CD27 expression by a distinct subpopulation of human B lymphocytes

A guide to adaptive immune memory

Immune memory - comprising T cells, B cells and plasma cells and their secreted antibodies - is crucial for human survival. It enables the rapid and effective clearance of a pathogen after re-exposure, to minimize damage to the host. When antigen-experienced, memory T cells become activated, they proliferate and produce effector molecules at faster rates and in greater magnitudes than antigen-inexperienced, naive cells. Similarly, memory B cells become activated and differentiate into antibody-secreting cells more rapidly than naive B cells, and they undergo processes that increase their affinity for antigen. The ability of T cells and B cells to form memory cells after antigen exposure is the rationale behind vaccination. Understanding immune memory not only is crucial for the design of more-efficacious vaccines but also has important implications for immunotherapies in infectious disease and cancer. This 'guide to' article provides an overview of the current understanding of the phenotype, function, location, and pathways for the generation, maintenance and protective capacity of memory T cells and memory B cells.

Cerebrospinal fluid soluble CD27 is associated with CD8+ T cells, B cells and biomarkers of B cell activity in relapsing-remitting multiple sclerosis

Cerebrospinal fluid (CSF) soluble CD27 (sCD27) is a sensitive biomarker of intrathecal inflammation. Although generally considered a biomarker of T cell activation, CSF sCD27 has been shown to correlate with biomarkers of B cell activity in multiple sclerosis. We analyzed CSF from 40 patients with relapsing-remitting multiple sclerosis (RRMS) and nine symptomatic controls using flow cytometry and multiplex electrochemiluminescence immunoassays. CSF sCD27 levels were increased in RRMS and correlated with IgG index, soluble B cell maturation antigen, cell count, B cell frequency and CD8+ T cell frequency. We provide new data indicating that CSF sCD27 is associated with CD8+ T cells and B cells in RRMS.

Understanding the Bioactivity and Prognostic Implication of Commonly Used Surface Antigens in Multiple Myeloma

Multiple myeloma (MM) progression is dependent on its interaction with the bone marrow microenvironment and the immune system and is mediated by key surface antigens. Some antigens promote adhesion to the bone marrow matrix and stromal cells, while others are involved in intercellular interactions that result in differentiation of B-cells to plasma cells (PC). These interactions are also involved in malignant transformation of the normal PC to MM PC as well as disease progression. Here, we review selected surface antigens that are commonly used in the flow cytometry analysis of MM for identification of plasma cells (PC) and the discrimination between normal and malignant PC as well as prognostication. These include the markers: CD38, CD138, CD45, CD19, CD117, CD56, CD81, CD27, and CD28. Furthermore, we will discuss the novel marker CD24 and its involvement in MM. The bioactivity of each antigen is reviewed, as well as its expression on normal vs. malignant PC, prognostic implications, and therapeutic utility. Understanding the role of these specific surface antigens, as well as complex co-expressions of combinations of antigens, may allow for a more personalized prognostic monitoring and treatment of MM patients.

Targeting the CD27-CD70 Pathway to Improve Outcomes in Both Checkpoint Immunotherapy and Allogeneic Hematopoietic Cell Transplantation

Immune checkpoint inhibitor therapies and allogeneic hematopoietic cell transplant (alloHCT) represent two distinct modalities that offer a chance for long-term cure in a diverse array of malignancies and have experienced many breakthroughs in recent years. Herein, we review the CD27-CD70 co-stimulatory pathway and its therapeutic potential in 1) combination with checkpoint inhibitor and other immune therapies and 2) its potential ability to serve as a novel approach in graft-versus-host disease (GVHD) prevention. We further review recent advances in the understanding of GVHD as a complex immune phenomenon between donor and host immune systems, particularly in the early stages with mixed chimerism, and potential novel therapeutic approaches to prevent the development of GVHD.

Targeting B Cells and Plasma Cells in Autoimmune Diseases

Success with B cell depletion using rituximab has proven the concept that B lineage cells represent a valid target for the treatment of autoimmune diseases, and has promoted the development of other B cell targeting agents. Present data confirm that B cell depletion is beneficial in various autoimmune disorders and also show that it can worsen the disease course in some patients. These findings suggest that B lineage cells not only produce pathogenic autoantibodies, but also significantly contribute to the regulation of inflammation. In this review, we will discuss the multiple pro- and anti-inflammatory roles of B lineage cells play in autoimmune diseases, in the context of recent findings using B lineage targeting therapies.

T cells and costimulation in cancer

Optimal T cell response is dependent not only on T cell receptor activation, but also on additional signaling from coreceptors. The main coreceptors include B7 and tumor necrosis factor family members. They exert costimulatory or coinhibitory effects, and their balance determines the fate of T cell response. In normal conditions, costimulators facilitate the development of protective immune response, whereas coinhibitors dampen inflammation to avoid organ/tissue damage from excessive immune reaction. In the tumor microenvironment, the balance is garbled: inhibitory pathways predominate, and T cell response is impaired. The importance of cosignaling in the tumor immune response has been experimentally and clinically demonstrated. New therapeutic strategies targeting T cell cosignaling, especially coinhibitory molecules, are under active experimental and clinical investigation. This review summarizes the functions of main T cell cosignaling axes and discusses their clinical application.

The majority of human memory B cells recognizing RhD and tetanus resides in IgM+ B cells

B cell memory to T cell-dependent (TD) Ags are considered to largely reside in class-switched CD27(+) cells. However, we previously observed that anti-RhD (D) Igs cloned from two donors, hyperimmunized with D(+) erythrocytes, were predominantly of the IgM isotype. We therefore analyzed in this study the phenotype and frequency of D- and tetanus toxoid-specific B cells by culturing B cells in limiting dilution upon irradiated CD40L-expressing EL4.B5 cells and testing the culture supernatant. Most Ag-specific B cells for both TD Ags were found to reside in the IgM-expressing B cells, including CD27(-) B cells, in both hyperimmunized donors and nonhyperimmunized volunteers. Only shortly after immunization a sharp increase in Ag-specific CD27(+)IgG(+) B cells was observed. Next, B cells were enriched with D(+) erythrocyte ghosts and sorted as single cells. Sequencing of IGHV, IGLV, IGKV, and BCL6 genes from these D-specific B cell clones demonstrated that both CD27(-)IgM(+) and CD27(+)IgM(+) B cells harbored somatic mutations, documenting their Ag-selected nature. Furthermore, sequencing revealed a clonal relationship between the CD27(-)IgM(+), CD27(+)IgM(+), and CD27(+)IgG(+) B cell subsets. These data strongly support the recently described multiple layers of memory B cells to TD Ags in mice, where IgM(+) B cells represent a memory reservoir which can re-enter the germinal center and ensure replenishment of class-switched memory CD27(+) B cells from Ag-experienced precursors.

The human fetal lymphocyte lineage: identification by CD27 and LIN28B expression in B cell progenitors

CD27, a member of the TNFR superfamily, is used to identify human memory B cells. Nonetheless, CD27(+) B cells are present in patients with HIGM1 syndrome who are unable to generate GCs or memory B cells. CD27(+)IgD(+) fetal B cells are present in umbilical cord blood, and CD27 may also be a marker of the human B1-like B cells. To define the origin of naïve CD27(+)IgD(+) human B cells, we studied B cell development in both fetal and adult tissues. In human FL, most CD19(+) cells coexpressed CD10, a marker of human developing B cells. Some CD19(+)CD10(+) B cells expressed CD27, and these fetal CD27(+) cells were present in the pro-B, pre-B, and immature/transitional B cell compartments. Lower frequencies of phenotypically identical cells were also identified in adult BM. CD27(+) pro-B, pre-B, and immature/transitional B cells expressed recombination activating gene-1, terminal deoxynucleotidyl transferase and Vpre-B mRNA comparably to their CD27(-) counterparts. CD27(+) and CD27(-) developing B cells showed similar Ig heavy chain gene usage with low levels of mutations, suggesting that CD27(+) developing B cells are distinct from mutated memory B cells. Despite these similarities, CD27(+) developing B cells differed from CD27(-) developing B cells by their increased expression of LIN28B, a transcription factor associated with the fetal lymphoid lineages of mice. Furthermore, CD27(+) pro-B cells efficiently generated IgM(+)IgD(+) immature/transitional B cells in vitro. Our observations suggest that CD27 expression during B cell development identifies a physiologic state or lineage for human B cell development distinct from the memory B cell compartment.

Enhanced insight into the autoimmune component of glaucoma: IgG autoantibody accumulation and pro-inflammatory conditions in human glaucomatous retina

BACKGROUND

There is accumulating evidence that autoimmune components, such as autoantibodies and autoantibody depositions, play a role in the pathogenesis of neurodegenerative diseases like Alzheimeŕs disease or Multiple Sclerosis. Due to alterations of autoantibody patterns in sera and aqueous humor, an autoimmune component is also assumed in the pathogenesis of glaucoma, a common reason for irreversible blindness worldwide. So far there has been no convincing evidence that autoantibodies are accumulated in the retina of glaucoma patients and that the local immune homeostasis might be affected.

METHODS AND RESULTS

Six human glaucomatous donor eyes and nine samples from donors with no recorded ocular disease were included. Antibody microarrays were used to examine the patterns of pro-inflammatory proteins and complement proteins. Analysis of TNF-α and interleukin levels revealed a slight up-regulation exclusively in the glaucomatous group, while complement protein levels were not altered. IgG autoantibody accumulations and/or cellular components were determined by immunohistology (n = 4 per group). A significantly reduced number of retinal ganglion cells was found in the glaucomatous group (healthy: 104±7 nuclei/mm, glaucoma: 67±9 nuclei/mm; p = 0.0007). Cell loss was accompanied by strong retinal IgG autoantibody accumulations, which were at least twice as high as in healthy subjects (healthy: 5.0±0.5 IgG deposits/100 cells, glaucoma: 9.4±1.9 IgG deposits/100 cells; p = 0.004). CD27(+) cells and CD27(+)/IgG(+) plasma cells were observed in all glaucomatous subjects, but not in controls.

CONCLUSION

This work provides serious evidence for the occurrence of IgG antibody deposition and plasma cells in human glaucomatous retina. Moreover, the results suggest that these IgG deposits occurred in a pro-inflammatory environment which seems to be maintained locally by immune-competent cells like microglia. Thereby, glaucoma features an immunological involvement comparable to other neurodegenerative diseases, but also shows a multifactorial pathomechanism, which diverges and might be linked to the specific nature of both eye and retina.

Porcine CD27: identification, expression and functional aspects in lymphocyte subsets in swine

Up to now for Swine Workshop Cluster 2 (SWC2) the orthologous human CD molecule was unknown. By use of the SWC2-specific mAb b30c7 and a retroviral cDNA expression library derived from stimulated porcine peripheral blood mononuclear cells we could identify SWC2 as porcine CD27. Phenotypic analyses of lymphocytes isolated from blood and lymphatic organs revealed that mature T cells in thymus and T cells in the periphery with a naïve phenotype were CD27(+). However, within CD8α(+) T helper and CD8α(+) γδ T cells also CD27(-) cells were present, indicating a down-regulation after antigen contact in vivo. B cells lacked CD27 expression, whereas NK cells expressed intermediate levels. Furthermore, plate-bound mAb b30c7 showed a costimulatory capacity on CD3-activated T cells for proliferation, IFN-γ and TNF-α production. Hence, our data indicate an important role of porcine CD27 for T-cell differentiation and activation as described for humans and mice.

Germinal center selection and the development of memory B and plasma cells

A hallmark of adaptive immune responses is the generation of long-lived protection after primary exposure to a pathogen. In humoral responses, this protection stems from a combination of sustained antibody titers and long-lived memory B cells (MBCs), with the former deriving from long-lived plasma cells (PCs). Both types of cell are thought to primarily derive from the germinal center (GC), a unique structure that forms during the immune response to many types of antigenic stimuli. GCs are seeded by antigen-specific B and T cells that were previously activated in the early stages of the response. The GC does not directly or immediately generate effector function; rather, it is a site of intense B-cell proliferation and cell death. GC B cells undergo both somatic hypermutation and isotype switch, and a Darwinian process very efficiently selects B cells with higher fitness for survival and expansion. GC B cells adopt a unique activation and transcriptional state, and the cells become poised to differentiate to either MBCs or PCs. Despite this general understanding of the events in the GC, the mechanisms that control both affinity selection as well as differentiation have not been well worked out. In this review, we address what is known about what determines whether GC B cells become MBCs or PCs. This is discussed in the broader context of the origins of both cell types, whether from the GC or potentially other sources. We present a model encompassing recent data from several laboratories including our own that suggests that the GC undergoes a temporal switch that alters the nature of its output from MBCs to PCs as the response progresses. We will discuss B-cell receptor signaling in the GC as it relates to potential mechanisms for affinity-based selection during the reaction.

The role of CD19 and CD27 in the diagnosis of multiple myeloma by flow cytometry: a new statistical model

We have developed a new statistical diagnostic model that examines the correlation between immunophenotype and clonality as detected by flow cytometry (FC) and histology, defining the diagnostic role of FC in multiple myeloma (MM). The 192 bone marrow samples from patients and control subjects were studied for routine diagnostic analysis of MM; a minimum of 100 plasma cells (PCs) were analyzed for each patient sample. A direct 7- or 8-color method was applied to study the immunophenotype of PCs, utilizing a FACSCanto II (BD Biosciences, San Jose, CA). Samples were labeled with fluorochrome-conjugated monoclonal antibodies (AmCyan, Pac Blue, fluorescein isothiocyanate, phycoerythrin [PE], PECy7, peridinin-chlorophyll protein, allophycocyanin [APC], and APC-Cy7) to the following antigens: CD138, CD81, CD200, CD221, CD45, CD38, CD28, CD19, CD27, CD117, CD38, CD33, CD20, CD56, CD10, and immunoglobulin κ and λ light chains. Among all antigens tested, CD19 and CD27, when applied to our model, resulted in optimal concordance with histology. This model defines the effective diagnostic role FC could have in MM and in the detection of minimal residual disease.

Extraosseous (extramedullary) plasmacytomas: a clinicopathologic and immunophenotypic study of 32 Chinese cases

Background

Extraosseous plasmacytoma, so called extramedullary plasmacytoma (EMP) is relatively rare in China. The aim was investigate the clinicopathologic features of EMP and the role of Immunophenotype and genotype detection in diagnosis of EMP.

Methods

Thirty-two cases of EMP were investigated retrospectively by histopathology, immunophenotype, genotype and survival analysis.

Results

Clinically, the mean age of the patients was 53.4. Most of the patients received no treatment after the diagnosis was established, and the prognosis was relatively poor. Histologically, in 40% of the cases, the neoplastic cells were grade II or III. The neoplastic cells expressed one or more PC associated antigens. The immunophenotype of EMP and inflammation of sinonasal regions with numerous PC infiltrations were compared and showed some difference in expression of CD45, CD27, CD44v6 and Bcl-2 as well. Ig light chain restriction was detected in 87.5% of the cases.

Conclusions

we described 32 Chinese cases of EMP, compare with that reported in the literature, some differences are presented, including higher percentage of grade II and III cases, clinically inconsistent treatment and management as well as poor outcome of the disease.

Exploiting human memory B cell heterogeneity for improved vaccine efficacy

The major goal in vaccination is establishment of long-term, prophylactic humoral memory to a pathogen. Two major components to long-lived humoral memory are plasma cells for the production of specific immunoglobulin and memory B cells that survey for their specific antigen in the periphery for later affinity maturation, proliferation, and differentiation. The study of human B cell memory has been aided by the discovery of a general marker for B cell memory, expression of CD27; however, new data suggests the existence of CD27⁻ memory B cells as well. These recently described non-canonical memory populations have increasingly pointed to the heterogeneity of the memory compartment. The novel B memory subsets in humans appear to have unique origins, localization, and functions compared to what was considered to be a "classical" memory B cell. In this article, we review the known B cell memory subsets, the establishment of B cell memory in vaccination and infection, and how understanding these newly described subsets can inform vaccine design and disease treatment.

B cell subsets in healthy children: reference values for evaluation of B cell maturation process in peripheral blood

BACKGROUND

The process of maturation of the immune system leads to generation of various lymphoid cell populations having the ability to react in specific way and expressing various markers on the cell surface. The study was set up to establish reference values for B lymphocyte subpopulations in peripheral blood of children and young adults to find the spectrum of their physiological age-related variation.

METHODS

Blood samples were taken from 292 children and young adults aged 0-31 years and tested for distribution of B cell subsets. Relative and absolute sizes of non-memory and memory, transitional, naïve, immature marginal zone-like/IgM-only memory, class-switched memory, double negative, activated, and plasmacytoid cell populations were determined by four-color flow cytometry, based on differential expression of CD19, IgM, IgD, CD21, CD27, and CD38. Significant variation both in relative, as well as in absolute numbers of individual cell populations in tested groups was observed.

RESULTS

The reference values for age-related B cell subsets in eleven age groups, established as result of this study, may be used in diagnostics of any pathology related to B cell maturation process, as well as in attempts of correlating laboratory results with clinical symptoms of many defects affecting antibody production in pediatric population.

CONCLUSION

Determination of B cell subpopulations carried in patients with antibody deficiencies may help to understand the nature of the disease and prevent its complications.

T(11;18)(q21;q21)-positive gastrointestinal MALT lymphomas are heterogeneous with respect to the VH gene mutation status

AIM: To investigate how t(11;18)(q21;q21)-positive gastrointestinal MALT lymphomas relate to other marginal zone lymphomas with respect to the somatic mutation pattern of the V_H genes and the expression of the marker CD27.

METHODS: The V_H gene of 7 t(11;18)(q21;q21)-positive gastrointestinal MALT lymphomas was amplified by PCR using family specific V_H primers and a consensus J_H primer. PCR products were sequenced and mutation analysis of the CDR and the FR regions was performed. All cases were immunostained for CD27.

RESULTS: One case showed unmutated V_H genes while the others showed mutated V_H genes with mutation frequencies ranging from 1.3 to 14.7% and with evidence of antigen selection in 2 cases. These data suggest that the translocation t(11;18)(q21;q21) can target either B-cells at different stages of differentiation or naive B-cells that retain the capacity to differentiate upon antigen stimulation. All cases but one displayed weak to strong CD27 expression which did not correlate with the V_H gene mutation status.

CONCLUSION: t(11;18)(q21;q21)-positive gastrointestinal MALT lymphomas are heterogeneous with respect to the V_H mutation status and CD27 is not a marker of somatically mutated B-cells.

Double-positive CD21+CD27+ B cells are highly proliferating memory cells and their distribution differs in mucosal and peripheral tissues

BACKGROUND

Several B-cell defects arise in HIV infected patients, particularly in patients with chronic infection and high viral load. Loss of memory B cells (CD27(+) B cells) in peripheral blood and lymphoid tissues is one of the major B cell dysfunctions in HIV and simian immunodeficiency virus (SIV) infection. Despite several studies, definitive identification of memory B cells based on CD27 surface expression has not been described. Similarly, the rates of cell turnover in different B cell subpopulation from lymphoid and mucosal tissues have not been well documented. In this study, we demonstrate the presence of memory B cell populations and define their distribution, frequency and immunophenotype with regards to activation, proliferation, maturation, and antibody production in normal rhesus macaques from different lymphoid tissues.

METHODOLOGY/PRINCIPAL FINDINGS

Thirteen healthy, uninfected rhesus macaques were selected for this study. CD20(+) B cells were isolated from peripheral blood and sorted based on CD27 and CD21 surface markers to define memory B cell population. All the B cell subpopulation was further characterized phenotypically and their cell turnover rates were evaluated in vivo following bromodeoxyuridine (BrdU) inoculation. Double positive (DP) CD21(+)CD27(+) B cells in both peripheral and lymphoid tissues are memory B cells, able to produce antibody by polyclonal activation, and without T cell help. Peripheral and lymphoid DP CD21(+)CD27(+) B cells were also able to become activated and proliferate at higher rates than other B cell subpopulations. Increased turnover of tonsillar memory B cells were identified compared to other tissues examined.

CONCLUSIONS/SIGNIFICANCE

We suggest that this DP memory B cells play a major role in the immune system and their function and proliferation might have an important role in HIV/SIV mediated B cell dysregulation and pathogenesis.

Human B1 cells in umbilical cord and adult peripheral blood express the novel phenotype CD20+ CD27+ CD43+ CD70-

Human B1 cells consist of CD20⁺CD27⁺CD43⁺CD70⁻ cells bearing a skewed B cell receptor repertoire, and are present in umbilical cord and adult peripheral blood.

B1 cells differ in many ways from conventional B cells, most prominently in the production of natural immunoglobulin, which is vitally important for protection against pathogens. B1 cells have also been implicated in the pathogenesis of autoimmune dyscrasias and malignant diseases. It has been impossible to accurately study B1 cells during health and illness because the nature of human B1 cells has not been successfully defined. This has produced controversy regarding the existence of human B1 cells. Here, we determined the phenotype of human B1 cells by testing sort-purified B cell fractions for three fundamental B1 cell functions based on mouse studies: spontaneous IgM secretion, efficient T cell stimulation, and tonic intracellular signaling. We found that a small population of CD20⁺CD27⁺CD43⁺ cells present in both umbilical cord and adult peripheral blood fulfilled these criteria and expressed a skewed B cell receptor repertoire. These B cells express little or no surface CD69 and CD70, both of which are markedly up-regulated after activation of CD20⁺CD27⁻CD43⁻ (naive) and CD20⁺CD27⁺CD43⁻ (memory) B cells. This work identifies human B1 cells as CD20⁺CD27⁺CD43⁺CD70⁻. We determined that the proportion of B1 cells declines with age, which may contribute to disease susceptibility. Identification of human B1 cells provides a foundation for future studies on the nature and role of these cells in human disease.

Alterations on peripheral blood B-cell subpopulations in very early arthritis patients

OBJECTIVE

To characterize circulating B-cell subpopulations of arthritis patients with <6 weeks of disease duration.

METHODS

Peripheral blood samples were collected from very early untreated polyarthritis patients, with <6 weeks of disease duration, for flow cytometric evaluation of B-cell subpopulations. Samples from patients who were later diagnosed as RA [very early RA (VERA)] were also collected 4-6 weeks after starting a low dose of prednisone (5-10 mg) and 4 months after reaching the minimum effective dose of MTX. A matched healthy group was used as a control.

RESULTS

VERA patients have a lower percentage of total peripheral blood memory B cells (CD19(+)CD27(+)) and a significant decrease in the frequency of circulating pre-switch memory B cells (CD19(+)IgD(+)CD27(+)) as compared with controls. Therapy with corticosteroids or MTX was unable to restore the normal frequencies of these B-cell subpopulations. A significant decrease in peripheral pre-switch memory B cells is equally observed in other early arthritis patients. Furthermore, no significant differences are found in the frequencies of CD4(+) and CD8(+) T cells in all patient groups.

CONCLUSIONS

In very early polyarthritis patients, there is a reduction in circulating pre-switch memory B cells. The reasons that may account for this effect are still unknown. Short-term corticosteroids and MTX do not seem to have a direct effect on circulating B-cell subpopulations in VERA patients.

Timing and tuning of CD27-CD70 interactions: the impact of signal strength in setting the balance between adaptive responses and immunopathology

SUMMARY

After binding its natural ligand cluster of differentiation 70 (CD70), CD27, a tumor necrosis factor receptor (TNFR)-associated factor-binding member of the TNFR family, regulates cellular activity in subsets of T, B, and natural killer cells as well as hematopoietic progenitor cells. In normal immune responses, CD27 signaling appears to be limited predominantly by the restricted expression of CD70, which is only transiently expressed by cells of the immune system upon activation. Studies performed in CD27-deficient and CD70-transgenic mice have defined a non-redundant role of this receptor-ligand pair in shaping adaptive T-cell responses. Moreover, adjuvant properties of CD70 have been exploited for the design of anti-cancer vaccines. However, continuous CD27-CD70 interactions may cause immune dysregulation and immunopathology in conditions of chronic immune activation such as during persistent virus infection and autoimmune disease. We conclude that optimal tuning of CD27-CD70 interaction is crucial for the regulation of the cellular immune response. We provide a detailed comparison of costimulation through CD27 with its closely related family members 4-1BB (CD137), CD30, herpes virus entry mediator, OX40 (CD134), and glucocorticoid-induced TNFR family-related gene, and we argue that these receptors do not have a unique function per se but that rather the timing, context, and intensity of these costimulatory signals determine the functional consequence of their activity.

The CD70/CD27 pathway is critical for stimulation of an effective cytotoxic T cell response against B cell precursor acute lymphoblastic leukemia

For effective immunotherapy, maintaining the frequency and cytotoxic potential of effector cells is critical. In this context costimulation via the CD70/CD27 pathway has been proven essential. CD70 has been reported to be expressed to varying degrees on malignant B cells. However, in B cell precursor acute lymphoblastic leukemia, the most common childhood malignancy, the role of CD70 in stimulation of antileukemic T cell responses has so far not been delineated. Herein we demonstrate that in B cell precursor acute lymphoblastic leukemia expression of CD70 is low but can be induced upon blast activation via CD40. Both CD70 and CD80/CD86 up-regulated on CD40-stimulated blasts contribute to primary stimulation of T cell proliferation and cytokine production in an additive manner. These two signals also cooperate in the prevention of T cell anergy. In contrast to blockade of CD70 during the effector phase, inhibition of CD70-mediated costimulation during generation of antileukemic T cells prevents effector cell proliferation and reduces their cytotoxic capacity. Modulation of the CD70/CD27 pathway may thus represent a novel therapeutic approach for augmenting magnitude and quality of the antileukemic response in B cell precursor acute lymphoblastic leukemia.

Functional Epstein-Barr virus reservoir in plasma cells derived from infected peripheral blood memory B cells

The Epstein-Barr virus (EBV) causes infectious mononucleosis, establishes latency in resting memory B lymphocytes, and is involved in oncogenesis through poorly understood mechanisms. The EBV lytic cycle is initiated during plasma cell differentiation by mRNAs transcripts encoded by BZLF1, which induce the synthesis of EBV proteins such as the immediate-early antigen ZEBRA and the late membrane antigen gp350. Therefore, we assessed the capacity of circulating EBV-infected B lymphocytes from healthy EBV-seropositive subjects to enter and complete the EBV lytic cycle. Purified B lymphocytes were polyclonally stimulated and BZLF1- or gp350-secreting cells (BZLF1-SCs or gp350-SCs) were enumerated by ELISpot assays. The number of BZLF1-SCs ranged from 50 to 480/107 lymphocytes (median, 80; 25th-75th percentiles, 70-150) and gp350-SCs from 10 to 40/107 lymphocytes (median, 17; 25th-75th percentiles, 10-20). gp350-SCs represented only 7.7% to 28.6% of BZLF1-SCs (median, 15%; 25th-75th percentiles, 10.5%-20%). This EBV functional reservoir was preferentially restricted to plasma cells derived from CD27(+) IgD(-) memory B lymphocytes. In 9 of 13 subjects, EBV DNA quantification in B-cell culture supernatants gave evidence of completion of EBV lytic cycle. These results demonstrate that EBV proteins can be secreted by EBV-infected B lymphocytes from healthy carriers, a majority generating an abortive EBV lytic cycle and a minority completing the cycle.

Key developmental transitions in human germinal center B cells are revealed by differential CD45RB expression

We previously reported that RO(+) expression correlated with increased mutation, activation, and selection among human germinal center (GC) B cells. Here, we subdivided human tonsillar B cells, including IgD(-)CD38(+) GC B cells, into different fractions based on RB expression. Although each subset contained RB(+) cells, when used as an intrasubset marker, differential RB expression effectively discriminated between phenotypically distinct cells. For example, RB(+) GC B cells were enriched for activated cells with lower AID expression. RB inversely correlated with mutation frequency, demonstrating a key difference between RB- and RO-expressing GC B cells. Reduced RB expression during the transition from pre-GC (IgM(+)IgD(+)CD38(+)CD27(-)) to GCB cells was followed by a dramatic increase during the GC-to-plasmablast (IgD(-)CD38(++)CD27(+)) and memory (IgD(-)CD38(-)CD27(+)) transition. Interestingly, RB(+) GC B cells showed increased signs of terminal differentiation toward CD27(+) post-GC early plasmablast (increased CD38 and RO) or early memory (decreased CD38 and RO) B cells. We propose that as in T cells, differential RB expression directly correlates with development- and function-based transitions in tonsillar B cells. Application of this RB:RO system should advance our understanding of normal B-cell development and facilitate the isolation of more discrete B-cell populations with potentially different propensities in disease pathogenesis.

Late signals from CD27 prevent Fas-dependent apoptosis of primary CD8+ T cells

The role of costimulation has previously been confined to the very early stages of the CD8+ T cell response. In this study, we demonstrate the requirement for CD27 costimulation during the later phase, but not programming of the primary CD8+ T cell response to influenza virus and reveal a novel mechanism of action for CD27 costimulation. CD27 signals, during the later phase of the primary CD8+ T cell response, prevent apoptosis of Ag-specific CD8+ T cells. Blocking CD27L (CD70) on days 6 and 8 after infection reduces the number of NP(366-374)-specific CD8+ T cells, increases their sensitivity to CD95/Fas-mediated apoptosis, and up-regulates FasL on CD4+ T cells. This reduction of NP(366-374)-specific CD8+ T cells requires the presence of CD4+ T cells and Fas signaling. Lack of CD27 signals also decreases the quality of memory CD8+ T cell responses. Memory CD8+ T cells, which express surface CD27 similar to naive cells, however, do not require CD27 costimulation during a secondary response. Thus, CD27 acts indirectly to regulate primary Ag-specific CD8+ T cell responses by preventing apoptosis of CD8+ T cells during the later phase of the primary response and is required for optimal quality of memory cells, but is not required during normally primed secondary CD8+ T cell responses.

Systematic comparison of gene expression between murine memory and naive B cells demonstrates that memory B cells have unique signaling capabilities

Memory B cells play essential roles in the maintenance of long-term immunity and may be important in the pathogenesis of autoimmune disease, but how these cells are distinguished from their naive precursors is poorly understood. To address this, it would be important to understand how gene expression differs between memory and naive B cells to elucidate memory-specific functions. Using model systems that help overcome the lack of murine memory-specific markers and the low frequency of Ag-specific memory and naive cells, we undertook a global comparison of gene expression between memory B cells and their naive precursors. We identified genes with differential expression and confirmed the differential expression of many of these by quantitative RT-PCR and of some of these at the protein level. Our initial analysis revealed differential expression patterns of genes that regulate signaling. Memory B cells have increased expression of genes important in regulating adenosine signaling and in modulating cAMP responses. Furthermore, memory B cells up-regulate receptors that are essential for embryonic stem cell self-renewal. We further demonstrate that one of these, leukemia inhibitory factor receptor, can initiate functional signaling in memory B cells whereas it does not in naive B cells. Thus, memory and naive B cells are intrinsically wired to signal differently from one another and express a functional signaling pathway that is known to maintain stem cells in other lineages.

Expression of bone specific alkaline phosphatase on human B cells

We here report for the first time that human B cell express bone specific alkaline phosphatase. Using a monoclonal antibody against bone specific alkaline phosphatase (BAP), its expression was detected in approximately 50% of circulating B cells but not T cells. Using RT-PCR, BAP specific transcripts were detected in the B cells expressing surface BAP but not in those not expressing BAP. Activation of B lymphocytes using phorbal ester, PMA with or without ionomycin did not affect change in BAP expression. Following stimulations with Pokeweed Mitogen (PWM) and Staphylococcus aureus Cowan I (SAC), BAP expression on human B cells was increased. This paralleled the increase in production of immunoglobulins and BAP, detected by ELISA and enzyme assay with p-nitrophenyl phosphate, respectively. The role of BAP in B cell biology is uncertain. However, these data suggest that BAP may play an important role in differentiation and maturation of human B cells.

High expression of CD40 on B-cell precursor acute lymphoblastic leukemia blasts is an independent risk factor associated with improved survival and enhanced capacity to up-regulate the death receptor CD95

CD40 and CD27, members of the tumor necrosis factor receptor (TNFR) family, are critical regulators of lymphocyte growth and differentiation. In B-cell precursor acute lymphoblastic leukemia (BCP-ALL), we prospectively assessed the impact of CD40 and CD27 on outcome in 121 children treated according to the CoALL06-97 protocol. Expression of both CD40 and CD27 was found to be significantly higher in low- than in high-risk patients as defined by standard clinical risk parameters such as age and white blood cell count. In addition, in multivariable analysis, a very high percentage of CD40(+) blasts at diagnosis was identified as an independent favorable prognostic factor for relapse-free survival. Of note, high CD40 expression particularly protected against late relapse. In B cells, CD40 is known to enhance both antigen-presenting capacity and sensitivity to proapoptotic signals. Yet, although CD40 ligation does result in significant up-regulation of CD80/CD86 in our cohort, it is up-regulation of the death receptor CD95 that significantly correlates with the percentage of CD40(+) blasts. Thus very high expression of CD40 on BCP-ALL blasts is an independent prognostic marker indicative of superior relapse-free survival that may in part be due to CD40-dependent death receptor up-regulation.

Roles of TRAF molecules in B lymphocyte function

Tumor necrosis factor receptor associated factors (TRAFs) play a variety of interesting and important roles in the regulation of B lymphocyte function. They act both as cytoplasmic regulatory molecules, and as signal transducers for receptors involved in both innate and adaptive humoral immune responses. In this brief review, we highlight the current state of knowledge of the diverse roles of TRAF molecules in the functions of B lymphocytes.

Elevated numbers of immature/transitional CD21- B lymphocytes and deficiency of memory CD27+ B cells identify patients with active chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HSCT) and a leading cause of non-relapse mortality (NRM). Currently, biology-based markers are lacking both for diagnosis and for monitoring the activity of cGVHD. Seventy patients who received HSCT were enrolled in a pilot study, including 21 without cGVHD and 49 with active or resolved cGVHD. Evaluations were comprised of clinical parameters including cGVHD severity and infections. Peripheral blood cells were analyzed by multi-parameter flow cytometry. The CD19+ B cell compartment was further subdivided by staining for surface IgD, CD21 and CD27. No significant differences in absolute B, T, and natural killer (NK) cell numbers were observed between the groups with and without cGVHD. However, elevated numbers (>15% of B lymphocytes) of immature/transitional CD19+/CD21(-) B cells were associated with the occurrence of severe infections (P = .003). Most significantly, all patients with active cGVHD and elevated numbers of CD19+/CD21(-) B lymphocytes experienced severe infections (P = .00016). The numbers of both non-class-switched and class-switched memory B cells were significantly lower in patients with active cGVHD when compared to patients who never experienced cGVHD (P = .002 and P = .001). Perturbation of circulating B lymphocyte compartments may serve as a novel biomarker for monitoring cGVHD activity and its impact on the immune system. A prospective study on unselected patients assessed serially for B cell reconstitution after HSCT is warranted.

The human immunomodulatory CD25+ B cell population belongs to the memory B cell pool

We have shown that human CD20(+)25(+) B cells display immunomodulatory properties. The aim of this study was to investigate if CD25(+) B cells are found within the CD27 memory B cell population, and to analyse pattern of their cytokine production. B cells isolated from healthy subjects, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients were analysed regarding the frequency of CD25(+) B cells within certain B cell subsets. Purified CD25(+) B cells from healthy subject were used in vitro to evaluate their production of immunomodulatory cytokines. In healthy subjects the majority (60%) of memory B cells (CD20(+)27(+)) also co-expressed CD25 while only 10-20% of the naïve B cells (CD20(+)27(-)) and plasmablasts (CD20-27(+)) expressed CD25. In RA and SLE patients, we found that 51% and 48%, respectively, co-expressed CD25 in the memory population, whereas only 11% and 9% co-expressed CD25 in the naïve B cell population. Phenotypic analysis of the CD20(+)25(+)27(+) and CD20(+)25(+)27(-) cells using CD10, CD24, CD38, CD45, CD71, CD80, CD86, CD95, CD138, BAFF-R, TACI, IgA, IgD, IgG and IgM showed that CD20(+)25(+)27(+) B cells preferentially represent highly activated, Ig class switched memory B cells. Cytokine profile analysis showed that CD25(+) B cells secreted significantly higher levels of IL-10 versus CD25(-) B cells. In contrast, TGF-beta1 secretion was similar between the CD25(+) and CD25(-) sub-populations. In conclusion, CD20(+)25(+) B cells constitute a unique subpopulation preferentially occurring among CD20(+)27(+) memory B cells. We suggest that CD25 can be used as a marker for a memory B cell subset.

New markers for murine memory B cells that define mutated and unmutated subsets

The study of murine memory B cells has been limited by small cell numbers and the lack of a definitive marker. We have addressed some of these difficulties with hapten-specific transgenic (Tg) mouse models that yield relatively large numbers of antigen-specific memory B cells upon immunization. Using these models, along with a 5-bromo-2′-deoxyuridine (BrdU) pulse-label strategy, we compared memory cells to their naive precursors in a comprehensive flow cytometric survey, thus revealing several new murine memory B cell markers. Most interestingly, memory cells were phenotypically heterogeneous. Particularly surprising was the finding of an unmutated memory B cell subset identified by the expression of CD80 and CD35. We confirmed these findings in an analogous V region knock-in mouse and/or in non-Tg mice. There also was anatomic heterogeneity, with BrdU⁺ memory cells residing not just in the marginal zone, as had been thought, but also in splenic follicles. These studies impact the current understanding of murine memory B cells by identifying new phenotypes and by challenging assumptions about the location and V region mutation status of memory cells. The apparent heterogeneity in the memory compartment implies either different origins and/or different functions, which we discuss.

Human IgM+CD27+ B cells: memory B cells or "memory" B cells?

Memory B cells are generated in germinal centers (GC) and contribute to serological immunity by rapidly differentiating into plasma cells. Human memory B cells can be identified by the expression of CD27. These cells exhibit more rapid responses than naive (CD27-) B cells following stimulation in vitro, consistent with the heightened kinetics of secondary responses in vivo. CD27+ B cells express mutated Ig V region genes; however a significant proportion continue to express IgM, suggesting the existence of IgM+ memory B cells. The observation that mutated IgM+CD27+ B cells are generated in humans who cannot form GC led to the conclusions that these cells are generated independently of GC and thus are not memory cells and that they mediate responses to T cell-independent Ag. Although some studies support the idea that IgM+CD27+ B cells participate in T cell-independent responses, many others do not. In this review we will provide alternate interpretations of the biology of IgM+CD27+ B cells and propose that they are indeed memory cells.

Decreased expression of tumor necrosis factor family receptors involved in humoral immune responses in preterm neonates

Neonates have an increased rate of infection with encapsulated bacteria compared with older children and adults because of diminished antibody responses to T-independent (TI) antigens such as bacterial polysaccharides. Because the interactions of tumor necrosis factor (TNF) family ligands BAFF and APRIL with the TNF family receptors (TNFRs) TACI, BCMA, and BAFF-R are crucial to TI antibody responses, we measured the expression of these receptors on adult and cord blood-derived term and preterm neonatal B cells. Preterm neonatal B cells expressed less TACI, BCMA, and BAFF-R compared with adult B cells and had significantly less proliferation compared with adult B cells after stimulation with human recombinant BAFF and anti-IgM in an assay in which TACI-Fc fusion protein inhibits B-cell proliferation. In addition, neonatal dendritic cells had diminished expression of B7-1, B7-2, and CD40 compared with adult cells. Finally, neonatal B cells, particularly preterm B cells, exhibited markedly decreased production of IgG and IgA in response to CD40L and IL-10. Overall, this study shows that maturational delay in TNFR expression particularly by preterm neonatal B cells may interfere with effective antibody responses to TI antigens, cognate T- and B-cell interactions and normal isotype switching.

Metalloprotease inhibitors block release of soluble CD27 and enhance the immune stimulatory activity of chronic lymphocytic leukemia cells

OBJECTIVE

Chronic lymphocytic leukemia (CLL) B cells from most patients express both membrane-bound CD27 (mCD27) and soluble CD27 (sCD27). Expression of sCD27 inhibits CD27-dependent T-cell or CLL-cell activation mediated by its ligand, CD70. In this study, we evaluated whether protease inhibitors could inhibit the release of sCD27 from CLL cells and enhance T-cell activation mediated by CD27-CD70 interaction.

METHODS

CLL cells exposed to hydroxamic acid-based matrix metalloprotease (MMP) inhibitors were evaluated for the release of sCD27 by sandwich enzyme-linked immunosorbent assay and immunoprecipitation. We examined for phenotypic changes in CLL cells treated with MMP inhibitors by flow cytometry and T-cell activation by CLL cells was assessed by [(3)H] thymidine incorporation assay and the production of interferon-gamma.

RESULTS

Treatment of CLL cells with MMP inhibitors blocked the release of sCD27 to the culture supernatant. In contrast, a non-hydroxamic acid control compound or inhibitors of other proteases, including serine, cysteine, and aspartyl proteases, were ineffective. Furthermore, CLL cells treated with MMP inhibitors expressed significantly higher levels of accessory molecules, such as CD54, CD80, and CD95. Consistent with such changes, we found that CLL cells treated with MMP inhibitors, but not control treated cells, could stimulate allogeneic and autologous T cells in mixed lymphocyte reactions.

CONCLUSION

These data reveal that metalloprotease inhibitors can block production of sCD27, which can interfere with mCD27-CD70 interactions that induce expression of immune costimulatory molecules on CLL B cells. Conceivably, treatment of CLL cells with metalloprotease inhibitors may enhance their potential for stimulating cellular immune recognition of leukemia-associated antigens.

Intrinsic properties of human and murine memory B cells

The central question of how the immune system responds in a qualitatively and quantitatively better way upon re-exposure to a pathogen is largely unanswered. Both the increased frequency of antigen-specific memory cells and the intrinsic properties that memory cells acquire after antigen experience could contribute to the faster and more robust responses seen after repeated exposure to antigen. In the case of the memory B-cell response, it has been difficult to discern the individual contributions of these two effects. However, because of recent advances in identifying memory B cells, there is an increasing understanding of the intrinsic properties of these cells. The current insights into the unique properties of memory B cells and the progress that has been made in understanding how these affect secondary responses in both the human and the mouse systems are discussed. In addition, we compare the various advantages and disadvantages inherent in each of these systems, in terms of studying the intrinsic properties of memory B cells, and introduce the details of the system that we have developed using conventional heavy chain transgenic (Tgic) mice, which addresses some of the drawbacks of traditional memory models.

Expression of CD27-CD70 on early B cell progenitors in the bone marrow: implication for diagnosis and therapy of childhood ALL

OBJECTIVE

CD27, a member of the TNF receptor family, plays an important role in lymphoid proliferation, differentiation and apoptosis. This study addresses the expression of CD27 and its ligand, CD70, in children with acute lymphoblastic leukemia (ALL) and the possible role of this receptor-ligand pair in the pathogenesis of ALL.

PATIENTS AND METHODS

Expression of CD27 and CD70 was evaluated with three-color flow cytometry in blood and bone marrow (BM) samples in children with ALL and controls. The biological role of these molecules on leukemic cell proliferation was studied in an in vitro culture system.

RESULTS

The expression of the membrane bound CD27, as well as membrane bound CD70, on CD19(+) cells in the BM was significantly increased in ALL children compared to the expression found in the controls. Importantly, a substantial reduction in the in vitro proliferation of leukemic cells could be observed when the leukemic cells were cultured in presence of a blocking anti-human CD70 monoclonal antibody. The level of soluble CD27 (sCD27) in serum was also investigated and found to be significantly elevated in leukemic children as compared to healthy children.

CONCLUSION

The high expression of CD27 and CD70 on ALL cells may represent an amplification of the normal CD27-CD70 expression present on early B cell progenitors. Our finding suggests that interference with CD27-CD70 interaction may represent novel treatment opportunities in ALL. Further studies are required to pin-point the role of this receptor-ligand pair in normal and malignant hematopoiesis.

Regulation of Aged Humoral Immune Defense against Pneumococcal Bacteria by IgM Memory B Cell

Elderly persons have a high incidence of lethal infections by encapsulated bacteria. However, mechanisms involved in their poor defense and maintenance of immunological memory have been poorly understood. The present study characterized the population of B cells known as IgM memory B cell compartment and their response by pneumococcal vaccine in elderly people. CD27+ memory B cells, particularly IgD+IgM+CD27+ IgM memory B cells, had dramatically declined in the aged. Their Ig syntheses by B cells and the differentiation into plasma cells were diminished in vitro compared with those in adults. A rise of anti-pneumococcal IgM in sera of elderly persons was found with lower levels compared with those in adults after pneumococcal vaccination. Although diminished function itself of aged B cells surely exist, decline of the IgM memory B cell pool is expected to result in a poor humoral immunity against pneumococcal infection in elderly people.

Children with chronic renal failure have reduced numbers of memory B cells

Reduced serum IgG and subclass levels have been demonstrated in children with chronic renal failure. To study possible causes of this reduction, we analysed B cell subset composition, T helper cell frequencies and immunoglobulin (Ig) production capacity in vitro in children with chronic renal failure, with or without dialysis treatment. B cell subsets were characterized by determining CD27, IgM, IgD and CD5 expression within the CD19(+) population. Intracellular expression of interferon (IFN)-gamma, interleukin (IL)-2 and IL-4 in PMA/ionomycin-stimulated peripheral blood mononuclear cells (PBMC) was used to evaluate T helper frequencies. The capacity of B cells to secrete Ig in vitro was determined by measuring IgG(1), IgG(2) and IgM in culture supernatants of anti-CD2/CD28 monoclonal antibody (MoAb)- or SAC/IL-2-stimulated PBMC. Memory B cell numbers (identified as percentage or absolute number of CD19(+) IgM-IgD- or CD19(+)CD27(+) lymphocytes) were lower in children treated with haemodialysis (HD), peritoneal dialysis (PD) and children with chronic renal failure before starting dialysis treatment (CRF) compared to healthy controls (HC) (P < 0.05). Compared with HC, CD5(+) (naive) B cells were reduced in HD-treated patients but not for PD or for children with chronic renal failure before starting dialysis treatment (CRF). No significant differences in CD4(+) T helper cell subsets were found between the groups. However, CRF children had a higher percentage of IFN-gamma producing CD8(+) T lymphocytes compared to HC (P = 0.02). Finally, IgG(1), IgG(2) and IgM production in vitro was similar in the four groups. In conclusion, significantly lower numbers of memory type B cells were found in children with chronic renal failure compared to healthy controls. This reduction may contribute to the low Ig levels found in these children.

CD27 is acquired by primed B cells at the centroblast stage and promotes germinal center formation

Studies on human B cells have featured CD27 as a marker and mediator of the B cell response. We have studied CD27 expression and function on B cells in the mouse. We find that B cells acquire CD27 at the centroblast stage and lose it progressively upon further differentiation. It is not a marker for somatically mutated B cells and is present at very low frequency on memory B cells. Enrichment of CD27 among centroblasts and the presence of its ligand CD70 on occasional T and B cells in or near germinal centers (GCs) suggested a role for CD27/CD70 interactions in clonal B cell expansion. Accordingly, GC formation in response to influenza virus infection was delayed in CD27 knockout mice. CD27 deficiency did not affect somatic hypermutation or serum levels of virus-specific IgM, IgG, and IgA attained in primary and recall responses. Adoptive transfer of T and B cells into CD27/CD28(-/-) mice revealed that CD27 promotes GC formation and consequent IgG production by two distinct mechanisms. Stimulation of CD27 on B cells by CD28(+) Th cells accelerates GC formation, most likely by promoting centroblast expansion. In addition, CD27 on T cells can partially substitute for CD28 in supporting GC formation.

Common variable immunodeficiency patient classification based on impaired B cell memory differentiation correlates with clinical aspects

Common variable immunodeficiency (CVID) is a very heterogeneous syndrome defined by impaired immunoglobulin production. The functional classification of CVID patients on the basis of in vitro immunoglobulin production is time consuming and has never shown any predictive value. We propose a classification based on the quantitative repartition of naive/memory B cells according to the dual expression of IgD and CD27. Fifty-seven patients were categorized into three groups: Group MB2 (11 patients, 19%) with normal memory B cells; Group MB1 (19 patients, 33%) with defective switched memory (IgD-CD27+) but normal nonswitched memory B cells (IgD+CD27+); Group MB0 (27 patients, 47%) with almost no memory B cells. In addition, a downexpression of activation markers (CD25, CD21, CD80, CD86) on B cells characterized the group MB1 patients and was associated with an upexpression of activation markers (HLA-DR, CD95, CD57) on T cells. This classification correlates with some clinical aspects showing a higher prevalence of splenomegaly (16/27, 59%), lymphoid proliferation (13/27, 48%) and granulomatous disease (12/27, 44%) in group MB0. Splenomegaly was also frequent in group MB1 (8/19, 42%). In contrast, autoimmunity was observed with similar prevalence in all three groups. Moreover, by analyzing B cell phenotype, immunoglobulin transcript expression, and somatic mutations, we propose different putative mechanisms responsible for impaired B cell activation and memory differentiation in this syndrome.

CD27-triggering on primary plasma cell leukaemia cells has anti-apoptotic effects involving mitogen activated protein kinases

Primary plasma cell leukaemia (PCL) is a rare plasma cell malignancy, which is related to multiple myeloma (MM) and is characterized by a poor prognosis. In a previous study we demonstrated that PCL plasma cells display a high expression of CD27, in contrast to MM plasma cells. The present study was set out to assess the functional properties of CD27 expressed on PCL plasma cells by triggering with its ligand CD70. Using CD27-expressing purified plasma cells from a PCL patient we demonstrated that CD27-triggering modestly inhibited spontaneous and dexamethasone-induced apoptosis. In vitro stimulation and Western blotting showed that activation of p38 and extracellular-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinases (MAPK) was associated with CD27-mediated signal transduction. Specific inhibition of p38 and ERK1/2 MAPK abolished the anti-apoptotic effects of CD27-triggering. Interestingly, simultaneous inhibition of p38 and ERK1/2 strongly sensitized PCL cells for dexamethasone-induced apoptosis. Finally, in dexamethasone-treated PCL cells, CD27-triggering was associated with persistent DNA-binding activity of activator protein 1 (AP-1) but not of nuclear factor-kappaB. These findings suggest that, in primary PCL, specific anti-apoptotic pathways exist that might provide novel therapeutic targets.

Induction of various immune modulatory molecules in CD34+hematopoietic cells

Lipopolysaccharide (LPS) has been shown to induce proliferation of human T-lymphocytes only in the presence of monocytes and CD34(+) hematopoietic cells (HCs) from peripheral blood. This finding provided evidence of an active role of CD34(+) HCs during inflammation and immunological events. To investigate mechanisms by which CD34(+) HCs become activated and exert their immune-modulatory function, we used the human CD34(+) acute myeloid leukemia cell line KG-1a and CD34(+) bone marrow cells (BMCs). We showed that culture supernatants of LPS-stimulated mononuclear cells (SUP(LPS)) as well as tumor necrosis factor alpha (TauNF-alpha), but not LPS alone, can activate nuclear factor-kappaB in KG-1a cells. By cDNA subtraction and multiplex polymerase chain reaction, we revealed differential expression of cellular inhibitor of apoptosis protein-1, inhibitor of kappaB (IkappaB)/IkappaBalpha (MAD-3), and intercellular adhesion molecule-1 (ICAM-1) in SUP(LPS)-stimulated KG-1a cells and up-regulation of interferon (IFN)-inducible T cell-chemoattractant, interleukin (IL)-8, macrophage-inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, RANTES, CD70, granulocyte macrophage-colony stimulating factor, and IL-1beta in stimulated KG-1a cells and CD34(+) BMCs. Although monokine induced by IFN-gamma, IFN-inducible protein 10, and IFN-gamma were exclusively up-regulated in KG-1a cells, differential expression of monocyte chemoattractant protein-1 (MCP-1), macrophage-derived chemokine, myeloid progenitor inhibitory factor-2, and IL-18 receptor was only detectable in CD34(+) BMCs. More importantly, CD34(+) BMCs stimulated by TNF-alpha also showed enhanced secretion of MCP-1, MIP-1alpha, MIP-1beta, and IL-8, and increased ICAM-1 protein expression could be detected in stimulated KG-1a cells and CD34(+) BMCs. Furthermore, we revealed that T cell proliferation can be induced by TNF-alpha-stimulated KG-1a cells, which is preventable by blocking anti-ICAM-1 monoclonal antibodies. Our results demonstrate that CD34(+) HCs have the potential to express a variety of immune-regulatory mediators upon stimulation by inflammatory cytokines including TNF-alpha, which may contribute to innate- and adaptive-immune processes.

Functional analysis of human memory B-cell subpopulations: IgD+CD27+ B cells are crucial in secondary immune response by producing high affinity IgM

The number of memory B cells in peripheral blood has been assayed in various diseases by using CD27 as a memory B-cell marker. However, the defining differences of characteristic and function between the two memory B-cell subpopulations separated by immunoglobulin (Ig)D expression remain to be clearly elucidated. We analyzed here IgD(+)CD27(+) B cells (circulating B cells 2, cB2) and IgD(-)CD27(+) memory B cells (cB3) in comparison with IgD(+)CD27(-) naive B cells (cB1). cB2 were found to be morphologically similar to cB3 with abundant cytoplasm, whereas cB3 expressed CD80, CD86, and CD95 on their surface more predominantly than cB2. A majority of cB2 expressed both IgD and IgM, and cB3 expressed IgA or IgG. Mature gamma1 and gamma2 transcripts were found in cB3, but at very low levels in cB2, and activation-induced cytidine deaminase (AID) mRNA expression was recognized only in cB3. The frequencies of somatic hypermutation in cB2 and cB3 were comparable levels studied by VH5. cB2 did not shift to cB3 in vitro by the stimuli such as via B-cell receptor or CD40. cB2 produced large amounts of IgM predominantly and promptly, which is in accordance with the known characteristics of memory B cells. Taken together, although cB2 are unclass-switched, cB2 have the functions of memory B cells and are not in the process of transition from naive to switched memory B cells, playing a crucial role in secondary immune response by producing high-affinity IgM in the early phase of infections.

CD27 is heterogeneously expressed in multiple myeloma: low CD27 expression in patients with high-risk disease

Expression of CD27 on malignant plasma cells (PC) (CD138+CD38++) was analysed in a cross-sectional study of bone marrow (BM) samples from multiple myeloma (MM) patients (n = 28), monoclonal gammopathy of undetermined significance (MGUS) patients (n = 6) and BM PC from healthy donors (n = 4). MM PC expressed CD27 with a variable, lower intensity pattern compared with the consistent high expression in MGUS and healthy donors. MM patients in complete clinical remission displayed a higher percentage of CD27+ PC compared with patients at diagnosis, relapse or in partial remission. In MM, loss of CD27 correlated with loss of CD19 (R2 = 0.4, P < 0.0001). Human MM cell lines (n = 9) did not express CD27 whereas de novo plasma cell leukaemia (PCL) (n = 3) had a high expression. Re-analysis of a cDNA microarray data set, generated from newly diagnosed MM patients (n = 74), demonstrated that the MM subgroup with the highest prevalence of poor prognostic factors had the lowest CD27 mRNA expression. Fluorescence-activated cell sorting and allele-specific oligonucleotide polymerase chain reaction showed that both CD27+ and CD27- PC subpopulations in MM can belong to the clonal disorder. In conclusion, CD27 is heterogeneously expressed on MM PC and loss of CD27 expression might have prognostic value in MM.

Blood and intragraft CD27 gene expression in cardiac transplant recipients

The present study investigated gene expression of costimulatory molecule CD27 in relation to the occurrence of acute cardiac rejection. CD27 transcripts were measured by means of quantitative competitive reverse transcriptase-polymerase chain reaction in 120 endomyocardial biopsies and in 89 samples of blood mononuclear cells from 31 recipients. Higher levels of CD27 transcripts were observed in biopsies with rejection than in samples without rejection (medians, 7.1 and 1.9; P = 0.06). In contrast, blood mononuclear cells collected during rejection showed lower levels than blood mononuclear cells from rejection-free periods (medians, 3.3 vs. 7.9; P = 0.03). Considering only endomyocardial biopsies without rejection, the values were lower in samples from recipients who did not present any rejection during the first 6 months after transplantation than in those from recipients who had at least one rejection during the same period (medians, 0 vs. 3.5, P < 0.001; percentage of biopsies expressing CD27, 44% vs. 77%). In conclusion, the presence of intragraft CD27 mRNA may identify recipients at risk for developing acute rejection.

Isotype switching by human B cells is division-associated and regulated by cytokines

Isotype switching by murine B cells follows a pattern whereby the proportion of cells undergoing switching increases with division number and is regulated by cytokines. Here we explored whether human B cells behaved in a similar manner. The effect of IL-4, IL-10, and IL-13, alone or in combination, on Ig isotype switching by highly purified naive human CD40 ligand (CD40L)-activated B cells was measured against division number over various harvest times. Switching to IgG was induced by IL-4 and, to a lesser extent, IL-13 and IL-10. The combination of IL-10 with IL-4, but not IL-13, induced a higher percentage of cells to undergo switching. Isotype switching to IgG by human CD40L-activated naive B cells was found to be linked to the division history of the cells: IgG(+) cells appeared in cultures of B cells stimulated with CD40L and IL-4 after approximately the third cell division, with the majority expressing IgG1, thus revealing a predictable pattern of IgG isotype switching. These results reveal a useful quantitative framework for monitoring the effects of cytokines on proliferation and isotype switching that should prove valuable for screening Ig immunodeficiencies and polymorphisms in the population for a better understanding of the regulation of human humoral immune responses.