Use of the intracellular fluorescent dye CFSE to monitor lymphocyte migration and proliferation

Phenotypic and functional characterization of cytotoxic T lymphocytes by flow cytometry

Cytotoxic T lymphocytes (CTLs) are important constituents of the adaptive immune system. Development of CTLs are particularly important for bacterial and viral infections, in addition to tumor surveillance. Measuring T cell immune function is important in evaluating host defense, allergy, autoimmunity, transplant rejection, and tumor immunity. In these recent years it has become possible to measure multiple effector functions in a single cell such as cytokine, transcription factors, and cytolytic function. In addition these parameters can be evaluated in conjunction with cellular proliferation. In this chapter we detail these cellular based assays and the methods used to characterize and quantify both phenotype and function of CTL.

Microgravity inhibits resting T cell immunity in an exposure time-dependent manner

BACKGROUND

Decline immune function is well documented after spaceflights. Microgravity is one of the key factors directly suppressing the function of immune system. Though T cell immune response was inhibited by microgravity, it is not clearly whether activation would be inhibited after a pre-exposure of microgravity on T lymphocytes at the resting state.

METHODS

We herein investigated the response ability of resting CD4⁺ and CD8⁺ T cells experiencing pre-exposure of modeled microgravity (MMg) for 0, 8, 16 and 24 hrs to concanavalin A (ConA) stimulation. The phenotypes and subsets of immune cells were determined by flow cytometry.

RESULTS

Both CD4⁺ and CD8⁺ T cells with an MMg pre-exposure exhibited decreased expressions of activation-markers including CD25, CD69 and CD71, inflammatory cytokine secretion and cell proliferation in response to ConA compared with T cells with 1g controls in an MMg exposure time- dependent manner. Moreover, short term MMg treatment caused more severe decreased proliferation in CD4⁺ T cells than in CD8⁺ T cells.

CONCLUSIONS

MMg can directly impact on resting T cell subsets. CD4⁺ T cells were more sensitive to the microgravity inhibition than CD8⁺ T cells in respect of cell proliferation. These results offered new insights for the MMg-caused T cell functional defects.

Expression of the B-cell receptor component CD79a on immature myeloid cells contributes to their tumor promoting effects

The role of myeloid derived suppressor cells (MDSCs) in promoting tumorigenesis is well-established, and significant effort is being made to further characterize surface markers on MDSCs both for better diagnosis and as potential targets for therapy. Here we show that the B cell receptor adaptor molecule CD79a is unexpectedly expressed on immature bone marrow myeloid cells, and is upregulated on MDSCs generated in multiple different mouse models of metastatic but not non-metastatic cancer. CD79a on MDSCs is upregulated and activated in response to soluble factors secreted by tumor cells. Activation of CD79a on mouse MDSCs, by crosslinking with a specific antibody, maintained their immature phenotype (CD11b+Gr1+), enhanced their migration, increased their suppressive effect on T cell proliferation, and increased secretion of pro-tumorigenic cytokines such as IL-6 and CCL22. Furthermore, crosslinking CD79a on myeloid cells activated signaling through Syk, BLNK, ERK and STAT3 phosphorylation. In vivo, CD79+ myeloid cells showed enhanced ability to promote primary tumor growth and metastasis. Finally we demonstrate that CD79a is upregulated on circulating myeloid cells from lung cancer patients, and that CD79a+ myeloid cells infiltrate human breast tumors. We propose that CD79a plays a functional role in the tumor promoting effects of myeloid cells, and may represent a novel target for cancer therapy.

Asymmetry of Cell Division in CFSE-Based Lymphocyte Proliferation Analysis

Flow cytometry-based analysis of lymphocyte division using carboxyfluorescein succinimidyl ester (CFSE) dye dilution permits acquisition of data describing cellular proliferation and differentiation. For example, CFSE histogram data enable quantitative insight into cellular turnover rates by applying mathematical models and parameter estimation techniques. Several mathematical models have been developed using different types of deterministic or stochastic approaches. However, analysis of CFSE proliferation assays is based on the premise that the label is halved in the two daughter cells. Importantly, asymmetry of protein distribution in lymphocyte division is a basic biological feature of cell division with the degree of the asymmetry depending on various factors. Here, we review the recent literature on asymmetric lymphocyte division and CFSE-based lymphocyte proliferation analysis. We suggest that division- and label-structured mathematical models describing CFSE-based cell proliferation should take into account asymmetry and time-lag in cell proliferation. Utilization of improved modeling algorithms will permit straightforward quantification of essential parameters describing the performance of activated lymphocytes.

CD24 expression identifies teratogen-sensitive fetal neural stem cell subpopulations: evidence from developmental ethanol exposure and orthotopic cell transfer models

Background

Ethanol is a potent teratogen. Its adverse neural effects are partly mediated by disrupting fetal neurogenesis. The teratogenic process is poorly understood, and vulnerable neurogenic stages have not been identified. Identifying these is a prerequisite for therapeutic interventions to mitigate effects of teratogen exposures.

Methods

We used flow cytometry and qRT-PCR to screen fetal mouse-derived neurosphere cultures for ethanol-sensitive neural stem cell (NSC) subpopulations, to study NSC renewal and differentiation. The identity of vulnerable NSC populations was validated in vivo, using a maternal ethanol exposure model. Finally, the effect of ethanol exposure on the ability of vulnerable NSC subpopulations to integrate into the fetal neurogenic environment was assessed following ultrasound guided, adoptive transfer.

Results

Ethanol decreased NSC mRNAs for c-kit, Musashi-1and GFAP. The CD24⁺ NSC population, specifically the CD24⁺CD15⁺ double-positive subpopulation, was selectively decreased by ethanol. Maternal ethanol exposure also resulted in decreased fetal forebrain CD24 expression. Ethanol pre-exposed CD24⁺ cells exhibited increased proliferation, and deficits in cell-autonomous and cue-directed neuronal differentiation, and following orthotopic transplantation into naïve fetuses, were unable to integrate into neurogenic niches. CD24^depleted cells retained neurosphere regeneration capacity, but following ethanol exposure, generated increased numbers of CD24⁺ cells relative to controls.

Conclusions

Neuronal lineage committed CD24⁺ cells exhibit specific vulnerability, and ethanol exposure persistently impairs this population’s cell-autonomous differentiation capacity. CD24⁺ cells may additionally serve as quorum sensors within neurogenic niches; their loss, leading to compensatory NSC activation, perhaps depleting renewal capacity. These data collectively advance a mechanistic hypothesis for teratogenesis leading to microencephaly.

L-asparaginase II produced by Salmonella typhimurium inhibits T cell responses and mediates virulence

Salmonella enterica serovar Typhimurium avoids clearance by the host immune system by suppressing T cell responses; however, the mechanisms that mediate this immunosuppression remain unknown. We show that S. Typhimurium inhibit T cell responses by producing L-Asparaginase II, which catalyzes the hydrolysis of L-asparagine to aspartic acid and ammonia. L-Asparaginase II is necessary and sufficient to suppress T cell blastogenesis, cytokine production, and proliferation and to downmodulate expression of the T cell receptor. Furthermore, S. Typhimurium-induced inhibition of T cells in vitro is prevented upon addition of L-asparagine. S. Typhimurium lacking the L-Asparaginase II gene (STM3106) are unable to inhibit T cell responses and exhibit attenuated virulence in vivo. L-Asparaginases are used to treat acute lymphoblastic leukemia through mechanisms that likely involve amino acid starvation of leukemic cells, and these findings indicate that pathogens similarly use L-asparagine deprivation to limit T cell responses.

Casitas B lineage lymphoma b is a key regulator of peripheral tolerance in systemic lupus erythematosus

OBJECTIVE

To analyze whether the expression and modulation of T cell receptor (TCR) signaling is dependent on Casitas B lineage lymphoma b (Cbl-b) in T cells from patients with systemic lupus erythematosus (SLE) upon stimulation with a tolerogenic substance.

METHODS

Peripheral blood mononuclear cells were obtained from 20 patients with SLE (active disease or in remission) and 20 healthy controls. Levels of Cbl-b expression were measured using reverse transcription-polymerase chain reaction and Western blotting in peripheral CD4+ T cells from SLE patients and healthy controls upon anergy induction. Cell proliferation was measured using the carboxyfluorescein diacetate succinimidyl ester dilution method. Cytokine production was analyzed by luminometry, and surface expression of activation markers was assessed by flow cytometry. Transfection assays were performed to induce overexpression of Cbl-b, and phosphorylation of TCR-associated kinases was evaluated.

RESULTS

CD4+ T cells from SLE patients displayed resistance to anergy (as evidenced by increased cell proliferation, interleukin-2 production, and expression of activation and costimulatory markers), and this was associated with altered Cbl-b expression. Upon ionomycin treatment, primary T cells showed enhanced MAPK activity and decreased Akt phosphorylation, which was representative of the anergic state. In T cells from lupus patients, Cbl-b overexpression led to increased expression of phosphorylated MAPK, thus indicating the reversibility of anergy resistance.

CONCLUSION

These findings suggest that abnormal peripheral tolerance in SLE is caused by a deficiency in Cbl-b, and that this ubiquitin ligase plays a key role in regulating TCR signaling during the induction of peripheral tolerance.

Flow cytometric analysis of cell division by dilution of CFSE and related dyes

The technique described in this unit uses the intracellular fluorescent label carboxyfluorescein diacetate succinimidyl ester (CFSE) to track proliferating cells. Covalently bound CFSE is divided equally between daughter cells, allowing discrimination of successive rounds of cell division. The technique is applicable to in vitro cell division, as well as to in vivo division of adoptively transferred cells and can resolve eight or more successive generations. CFSE is long lived, permitting analysis for several months after cell transfer, and has the same spectral characteristics as fluorescein, so monoclonal antibodies conjugated to phycoerythrin or other compatible fluorochromes may be used to immunophenotype the dividing cells. In addition, information is given on a second-generation dye, Cell Trace Violet (CTV), excited by 405-nm blue laser light. CTV is chemically related to CFSE, but allows the 488-nm line of the Argon laser to be used for other probes.

Silymarin inhibits ultraviolet radiation-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells

Silymarin inhibits UVB-induced immunosuppression in mouse skin. To identify the molecular mechanisms underlying this effect, we used an adoptive transfer approach in which dendritic cells (DCs) from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) were transferred into naïve recipient mice. The contact hypersensitivity (CHS) response of the recipient mice to DNFB was then measured. When DCs were obtained from UVB-exposed donor mice that were not treated with silymarin, the CHS response was suppressed confirming the role of DCs in the UVB-induced immunosuppression. Silymarin treatment of UVB-exposed donor mice relieved this suppression of the CHS response in the recipients. Silymarin treatment was associated with rapid repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in DCs and silymarin treatment did not prevent UV-induced immunosuppression in XPA-deficient mice which are unable to repair UV-induced DNA damage. The CHS response in mice receiving DCs from silymarin-treated UV-exposed donor mice also was associated with enhanced secretion of Th1-type cytokines and stimulation of T cells. Adoptive transfer of T cells revealed that transfer of either CD8(+) or CD4(+) cells from silymarin-treated, UVB-exposed donors resulted in enhancement of the CHS response. Cell culture study showed enhanced secretion of IL-2 and IFNγ by CD8(+) T cells, and reduced secretion of Th2 cytokines by CD4(+) T cells, obtained from silymarin-treated UVB-exposed mice. These data suggest that DNA repair-dependent functional activation of DCs, a reduction in CD4(+) regulatory T-cell activity, and stimulation of CD8(+) effector T cells contribute to silymarin-mediated inhibition of UVB-induced immunosuppression.

Analysis of the K+ current in human CD4+ T lymphocytes in hypercholesterolemic state

Atherosclerosis involves immune mechanisms: T lymphocytes are found in atherosclerotic plaques, suggesting their activation during atherogenesis. The predominant voltage-gated potassium channel of T cells, Kv1.3 is a key regulator of the Ca(2+)-dependent activation pathway. In the present experiments we studied the proliferation capacity and functional changes of Kv1.3 channels in T cells from healthy and hypercholestaeremic patients. By means of CFSE-assay (carboxyfluorescein succinimidyl ester) we showed that spontaneous activation rate of lymphocytes in hypercholesterolemia was elevated and the antiCD3/antiCD28 co-stimulation was less effective as compared to the healthy group. Using whole-cell patch-clamping we obtained that the activation and deactivation kinetics of Kv1.3 channels were faster in hypercholesterolemic state but no change in other parameters of Kv1.3 were found (inactivation kinetics, steady-state activation, expression level). We suppose that incorporation of oxLDL species via its raft-rupturing effect can modify proliferative rate of T cells as well as the gating of Kv1.3 channels.

Bioactive grape proanthocyanidins enhance immune reactivity in UV-irradiated skin through functional activation of dendritic cells in mice

Ultraviolet (UV) radiation-induced immunosuppression has been implicated in skin carcinogenesis. Grape seed proanthocyanidins (GSPs) have anti-skin carcinogenic effects in mice and GSPs-fed mice exhibit a reduction in UV-induced suppression of allergic contact hypersensitivity (CHS), a prototypic T-cell-mediated response. Here, we report that dietary GSPs did not inhibit UVB-induced suppression of CHS in xeroderma pigmentosum complementation group A (XPA)-deficient mice, which lack nucleotide excision repair mechanisms. GSPs enhanced repair of UVB-induced DNA damage (cyclobutane pyrimidine dimers) in wild-type, but not XPA-deficient, dendritic cells (DC). Co-culture of CD4(+) T cells with DCs from UVB-irradiated wild-type mice resulted in suppression of T-cell proliferation and secretion of T-helper (TH) 1-type cytokines that was ameliorated when the DCs were obtained from GSP-fed mice, whereas DCs obtained from GSP-fed XPA-KO mice failed to restore T-cell proliferation. In adoptive transfer experiments, donor DCs were positively selected from the draining lymph nodes of UVB-exposed donor mice that were sensitized to 2,4,-dinitrofluorobenzene were transferred into naïve recipient mice and the CHS response assessed. Naïve recipients that received DCs from UVB-exposed wild-type donors that had been fed GSPs exhibited a full CHS response, whereas no significant CHS was observed in mice that received DCs from XPA-KO mice fed GSPs. These results suggest that GSPs prevent UVB-induced immunosuppression through DNA repair-dependent functional activation of dendritic cells in mice. Cancer Prev Res; 6(3); 242-52. ©2013 AACR.

Neurogenic and neuro-protective potential of a novel subpopulation of peripheral blood-derived CD133+ ABCG2+CXCR4+ mesenchymal stem cells: development of autologous cell-based therapeutics for traumatic brain injury

INTRODUCTION

Nervous system injuries comprise a diverse group of disorders that include traumatic brain injury (TBI). The potential of mesenchymal stem cells (MSCs) to differentiate into neural cell types has aroused hope for the possible development of autologous therapies for central nervous system injury.

METHODS

In this study we isolated and characterized a human peripheral blood derived (HPBD) MSC population which we examined for neural lineage potential and ability to migrate in vitro and in vivo. HPBD CD133+, ATP-binding cassette sub-family G member 2 (ABCG2)+, C-X-C chemokine receptor type 4 (CXCR4)+ MSCs were differentiated after priming with β-mercaptoethanol (β-ME) combined with trans-retinoic acid (RA) and culture in neural basal media containing basic fibroblast growth factor (FGF2) and epidermal growth factor (EGF) or co-culture with neuronal cell lines. Differentiation efficiencies in vitro were determined using flow cytometry or fluorescent microscopy of cytospins made of FACS sorted positive cells after staining for markers of immature or mature neuronal lineages. RA-primed CD133+ABCG2+CXCR4+ human MSCs were transplanted into the lateral ventricle of male Sprague-Dawley rats, 24 hours after sham or traumatic brain injury (TBI). All animals were evaluated for spatial memory performance using the Morris Water Maze (MWM) Test. Histological examination of sham or TBI brains was done to evaluate MSC survival, migration and differentiation into neural lineages. We also examined induction of apoptosis at the injury site and production of MSC neuroprotective factors.

RESULTS

CD133+ABCG2+CXCR4+ MSCs consistently expressed markers of neural lineage induction and were positive for nestin, microtubule associated protein-1β (MAP-1β), tyrosine hydroxylase (TH), neuron specific nuclear protein (NEUN) or type III beta-tubulin (Tuj1). Animals in the primed MSC treatment group exhibited MWM latency results similar to the uninjured (sham) group with both groups showing improvements in latency. Histological examination of brains of these animals showed that in uninjured animals the majority of MSCs were found in the lateral ventricle, the site of transplantation, while in TBI rats MSCs were consistently found in locations near the injury site. We found that levels of apoptosis were less in MSC treated rats and that MSCs could be shown to produce neurotropic factors as early as 2 days following transplantation of cells. In TBI rats, at 1 and 3 months post transplantation cells were generated which expressed markers of neural lineages including immature as well as mature neurons.

CONCLUSIONS

These results suggest that PBD CD133+ABCG2+CXCR4+ MSCs have the potential for development as an autologous treatment for TBI and neurodegenerative disorders and that MSC derived cell products produced immediately after transplantation may aid in reducing the immediate cognitive defects of TBI.

Linear fidelity in quantification of anti-viral CD8+ T cells

Enumeration of anti-viral CD8(+) T cells to make comparisons between mice, viruses and vaccines is a frequently used approach, but controversy persists as to the most appropriate methods. Use of peptide-MHC tetramers (or variants) and intracellular staining for cytokines, in particular IFNγ, after a short ex vivo stimulation are now common, as are a variety of cytotoxicity assays, but few direct comparisons have been made. It has been argued that use of tetramers leads to the counting of non-functional T cells and that measurement of single cytokines will fail to identify cells with alternative functions. Further, the linear range of these methods has not been tested and this is required to give confidence that relative quantifications can be compared across samples. Here we show for two acute virus infections and CD8(+) T cells activated in vitro that DimerX (a tetramer variant) and intracellular staining for IFNγ, alone or in combination with CD107 to detect degranulation, gave comparable results at the peak of the response. Importantly, these methods were highly linear over nearly two orders of magnitude. In contrast, in vitro and in vivo assays for cytotoxicity were not linear, suffering from high background killing, plateaus in maximal killing and substantial underestimation of differences in magnitude of responses.

Human epidermal Langerhans cells maintain immune homeostasis in skin by activating skin resident regulatory T cells

Recent studies have demonstrated that the skin of a normal adult human contains 10-20 billion resident memory T cells, including various helper, cytotoxic, and regulatory T cell subsets, that are poised to respond to environmental antigens. Using only autologous human tissues, we report that both in vitro and in vivo, resting epidermal Langerhan cells (LCs) selectively and specifically induced the activation and proliferation of skin resident regulatory T (Treg) cells, a minor subset of skin resident memory T cells. In the presence of foreign pathogen, however, the same LCs activated and induced proliferation of effector memory T (Tem) cells and limited Treg cells' activation. These underappreciated properties of LCs, namely maintenance of tolerance in normal skin, and activation of protective skin resident memory T cells upon infectious challenge, help clarify the role of LCs in skin.

Standardizing immunophenotyping for the Human Immunology Project

The heterogeneity in the healthy human immune system, and the immunological changes that portend various diseases, have been only partially described. Their comprehensive elucidation has been termed the 'Human Immunology Project'. The accurate measurement of variations in the human immune system requires precise and standardized assays to distinguish true biological changes from technical artefacts. Thus, to be successful, the Human Immunology Project will require standardized assays for immunophenotyping humans in health and disease. A major tool in this effort is flow cytometry, which remains highly variable with regard to sample handling, reagents, instrument setup and data analysis. In this Review, we outline the current state of standardization of flow cytometry assays and summarize the steps that are required to enable the Human Immunology Project.

Adipose-derived stromal cells cultured in a low-serum medium, but not bone marrow-derived stromal cells, impede xenoantibody production

BACKGROUND

Although the immunomodulatory effects of mesenchymal stromal cells (MSC) on T cells have been elucidated, little is known about their effects on B cells. Recently, we have established a novel culture method for adipose-derived MSC (ASC) using low (2%) serum medium containing fibroblast growth factor-2. We showed that low serum-cultured ASC (LASC) was superior to high (20%) serum-cultured ASC (HASC) when used in regenerative therapy. The aim of this study was to compare the action of LASC, HASC, and bone marrow-derived MSC (BM-MSC), on xenoantibody production by B cells.

METHODS

Adipose-derived mesenchymal stromal cells and BM-MSC were obtained from humans or F344 rats and expanded in a low-serum or a high-serum culture medium. Proliferation of human peripheral mononuclear cells (PBMC) or rat splenocytes was induced by phytohemagglutinin (PHA) or anti-IgM-antibody. These cells were then co-cultured with LASC, HASC, or BM-MSC, and cell proliferation was studied. Porcine red blood cells (pRBC) were intraperitoneally injected into Lewis rats, and LASC, HASC, or BM-MSC obtained from F344 rats were injected intravenously or intraperitoneally. The levels of antibodies (IgM and IgG) against pRBC were examined using flow cytometry.

RESULTS

Human LASC suppressed PBMC proliferation more effectively than human HASC. Human LASC suppressed both T-cell and B-cell proliferation when incubated with PHA (a T-cell stimulus). However, human LASC did not suppress B-cell proliferation after incubation with anti-IgM-antibody (a T-cell-independent stimulus). Rat LASC suppressed PHA-stimulated splenocyte proliferation more effectively than rat HASC or rat BM-MSC. In vivo studies showed that intravenous injection of rat LASC significantly reduced the levels of IgG antibodies against pRBC, while intravenous administration of the other two types of MSC (rat HASC or rat BM-MSC) or intraperitoneal administration of rat LASC did not impede IgG production. A significant number of LASC were observed in the spleen when injected intravenously while only a few LASC were observed when given intraperitoneally.

CONCLUSIONS

Administration of LASC effectively impeded xenoantibody production by B cells through the inhibition of T-cell function, while HASC or BM-MSC showed less promising effects. These results suggest that intravenous injection of LASC may be useful in attenuating antibody-mediated rejection.

Sensitization to gliadin induces moderate enteropathy and insulitis in nonobese diabetic-DQ8 mice

Celiac disease (CD) is frequently diagnosed in patients with type 1 diabetes (T1D), and T1D patients can exhibit Abs against tissue transglutaminase, the auto-antigen in CD. Thus, gliadin, the trigger in CD, has been suggested to have a role in T1D pathogenesis. The objective of this study was to investigate whether gliadin contributes to enteropathy and insulitis in NOD-DQ8 mice, an animal model that does not spontaneously develop T1D. Gliadin-sensitized NOD-DQ8 mice developed moderate enteropathy, intraepithelial lymphocytosis, and barrier dysfunction, but not insulitis. Administration of anti-CD25 mAbs before gliadin-sensitization induced partial depletion of CD25(+)Foxp3(+) T cells and led to severe insulitis, but did not exacerbate mucosal dysfunction. CD4(+) T cells isolated from pancreatic lymph nodes of mice that developed insulitis showed increased proliferation and proinflammatory cytokines after incubation with gliadin but not with BSA. CD4(+) T cells isolated from nonsensitized controls did not response to gliadin or BSA. In conclusion, gliadin sensitization induced moderate enteropathy in NOD-DQ8 mice. However, insulitis development required gliadin-sensitization and partial systemic depletion of CD25(+)Foxp3(+) T cells. This humanized murine model provides a mechanistic link to explain how the mucosal intolerance to a dietary protein can lead to insulitis in the presence of partial regulatory T cell deficiency.

Mucosal immunization with a Staphylococcus aureus IsdA-cholera toxin A2/B chimera induces antigen-specific Th2-type responses in mice

Staphylococcus aureus is a leading cause of opportunistic infection worldwide and a significant public health threat. The iron-regulated surface determinant A (IsdA) adhesin is essential for S. aureus colonization on human nasal epithelial cells and plays an important role in iron acquisition and resistance to human skin defenses. Here we investigated the murine immune response to intranasal administration of a cholera toxin A(2)/B (CTA(2)/B) chimera containing IsdA. Plasmids were constructed to express the IsdA-CTA(2)/B chimera and control proteins in Escherichia coli. Proper construction of the chimera was verified by SDS-PAGE, Western blotting, GM1 enzyme-linked immunosorbent assay (ELISA), and confocal microscopy. Groups of female BALB/c mice were mock immunized or immunized with IsdA-CTA(2)/B, IsdA mixed with CTA(2)/B, or IsdA alone, followed by one booster immunization at 10 days postpriming. Analysis of serum IgG and nasal, intestinal, and vaginal IgA suggested that mucosal immunization with IsdA-CTA(2)/B induces significant IsdA-specific humoral immunity. Functional in vitro assays revealed that immune serum significantly blocks the adherence of S. aureus to human epithelial cells. Splenocytes from mice immunized with IsdA-CTA(2)/B showed specific cellular proliferation and production of interleukin-4 (IL-4) after in vitro stimulation. Immunization with IsdA-CTA(2)/B drove isotype switching to IgG1, indicative of a Th2-type response. Our results suggest that the immunogenicity of the S. aureus IsdA-CTA(2)/B chimera merits further investigation as a potential mucosal vaccine candidate.

Theiler's murine encephalomyelitis virus as a vaccine candidate for immunotherapy

The induction of sterilizing T-cell responses to tumors is a major goal in the development of T-cell vaccines for treating cancer. Although specific components of anti-viral CD8+ immunity are well characterized, we still lack the ability to mimic viral CD8+ T-cell responses in therapeutic settings for treating cancers. Infection with the picornavirus Theiler's murine encephalomyelitis virus (TMEV) induces a strong sterilizing CD8+ T-cell response. In the absence of sterilizing immunity, the virus causes a persistent infection. We capitalized on the ability of TMEV to induce strong cellular immunity even under conditions of immune deficiency by modifying the virus to evaluate its potential as a T-cell vaccine. The introduction of defined CD8+ T-cell epitopes into the leader sequence of the TMEV genome generates an attenuated vaccine strain that can efficiently drive CD8+ T-cell responses to the targeted antigen. This virus activates T-cells in a manner that is capable of inducing targeted tissue damage and glucose dysregulation in an adoptive T-cell transfer model of diabetes mellitus. As a therapeutic vaccine for the treatment of established melanoma, epitope-modified TMEV can induce strong cytotoxic T-cell responses and promote infiltration of the T-cells into established tumors, ultimately leading to a delay in tumor growth and improved survival of vaccinated animals. We propose that epitope-modified TMEV is an excellent candidate for further development as a human T-cell vaccine for use in immunotherapy.

The use of carboxyfluorescein diacetate succinimidyl ester (CFSE) to monitor lymphocyte proliferation

Carboxyfluorescein succinimidyl ester (CFSE) is an effective and popular means to monitor lymphocyte division^1-3. CFSE covalently labels long-lived intracellular molecules with the fluorescent dye, carboxyfluorescein. Thus, when a CFSE-labeled cell divides, its progeny are endowed with half the number of carboxyfluorescein-tagged molecules and thus each cell division can be assessed by measuring the corresponding decrease in cell fluorescence via Flow cytometry. The capacity of CFSE to label lymphocyte populations with a high fluorescent intensity of exceptionally low variance, coupled with its low cell toxicity, make it an ideal dye to measure cell division. Since it is a fluorescein-based dye it is also compatible with a broad range of other fluorochromes making it applicable to multi-color flow cytometry. This article describes the procedures typically used for labeling mouse lymphocytes for the purpose of monitoring up to 8 cell divisions. These labeled cells can be used both for in vitro and in vivo studies.

HIV-1 Gag p17 presented as virus-like particles on the E2 scaffold from Geobacillus stearothermophilus induces sustained humoral and cellular immune responses in the absence of IFNγ production by CD4+ T cells

We have constructed stable virus-like particles displaying the HIV-1 Gag(p17) protein as an N-terminal fusion with an engineered protein domain from the Geobacillus stearothermophilus pyruvate dehydrogenase subunit E2. Mice immunized with the Gag(p17)-E2 60-mer scaffold particles mounted a strong and sustained antibody response. Antibodies directed to Gag(p17) were boosted significantly with additional immunizations, while anti-E2 responses reached a plateau. The isotype of the induced antibodies was biased towards IgG1, and the E2-primed CD4+ T cells did not secrete IFNγ. Using transgenic mouse model systems, we demonstrated that CD8+ T cells primed with E2 particles were able to exert lytic activity and produce IFNγ. These results show that the E2 scaffold represents a powerful vaccine delivery system for whole antigenic proteins or polyepitope engineered proteins, evoking antibody production and antigen specific CTL activity even in the absence of IFNγ-producing CD4+ T cells.

CD57 defines a functionally distinct population of mature NK cells in the human CD56dimCD16+ NK-cell subset

Natural killer (NK) cells are innate immune lymphocytes that express a heterogeneous repertoire of germline-encoded receptors and undergo a distinct pattern of maturation. CD57 is a marker of terminal differentiation on human CD8(+) T cells. Very few newborn or fetal NK cells express CD57; however, the frequency of CD57-bearing NK cells increases with age. We assessed the transcriptional, phenotypic, and functional differences between CD57(+) and CD57(-) NK cells within the CD56(dim) mature NK subset. CD57(+) NK cells express a repertoire of NK-cell receptors, suggestive of a more mature phenotype, and proliferate less when stimulated with target cells and/or cytokines. By contrast, a higher frequency of CD57(+) NK cells produced interferon-γ and demonstrated more potent lytic activity when these cells were stimulated through the activating receptor CD16; however, they are less responsive to stimulation by interleukin-12 and interleukin-18. Finally, CD57 expression is induced on CD57(-)CD56(dim) NK cells after activation by interleukin-2. A combination of a mature phenotype, a higher cytotoxic capacity, a higher sensitivity to stimulation via CD16, with a decreased responsiveness to cytokines, and a decreased capacity to proliferate suggest that CD57(+) NK cells are highly mature and might be terminally differentiated.

A novel HLA (HLA-A*0201) transgenic rabbit model for preclinical evaluation of human CD8+ T cell epitope-based vaccines against ocular herpes

We introduced a novel humanized HLA-A*0201 transgenic (HLA Tg) rabbit model to assess the protective efficacy of a human CD8(+) T cell epitope-based vaccine against primary ocular herpes infection and disease. Each of the three immunodominant human CD8(+) T cell peptide epitopes from HSV-1 glycoprotein D (gD(53-61), gD(70-78), and gD(278-286)) were joined with a promiscuous human CD4(+) T cell peptide epitope (gD(49-82)) to construct three separate pairs of CD4-CD8 peptides. Each CD4-CD8 peptide pair was then covalently linked to an N(epsilon)-palmitoyl-lysine residue via a functional base lysine amino group to construct CD4-CD8 lipopeptides. HLA Tg rabbits were immunized s.c. with a mixture of the three CD4-CD8 HSV-1 gD lipopeptides. The HSV-gD-specific T cell responses induced by the mixture of CD4-CD8 lipopeptide vaccine and the protective efficacy against acute virus replication and ocular disease were determined. Immunization induced HSV-gD(49-82)-specific CD4(+) T cells in draining lymph node (DLN); induced HLA-restricted HSV-gD(53-61), gD(70-78), and gD(278-286)-specific CD8(+) T cells in DLN, conjunctiva, and trigeminal ganglia and reduced HSV-1 replication in tears and corneal eye disease after ocular HSV-1 challenge. In addition, the HSV-1 epitope-specific CD8(+) T cells induced in DLNs, conjunctiva, and the trigeminal ganglia were inversely proportional with corneal disease. The humanized HLA Tg rabbits appeared to be a useful preclinical animal model for investigating the immunogenicity and protective efficacy of human CD8(+) T cell epitope-based prophylactic vaccines against ocular herpes. The relevance of HLA Tg rabbits for future investigation of human CD4-CD8 epitope-based therapeutic vaccines against recurrent HSV-1 is discussed.

Three Epstein-Barr virus latency proteins independently promote genomic instability by inducing DNA damage, inhibiting DNA repair and inactivating cell cycle checkpoints

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of human malignancies, but its contribution to tumorigenesis is not well understood. EBV carriage is associated with increased genomic instability in Burkitt's lymphoma, suggesting that viral products may induce this tumor phenotype. Using a panel of transfected sublines of the B-lymphoma line BJAB expressing the viral genes associated with latent infection, we show that the EBV nuclear antigens, EBNA-1 and EBNA-3C, and the latent membrane protein 1, LMP-1, independently promote genomic instability, as detected by nonclonal chromosomal aberrations, DNA breaks and phosphorylation of histone H2AX. EBNA-1 promotes the generation of DNA damage by inducing reactive oxygen species (ROS), whereas DNA repair is inhibited in LMP-1-expressing cells through downregulation of the DNA damage-sensing kinase, ataxia telangiectasia mutated (ATM), reduction of phosphorylation of its downstream targets Chk2 and inactivation of the G(2) checkpoint. EBNA-3C enhances the propagation of damaged DNA through inactivation of the mitotic spindle checkpoint and transcriptional downregulation of BubR1. Thus, multiple cellular functions involved in the maintenance of genome integrity seem to be independently targeted by EBV, pointing to the induction of genomic instability as a critical event in viral oncogenesis.