression of apoptotic regulatory proteins and sensitizes non-Hodgkin's lymphoma and multiple myeloma cell lines to paclitaxel-induced apoptosis

Resveratrol (trans-3,4,5-trihydroxystilbene) has received attention for its potential chemopreventive and antitumor effects in experimental systems. Recent evidence suggests that paclitaxel, alone or in combination with other drugs, can be effectively used in the treatment of non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This study investigated whether resveratrol can sensitize NHL and MM cell lines to paclitaxel-mediated apoptosis and to delineate the underlying molecular mechanism of sensitization. Both resveratrol and paclitaxel negatively modulated tumor cell growth by arresting the cells at the G2-M phase of the cell cycle. Low concentrations of resveratrol exerted a sensitizing effect on drug-refractory NHL and MM cells to apoptosis induced by paclitaxel. Resveratrol selectively down-regulated the expression of antiapoptotic proteins Bcl-xL and myeloid cell differentiation factor-1 (Mcl-1) and up-regulated the expression of proapoptotic proteins Bax and apoptosis protease activating factor-1 (Apaf-1). Paclitaxel down-regulated the expression of Bcl-xL, Mcl-1, and cellular inhibitor of apoptosis protein-1 antiapoptotic proteins and up-regulated Bid and Apaf-1. Combination treatment resulted in apoptosis through the formation of tBid, mitochondrial membrane depolarization, cytosolic release of cytochrome c and Smac/DIABLO, activation of the caspase cascade, and cleavage of poly(adenosine diphosphate-ribose) polymerase. Combination of resveratrol with paclitaxel had minimal cytotoxicity against quiescent and mitogenically stimulated human peripheral blood mononuclear cells. Inhibition of Bcl-xL expression by resveratrol was critical for chemosensitization and its functional impairment mimics resveratrol-mediated sensitization to paclitaxel-induced apoptosis. Inhibition of Bcl-xL expression by resveratrol was due to the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and diminished activator protein-1-dependent Bcl-xL expression. The findings by resveratrol were corroborated with inhibitors of the ERK1/2 pathway. This study demonstrates that in resistant NHL and MM cell lines resveratrol and paclitaxel selectively modify the expression of regulatory proteins in the apoptotic signaling pathway and the combination, via functional complementation, results in synergistic apoptotic activity.

Vulnerability of human neurons to T cell-mediated cytotoxicity

Axonal and neuronal loss occurs in inflammatory diseases of the CNS such as multiple sclerosis. The cause of the loss remains unclear. We report that polyclonally activated T cells align along axons and soma of cultured human neurons leading to substantial neuronal death. This occurs in an allogeneic and syngeneic manner in the absence of added Ag, requires T cells to be activated, and is mediated through cell contact-dependent mechanisms involving FasL, LFA-1, and CD40 but not MHC class I. Activated CD4(+) and CD8(+) T cell subsets are equally neuronal cytotoxic. In contrast to neurons, other CNS cell types (oligodendrocytes and astrocytes) are not killed by T cells. These results demonstrate for the first time the high and selective vulnerability of human neurons to T cells, and suggest that when enough activated T cells accumulate in the CNS, neuronal cytotoxicity can result through Ag-independent non-MHC class I mechanisms.

Expression of costimulatory molecules in human neuroblastoma. Evidence that CD40+ neuroblastoma cells undergo apoptosis following interaction with CD40L

Tumour cells display low to absent expression of costimulatory molecules. Here, we have investigated the expression of costimulatory molecules (CD40, CD80, CD86, PD-1L, B7H2, OX40L and 4-1BBL) in human neuroblastoma (NB) cells, since virtually no information is available on this issue. Both established NB cell lines and primary tumours were tested by RT-PCR and flow cytometry. Neuroblastoma cell lines expressed the transcripts of all costimulatory molecule genes, but not the corresponding proteins. Culture of NB cell lines with human recombinant (r)IFN-gamma induced surface expression of CD40 in half of them. Primary NB cells showed CD40, CD80, CD86, OX40L, 4-1BBL, but not PD-1L and B7H2, mRNA expression. Surface CD40 was consistently detected on primary NB cells by flow cytometry. Interferon-gamma gene-transfected NB cells expressed constitutively surface CD40 and were induced into apoptosis by incubation with rCD40L through a caspase-8-dependent mechanism. CD40 may represent a novel therapeutic target in NB.