Analysis of the proliferative T cell response to human cytomegalovirus major immediate-early protein (IE1): phenotype, frequency and variability

A Prospective Study of Cytomegalovirus-Specific Cell-Mediated Immune Monitoring and Cytomegalovirus Infection in Patients With Active Systemic Lupus Erythematosus Receiving Immunosuppressants

Background

The effects of cytomegalovirus (CMV)-specific cell-mediated immunity (CMI) on CMV infection in patients with autoimmune diseases receiving immunosuppressants have not been explored.

Methods

Patients with active systemic lupus erythematosus (SLE) were preemptively monitored for clinically significant CMV infection (CsCMVI; defined as plasma CMV DNA loads >3 log10 IU/mL). CMV-specific CMI was assessed using an enzyme-linked immunosorbent assay (QuantiFERON-CMV [QF]) before as well as 1 and 3 months after intense immunosuppressive therapy.

Results

The study included 55 patients with active SLE; patients were a mean age (SD) of 34 (13) years and had a median SLE Disease Activity Index 2000 score (SD) of 14 (8), and 93% were female. Most patients had renal involvement (67%), received methylprednisolone (93%), and were CMV-seropositive (95%). Thirteen (23.6%) patients developed CsCMVI. Among patients with active SLE who were QF-negative (QF-) and QF-positive (QF+) before receiving immunosuppressive therapy, 28.6% and 25% developed CsCMVI, respectively (P = .69). However, 1 month postimmunosuppression, more QF- than QF+ patients developed CsCMVI (44.4% vs 11.8%; P = .03; adjusted hazard ratio, 4.97; 95% CI, 1.07-23.10; P = .04).

Conclusions

Patients with active SLE and low CMV-specific T-cell responses could develop CMV infection after receiving immunosuppressants. Further studies should focus on CMV-specific CMI among patients with autoimmune diseases.

Cytomegalovirus-Specific T Cells Isolated by IFN-γ Secretion Assay Do Not Induce Significant Graft-Versus-Host Reactions In Vitro

BACKGROUND

Graft-versus-host (GvH) disease (GvHD) remains a serious concern for patients undergoing antiviral cellular therapy. Despite the major improvements in cellular immunotherapy, the immunogenicity of virus-specific T cells has not yet been fully defined. This present study aims to examine how cytomegalovirus (CMV)-specific cytotoxic T lymphocytes (CTLs) respond to allogeneic antigen stimulation and whether they give rise to GvHD target tissue damage.

METHODS

Cytomegalovirus-specific CTLs were isolated by the IFN-γ secretion assay (gamma-catch) from healthy seropositive volunteers and expanded in vitro. The levels of intracellular IFN-γ, cytotoxic activity, IFN-γ and granzyme B secretion, and CD25 expression were measured using flow cytometry (fluorescence-activated cell sorting). The ability of CMV-CTLs to induce GvHD target tissue damage was evaluated using the human in vitro skin explant assay (skin explant assay).

RESULTS

Cytomegalovirus-specific CTLs responded specifically to CMV-phosphoprotein 65 stimulation by secreting IFN-γ and killing virus peptide loaded autologous phytohemagglutinin (PHA) blasts. Compared with unselected peripheral blood mononuclear cells, CMV-CTLs induced significantly less severe cutaneous GvH tissue damage. This observation coincided with low levels of CD25 expression, as well as IFN-γ and granzyme B secretion after allogeneic antigen stimulation in both the mixed lymphocyte reaction and in the skin explant assay.

CONCLUSIONS

Cytomegalovirus-specific CTLs isolated by the IFN-γ secretion assay from HLA-unmatched healthy donors exhibited a high level of anti-CMV potency without inducing significant cutaneous GvH tissue damage in vitro. This finding provides novel evidence supporting the safe use of in vitro expanded CMV-CTLs as an antiviral therapy in transplant patients with refractory CMV infections.

A Diverse Repertoire of CD4 T Cells Targets the Immediate-Early 1 Protein of Human Cytomegalovirus

T-cell responses to the immediate-early 1 (IE-1) protein of human cytomegalovirus (HCMV) are associated with protection from viral disease. Thus, IE-1 is a promising target for immunotherapy. CD8 T-cell responses to IE-1 are generally strong. In contrast, CD4 T-cell responses to IE-1 were described to be comparatively infrequent or undetectable in HCMV carriers, and information on their target epitopes and their function has been limited. To analyze the repertoire of IE-1-specific CD4 T cells, we expanded them from healthy donors with autologous IE-1-expressing mini-Epstein–Barr virus-transformed B-cell lines and established IE-1-specific CD4 T-cell clones. Clones from seven out of seven HCMV-positive donors recognized endogenously processed IE-1 epitopes restricted through HLA-DR, DQ, or DP. Three to seven IE-1 epitopes were recognized per donor. Cumulatively, about 27 different HLA/peptide class II complexes were recognized by 117 IE-1-specific clones. Our results suggest that a highly diversified repertoire of IE-1-specific CD4 T cells targeting multiple epitopes is usually present in healthy HCMV carriers. Therefore, multiepitope approaches to immunomonitoring and immunotherapy will make optimal use of this potentially important class of HCMV-specific effector cells.

Natural and adoptive T-cell immunity against herpes family viruses after allogeneic hematopoietic stem cell transplantation

Reactivated infections with herpes family-related cytomegalovirus, Epstein-Barr virus and varicella zoster virus are serious and sometimes life-threatening complications for patients undergoing allogeneic hematopoietic stem cell transplantation. The pathogenesis of these infections critically involves the slow and inefficient recovery of antiviral T-cell immunity after transplantation. Although efficient drugs to decrease viral load during this vulnerable period have been developed, long-term control of herpes viruses and protection from associated diseases require the sufficient reconstitution of virus-specific memory T cells. To heal the deficiency by immunotherapeutic means, numerous research groups have developed antiviral vaccines and strategies based on the adoptive transfer of virus-specific T cells. This article summarizes the substantial progress made in this field during the past two decades and gives future perspectives about challenges that need to be addressed before antigen-specific immunotherapy against herpes family viruses can be implemented in general clinical practice.

Human cytomegalovirus immunity and immune evasion

Human cytomegalovirus (HCMV) infection induces both innate immune responses including Natural Killer cells as well as adaptive humoral and cell mediated (CD4+ helper, CD8+ cytotoxic and γδ T cell) responses which lead to the resolution of acute primary infection. Despite such a robust primary immune response, HCMV is still able to establish latency. Long term memory T cell responses are maintained at high frequency and are thought to prevent clinical disease following periodic reactivation of the virus. As such, a balance is established between the immune response and viral reactivation. Loss of this balance in the immunocompromised host can lead to unchecked viral replication following reactivation of latent virus, with consequent disease and mortality. HCMV encodes multiple immune evasion mechanisms that target both the innate and acquired immune system. This article describes the current understanding of Natural killer cell, antibody and T cell mediated immune responses and the mechanisms that the virus utilizes to subvert these responses.

Maintenance of cytomegalovirus-specific CD4pos T-cell response in rheumatoid arthritis patients receiving anti-tumor necrosis factor treatments

INTRODUCTION

Anti-tumor necrosis factor (TNF)-α biotherapies have considerably changed the treatment of rheumatoid arthritis (RA). However, serious infections are a major concern in patients with rheumatic diseases treated with anti-TNF-α. Little is known about viral, especially latent, infections in anti-TNF-α treatments. Infections by cytomegalovirus (CMV), a β-herpes virus, are frequent and induce a strong CD4pos T-cell immunity, which participates in the control of infection. We thus have chosen to analyze the CD4pos T-cell response to CMV antigens as a model of antiviral response in RA patients treated with anti-TNF-α. CD28 expression was evaluated.

METHODS

We have measured the CD4pos response to CMV antigens in RA patients, before and after initiation of treatment with an anti-TNF-α agent. The intracellular production of interferon (IFN)-γ in total and CD28neg CD4pos T cells in response to CMV antigens (Ags) was evaluated with flow cytometry. The proliferation of total CD4pos T cells in the presence of CMV antigens was measured with 3H-thymidine incorporation.

RESULTS

Anti-TNF-α treatments impaired neither the anti-CD4pos anti-CMV IFN-γ response nor the proliferative response in patients. The percentage of CD28neg CD4pos cells remained constant.

CONCLUSIONS

Our data suggest that the CD4pos T-cell response against CMV is not altered by anti-TNF-α treatments and that infection remains controlled in treated RA patients latently infected with CMV. Our observation brings new insight into the current knowledge of the risks of infection in patients treated with anti-TNF-α biotherapies.

Dynamics of T cell memory in human cytomegalovirus infection

Primary human cytomegalovirus (HCMV) infection of an immunocompetent individual leads to the generation of a robust CD4+ and CD8+ T cell response which subsequently controls viral replication. HCMV is never cleared from the host and enters into latency with periodic reactivation and viral replication, which is controlled by reactivation of the memory T cells. In this article, we discuss the magnitude, phenotype and clonality of the T cell response following primary HCMV infection, the selection of responding T cells into the long-term memory pool and maintenance of this memory T cell population in the face of a latent/persistent infection. The article also considers the effect that this long-term surveillance of HCMV has on the T cell memory phenotype, their differentiation, function and the associated concepts of T cell memory inflation and immunosenescence.

CMV pp65 and IE-1 T cell epitopes recognized by healthy subjects

Background

Adoptive immune and vaccine therapies have been used to prevent cytomegalovirus (CMV) disease in recipients of hematopoietic progenitor cell transplants, but the nature of T cell responses to CMV have not been completely characterized.

Methods

Peptide pools and individual peptides derived from the immune-dominant CMV proteins pp65 and IE-1 and antigen-specific, cytokine flow cytometry were used to characterize the prevalence and frequency of CD4+ and CD8+ memory T cells in 20 healthy CMV-seropositive subjects.

Results

CD8+ T cell responses to pp65 were detected in 35% of subjects and to IE-1 in 40% of subjects. CD4+ T cell responses to pp65 were detected in 50% of subjects, but none were detected to IE-1. Several new IE-1 HLA class I epitopes were identified, including 4 restricted to HLA-C antigens. One region of IE-1 spanning amino acids 300 to 327 was rich in class I epitopes. The HLA class I restrictions of IE-1 peptides were more promiscuous than those of pp65 peptides.

Conclusion

Since naturally occurring CD4+ and CD8+ T cell responses to pp65 were detectable in many subjects, but only CD8+ T cell responses to IE-1 were detected, pp65 may be better than IE-1 for use in vaccine and adoptive immune therapies.

Mouse cytomegalovirus crosses the species barrier with help from a few human cytomegalovirus proteins

Strong species specificity and similar tropisms suggest mouse cytomegalovirus (mCMV) as a potential vector for transgenes into human cells. We reexamined the dogma that mouse cytomegalovirus cannot productively replicate in human cells and found that mouse cytomegalovirus can produce infectious particles albeit at a level that does not sustain an infection. This finding demonstrates that mouse cytomegalovirus can undergo all processes of its life cycle in human cells but may not be well adapted to circumvent the human cell's intrinsic defenses. The suppression of mCMV production in human cells is affected at several levels, which additively or synergistically result in the appearance of species specificity. Hydrolysis of most newly replicated viral DNA and very low capsid protein transcription reduced the potential particle production to insignificant levels. These effects can be ameliorated by adding human cytomegalovirus tegument proteins and immediate-early protein 1. They function synergistically to produce significant amounts of mCMV in human cells. While the possibility that mouse cytomegalovirus might replicate in human cells raises caution in the use of this virus as a transgene vector, manipulation of the mouse cytomegalovirus genome to allow limited spread to other human cells might also provide an advantage for the distribution of certain transgenic products.

Macrophage cultures are susceptible to lytic productive infection by endothelial-cell-propagated human cytomegalovirus strains and present viral IE1 protein to CD4+ T cells despite late downregulation of MHC class II molecules

The contribution of CD4(+) T cells to control of human cytomegalovirus (HCMV) has been shown and infected tissue macrophages might contribute to this response by antigen presentation. As shown previously, CD4(+) T cells recognize HCMV immediate-early antigen IE1 on glioblastoma cells manipulated to express MHC class II molecules. Here, the possible interference of virus-induced MHC class II downmodulation with the presentation of IE1 by natural target cells was analysed. The capacity of IE1-specific CD4(+) T-cell clones to recognize HCMV-infected monocyte-derived macrophages was tested. Various HCMV strains were used to achieve efficient infection of macrophages. Activation of CD4(+) T cells by infected macrophages was evaluated at different time points after infection. Endothelial-cell-adapted HCMV strains efficiently infected cultured human macrophages. However, the immediate-early and early phases of replication were prolonged. Infected cells entered the late replication phase only after 3 days of infection, which was associated with downmodulation of MHC class II molecules at the surface of infected cells. Strong stimulation of IE1-specific CD4(+) T cells resulted from endogenous de novo antigen production and presentation by infected macrophages during the first 3 days of virus replication, despite MHC class II downmodulation in the late replication phase. Therefore, infected macrophages are assumed to contribute to the antiviral immune response in infected organs.

Optimization of CD4+ T lymphocyte response to human cytomegalovirus nuclear IE1 protein through modifications of both size and cellular localization

We have previously reported that the CD4+ T lymphocyte response against nuclear human CMV IE1 protein depends in part on endogenous MHC class II presentation. To optimize presentation by HLA-DR of the nuclear IE1 protein and increase the response by CD4+ T cells, we have constructed two different adenovirus vectors containing mutant versions of IE1, containing a HLA-DR3 epitope, fused to GFP. The first construct consisted of a sequence of 46 aa encoded by exon 4, called GFP-IE1 (86-131). The second construct consisted of the whole IE1 mutated on exon 4 nuclear localization signals, identified in this study, and deleted of already known exon 2 nuclear localization signals (GFP-IE1M). Both of these IE1 vectors expressed proteins with cytoplasmic localization, as evidenced by GFP expression, as opposed to control GFP-IE1, which was nuclear. GFP-IE1 (86-131) induced IE1-specific CD4+ T cell clone response that was >30-fold more potent than that against GFP-IE1 and GFP-IE1M. The CD4+ T cell response was due to endogenous presentation followed by exogenous presentation at later time points. Presentation was dependent on both proteasome and acidic compartments. GFP-IE1 (86-131) was rapidly degraded by the APC, which may account for better presentation. Our data show potentiation of the CD4+ T cell response to a specific epitope through shortening and relocation of an otherwise nuclear protein and suggest applications in vaccination.

Human cytomegalovirus-specific CD4(+) T-cell clones recognize cross-reactive peptides from the immediate early 1 protein

Human cytomegalovirus (HCMV) is a beta-herpes virus that persists in a latent state in immunocompetent individuals. Both CD4(+) and CD8(+) T lymphocytes have been reported to be present at a high frequency in HCMV-seropositive individuals and are involved in the control of infection. How such frequencies are maintained is not completely understood. We have observed that the canonical HLA-DR8 epitope of the immediate early 1 protein (IE1) contained in the IE1 (156--175) sequence shares homologies with an IE1 sequence contained in part in the previously reported HLA-DR3 epitope, IE1 (91-110). We thus wondered whether such homology in a single protein would translate into recognition of the IE1 homolog sequence by HLA-DR8-restricted CD4(+) cells in addition to the canonical epitope. We found that established HLA-DR8-restricted T cell clones are also able to cross-recognize the IE1 (91--110) peptide, as well as a shorter 14-mer, IE1 (91--104). Moreover, the homolog peptide IE1 (91-110) was able to generate, from a seropositive blood donor, new IE1-specific, HLA-DR8-restricted CD4(+) T cell clones that were also cross-reactive. Those findings may provide clues to the formation and regulation of the T-cell repertoire and memory.

Use of a lentiviral vector encoding a HCMV-Chimeric IE1-pp65 protein for epitope identification in HLA-Transgenic mice and for ex vivo stimulation and expansion of CD8+ cytotoxic T cells from human peripheral blood cells

H2-deleted, HLA-A2, or HLA-B7 transgenic mice were used to identify new human cytomegalovirus (HCMV)-derived major histocompatibility complex class I-restricted epitopes. Three different approaches for mice immunization were compared for their ability to induce a cytotoxic CD8(+) T cell (CTL) response: (1). inoculation of infectious HCMV, (2). injection of immunogenic synthetic peptides, and (3). infection with a newly designed HIV-derived central DNA flap positive lentiviral vector encoding the chimeric IE1-pp65 protein (Trip-IE1-pp65). Targets pulsed with either known immunogenic peptides or computer predicted ones were used to characterize CTL. Most of the mice immunized with the pp65 (495-NLVPMVATV-503) immunodominant peptide responded after one injection whereas only two of six mice responded to two successive inoculations with HCMV. Infection of mice with Trip-IE1-pp65 induced activation and expansion of CTL directed against peptides from both pp65 and IE1 and allowed identification of new epitopes. We further demonstrated the high capacity of monocyte-macrophage cells transduced with Trip-IE1-pp65 to activate and expand CTL directed against pp65 from peripheral blood mononuclear cells of HCMV-seropositive donors. Altogether these results suggest that Trip-IE1-pp65 is a powerful construct both to characterize new epitopes in combination with human leukocyte antigen-transgenic mice immunization and to provide an alternative to the use of known infectious and noninfectious approaches to expand effector T cells for adoptive immunotherapy.

Dendritic cells and HCMV cross-presentation

The outcome of a viral infection is the result of an endless fight between the organism whose task is to mount an antiviral response and the virus that adapts strategies to circumvent the host response. Human cytomegalovirus (HCMV), a latent herpesvirus, can be considered as a spearhead in exploiting co-existence with the host to develop numerous immuno-evasion mechanisms. The ability of the organism to initiate a primary immune response against viruses such as HCMV is highly dependent on the capacity of professional antigen-presenting cells (APCs), namely dendritic cells (DCs), to prime and activate specific effector T cells. Recent findings emerging from the murine cytomegalovirus (MCMV) animal model demonstrated that infection of murine DCs with MCMV impaired their capacity to prime an effective T cell response. Even though data on interference of HCMV with DC functions are still limited, immunosuppressive effects identical to those reported for MCMV can be suspected and we may then ask how a cytotoxic T lymphocyte (CTL) response is generated in these unfavourable conditions. In response to this question, cross-presentation of HCMV antigens by uninfected DCs to CD8+ T cells could be considered a key process in initiating an immune response. In this chapter we discuss the mechanisms through which DCs could acquire HCMV antigens and how cross-presentation could be modulated throughout infection. Moreover, further knowledge of DC functions is key for the development of DC-based immunotherapy against HCMV.

The human cytomegalovirus

Human cytomegalovirus (HCMV), a betaherpesvirus, represents the major infectious cause of birth defects, as well as an important pathogen for immunocompromised individuals. The viral nucleocapsid containing a linear double-stranded DNA of 230 kb is surrounded by a proteinaceous tegument, which is itself enclosed by a loosely applied lipid bilayer. Expression of the HCMV genome is controlled by a cascade of transcriptional events that leads to the synthesis of three categories of viral proteins designated as immediate-early, early, and late. Clinical manifestations can be seen following primary infection, reinfection, or reactivation. About 10% of infants are infected by the age of 6 months following transmission from their mothers via the placenta, during delivery, or by breastfeeding. HCMV is a significant post-allograft pathogen and contributes to graft loss independently from graft rejection. Histopathologic examination of necropsy tissues demonstrates that the virus enters via the epithelium of the upper alimentary, respiratory, or genitourinary tracts. Hematogenous spreading is typically followed by infection of ductal epithelial cells. Infections are kept under control by the immune system. However, total HCMV clearance is rarely achieved, and the viral genome remains at selected sites in a latent state. Virological and molecular detection of HCMV, as well as serological demonstration of a specific immune response, are used for diagnosis. Treatment of HCMV infections is difficult because there are few options. The presently available drugs produced a significant clinical improvement, but suffer from poor oral bioavailability, low potency, development of resistance in clinical practice, and dose-limiting toxicities.

IE1-pp65 recombinant protein from human CMV combined with a nanoparticulate carrier, SMBV, as a potential source for the development of anti-human CMV adoptive immunotherapy

BACKGROUND

Human cytomegalovirus (HCMV) infection and reactivation following allogeneic bone marrow transplantation is a major source of complications in grafted patients including pneumonitis, graft rejection and even death. Adoptive immunotherapy consisting in transfer of CD4(+) and CD8(+) T cells directed against HCMV has proved its worth. Nevertheless, established procedures have to be improved in terms of safety and waiting period required to obtain specific T cells.

METHODS

As an alternative to infectious virus used in current strategies, we purified a recombinant protein IE1-pp65 resulting from the fusion of the regulatory IE1 and matrix pp65 proteins, both known as the major targets of the overall anti-HCMV T cell response. Based on our previous data demonstrating its use for in vitro stimulation and expansion of anti-HCMV CD4(+) and CD8(+) T cells (Vaz-Santiago et al, 2001, J.Virol, 75:7840-47) from peripheral blood mononuclear cells (PBMC) of seropositive donors, we planned to improve its in vitro immunogenicity through association with a nanoparticulate carrier, SMBV.

RESULTS

We demonstrated that using of SMBV/IE1-pp65 formulation allowed to potentiate in vitro activation of T cells and to expand more CD8(+) T cells than with soluble IE1-pp65, following stimulation of PBMC.

DISCUSSION

These data suggest the use of SMBV/IE1-pp65 formulation as a potential source of antigen for efficient T cells expansion in the development of safe anti-HCMV immunotherapy.

Infection of APC by human cytomegalovirus controlled through recognition of endogenous nuclear immediate early protein 1 by specific CD4(+) T lymphocytes

Infections by human CMV are controlled by cellular immune responses. Professional APC such as monocytes and macrophages can be infected in vivo and are considered as a reservoir of virus. However, CMV-specific CD4(+) responses against infected APC have not been reported. To develop a model of CD4-infected APC interaction, we have transfected the U373MG astrocytoma cell line with the class II transactivator (CIITA). Confocal microscopy experiments showed that U373MG-CIITA cells expressed markers characteristic of APC. Functional assays demonstrated that infected U373MG-CIITA APC processed and presented both exogenous and endogenously neosynthesized nuclear immediate early (IE) protein 1 through the MHC class II pathway. More importantly, endogenous presentation of IE1 by infected APC lead to efficient control of CMV infection as revealed by decreased viral titer. Thus, these results describe the endogenous presentation of a nuclear viral protein by the MHC class II pathway and suggest that IE1-specific CD4(+) T cells may play an important role in CMV infection by directly acting against infected APC.

Vaccines against persistent DNA virus infections

Persistent viruses present some particular problems for vaccine design. As for acute non-persistent viruses, the prime goal of a vaccine should be to prevent primary infection. Vaccines might also be used to modify the course of established persistent virus infections - so-called postinfective immunisation. This chapter deals with selected persistent DNA viruses, in particular the human herpes viruses.

Ex vivo stimulation and expansion of both CD4(+) and CD8(+) T cells from peripheral blood mononuclear cells of human cytomegalovirus-seropositive blood donors by using a soluble recombinant chimeric protein, IE1-pp65

The transfer of anti-human cytomegalovirus (HCMV) effector T cells to allogeneic bone marrow recipients results in protection from HCMV disease associated with transplantation, suggesting the direct control of CMV replication by T cells. IE1 and pp65 proteins, both targets of CD4(+) and CD8(+) T cells, are considered the best candidates for immunotherapy and vaccine design against HCMV. In this report, we describe the purification of a 165-kDa chimeric protein, IE1-pp65, and its use for in vitro stimulation and expansion of anti-HCMV CD4(+) and CD8(+) T cells from peripheral blood mononuclear cells (PBMC) of HCMV-seropositive donors. We demonstrate that an important proportion of anti-HCMV CD4(+) T cells was directed against IE1-pp65 in HCMV-seropositive donors and that the protein induced activation of HLA-DR3-restricted anti-IE1 CD4(+) T-cell clones, as assessed by gamma interferon (IFN-gamma) secretion and cytotoxicity. Moreover, soluble IE1-pp65 stimulated and expanded anti-pp65 CD8(+) T cells from PBMC of HLA-A2, HLA-B35, and HLA-B7 HCMV-seropositive blood donors, as demonstrated by cytotoxicity, intracellular IFN-gamma labeling, and quantitation of peptide-specific CD8(+) cells using an HLA-A2-peptide tetramer and staining of intracellular IFN-gamma. These results suggest that soluble IE1-pp65 may provide an alternative to infectious viruses used in current adoptive strategies of immunotherapy.

Human cytomegalovirus pp65- and immediate early 1 antigen-specific HLA class I-restricted cytotoxic T cell responses induced by cross-presentation of viral antigens

Dendritic cells (DCs) play a pivotal role in the development of anti-viral CD8(+) CTL responses. This is straightforward if they are directly infected with virus, but is less clear in response to viruses that cannot productively infect DCS: Human CMV (HCMV) shows strain-specific cell tropism: fibroblast (Fb)-adapted laboratory strains (AD169) and recent clinical isolates do not infect DCs, whereas endothelial cell-adapted strains (TB40/E) result in productive lytic DC infection. However, we show here that uninfected DCs induce CD8(+) T cell cytotoxicity and IFN-gamma production against HCMV pp65 and immediate early 1 Ags following in vitro coculture with HCMV-AD169-infected Fbs, regardless of the HLA type of these FBS: CD8(+) T cell stimulation was inhibited by pretreatment of DCs with cytochalasin B or brefeldin A, indicating a phagosome/endosome to cytosol pathway. HCMV-infected Fbs were not apoptotic as measured by annexin V binding, and induction of apoptosis of infected Fbs in vitro did not augment CTL induction by DCs, suggesting a mechanism other than apoptosis in the initiation of cross-presentation. Furthermore, HCMV-infected Fbs provided a maturation signal for immature DCs during coculture, as evidenced by increased CD83 and HLA class II expression. Cross-presentation of HCMV Ags by host DCs enables these professional APCs to bypass some of the evasion mechanisms HCMV has developed to avoid T cell recognition. It may also serve to explain the presence of immediate early 1 Ag-specific CTLs in the face of pp65-induced inhibition of Ag presentation at the level of the infected cell.

CD4(+) lymphocyte-mediated suppression of cytomegalovirus expression in human astrocytes

Cytomegalovirus-stimulated CD4(+) lymphocytes from seropositive but not seronegative donors suppressed viral gene expression in primary human astrocytes. This suppressive activity was mediated through soluble factors. These findings suggest that CD4(+) lymphocytes play a role in defense of the brain against cytomegalovirus.

Immune reconstitution in the HAART era, Part 1: Immune abnormalities in HIV/AIDS

Highly active antiretroviral therapy (HAART) has dramatically altered the course of HIV infection. HAART has been associated with a substantial decrease in HIV-related morbidity and mortality and an improved quality of life for many persons living with HIV/AIDS. This improvement is due to suppression of viral replication and subsequent repletion of CD4+ T lymphocytes. However, it is not known if HAART can restore the deficits in immune function that are induced by HIV infection, such as anergy and disturbances in cellular phenotypes. In this first part of a two-part series, the immune abnormalities associated with HIV infection will be reviewed, and the concept of immune reconstitution will be introduced. In Part 2, the clinical significance of immune reconstitution will be discussed.

Escape of human cytomegalovirus from HLA-DR-restricted CD4(+) T-cell response is mediated by repression of gamma interferon-induced class II transactivator expression

Human cytomegalovirus (HCMV), a betaherpesvirus, is a pathogen which escapes immune recognition through various mechanisms. In this paper, we show that HCMV down regulates gamma interferon (IFN-gamma)-induced HLA-DR expression in U373 MG astrocytoma cells due to a defect downstream of STAT1 phosphorylation and nuclear translocation. Repression of class II transactivator (CIITA) mRNA expression is detected within the first hours of IFN-gamma-HCMV coincubation and results in the absence of HLA-DR synthesis. This defect leads to the absence of presentation of the major immediate-early protein IE1 to specific CD4(+) T-cell clones when U373 MG cells, used as antigen-presenting cells, are treated with IFN-gamma plus HCMV. However, presentation of endogenously synthesized IE1 can be restored when U373 MG cells are transfected with CIITA prior to infection with HCMV. Altogether, the data indicate that the defect induced by HCMV resides in the activation of the IFN-gamma-responsive promoter of CIITA. This is the first demonstration of a viral inhibition of CIITA expression.

Characterization of an epitope of the human cytomegalovirus protein IE1 recognized by a CD4+ T cell clone

CD4+ T cells specific for human cytomegalovirus (HCMV) IE1 protein are potential effectors of the control of HCMV infection through cytokine production. Better knowledge of major histocompatibility complex (MHC)-peptide-T cell receptor (TcR) interactions in the CD4+ T cell response should result in a better design of immunizing peptides and is a prerequisite for the development of vaccines or anti-cytomegalovirus therapy. In this study, the recombinant protein comprising residues 86-491 encoded by exon 4 of IE1 (GST-e4) was cleaved by enzymatic digestion and analyzed by high pressure liquid chromatography-mass spectroscopy (HPLC-MS). We identified the 14-residue epitope 162-DKREMWMACIKELH-175 recognized by an HLA-DR8-restricted clone, BeA3. Synthetic elongated, truncated and di-Ala-substituted peptides of the 18-mer IE1 158-IVPEDKREMWMACIKELH-175 sequence were used to analyze the amino acid motifs involved in binding to HLA-DR8 and recognition by the BeA3 clone. Substitutions which abolished (MW --> AA), or decreased (RE --> AA and MA --> AA) T cell clone proliferation, cytokine production and cytotoxicity were identified. Loss of T cell function induced by the MW --> AA substitution was associated with poor HLA-DR8 binding. Decreased T cell function (RE --> AA and MA --> AA) was associated with good HLA-DR8 binding, which suggested that these motifs were involved in TcR binding. Other substitutions induced potentiation of the T cell clone response: the IV --> AA substitution induced stronger proliferation, but equivalent cytokine production, when compared with the reference peptide IE1 (158-175). CI --> AA substitution induced strong potentiation of HLA-DR8 binding, proliferation and interferon-gamma and interleukin-4 production, possibly due to the removal of negative effects of Cys, Ile, or both side chains. Cytotoxicity was not improved by any substitution. Our results show modulation of the CD4+ T cell response according to the peptide residues involved in the HLA-DR8-peptide-TcR interaction.

Anti-human cytomegalovirus activity of cytokines produced by CD4+ T-cell clones specifically activated by IE1 peptides in vitro

The control of latent cytomegalovirus (CMV) infections by the immune system is poorly understood. We have previously shown that CD4+ T cells specific for the human CMV major regulatory protein IE1 are frequent in latently infected healthy blood donors. In order to learn about the possible role of these cells, we have developed IE1-specific CD4+ T-cell clones and, in this study, analyzed their epitope specificity and function in vitro. We measured their cytokine production when stimulated with specific IE1 peptides or whole recombinant IE1 protein. Their cytokine profiles, as deduced from gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin-4 (IL-4) and IL-6 production, were of the Th0- and Th1-like phenotypes. Supernatants from IE1-specific clones producing IFN-gamma and TNF-alpha were shown to inhibit CMV replication in U373 MG cells. This effect was due, as found by using cytokine-specific neutralizing antibodies, mostly to IFN-gamma, which was secreted at higher levels than TNF-alpha. To better assess the anti-CMV activity of cytokines, recombinant IFN-gamma and TNF-alpha were used and shown to have a synergistic effect on the inhibition of CMV replication and protein expression. Thus, IE1-specific CD4+ T cells display in vitro anti-CMV activity through cytokine secretion and may play a role in the control of in vivo latent infections.

Combination of human cytomegalovirus recombinant immediate-early protein (IE1) with 80 nm cationic biovectors: protection from proteolysis and potentiation of presentation to CD4+ T-cell clones in vitro

We have shown in a previous study that the proliferative CD4+ T-cell response to the regulatory immediate-early protein IE1 was a major component of the overall anti viral response in human cytomegalovirus (HCMV) seropositive blood donors. This viral antigen may be valuable in subunit vaccine design, since anti IE1 CD4+ T cells might provide help for production of antibodies and cytotoxic T lymphocytes (CTL) responses, and could take part in the control of viral infection. Preliminary to the elaboration of future vaccine formulations, we developed immunogenic complexes resulting from the combination of a purified recombinant protein derived from the fusion of Escherichia coli glutathione-S-transferase (GST) and a large C-terminal fragment (e4) of IE1, with new 80 nm cationic synthetic particles called Biovectors. We have shown that the antigen GST-e4 was stably complexed to vectors and that, contrary to the soluble form, it was protected from proteolysis in cell culture medium. By confocal microscopy we observed that the synthetic vectors were internalized by lymphoblastoid B cells, providing a significant enhancement of antigen delivery in antigen presenting cells (APC). Indeed, we demonstrated that the previous combination of antigen with particles, significantly enhanced the proliferation of specific CD4+ T-cell clones directed against IE1 in vitro, when either HLA-matched isolated peripheral blood mononuclear cells or EBV transformed B cell lines were used as APC. The relevance of these observations to the use of these new vectors for vaccine design against HCMV is discussed.