CD40 ligand is a critical effector of Epstein-Barr virus in host cell survival and transformation

Ongoing phase 2 agents for multiple sclerosis: could we break the phase 3 trial deadlock?

INTRODUCTION

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the central nervous system. While disease-modifying therapies have significantly improved the management of relapsing MS, progressive MS remains a major clinical challenge.

AREAS COVERED

This review provides a general overview of recent and ongoing phase 2 clinical trials investigating treatments for MS, summarizing emerging results when available. The trials are categorized based on the desired therapeutic effect: immunomodulatory treatments, neuroprotection, and remyelination. A comprehensive literature search was conducted using databases such as PubMed and ClinicalTrials.gov to identify relevant studies, with a focus on promising therapies that address both inflammatory and neurodegenerative processes in MS.

EXPERT OPINION

Despite promising results from phase 2 trials, many phase 3 trials fail to demonstrate significant efficacy. This discrepancy is partly due to limitations in biomarkers, which often lack disease specificity and fail to predict long-term outcomes. Additionally, smaller, narrowly focused phase 2 trials may overestimate efficacy, leading to challenges when transitioning to larger, more inclusive phase 3 trials. Recruitment of patients with less aggressive disease further complicates phase 3 success. Addressing these challenges requires the refinement of biomarkers, adoption of unified definitions for outcomes like progression independent of relapse activity (PIRA), and trial designs that better capture the complexity of MS progression.

Therapeutic advances in multiple sclerosis: Novel therapies (immune checkpoint inhibitors, CAR-T, Anti-CD40L)

As patients with multiple sclerosis (MS) age, the risk of cancer also increases. Immune checkpoint inhibitors (ICIs) are novel monoclonal antibodies that have revolutionized cancer treatment. However, their use is limited by immune related adverse events. In patients with MS and pre-existing autoimmune disease there is concern that use of ICIs could worsen disease outcome. In the first part of this review we discuss the current data on ICIs and MS which overall suggest that they are well tolerated from the standpoint of MS disease activity. We recommend that MS not be a strict contraindication to ICI use which should depend on an individualized risk benefit discussion. In the second part, we focus on novel therapies for MS including CAR-T cell and anti-CD40L treatments. These newer therapies have the potential to address an unmet need in MS as they can cross the blood-brain and have the potential to target compartmentalized central nervous inflammation that may underly the pathophysiology of progressive MS.

Inhibition of CD40L with Frexalimab in Multiple Sclerosis

BACKGROUND

The CD40-CD40L costimulatory pathway regulates adaptive and innate immune responses and has been implicated in the pathogenesis of multiple sclerosis. Frexalimab is a second-generation anti-CD40L monoclonal antibody being evaluated for the treatment of multiple sclerosis.

METHODS

In this phase 2, double-blind, randomized trial, we assigned, in a 4:4:1:1 ratio, participants with relapsing multiple sclerosis to receive 1200 mg of frexalimab administered intravenously every 4 weeks (with an 1800-mg loading dose), 300 mg of frexalimab administered subcutaneously every 2 weeks (with a 600-mg loading dose), or the matching placebos for each active treatment. The primary end point was the number of new gadolinium-enhancing T1-weighted lesions seen on magnetic resonance imaging at week 12 relative to week 8. Secondary end points included the number of new or enlarging T2-weighted lesions at week 12 relative to week 8, the total number of gadolinium-enhancing T1-weighted lesions at week 12, and safety. After 12 weeks, all the participants could receive open-label frexalimab.

RESULTS

Of 166 participants screened, 129 were assigned to a trial group; 125 participants (97%) completed the 12-week double-blind period. The mean age of the participants was 36.6 years, 66% were women, and 30% had gadolinium-enhancing lesions at baseline. At week 12, the adjusted mean number of new gadolinium-enhancing T1-weighted lesions was 0.2 (95% confidence interval [CI], 0.1 to 0.4) in the group that received 1200 mg of frexalimab intravenously and 0.3 (95% CI, 0.1 to 0.6) in the group that received 300 mg of frexalimab subcutaneously, as compared with 1.4 (95% CI, 0.6 to 3.0) in the pooled placebo group. The rate ratios as compared with placebo were 0.11 (95% CI, 0.03 to 0.38) in the 1200-mg group and 0.21 (95% CI, 0.08 to 0.56) in the 300-mg group. Results for the secondary imaging end points were generally in the same direction as those for the primary analysis. The most common adverse events were coronavirus disease 2019 and headaches.

CONCLUSIONS

In a phase 2 trial involving participants with multiple sclerosis, inhibition of CD40L with frexalimab had an effect that generally favored a greater reduction in the number of new gadolinium-enhancing T1-weighted lesions at week 12 as compared with placebo. Larger and longer trials are needed to determine the long-term efficacy and safety of frexalimab in persons with multiple sclerosis. (Funded by Sanofi; ClinicalTrials.gov number, NCT04879628.).

Inborn Errors of Immunity and Cytokine Storm Syndromes

Inborn errors of immunity (IEI) are a diverse and growing category of more than 430 chronic disorders that share susceptibilities to infections. Whether the result of a genetic lesion that causes defective granule-dependent cytotoxicity, excessive lymphoproliferation, or an overwhelming infection represents a unique antigenic challenge, IEIs can display a proclivity for cytokine storm syndrome (CSS) development. This chapter provides an overview of CSS pathophysiology as it relates to IEIs. For each IEI, the immunologic defect and how it promotes or discourages CSS phenomena are reviewed. The IEI-associated molecular defects in pathways that are postulated to be critical to CSS physiology (i.e., toll-like receptors, T regulatory cells, the IL-12/IFNγ axis, IL-6) and, whenever possible, review strategies for treating CSS in IEI patients with molecularly directed therapies are highlighted.

The pathogenesis of multiple sclerosis: a series of unfortunate events

Multiple sclerosis (MS) is characterized by the chronic inflammatory destruction of myelinated axons in the central nervous system. Several ideas have been put forward to clarify the roles of the peripheral immune system and neurodegenerative events in such destruction. Yet, none of the resulting models appears to be consistent with all the experimental evidence. They also do not answer the question of why MS is exclusively seen in humans, how Epstein-Barr virus contributes to its development but does not immediately trigger it, and why optic neuritis is such a frequent early manifestation in MS. Here we describe a scenario for the development of MS that unifies existing experimental evidence as well as answers the above questions. We propose that all manifestations of MS are caused by a series of unfortunate events that usually unfold over a longer period of time after a primary EBV infection and involve periodic weakening of the blood-brain barrier, antibody-mediated CNS disturbances, accumulation of the oligodendrocyte stress protein αB-crystallin and self-sustaining inflammatory damage.

A gene regulatory network approach harmonizes genetic and epigenetic signals and reveals repurposable drug candidates for multiple sclerosis

Multiple sclerosis (MS) is a complex dysimmune disorder of the central nervous system. Genome-wide association studies (GWAS) have identified 233 genetic variations associated with MS at the genome-wide significant level. Epigenetic studies have pinpointed differentially methylated CpG sites in MS patients. However, the interplay between genetic risk factors and epigenetic regulation remains elusive. Here, we employed a network model to integrate GWAS summary statistics of 14 802 MS cases and 26 703 controls with DNA methylation profiles from 140 MS cases and 139 controls and the human interactome. We identified differentially methylated genes by aggregating additive effects of differentially methylated CpG sites within promoter regions. We reconstructed a gene regulatory network (GRN) using literature-curated transcription factor knowledge. Colocalization of the MS GWAS and methylation quantitative trait loci (mQTL) was performed to assess the GRN. The resultant MS-associated GRN highlighted several single nucleotide polymorphisms with GWAS-mQTL colocalization: rs6032663, rs6065926 and rs2024568 of CD40 locus, rs9913597 of STAT3 locus, and rs887864 and rs741175 of CIITA locus. Moreover, synergistic mQTL and expression QTL signals were identified in CD40, suggesting gene expression alteration was likely induced by epigenetic changes. Web-based Cell-type Specific Enrichment Analysis of Genes (WebCSEA) indicated that the GRN was enriched in T follicular helper cells (P-value = 0.0016). Drug target enrichment analysis of annotations from the Therapeutic Target Database revealed the GRN was also enriched with drug target genes (P-value = 3.89 × 10-4), revealing repurposable candidates for MS treatment. These candidates included vorinostat (HDAC1 inhibitor) and sivelestat (ELANE inhibitor), which warrant further investigation.

Genetic and transcriptomic analyses support a switch to lytic phase in Epstein Barr virus infection as an important driver in developing Systemic Lupus Erythematosus

To investigate the molecular mechanisms through which Epstein-Barr virus (EBV) may contribute to Systemic Lupus Erythematosus (SLE) pathogenesis, we interrogated SLE genetic risk loci for signatures of EBV infection. We first compared the gene expression profile of SLE risk genes across 459 different cell/tissue types. EBV-infected B cells (LCLs) had the strongest representation of highly expressed SLE risk genes. By determining an SLE risk allele effect on gene expression (expression quantitative trait loci, eQTL) in LCLs and 16 other immune cell types, we identified 79 SLE risk locus:gene pairs putatively interacting with EBV infection. A total of 10 SLE risk genes from this list (CD40, LYST, JAZF1, IRF5, BLK, IKZF2, IL12RB2, FAM167A, PTPRC and SLC15A) were targeted by the EBV transcription factor, EBNA2, differentially expressed between LCLs and B cells, and the majority were also associated with EBV DNA copy number, and expression level of EBV encoded genes. Our final gene network model based on these genes is suggestive of a nexus involving SLE risk loci and EBV latency III and B cell proliferation signalling pathways. Collectively, our findings provide further evidence to support the interaction between SLE risk loci and EBV infection that is in part mediated by EBNA2. This interplay may increase the tendency towards EBV lytic switching dependent on the presence of SLE risk alleles. These results support further investigation into targeting EBV as a therapeutic strategy for SLE.

Updating targets for natural killer/T-cell lymphoma immunotherapy

Natural killer/T-cell lymphoma (NKTCL) is a highly invasive subtype of non-Hodgkin lymphoma, typically positive for cytoplasmic CD3, CD56, cytotoxic markers, including granzyme B and TIA1, and Epstein-Barr virus (EBV). The current treatment methods for NKTCL are associated with several drawbacks. For example, chemotherapy can lead to drug resistance, while treatment with radiotherapy alone is inadequate and results in frequent relapses. Moreover, hematopoietic stem cell transplantation exhibits limited efficacy and is not well recognized by domestic and foreign experts. In recent years, immunotherapy has shown good clinical results and has become a hot spot in cancer research. Clinical activity of targeted antibodies, such as daratumumab (anti-CD38 antibody) and brentuximab vedotin (anti-CD30 antibody), have been reported in NKTCL. Additionally, dacetuzumab and Campath-1H have demonstrated promising results. Further encouraging data have been obtained using checkpoint inhibitors. The success of these immunotherapy agents is attributed to high expression levels of programmed death-ligand 1 in NKTCL. Furthermore, anti-CCR4 monoclonal antibodies (mAbs) exert cytotoxic actions on both CCR4+ tumor cells and regulatory T cells. Depletion of these cells and the long half-life of anti-CCR4 mAbs result in enhanced induction of antitumor effector T cells. The role of IL10 in NKTCL has also been investigated. It has been proposed that exploitation of this cytokine might provide potential novel therapeutic strategies. Cellular immunotherapy with engineered cytotoxic T lymphocytes targeted against LMP1 and LMP2 has shown promising results and sustained remission. Cellular immunotherapy may be used either as maintenance therapy following initial induction chemotherapy or in cases of relapsed/refractory disease. The present review outlines the known immunotherapy targets for the treatment of NKTCL.

Potential anti-proliferative effects of chemical constituents and hemisynthetic derivatives from Scadoxus pseudocaulus (Amarillydaceae)

Background

Biological significance of Amaryllidaceae is well advocated from the literature. In Cameroon, plants from this family are routinely used for the cure of liver, cancer and cardiovascular diseases. To date, no scientific investigation corresponding to the anti-cancer activity of extracts and isolated compounds of Scadoxus pseudocaulus is available.

Objective

Current study is focused to elaborate the anti-proliferative effects of natural isolates (compounds 1–6, 9) and hemi-synthetic analogs (compounds 7–8) extracted from S. pseudocaulu.

Methods

Column chromatography of the ethyl acetate extract followed by purification of different fractions led to the isolation of seven compounds (1 – 6, 9). Esterification reaction of compound 6 was carried out using butyroyl chlorides and triethylamin to produce two derivatives (7 – 8). The cytotoxic activity was performed after staining of treated cells with florescent dye propidium iodide. Dead cells were detected using cytometer FL2 or FL3 channels/filters.

Results

Trans-derivative of narciclasine (a natural isolate from S. pseudocaulus), was found to be most potent among all tested compounds. Its effects were more significant on low malignant follicular lymphoma (DoHH2 cells) as compared to highly malignant (EBV infected) Burkitts lymphoma (Raji cells).

Conclusion

From our results, narciclasine appears to hold the potential of a lead molecule that can be used to bridge the therapeutic gaps in cancer research.

Association of Epstein-Barr virus serological reactivation with transitioning to systemic lupus erythematosus in at-risk individuals

OBJECTIVE

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with unknown aetiology. Epstein-Barr virus (EBV) is an environmental factor associated with SLE. EBV maintains latency in B cells with frequent reactivation measured by antibodies against viral capsid antigen (VCA) and early antigen (EA). In this study, we determined whether EBV reactivation and single nucleotide polymorphisms (SNPs) in EBV-associated host genes are associated with SLE transition.

METHODS

SLE patient relatives (n=436) who did not have SLE at baseline were recontacted after 6.3 (±3.9) years and evaluated for interim transitioning to SLE (≥4 cumulative American College of Rheumatology criteria); 56 (13%) transitioned to SLE prior to the follow-up visit. At both visits, detailed demographic, environmental, clinical information and blood samples were obtained. Antibodies against viral antigens were measured by ELISA. SNPs in IL10, CR2, TNFAIP3 and CD40 genes were typed by ImmunoChip. Generalised estimating equations were used to test associations between viral antibody levels and transitioning to SLE.

RESULTS

Mean baseline VCA IgG (4.879±1.797 vs 3.866±1.795, p=0.0003) and EA IgG (1.192±1.113 vs 0.7774±0.8484, p=0.0236) levels were higher in transitioned compared with autoantibody negative non-transitioned relatives. Increased VCA IgG and EA IgG were associated with transitioning to SLE (OR 1.28 95% CI 1.07 to 1.53, p=0.007, OR 1.43 95% CI 1.06 to 1.93, p=0.02, respectively). Significant interactions were observed between CD40 variant rs48100485 and VCA IgG levels and IL10 variant rs3024493 and VCA IgA levels in transitioning to SLE.

CONCLUSION

Heightened serologic reactivation of EBV increases the probability of transitioning to SLE in unaffected SLE relatives.

Mechanisms of B-Cell Oncogenesis Induced by Epstein-Barr Virus

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus which asymptomatically infects the majority of the world population. Under immunocompromised conditions, EBV can trigger human cancers of epithelial and lymphoid origin. The oncogenic potential of EBV is demonstrated by in vitro infection and transformation of quiescent B cells into lymphoblastoid cell lines (LCLs). These cell lines, along with primary infection using genetically engineered viral particles coupled with recent technological advancements, have elucidated the underlying mechanisms of EBV-induced B-cell lymphomagenesis.

Chronic active Epstein-Barr virus infection: a bi-faceted disease with inflammatory and neoplastic elements

Chronic active Epstein-Barr virus infection (CAEBV) is one of the Epstein-Barr virus (EBV)-positive T- or NK-cell lymphoproliferative diseases. It is characterized by clonal proliferation of EBV-infected T or NK cells and their infiltration into systemic organs, leading to their failure. Inflammatory symptoms, fever, lymphadenopathy and liver dysfunction are main clinical findings of CAEBV. EBV itself contributes to the survival of the host cells via induction of CD40 and CD137 expression and constitutive activation of NF-κB. Accumulation of gene mutations in the infected cells may lead to the development of highly malignant lymphoma or leukemia. Furthermore, constitutive activation of STAT3 is detected in the infected cells, which not only promotes cell survival but also enhances production of inflammatory cytokines. Currently, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only effective treatment strategy for eradication of EBV-infected T or NK cells. However, active disease at the time of allo-HSCT (defined as presence of fever, liver dysfunction, progressive skin lesions, vasculitis or uveitis) is a negative prognostic factor. Establishment of chemotherapy regimens for effective resolution of disease activity in patients with CAEBV is a key imperative. Based on the recently unraveled molecular mechanisms CAEBV development, pathways mediated by NF-κB or JAK/STAT are potential novel therapeutic targets.

Advances in the Study of Chronic Active Epstein-Barr Virus Infection: Clinical Features Under the 2016 WHO Classification and Mechanisms of Development

Chronic active Epstein-Barr virus infection (CAEBV) is one of the Epstein-Barr virus (EBV)-positive T- or NK-lymphoproliferative diseases. It is considered rare and geographically limited to Japan and East Asia. However, CAEBV is drawing international attention, and the number of case reported worldwide is increasing, after its classification in the EBV-positive T- or NK-cell neoplasms, in the 2016 WHO classification. In this article, I review current advances in the study of CAEBV under the new definition and show future directions. In CAEBV, EBV-infected T or NK cells clonally proliferate and infiltrate multiple organs, leading to their failure. These characteristics define CAEBV as a lymphoid neoplasm. However, the main symptom of CAEBV is inflammation. Recently, the mechanisms underlying the development of CAEBV have gradually become clearer. EBV infection of T or NK cells can occur during the acute phase of primary infection with a high EBV load in the peripheral blood. In addition, it was reported that cytotoxic T cells decreased in numbers or showed dysfunction in CAEBV. These findings suggest that undetermined immunosuppressive disorders may underlie persistent infection of T or NK cells. Furthermore, EBV itself contributes to the survival of host cells. In vitro EBV infection of T cells induced intercellular survival-promoting pathways. Constitutive activation of NF-kB and STAT3 was observed in EBV-positive T or NK cells in CAEBV, promoting not only cell survival but also CAEBV development. During the disease course, CAEBV can lead to two lethal conditions: hemophagocytic lymphohistiocytosis and chemotherapy-resistant lymphoma. It is necessary to start treatment before these conditions develop. At present, the only effective treatment strategy for eradicating EBV-infected T or NK cells is allogeneic stem cell transplantation (allo-HSCT). However, patients with an active disease, in which the condition is accompanied by fever, liver dysfunction, progressive skin lesions, vasculitis, or uveitis, had worse outcomes after allo-HSCT, than patients with an inactive disease had. Unfortunately, current chemotherapies are insufficient to improve the activity of CAEBV. Based on the molecular mechanisms for the development of the disease, the NF-kB, or JAK/STAT mediating pathways are attractive candidate targets for new treatments.

DNA physical interaction mediated b-lymphoma treatment offered by tetra benzimidazole-substituted zinc (ii) phthalocyanine derivative

Role of heterocyclic compounds with nitrogen substitution in therapeutic frontiers is well established. The efforts made in this study are directed to dissect the biological significance of benzimidazole-substituted zinc phthalocyanine derivative. Its capacity to act as an anticancer agent against the 2 B-lymphoma cell lines (low-grade and high-grade malignancy) was found out by recording florescence using Alamar blue dye. Further cytotoxic effect at the DNA level was analyzed by performing agarose gel electrophoresis. Molecular docking studies made mechanistic details crystal clear by showing potential dual binding modes employed for interaction with DNA that include minor groove binding and intercalation between bases. This advocates this derivative as potential anticancer agent and deserves further rounds of mechanistic study for its final journey to serve as a marketed drug.

Role of exosomes as a proinflammatory mediator in the development of EBV-associated lymphoma

Epstein-Barr virus (EBV) causes various diseases in the elderly, including B-cell lymphoma such as Hodgkin's lymphoma and diffuse large B-cell lymphoma. Here, we show that EBV acts in trans on noninfected macrophages in the tumor through exosome secretion and augments the development of lymphomas. In a humanized mouse model, the different formation of lymphoproliferative disease (LPD) between 2 EBV strains (Akata and B95-8) was evident. Furthermore, injection of Akata-derived exosomes affected LPD severity, possibly through the regulation of macrophage phenotype in vivo. Exosomes collected from Akata-lymphoblastoid cell lines reportedly contain EBV-derived noncoding RNAs such as BamHI fragment A rightward transcript (BART) micro-RNAs (miRNAs) and EBV-encoded RNA. We focused on the exosome-mediated delivery of BART miRNAs. In vitro, BART miRNAs could induce the immune regulatory phenotype in macrophages characterized by the gene expressions of interleukin 10, tumor necrosis factor-α, and arginase 1, suggesting the immune regulatory role of BART miRNAs. The expression level of an EBV-encoded miRNA was strongly linked to the clinical outcomes in elderly patients with diffuse large B-cell lymphoma. These results implicate BART miRNAs as 1 of the factors regulating the severity of lymphoproliferative disease and as a diagnostic marker for EBV⁺ B-cell lymphoma.

EBV induces persistent NF-κB activation and contributes to survival of EBV-positive neoplastic T- or NK-cells

Epstein–Barr virus (EBV) has been detected in several T- and NK-cell neoplasms such as extranodal NK/T-cell lymphoma nasal type, aggressive NK-cell leukemia, EBV-positive peripheral T-cell lymphoma, systemic EBV-positive T-cell lymphoma of childhood, and chronic active EBV infection (CAEBV). However, how this virus contributes to lymphomagenesis in T or NK cells remains largely unknown. Here, we examined NF-κB activation in EBV-positive T or NK cell lines, SNT8, SNT15, SNT16, SNK6, and primary EBV-positive and clonally proliferating T/NK cells obtained from the peripheral blood of patients with CAEBV. Western blotting, electrophoretic mobility shift assays, and immunofluorescent staining revealed persistent NF-κB activation in EBV-infected cell lines and primary cells from patients. Furthermore, we investigated the role of EBV in infected T cells. We performed an in vitro infection assay using MOLT4 cells infected with EBV. The infection directly induced NF-κB activation, promoted survival, and inhibited etoposide-induced apoptosis in MOLT4 cells. The luciferase assay suggested that LMP1 mediated NF-κB activation in MOLT4 cells. IMD-0354, a specific inhibitor of NF-κB that suppresses NF-κB activation in cell lines, inhibited cell survival and induced apoptosis. These results indicate that EBV induces NF-κB-mediated survival signals in T and NK cells, and therefore, may contribute to the lymphomagenesis of these cells.

P-glycoprotein is expressed and causes resistance to chemotherapy in EBV-positive T-cell lymphoproliferative diseases

Epstein-Barr virus-positive T-cell lymphoproliferative diseases (EBV-T-LPDs) are rare lymphomas with poor prognosis. Although chemotherapeutic strategies such as CHOP have been often selected, they have exhibited only limited efficacy. To clarify the mechanism of chemoresistance, we examined P-glycoprotein (P-gp) expression. P-gp acts as an energy-dependent efflux pump that excretes drugs from the cytoplasm, resulting in low-intracellular drug concentrations and poor sensitivity to chemotherapy. We examined P-gp expression in EBV-positive cells by immunohistochemistry staining in three patients of EBV-T-LPDs and the expression was detected in all patients. We also examined mdr1 mRNA expression by reverse-transcriptase polymerase-chain reaction (RT-PCR) in EBV-positive tumor cells from these patients and additional three patients. The expression was detected in all examined patients. In five EBV-T-LPDs patients, P-gp function was detected by Rhodamine-123 efflux assay in these cells. The efflux was inhibited by treatment with a P-gp inhibitor, cyclosporine A (CsA). We also examined and detected P-gp expression in EBV-positive T-cell lines SNT8 and SNT16 established from EBV-T-LPDs patients, by RT-PCR and western blotting. The function was also detected by Rhodamine-123 efflux in these cell lines. Inhibition and knock down of P-gp by CsA and siRNA, respectively, enhanced etoposide- and doxorubicin-induced cell death in the EBV-positive T-cell lines. Finally, we infected the T-cell line MOLT4 with EBV, and found that mdr1 mRNA expression and Rhodamine 123 efflux were upregulated after infection. These results indicated that enhanced P-gp expression contributed to the chemoresistance of EBV-T-LPDs.

Primary Immunodeficiencies Associated with EBV Disease

Epstein-Barr virus (EBV) infects nearly all humans and usually is asymptomatic, or in the case of adolescents and young adults, it can result in infectious mononucleosis. EBV-infected B cells are controlled primarily by NK cells, iNKT cells, CD4 T cells, and CD8 T cells. While mutations in proteins important for B cell function can affect EBV infection of these cells, these mutations do not result in severe EBV infection. Some genetic disorders affecting T and NK cell function result in failure to control EBV infection, but do not result in increased susceptibility to other virus infections. These include mutations in SH2D1A, BIRC4, ITK, CD27, MAGT1, CORO1A, and LRBA. Since EBV is the only virus that induces proliferation of B cells, the study of these diseases has helped to identify proteins critical for interactions of T and/or NK cells with B cells. Mutations in three genes associated with hemophagocytic lymphohistocytosis, PRF1, STXBP2, and UNC13D, can also predispose to severe chronic active EBV disease. Severe EBV infection can be associated with immunodeficiencies that also predispose to other viral infections and in some cases other bacterial and fungal infections. These include diseases due to mutations in PIK3CD, PIK3R1, CTPS1, STK4, GATA2, MCM4, FCGR3A, CARD11, ATM, and WAS. In addition, patients with severe combined immunodeficiency, which can be due to mutations in a number of different genes, are at high risk for various infections as well as EBV B cell lymphomas. Identification of proteins important for control of EBV may help to identify new targets for immunosuppressive therapies.

LMP1-deficient Epstein-Barr virus mutant requires T cells for lymphomagenesis

Epstein-Barr virus (EBV) infection transforms B cells in vitro and is associated with human B cell lymphomas. The major EBV oncoprotein, latent membrane protein 1 (LMP1), mimics constitutively active CD40 and is essential for outgrowth of EBV-transformed B cells in vitro; however, EBV-positive diffuse large B cell lymphomas and Burkitt lymphomas often express little or no LMP1. Thus, EBV may contribute to the development and maintenance of human lymphomas even in the absence of LMP1. Here, we found that i.p. injection of human cord blood mononuclear cells infected with a LMP1-deficient EBV into immunodeficient mice induces B cell lymphomas. In this model, lymphoma development required the presence of CD4+ T cells in cord blood and was inhibited by CD40-blocking Abs. In contrast, LMP1-deficient EBV established persistent latency but did not induce lymphomas when directly injected into mice engrafted with human fetal CD34+ cells and human thymus. WT EBV induced lymphomas in both mouse models and did not require coinjected T cells in the cord blood model. Together, these results demonstrate that LMP1 is not essential for EBV-induced lymphomas in vivo and suggest that T cells supply signals that substitute for LMP1 in EBV-positive B cell lymphomagenesis.

CD137 expression is induced by Epstein-Barr virus infection through LMP1 in T or NK cells and mediates survival promoting signals

To clarify the mechanism for development of Epstein-Barr virus (EBV)-positive T- or NK-cell neoplasms, we focused on the costimulatory receptor CD137. We detected high expression of CD137 gene and its protein on EBV-positive T- or NK-cell lines as compared with EBV-negative cell lines. EBV-positive cells from EBV-positive T- or NK-cell lymphoproliferative disorders (EBV-T/NK-LPDs) patients also had significantly higher CD137 gene expression than control cells from healthy donors. In the presence of IL-2, whose concentration in the serum of EBV-T/NK-LPDs was higher than that of healthy donors, CD137 protein expression was upregulated in the patients' cells whereas not in control cells from healthy donors. In vitro EBV infection of MOLT4 cells resulted in induction of endogenous CD137 expression. Transient expression of LMP1, which was enhanced by IL-2 in EBV-T/NK-LPDs cells, induced endogenous CD137 gene expression in T and NK-cell lines. In order to examine in vivo CD137 expression, we used EBV-T/NK-LPDs xenograft models generated by intravenous injection of patients' cells. We identified EBV-positive and CD8-positive T cells, as well as CD137 ligand-positive cells, in their tissue lesions. In addition, we detected CD137 expression on the EBV infected cells from the lesions of the models by immune-fluorescent staining. Finally, CD137 stimulation suppressed etoposide-induced cell death not only in the EBV-positive T- or NK-cell lines, but also in the patients' cells. These results indicate that upregulation of CD137 expression through LMP1 by EBV promotes cell survival in T or NK cells leading to development of EBV-positive T/NK-cell neoplasms.

Constitutively CD40-activated B cells regulate CD8 T cell inflammatory response by IL-10 induction

B cells are exposed to high levels of CD40 ligand (CD40L, CD154) in chronic inflammatory diseases. In addition, B cells expressing both CD40 and CD40L have been identified in human diseases such as autoimmune diseases and lymphoma. However, how such constitutively CD40-activated B cells under inflammation may impact on T cell response remains unknown. Using a mouse model in which B cells express a CD40L transgene (CD40LTg) and receive autocrine CD40/CD40L signaling, we show that CD40LTg B cells stimulated memory-like CD4 and CD8 T cells to express IL-10. This IL-10 expression by CD8 T cells was dependent on IFN-I and programmed cell death protein 1, and was critical for CD8 T cells to counterregulate their overactivation. Furthermore, adoptive transfer of naive CD8 T cells in RAG-1(-/-) mice normally induces colitis in association with IL-17 and IFN-γ cytokine production. Using this model, we show that adoptive cotransfer of CD40LTg B cells, but not wild-type B cells, significantly reduced IL-17 response and regulated colitis in association with IL-10 induction in CD8 T cells. Thus, B cells expressing CD40L can be a therapeutic goal to regulate inflammatory CD8 T cell response by IL-10 induction.

Assessment of the effect of TLR7/8, TLR9 agonists and CD40 ligand on the transformation efficiency of Epstein-Barr virus in human B lymphocytes by limiting dilution assay

Infection of human B cells with Epstein-Barr virus (EBV) induces polyclonal activation in almost all infected cells, but a small proportion of infected cells are transformed to immortalized lymphoblastoid cell lines. Since B cells are activated also by CD40 ligand (CD40L) and Toll-like receptor (TLR) agonists via a similar signaling pathway, it is likely that costimulation through these molecules could result in synergistic enhancement of the transformation efficiency of EBV. In this study, the stimulatory effect of TLR7/8 (R848), TLR9 (CpG) agonists and/or CD40L on transformation efficiency of EBV in normal human B cells was assessed using the limiting dilution assay. Costimulation of peripheral blood mononuclear cells (PBMCs) with CpG and R848, but not CD40L, increased significantly the frequency of EBV transformed B cells (p < 0.001). Neither synergistic nor additive effects were observed between TLR agonists and CD40L and also TLR7/8 and TLR9 agonists. Costimulation with R848, CpG and CD40L enhanced the proliferative response of B cells infected with EBV. This effect was more evident when enriched B cells were employed, compared to PBMCs. The promoting effect of TLR agonists stimulation, implies that EBV may take advantage of the genes induced by the TLR stimulation pathway for viral latency and oncogenesis.

Effects of Epstein-Barr virus infection on the development of multiple myeloma after liver transplantation

Reduced cellular immune function in patients after liver transplantation easily results in many types of viral infections, such as Epstein-Barr virus. Epstein-Barr virus is a Γ-herpesvirus and is related to many malignant diseases, especially epithelial and lymph tumors. The abnormal interaction of cluster of differentiation 40 with cluster of differentiation 40 ligand and expression of cluster of differentiation 40 ligand are considered closely related to the development of myeloma cells. This study explored the influence and mechanism of Epstein-Barr virus infection on the phenotype and biological behavior of myeloma cells after liver transplantation. Flow cytometry was used to detect coexpression of cluster of differentiation 40 and cluster of differentiation 40 ligand in 10 samples of freshly isolated multiple myeloma cells. Cluster of differentiation 40 and cluster of differentiation 40 ligand were coexpressed in sample Nos. 5, 8, 9, and 10, particularly in sample No. 5. Western blot analysis was used to detect the expression of the Epstein-Barr virus antigens latent membrane protein 1 and Epstein-Barr virus nuclear antigen 2 in the multiple myeloma cell line RPMI 8226 infected with Epstein-Barr virus. The antigen expression indicated that Epstein-Barr virus can infect multiple myeloma virus cells in vitro. Reverse transcription-polymerase chain reaction revealed upregulated expression of cluster of differentiation 40 ligand on the infected RPMI 8226 cells, which may be involved in the anti-apoptosis activity of the infected cells. Confocal microscopy showed that pairs of molecules of cluster of differentiation 40, cluster of differentiation 40 ligand, and latent membrane protein 1 were colocalized on the surface of the infected cells. CXC chemokine receptor 4 was upregulated on the RPMI 8226 cells after Epstein-Barr virus infection. The migratory ability of the infected cells improved in the presence of the chemokine stromal cell-derived factor-1α. Anti-apoptosis and migration are known important biological characteristics of malignant cells. Our results indicate the involvement of Epstein-Barr virus in the origin and development of multiple myeloma. The risk of multiple myeloma increases when Epstein-Barr virus infects B cells in the germinal center, which may result in an anti-apoptosis effect of B cells and an improved ability to migrate from the germinal center to peripheral blood.

Augmented antibody response with premature germinal center regression in CD40L transgenic mice

Although CD40 signaling is required for activation and differentiation of B cells, including germinal center (GC) formation and generation of memory B cells, in vivo generation of CD40 signaling augments plasma cell differentiation but disrupts GCs. Thus, CD40 signaling is thought to direct B cells to extrafollicular plasma cell fate rather than GC formation. In this study, we analyzed CD40L transgenic (CD40LTg) mice that constitutively express CD40L on B cells. After immunization, activation of B cells, but not dendritic cells, was augmented, although dendritic cells can be activated by CD40 ligation. Bone marrow chimera carrying CD40LTg and nontransgenic B cells showed increased Ab production from transgenic, but not from coexisting nontransgenic, B cells, suggesting that CD40L on a B cell preferentially stimulates the same B cell through an autocrine pathway, thereby augmenting Ab production. Although GCs rapidly regressed after day 5 of immunization and failed to generate late-appearing high-affinity Ab, CD40LTg mice showed normal GC formation up to day 5, as well as normal generation of long-lived plasma cells and memory B cell responses. This observation suggests that CD40 signaling does not block GC formation or differentiation of GC B cells, but it inhibits sustained expansion of GC B cells and augments B cell differentiation.

Sensitization of SiHa cell to gemcitabine by CD40 activation and its overexpression in cervical carcinoma

CD40, a member of the tumor necrosis factor receptor superfamily, is widely expressed on various cell types. Some studies show that CD40 expression is related to several carcinomas, where its function remains largely unknown. This study investigated the expression of CD40 on cervical carcinoma and evaluated the effect of agnostic anti-CD40 mAb (5C11) on tumor cell line (SiHa). CD40 expression on the primary cervical carcinoma samples was detected by immunohistochemistry. Results showed that CD40 is commonly expressed in human cervical carcinoma, which is higher than that of normal cervix, cervical precancerous tissue and chronic cervicitis. Treatment of the SiHa cell with the agonistic anti-CD40 monoclonal antibody or Gemcitabine alone did not inhibit the proliferation of the SiHa cell in vitro, but the activation of CD40 on SiHa could enhance its sensitivity to Gemcitabine. Furthermore, CD40 activation blocked SiHa in the S phase, stimulated proapoptotic Bax and inhibited antiapoptotic Bcl-XL mRNA synthesis in the SiHa cell. Apoptosis in SiHa was associated with an increasing ratio of Bax to Bcl-XL in mRNA levels. It is concluded that use of the anti-CD40 mAb 5C11 in combination with chemotherapy may have significant therapeutic potential.

Early events associated with infection of Epstein-Barr virus infection of primary B-cells

Epstein Barr virus (EBV) is closely associated with the development of a vast number of human cancers. To develop a system for monitoring early cellular and viral events associated with EBV infection a self-recombining BAC containing 172-kb of the Epstein Barr virus genome BAC-EBV designated as MD1 BAC (Chen et al., 2005, J.Virology) was used to introduce an expression cassette of green fluorescent protein (GFP) by homologous recombination, and the resultant BAC clone, BAC-GFP-EBV was transfected into the HEK 293T epithelial cell line. The resulting recombinant GFP EBV was induced to produce progeny virus by chemical inducer from the stable HEK 293T BAC GFP EBV cell line and the virus was used to immortalize human primary B-cell as monitored by green fluorescence and outgrowth of the primary B cells. The infection, B-cell activation and cell proliferation due to GFP EBV was monitored by the expression of the B-cell surface antigens CD5, CD10, CD19, CD23, CD39, CD40 , CD44 and the intercellular proliferation marker Ki-67 using Flow cytometry. The results show a dramatic increase in Ki-67 which continues to increase by 6–7 days post-infection. Likewise, CD40 signals showed a gradual increase, whereas CD23 signals were increased by 6–12 hours, maximally by 3 days and then decreased. Monitoring the viral gene expression pattern showed an early burst of lytic gene expression. This up-regulation of lytic gene expression prior to latent genes during early infection strongly suggests that EBV infects primary B-cell with an initial burst of lytic gene expression and the resulting progeny virus is competent for infecting new primary B-cells. This process may be critical for establishment of latency prior to cellular transformation. The newly infected primary B-cells can be further analyzed for investigating B cell activation due to EBV infection.

CD40 signaling activated by Epstein-Barr virus promotes cell survival and proliferation in gastric carcinoma-derived human epithelial cells

CD40 signaling plays a critical role in the survival and proliferation of EBV-infected lymphocytes. Here we show that CD40 is constitutively expressed in the human gastric carcinoma-derived cell lines AGS, MKN28, and MKN74, and expression of CD40L is induced by in vitro infection with EBV. Blocking the interaction between CD40 and CD40L with CD40Ig, a fusion protein of CD40 and IgG, impaired proliferation of EBV-infected AGS cells and enhanced their calcium ionophore-induced apoptosis. These results suggest that CD40 signaling plays a critical role in the survival and proliferation of EBV-infected epithelial cells, as well as in the virus-infected lymphocytes.

Development of Langerhans cell histiocytosis associated with chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (CAEBV) infection is characterized by a status of lymphoproliferative disease of EBV-infected cells, resulting in chronic or recurrent infectious mononucleosis-like symptoms. CAEBV is always accompanied by life-threatening complications. We report the case of a 2-year-old female patient with CAEBV who subsequently developed Langerhans cell histiocytosis (LCH) presenting with bilateral exophthalmos, bone, and skin involvement. In situ hybridization for EBER revealed EBV-infected B-cells present in lesional tissue implying that interactions between EBV-infected B-cells and lesional Langerhans cells may be associated with the development of LCH.

EBV latent membrane protein 1 activates Akt, NFkappaB, and Stat3 in B cell lymphomas

Latent membrane protein 1 (LMP1) is the major oncoprotein of Epstein-Barr virus (EBV). In transgenic mice, LMP1 promotes increased lymphoma development by 12 mo of age. This study reveals that lymphoma develops in B-1a lymphocytes, a population that is associated with transformation in older mice. The lymphoma cells have deregulated cell cycle markers, and inhibitors of Akt, NFκB, and Stat3 block the enhanced viability of LMP1 transgenic lymphocytes and lymphoma cells in vitro. Lymphoma cells are independent of IL4/Stat6 signaling for survival and proliferation, but have constitutively activated Stat3 signaling. These same targets are also deregulated in wild-type B-1a lymphomas that arise spontaneously through age predisposition. These results suggest that Akt, NFκB, and Stat3 pathways may serve as effective targets in the treatment of EBV-associated B cell lymphomas.

Epstein-Barr virus (EBV) is linked to the development of multiple cancers, including post-transplant lymphoma, Hodgkin disease, and nasopharyngeal carcinoma. Latent membrane protein 1 (LMP1) is expressed in many EBV-associated cancers and is responsible for most of the altered cellular growth properties that are induced by EBV infection. This study reveals that LMP1 induces lymphomas in B-1a lymphocytes, a cell type that is susceptible to transformation in aged mice. The lymphomas require Akt, NFκB, and Stat3 signaling for enhanced growth and survival. The activation of the Stat3, Akt, and NFκB signaling pathways likely underlies the ability of LMP1 to promote malignant transformation.

Cell isolation and expansion using Dynabeads

This chapter describes the use of Dynabeads for cell isolation and expansion. Dynabeads are uniform polystyrene spherical beads that have been made magnetisable and superparamagnetic, meaning they are only magnetic in a magnetic field. Due to this property, the beads can easily be resuspended when the magnetic field is removed. The invention of Dynabeads made, by Professor John Ugelstad, has revolutionized the separation of many biological materials. For example, the attachment of target-specific antibodies to the surface of the beads allows capture and isolation of intact cells directly from a complex suspension such as blood. This is all accomplished under the influence of a simple magnetic field without the need for column separation techniques or centrifugation. In general, magnetic beads coated with specific antibodies can be used either for isolation or depletion of various cell types. Positive or negative cell isolation can be performed depending on the nature of the starting sample, the cell surface markers and the downstream application in question. Positive cell isolation is the method of choice for unprocessed samples, such as whole blood, and for downstream molecular applications. Positive cell isolation can also be used for any downstream application after detachment and removal of the beads. Negative cell isolation is the method of choice when it is critical that cells of interest remain untouched, i.e., no antibodies have been bound to any cell surface markers on the cells of interest. Some cell populations can only be defined by multiple cell surface markers. Such populations of cells can be isolated by the combination of negative and positive cell isolation. By coupling Dynabeads with antibodies directed against cell surface activation molecules, the beads can be used both for isolation and expansion of the cells. Dynabeads are currently used in two major clinical applications: 1) In the Isolex 300i Magnetic Cell Selection System for CD34 Stem Cell Isolation--2) For ex vivo T cell isolation and expansion using Dynabeads ClinExVivo CD3/CD28 for clinical trials in novel adoptive immunotherapy.

[Mechanisms of EBV-mediated oncogenesis]

Epstein-Barr virus (EBV) is the DNA tumor virus, which is known to be relevant to various cancers. EBV maintains latent infection in cancer cells, and there are three types of latent infection (type I-III) according to the patterns of viral latent genes expression. EBV has the ability to transform B cells into immortalized lymphoblastoid cell lines (LCL) showing type III latency, in which all latent genes are expressed. The mechanism of B-cell transformation has provided a model of EBV-associated lymphomas in immunosuppressed individuals. In type I and II latency, the limited numbers of latent genes are expressed. Previous studies have demonstrated the oncogenic functions of latent EBV genes including nuclear antigen EBNA1, membrane protein LMP1 and LMP2A. In addition, we have demonstrated that EBV-encoded small RNA EBERs play a significant role in oncogenesis. Here we summarize recent progresses in the studies on molecular mechanisms of EBV-mediated oncogenesis.

Primary CD4+ T-cell responses provide both helper and cytotoxic functions during Epstein-Barr virus infection and transformation of fetal cord blood B cells

Most humans carry Epstein-Barr virus (EBV) in circulating memory B cells as a latent infection that is controlled by an immune response. When infected by EBV, B lymphocytes in fetal cord blood are readily transformed to lymphoblastoid cell lines (LCL). It is frequently assumed that this high efficiency of transformation is due to the absence of a primary immune response. However, cord blood lymphocytes stimulated with autologous LCL yield CD4+ T cells that can completely inhibit the growth of LCL by a major histocompatibility complex-restricted cytotoxic mechanism mediated by granulysin and granzyme B. Because EBV-transformed B cells maintain the phenotype of antigen-activated B-cell blasts, they can potentially receive inhibitory or helper functions from CD4+ T cells. To assess these functions, the effect of EBV-specific CD4+ T cells on the efficiency of virus transformation of autologous B cells was assayed. Paradoxically, although the cytotoxic CD4+ T-cell lines reduced EBV B-cell transformation at a high effector/target ratio of 10:1, they caused a twofold increase in B-cell transformation at the lower effector/target ratio of 1:1. Th1-polarized CD4+ T cells were more effective at inhibiting B-cell transformation, but Th2-polarized cell lines had reduced cytotoxic activity, were unable to inhibit LCL growth, and caused a 10-fold increase in transformation efficiency. Tonsil lymphoid follicles lacked NK cells and CD8+ T cells but contained CD4+ T cells. We propose that CD4+ T cells provide helper or cytotoxic functions to EBV-transformed B cells and that the balance of these functions within tonsil compartments is critical in establishing asymptomatic primary EBV infection and maintaining a stable lifelong latent infection.

Immortalization of Epstein-Barr virus-negative human B lymphocytes with minimal chromosomal instability

The genes required for immortalization of human B cells infected by Epstein-Barr virus are multiple, and the precise mechanism of this process remains to be elucidated. In the present study HPV16 E6 and E7 were retrovirally transduced into human primary B cells stimulated by CD40-CD40L interaction, thereby establishing an Epstein-Barr virus negative immortalized human B cell line, which continued to proliferate for more than 2 years (100 population doublings). The established cell line had a high telomerase activity from the beginning of the culture period, and no shortening of the telomere length was observed. A chromosomal analysis revealed that a large portion of the HPV16E6E7 transduced cells had retained a normal karyotype. Similar to human epithelial cells, human B lymphocytes seem to require two steps for immortalization, namely, the inactivation of the p16/Rb pathway and the activation of telomerase, the latter that can be induced by the CD40-CD40L interaction. Furthermore, using this system, it is possible to analyze the role of individual genes in human B lymphocyte immortalization without the influence of a pre-existing Epstein-Barr virus genome.

Transcription factors TFE3 and TFEB are critical for CD40 ligand expression and thymus-dependent humoral immunity

TFE3 and TFEB are broadly expressed transcription factors related to the transcription factor Mitf. Although they have been linked to cytokine signaling pathways in nonlymphoid cells, their function in T cells is unknown. TFE3-deficient mice are phenotypically normal, whereas TFEB deficiency causes early embryonic death. We now show that combined inactivation of TFE3 and TFEB in T cells resulted in a hyper-immunoglobulin M syndrome due to impaired expression of CD40 ligand by CD4(+) T cells. Native TFE3 and TFEB bound to multiple cognate sites in the promoter of the gene encoding CD40 ligand (Cd40lg), and maximum Cd40lg promoter activity and gene expression required TFE3 or TFEB. Thus, TFE3 and TFEB are direct, physiological and mutually redundant activators of Cd40lg expression in activated CD4(+) T cells critical for T cell-dependent antibody responses.

Functional role of phosphatidylinositol 3-kinase/Akt pathway on cell growth and lytic cycle of Epstein-Barr virus in the Burkitt's lymphoma cell line, P3HR-1

The phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is involved in various malignancies, but the role of PI3-K/Akt pathway in Epstein-Barr virus (EBV) infected Burkitt's lymphoma (BL) cells remains unclear. To elucidate therapeutic targets for BL, this study investigates the effect of PI3-K/Akt pathway in: EBV-positive BL cell lines Raji, P3HR-1, Akata and Daudi; and EBV-negative BL cell lines Ramos and BJAB. Results of analyses indicate that Akt was constitutively phosphorylated in BJAB, P3HR-1, Akata, and Daudi but not in Ramos and Raji cells. We characterized Akt phosphorylation on cell growth and EBV lytic cycle in P3HR-1 cells, which were phosphorylated most intensively. The Akt was equally phosphorylated in cells cultured with and without fetal bovine serum for a few days. Akt phosphorylation and cell growth were inhibited by PI3-K specific inhibitor LY294002 in a dose-dependent manner. LY294002 markedly down regulated expression of EBV lytic gene BRLF1 protein Rta, BMRF1 protein EA-D, but not BZLF1 protein ZEBRA. The inhibitor reduced viral capsid antigen (VCA) positive cells. Down regulation of Rta by LY294002 occurred at the transcriptional level. These results demonstrate that PI3-K/Akt pathway is activated constitutively in P3HR-1 cells; it promotes cell growth and the lytic cycle cascade downstream of ZEBRA.

Pathogenesis of chronic active Epstein-Barr virus infection: is this an infectious disease, lymphoproliferative disorder, or immunodeficiency?

Chronic active Epstein-Barr virus infection (CAEBV) is characterised by chronic or recurrent infectious mononucleosis-like symptoms, such as fever, hepatosplenomegaly, persistent hepatitis and extensive lymphadenopathy. Patients with CAEBV have high viral loads in their peripheral blood and/or an unusual pattern of EBV-related antibodies. This disease is rare but severe with high morbidity and mortality. Nearly three decades have passed since this disease was first identified, and recent advances in technology have increased our understanding of CAEBV pathophysiology. There is accumulating evidence that the clonal expansion of EBV-infected T or natural killer (NK) cells plays a central role in the pathogenesis of CAEBV. However, it remains unclear whether CAEBV is truly a monoclonal lymphoproliferative disorder. EBV-infected T or NK cells are able to evade the host cellular immune system due to the limited expression of viral proteins of reduced antigenicity. Recent studies suggest that infection of T or NK cells is a common event during primary EBV infection. A defect or single nucleotide polymorphism in host immune-modulating genes may allow for the expansion of virus infected cells giving rise to CAEBV. In this review, I summarise our current understanding of the pathogenesis of CAEBV and propose a model of CAEBV pathogenicity.

Establishment and maintenance of long-term murine gammaherpesvirus 68 latency in B cells in the absence of CD40

Murine gammaherpesvirus 68 (gammaHV68), like Epstein-Barr virus (EBV), establishes a chronic infection in its host by gaining access to the memory B-cell reservoir, where it persists undetected by the host's immune system. EBV encodes a membrane protein, LMP1, that appears to function as a constitutively active CD40 receptor, and is hypothesized to play a central role in EBV-driven differentiation of infected naive B cells to a memory B-cell phenotype. However, it has recently been shown that there is a critical role for CD40-CD40L interaction in B-cell immortalization by EBV (K.-I. Imadome, M. Shirakata, N. Shimizu, S. Nonoyama, and Y. Yamanashi, Proc. Natl. Acad. Sci. USA 100:7836-7840, 2003), indicating that LMP1 does not adequately recapitulate all of the necessary functions of CD40. The role of CD40 receptor expression on B cells for the establishment and maintenance of gammaHV68 latency is unclear. Data previously obtained with a competition model, demonstrated that in the face of CD40-sufficient B cells, gammaHV68 latency in CD40-deficient B cells waned over time in chimeric mice (I.-J. Kim, E. Flano, D. L. Woodland, F. E. Lund, T. D. Randall, and M. A. Blackman, J. Immunol. 171:886-892, 2003). To further investigate the role of CD40 in gammaHV68 latency in vivo, we have characterized the infection of CD40 knockout (CD40(-/-)) mice. Here we report that, consistent with previous observations, gammaHV68 efficiently established a latent infection in B cells of CD40(-/-) mice. Notably, unlike the infection of normal C57BL/6 mice, significant ex vivo reactivation from splenocytes harvested from infected CD40(-/-) mice 42 days postinfection was observed. In addition, in contrast to gammaHV68 infection of C57BL/6 mice, the frequency of infected naive B cells remained fairly stable over a 3-month period postinfection. Furthermore, a slightly higher frequency of gammaHV68 infection was observed in immunoglobulin D (IgD)-negative B cells, which was stably maintained over a period of 3 months postinfection. The presence of virus in IgD-negative B cells indicates that gammaHV68 may either directly infect memory B cells present in CD40(-/-) mice or be capable of driving differentiation of naive CD40(-/-) B cells. A possible explanation for the apparent discrepancy between the failure of gammaHV68 latency to be maintained in CD40-deficient B cells in the presence of CD40-sufficient B cells and the stable maintenance of gammaHV68 B-cell latency in CD40(-/-) mice came from examining virus replication in the lungs of infected CD40(-/-) mice, where we observed significantly higher levels of virus replication at late times postinfection compared to those in infected C57BL/6 mice. Taken together, these findings are consistent with a model in which chronic virus infection of CD40(-/-) mice is maintained through virus reactivation in the lungs and reseeding of latency reservoirs.