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

Precision mouse models with expanded tropism for human pathogens

A major limitation of current humanized mouse models is that they primarily enable the analysis of human-specific pathogens that infect hematopoietic cells. However, most human pathogens target other cell types, including epithelial, endothelial and mesenchymal cells. Here, we show that implantation of human lung tissue, which contains up to 40 cell types, including nonhematopoietic cells, into immunodeficient mice (lung-only mice) resulted in the development of a highly vascularized lung implant. We demonstrate that emerging and clinically relevant human pathogens such as Middle East respiratory syndrome coronavirus, Zika virus, respiratory syncytial virus and cytomegalovirus replicate in vivo in these lung implants. When incorporated into bone marrow/liver/thymus humanized mice, lung implants are repopulated with autologous human hematopoietic cells. We show robust antigen-specific humoral and T-cell responses following cytomegalovirus infection that control virus replication. Lung-only mice and bone marrow/liver/thymus-lung humanized mice substantially increase the number of human pathogens that can be studied in vivo, facilitating the in vivo testing of therapeutics.

Implantation of lung tissue into humanized mice enables in vivo study of the human immune response to pathogens.

Naïve T cells are activated by autologous HCMV-infected endothelial cells through NKG2D and can control HCMV transmission in vitro

Apart from classical antigen-presenting cells (APCs) like dendritic cells and macrophages, there are semiprofessional APCs such as endothelial cells (ECs) and Langerhans' cells. Human cytomegalovirus (HCMV) infects a wide range of cell types including the ECs which are involved in the trafficking and homing of T cells. By investigating the interaction of naïve T cells obtained from HCMV-seronegative umbilical cord blood with autologous HCMV-infected human umbilical vein ECs (HUVECs), we could show that the activation of naïve T cells occurred after 1 day of peripheral blood mononuclear cell (PBMC) exposure to HCMV-infected HUVECs. The percentage of activated T cells increased over time and the activation of naïve T cells was not induced by either autologous uninfected HUVECs or by autologous HCMV-infected fibroblasts. The activation of T cells occurred also when purified T cells were co-cultured with HCMV-infected HUVECs. In addition, in most of the donors only CD8⁺ T cells were activated, when the purified T cells were exposed to HCMV-infected HUVECs. The activation of naïve T cells was inhibited when the NKG2D receptor was blocked on the surface of T cells and among the different NKG2D ligands, we identified two ligands (ULBP4 and MICA) on HCMV-infected HUVECs which might be the interaction partners of the NKG2D receptor. Using a functional cell culture assay, we could show that these activated naïve T cells specifically inhibited HCMV transmission. Altogether, we identified a novel specific activation mechanism of naïve T cells from the umbilical cord by HCMV-infected autologous HUVECs through interaction with NKG2D.

Human cytomegalovirus vaccination: progress and perspectives of recombinant gB

A vaccine for Human cytomegalovirus (HCMV) remains a high priority as complications following infection are observed in immunocompromised individuals and in congenitally infected neonates. Numerous preclinical and clinical studies have investigated vaccine strategies ranging from live attenuated preparations, nucleic acid-based approaches and recombinant delivery systems to subunit vaccines. These have defined the importance of both cell-mediated and humoral immunity to viral gB in the control of HCMV infection. This review will cover clinical trials investigating vaccine approaches that have incorporated gB and discuss the future perspectives of the recombinant gB subunit vaccine for HCMV.

Targeting cytomegalovirus-infected cells using T cells armed with anti-CD3 × anti-CMV bispecific antibody

Human cytomegalovirus (CMV) reactivation and infection can lead to poor outcomes after allogeneic stem cell transplantation. We hypothesized that anti-CD3 activated T cells (ATCs) armed with chemically heteroconjugated anti-CD3 × polyclonal anti-CMV bispecific antibody (CMVBi) will target and eliminate CMV-infected cells. Arming doses of CMVBi as low as 0.01 ng/10(6) ATCs was able to mediate specific cytotoxicity (SC) directed at CMV-infected target cells significant above unarmed ATCs at mutiplicities of infection (MOI) between 0.01 and 1. At effector-to-target ratios (E:T) of 25:1, 12.5:1, 6.25:1, and 3.125:1, armed ATCs significantly enhanced killing of CMV-infected targets compared with unarmed ATCs. At an MOI of 1.0, the mean % SC directed at CMV-infected targets cells for CMVBi-armed ATCs at E:T of 3.12, 6.25, and 12.5 were 79%, 81%, and 82%, respectively; whereas the mean % SC for unarmed ATCs at the same E:T were all <20%. ATCs, Cytogam(®), or CMVBi alone did not lyse uninfected or CMV-infected targets. Co-cultures of CMVBi-armed ATCs with CMV-infected targets induced cytokine and chemokine release from armed ATCs. This nonmajor histocompatibility complex restricted strategy for targeting CMV could be used to prevent or treat CMV infections after allogeneic stem cell transplantation or organ transplantation.

Heat shock protein 70/peptide complexes: potent mediators for the generation of antiviral T cells particularly with regard to low precursor frequencies

Background

Heat shock protein 70 (HSP70) has gained major attention as an adjuvant capable of inducing antigen-specific CD8⁺ and CD4⁺ T-cell responses. The ability of HSP70/peptide complexes to elicit cytotoxic T-cell (CTL) responses by cross-presentation of exogenous antigens via HLA class I molecules is of central interest in immunotherapy. We examined the role of HSP70/CMVpp65_495-503-peptide complex (HSP70/CMV-PC) in HLA class I-restricted cross-presentation for ex vivo expansion of CMV-specific CTLs.

Methods

CMV-specific T cells generated from PBMCs of HLA-A*02:01/CMV-seropositive donors were stimulated for 21 days with HSP70/CMV-PC and analyzed in functional assays. As a control PBMCs were cultured in the presence of CMVpp65_495-503 peptide or HSP70. Increase of CMV-specific CTLs was visualized by pentameric HLA-A*02:01/CMVpp65_495-503 complex.

Results

About 90% of HSP70/CMV-PC generated T cells were CMV-specific and exhibited significantly higher IFN-γ secretion, cytotoxic activity, and an increased heme oxygenase 1 (HO-1) gene expression as compared to about 69% of those stimulated with CMVpp65_495-503 peptide. We decided to classify the HLA-A*02:01/CMV-seropositive donors as weak, medium, and strong responder according to the frequency of generated A2/CMV-pentamer-positive CD8⁺ T cells. HSP70/CMV-PC significantly induces strong antiviral T-cell responses especially in those donors with low memory precursor frequencies. Blockage of CD91 with α2-macroglobulin markedly reduced proliferation of antiviral T cells suggesting a major role of this receptor in the uptake of HSP70/CMV-PC.

Conclusion

This study clearly demonstrates that HSP70/CMV-PC is a potent mediator to induce stronger T-cell responses compared to antiviral peptides. This simple and efficient technique may help to generate significant quantities of antiviral CTLs by cross-presentation. Thus, we propose HSP70 for chaperoning peptides to reach an efficient level of cross-presentation. HSP70/peptide complexes may be particularly useful to generate stronger T-cell responses in cases of low precursor frequencies and may help to improve the efficiency of antigen-specific T-cell therapy for minor antigens.

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.

Cross-presentation of HCMV chimeric protein enables generation and measurement of polyclonal T cells

CD8(+) T cell immunity has a critical function in controlling human cytomegalovirus (HCMV) infection. In immunocompromized individuals, HCMV reactivation or disease can lead to increased morbidity and mortality, particularly in transplant recipients. In this setting, adoptive transfer of HCMV-specific CD8(+) T cells is a promising vaccine strategy to restore viral immunity, with most clinical approaches focussing on the use of peptides for the generation of single epitope-specific CD8(+) T cells. We show that using an IE1-pp65 chimeric protein as the antigen source promotes effective cross-presentation, by monocyte-derived dendritic cells (MoDCs), to generate polyclonal CD8(+) T cell epitopes. By exploring human leukocyte antigen (HLA)-restricted immunodominance hierarchies both within and across two immunodominant proteins, we show that HLA-B7 epitopes elicit higher CD8(+) T cell responses compared with HLA-A1, -A2 or -B8. This study provides important evidence highlighting both the efficacy of the IE1-pp65 chimeric protein and the importance of immunodominance in designing future therapeutic vaccines.

Protective CD8+ T-cell responses to cytomegalovirus driven by rAAV/GFP/IE1 loading of dendritic cells

Background

Recent studies demonstrate that recombinant adeno-associated virus (rAAV)-based antigen loading of dendritic cells (DCs) generates in vitro, significant and rapid cytotoxic T-lymphocyte (CTL) responses against viral antigens.

Methods

We used the rAAV system to induce specific CTLs against CVM antigens for the development of cytomegalovirus HCMV) gene therapy. As an extension of the versatility of the rAAV system, we incorporated immediate-early 1 (IE1), expressed in HCMV. Our rAAV vector induced a strong stimulation of CTLs directed against the HCMV antigen IE1. We then investigated the efficiency of the CTLs in killing IE1 targeted cells.

Results

A significant MHC Class I-restricted, anti-IE1-specific CTL killing was demonstrated against IE1 positive peripheral blood mononuclear cells (PBMC) after one, in vitro, stimulation.

Conclusion

In summary, single PBMC stimulation with rAAV/IE1 pulsed DCs induces strong antigen specific-CTL generation. CTLs were capable to lyse low doses of peptides pulsed into target cells. These data suggest that AAV-based antigen loading of DCs is highly effective for generating human CTL responses against HCMV antigens.

Refinement in the production and purification of recombinant HCMV IE1-pp65 protein for the generation of epitope-specific T cell immunity

Human cytomegalovirus (HCMV) remains one of the most common opportunistic infections causing disease following stem cell transplantation, despite the availability of anti-viral therapies. Adoptive immunotherapy has the potential to further aid in counteracting chronic viral reactivation and subsequent disease by restoring viral immunity through the transfer of virus-specific T cells from transplant donors to their recipients. Our study refines the production and purification of a recombinant HCMV protein containing two of the most immunodominant antigens (IE1 and pp65) for the generation of polyclonal HCMV-specific T cells. In doing so, a 6x His-tagged IE1-pp65 protein was generated using a serum-free baculovirus/insect cell expression system and soluble IE1-pp65 protein was subsequently purified using Ni-NTA affinity chromatography under stringent conditions to obtain a highly pure product. The ability of the recombinant IE1-pp65 protein to elicit a functional T cell mediated immune response was demonstrated by the vigorous reactivation and expansion of HLA-A2-restricted pp65(495-503)-specific CD8+ T cells. This recombinant IE1-pp65 protein can potentially generate a multitude of HLA-restricted HCMV-specific T cells, providing a better alternative to using costly overlapping peptides or HCMV lysates for expansion of T cells for use in adoptive immunotherapy strategies.

Exogenous introduction of an immunodominant peptide from the non-structural IE1 protein of human cytomegalovirus into the MHC class I presentation pathway by recombinant dense bodies

Exogenous introduction of particle-associated proteins of human cytomegalovirus (HCMV) into the major histocompatibility complex (MHC) class I presentation pathway by subviral dense bodies (DB) is an effective way to sensitize cells against CD8 T-cell (CTL) recognition and killing. Consequently, these particles have been proposed as a platform for vaccine development. We have developed a strategy to refine the antigenic composition of DB. For proof of principle, an HCMV recombinant (RV-VM3) was generated that encoded the immunodominant CTL determinant IE1TMY from the IE1 protein in fusion with the major constituent of DB, the tegument protein pp65. To generate RV-VM3, a bacterial artificial chromosome containing the HCMV genome was modified by applying positive/negative selection based on the expression of the bacterial galactokinase in conjunction with lambda Red-mediated homologous recombination. This method allowed the efficient and seamless insertion of the DNA sequence encoding IE1TMY in frame into the pp65 open reading frame (UL83) of the viral genome. RV-VM3 expressed its fusion protein to high levels. The fusion protein was packaged into DB and into virions. Its delivery into fibroblasts by these viral particles led to the loading of the MHC class I presentation pathway with IE1TMY and to efficient killing by specific CTLs. This demonstrated that a heterologous peptide, not naturally present in HCMV particles, can be processed from a recombinant, DB-derived protein to be subsequently presented by MHC class I. The results presented here provide a rationale for the optimization of a vaccine based on recombinant DB.

Dendritic cell-induced apoptosis of human cytomegalovirus-infected fibroblasts promotes cross-presentation of pp65 to CD8+ T cells

An efficient host response to human cytomegalovirus (HCMV) infection may depend on rapid sensing of the infection by the innate immune response prior to deployment of viral immunosubversive functions. Control of HCMV dissemination could be ensured by apoptosis of cells immediately following infection. In the present report, it is demonstrated that changes in the ratio of c-FLIP to FLICE contributed to early sensitivity of HCMV-infected MRC5 fibroblasts to tumour necrosis factor alpha (TNF-alpha), providing an innate response to infection. Dendritic cells (DCs) co-cultured with HCMV-infected MRC5 cells acquired the ability to secrete TNF-alpha in an amount sufficient to kill infected fibroblasts. Blockage of TNF-alpha binding to its receptor on MRC5 cells with soluble TNF-R reduced the number of dead, HCMV-infected fibroblasts ingested by DCs, thus highlighting the impact of the apoptotic state of infected cells for efficient loading of DCs. Those DCs loaded with antigens available early in infection, such as input virion-associated pp65, could then engage antigen processing for cross-presentation to specific CD8(+) T cells. Cross-presentation was impaired when MRC5 cells were treated with the pan-caspase inhibitor ZVAD before co-culture with DCs. Altogether, our data suggest that the innate killing capacity of DCs at the early stage of infection plays a role in the activation of anti-HCMV CD8(+) T cells.

Activities of Z-ajoene against tumour and viral spreading in vitro

Z-ajoene is a garlic-derived compound with known anti-tumour properties. This report argues in favour of pro-apoptotic and cell cycle blockage activities of Z-ajoene on various cell lines involving activation of the p53-family gene products, p53, p63 and p73, at indicated doses. According to its known anti-proteasome activity, Z-ajoene induced a downregulation of MHC-class I expression at the surface of treated cells but did not impair their recognition by CD8+ T cells. We further demonstrated a new activity of Z-ajoene against human cytomegalovirus spreading in vitro that was mediated by an increased number of apoptotic cells after infection. Altogether our data point at the ubiquitous efficiency of Z-ajoene as a new compound to fight against cancers of various origins including those that put up viruses.

In vitro expansion of polyclonal T-cell subsets for adoptive immunotherapy by recombinant modified vaccinia Ankara

OBJECTIVE

Adoptive cellular therapy of cytomegalovirus (CMV)-specific T cells in allogeneic hematopoietic stem cell transplantation (HSCT) patients is a promising approach for controlling CMV viremia and its morbidity. We sought to develop a clinically suitable strategy to dually expand infusible CD8(+) and CD4(+) T-cell subsets specific for CMV.

METHODS

Polyclonal CMV T-cell lines were generated using peripheral blood mononuclear cell (PBMCs) treated with synthetic single-stranded CpG motif-containing oligodeoxynucleotides (ODNs) and infected with recombinant (r) modified vaccinia Ankara (MVA) expressing CMV antigens. Cultures derived from 12 healthy CMV-positive donors were analyzed using chromium release and lymphoproliferation assays, intracellular staining for interferon-gamma (IFN-gamma), and HLA tetramers.

RESULTS

A 3-day incubation with a combination of ODN 2006 and 2216 was found to reproducibly generate a highly rMVA infectable population of PBMCs with concomitant high expression of CMV antigens. CpG ODN-treated autologous PBMCs infected with rMVA elicited a 30-fold average expansion of both CMV-specific CD4(+) and CD8(+) T cells in 10 days. The enriched T-cell populations showed minimal alloreactivity, high levels of CMV-specific HLA class I tetramer binding, cytotoxic activity, and IFN-gamma production from both CD8(+) and CD4(+) T cells.

CONCLUSIONS

The ability to quickly produce autologous professional antigen-presenting cells, capable of stimulating clinically useful amounts of CMV-specific CD4(+) and CD8(+) T-cell lines, enhances the attractiveness of using rMVA for immunotherapeutic interventions to manage HSCT-related CMV disease.

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.

Vaccines for viral and parasitic diseases produced with baculovirus vectors

The baculovirus-insect cell expression system is an approved system for the production of viral antigens with vaccine potential for humans and animals and has been used for production of subunit vaccines against parasitic diseases as well. Many candidate subunit vaccines have been expressed in this system and immunization commonly led to protective immunity against pathogen challenge. The first vaccines produced in insect cells for animal use are now on the market. This chapter deals with the tailoring of the baculovirus-insect cell expression system for vaccine production in terms of expression levels, integrity and immunogenicity of recombinant proteins, and baculovirus genome stability. Various expression strategies are discussed including chimeric, virus-like particles, baculovirus display of foreign antigens on budded virions or in occlusion bodies, and specialized baculovirus vectors with mammalian promoters that express the antigen in the immunized individual. A historical overview shows the wide variety of viral (glyco)proteins that have successfully been expressed in this system for vaccine purposes. The potential of this expression system for antiparasite vaccines is illustrated. The combination of subunit vaccines and marker tests, both based on antigens expressed in insect cells, provides a powerful tool to combat disease and to monitor infectious agents.

In vitro induction of myeloid leukemia-specific CD4 and CD8 T cells by CD40 ligand-activated B cells gene modified to express primary granule proteins

The primary granule proteins (PGP) of myeloid cells are a source of multiple antigens with immunotherapeutic potential for myeloid leukemias. Therefore, we developed a method to induce T-cell responses to PGP protein sequences. We found that gene-transfected antigen-presenting cells efficiently expand functionally competent PGP-specific CD4 and CD8 T cells. The system was optimized using T-cell responses to autologous CD40-activated B cells (CD40-B) transfected with a cytomegalovirus pp65-encoding expression vector. To generate leukemia-specific T cells, expression vectors encoding the PGP proteinase 3 (PR3), human neutrophil elastase, and cathepsin-G were transfected into CD40-B cells to stimulate post-allogeneic stem cell transplantation T cells from five patients with myeloid and three with lymphoid leukemias. T-cell responses to PGP proteinase 3 and human neutrophil elastase were observed in CD8+ and CD4+ T cells only in patients with myeloid leukemias. T-cell responses against cathepsin-G occurred in both myeloid and lymphoblastic leukemias. T cells from a patient with chronic myelogenous leukemia (CML) and from a posttransplant CML patient, expanded against PGP, produced IFN-gamma or were cytotoxic to the patient's CML cells, demonstrating specific antileukemic efficacy. This study emphasizes the clinical potential of PGP for expansion and adoptive transfer of polyclonal leukemia antigen-specific T cells to treat leukemia.

Assessment of cellular immunity to human cytomegalovirus in recipients of allogeneic stem cell transplants

Effective reconstitution of cellular immunity following hematopoietic stem cell transplantation (HCT) is thought to be important for protection from the morbidity caused by cytomegalovirus (CMV) reactivation and disease. This review critically discusses current methods for assessment of CMV-specific cellular immune responses, with emphasis on flow cytometry-based methodologies such as MHC-I and MHC-II tetramer staining and intracellular cytokine assays. The advantages and weaknesses of these assays are considered in comparison to traditional immunologic techniques. Application of these newer methodologies has provided insight into the dynamics of the levels of CMV-specific CD4(+) and CD8(+) T-lymphocytes following HCT, and into the sources and diversity of these cells. Data from preliminary clinical studies suggest that CMV-specific CD8(+) T-lymphocyte levels greater than 1 x 10(7)/L of peripheral blood may correlate with protection from CMV disease. Studies on the functional phenotypes of CMV-specific CD8(+) T-lymphocytes such as cytokine production, degranulation, and cytotoxicity have indicated that these cells are heterogeneous with regard to these properties. Future research will focus on establishing whether any of these immunologic assays will serve as a correlate of protection and inform as to which patients are at high risk for CMV reactivation and disease. Identification of an informative assay may allow its incorporation into standard clinical practice for monitoring HCT patients.

Recognition of cmv pp65 protein antigen by human cd4 t-cell lines induced with an immunodominant peptide pool

Cellular immunity against cytomegalovirus (CMV) is essential for recovery from infection and control of viral latency. In immunocompromised hosts, this balance between CMV and cellular immunity is lost. Accordingly, restoration of the CD8 compartment specific for CMV is beneficial for immunocompromised patients. It is clear that CMV-specific CD4 cells provide helper functions facilitating long-term persistence of CD8 cells. Considering the dearth of data on CMV-specific T-helper cells, we investigated the CD4 responses to the immunodominant protein pp65 to define antigenic peptides. Such peptides were pooled and used to generate long-term T-cell lines. The lines were responsive to CMV and pp65. T cells were selected with individual peptides to produce monospecific lines for accurate definition of fine epitope specificity and to confirm human leukocyte antigen HLA-DR restriction. Furthermore, these lines lost alloreactivity, suggesting that they can be generated from the allodonor for adoptive immunoreconstitution of stem cell graft recipients.

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.

Attenuated poxviruses generate clinically relevant frequencies of CMV-specific T cells

Immunotherapeutic approaches to limit cytomegalovirus (CMV) morbidity and mortality after hematopoietic stem cell transplants (HSCTs) are currently under investigation as alternatives to antiviral drugs. In this context, we have inserted full-length and ubiquitin-modified CMV phosphoprotein 65 (pp65), phosphoprotein 150 (pp150), and immediate early protein 1 (IE1) immunodominant antigens into the virulent Western Reserve strain of vaccinia virus (VV) and the highly attenuated strain, modified vaccinia Ankara (MVA). Recombinant (r) VV or rMVA stimulated vigorous expansion of CMV-specific CD8+ T cells in CMV-positive donor peripheral blood mononuclear cells (PBMCs), which showed minimal alloreactivity and high levels of HLA tetramer binding, cytokine production, and cytotoxicity. Ubiquitinated antigens had a profound effect when expressed in VV. Single antigen rMVA expressing pp65 or IE1, either ubiquitin-modified or native, stimulated both cytotoxic T lymphocyte (CTL) populations to be expanded up to 500-fold in a 60-mL blood draw from the same donor. This result demonstrates the clinical feasibility of simultaneously amplifying multiple CMV-CTL populations. Transgenic HLA A2.1 (HHD II) mice, immunized with the same rMVA as used with human PBMCs, produced a robust cytotoxic response to both CMV pp65 and IE1. The specificity of the vigorous immunologic response to rMVA, both in vitro and in vivo, makes them candidates for clinical evaluation in the context of adoptive immunotherapy for hematopoietic stem cell transplant (HSCT) recipients or donor vaccination.

Identification and in vitro expansion of CD4+ and CD8+ T cells specific for human neutrophil elastase

Human neutrophil elastase (HNE) and proteinase 3 (PRO3) are myeloid tissue-restricted serine proteases, aberrantly expressed by myeloid leukemia cells. PRO3 and HNE share the PR1 peptide sequence that induces HLA-A*0201-restricted cytotoxic T cells (CTLs) with antileukemia reactivity. We studied the entire HNE protein for its ability to induce CTLs. In an 18-hour culture, HNE-loaded monocytes stimulated significant intracellular interferon gamma (IFN-gamma) production by CD4+ and CD8+ T cells in 12 of 20 and 8 of 20 healthy individuals, respectively. Lymphocytes from 2 HNE responders were pulsed weekly for 4 weeks to generate HNE-specific CTLs. One of 2 HLA-A*0201-negative individuals inhibited the colony formation of HLA-identical chronic myelogenous leukemia progenitor cells (73% inhibition at 50:1 effector-target [E/T] ratio), indicating that peptides other than PR1 can induce leukemia-reactive CTLs. Repetitive stimulations with HNE in 2 of 5 HLA-A*0201+ individuals increased PR1 tetramer-positive CD8+ T-cell frequencies from 0.1% to 0.29% and 0.02% to 0.55%, respectively. These CTLs recognized PR1 peptide or killed HNE-loaded targets. These results indicate that exogenously processed HNE is a source of PR1 peptide as well as other peptide sequences capable of inducing leukemia-specific CD8+ and CD4+ T cells. HNE could, therefore, be used in an HLA-unrestricted manner to induce leukemia-reactive CTLs for adoptive immunotherapy.

A novel MHCp binding prediction model

Many statistical and molecular mechanics models have been developed and tested for major histocompatibility complex peptide (MHCp) binding predictions during the last decade. The statistical model prediction using pooled peptide sequence data and three-dimensional modeling prediction by molecular mechanics calculations have been assessed for efficiency and human leukocyte antigen diversity coverage. We describe a novel predictive model using information gleaned from 29 human MHCp crystal structures. The validation for the new model is performed using four different sets of data: (1) MHCp crystal structures, (2) peptides with known IC(50) binding values, (3) peptides tested positive by tetramer staining, (4) peptides with known binding information at the MHCBN database. The model produces high prediction efficiencies (average 60 %) with good sensitivity (approximately 50%-73%) and specificity (52%-58%) values. The average positive predictive value of the model is 89%, while the average negative predictive value is only 18%. The efficiency is very high in predicting binders and very low in predicting nonbinders. This model is superior to many existing methods because of its potential application to any given MHC allele whose sequence is clearly defined.

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.

Induction of HLA-G-restricted human cytomegalovirus pp65 (UL83)-specific cytotoxic T lymphocytes in HLA-G transgenic mice

The non-classical major histocompatibility complex class I molecule HLA-G is expressed mainly by extravillous trophoblasts at the materno-foetal interface. HLA-G has been found to bind endogenously processed nonameric peptides but its function as a restriction element for a cytotoxic T cell response to viruses with tropism for trophoblastic cells has never been demonstrated. In this study, candidate viral peptides derived from human cytomegalovirus (HCMV) pp65 (UL83), which stabilized the HLA-G molecule on HLA-G-transfected T2 cells, were identified. The specific anti-pp65 cytotoxic T lymphocyte (CTL) response restricted by HLA-G in triple transgenic mice (HLA-G, human beta2m, human CD8alpha) was then investigated by injection of dendritic cells loaded with synthetic pp65-derived peptides or by infection with canarypox virus expressing pp65. Results showed that CTLs from HLA-G mice have the capacity to kill target cells either infected with recombinant vaccinia viruses expressing pp65 or loaded with specific pp65-derived peptides using HLA-G as an antigen-presenting molecule. It was also demonstrated that these HLA-G-restricted pp65-specific T cells are able to kill the human astrocytoma cell line U373, which was transfected with HLA-G and infected with HCMV. Moreover, using HLA-G tetramers refolded with a synthetic pp65-derived peptide, peptide-specific CD8(+) cells restricted by HLA-G have been detected in vivo. These findings provide the first evidence that HLA-G can select anti-HCMV-restricted CTLs in vivo, although the potency of this cytolytic response is limited (20-25 %). The weak HLA-G-restricted anti-HCMV response is probably due to HLA-G-mediated inhibitory signals on the development of an antiviral CTL response.

Diagnostic potential of tetramer-based monitoring of cytomegalovirus-specific CD8+ T lymphocytes in allogeneic stem cell transplantation

Cytomegalovirus (CMV) infection remains a significant problem in allogeneic stem cell transplant (SCT) recipients despite the availability of effective antiviral drugs. This problem concerns patients which are unable to mount an effective T-lymphocyte response against CMV. Therefore, the development and use of tetramer technology to enumerate CMV-specific T cells will be valuable to identify these patients as early as possible. Here, we review clinical studies in which CMV-specific CD8(+) T cells have been monitored in allogeneic SCT recipients using tetramers in the context of similar studies that are based on functional assays of CMV-specific T cells. The results thus far warrant the further development of tetramer technology as a diagnostic tool to monitor CMV-specific T cells in SCT recipients and other groups of immunocompromised patients threatened by CMV.

Cellular immunity to viral and fungal antigens after stem cell transplantation

Cellular immunity to viral and fungal antigens is often suppressed after stem cell transplantation. Viral infections, in particular infections with cytomegalovirus and Epstein-Barr virus, are often reactivated after allogeneic stem cell transplantation. Pathogenetic factors are immune deficiency and T-cell stimulation in the course of graft-versus-host reactions. Fungal infections are opportunistic infections derived with ubiquitous microorganisms. Immune deficiency, neutropenia, steroid treatment, and antibiotic treatment contribute to the pathogenesis. The study of viral and fungal immunity after allogeneic stem cell transplantation gives insight into the reconstitution of the immune system and tolerance.

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.

Clinical trials with CMV-specific T cells

BACKGROUND

Reactivation of latent CMV following allogeneic hematopoietic stem cell transplantation remains a major cause of morbidity despite improvements in surveillance protocols and antiviral drug therapies. Selective restoration of anti-CMV cellular immunity is an attractive alternative approach if it can be achieved in a non-toxic manner that can be widely utilized. The application of CMV-specific adoptive cellular therapies following the initial proof of principle provided almost a decade ago has been limited be a number of factors including the practical difficulties of exporting technically demanding and labor-intensive methodology to smaller transplant centers.

METHODS

We review the lessons learnt from studies in the setting of EBV-associated post transplant lymphoproliferative disease and the advances in both understanding and technology that have allowed the development of a multitude of new approaches for the generation of CMV-specific T cells suitable for adoptive transfer. These include the use of monoclytes, dendritic cells and B-lymphoblastoid cell lines as the presenting cells of antigen delivered by pulsing with exogenous proteins or peptides, or of antigen processed endogenously following transduction with one of a variety of viral vectors. We also discuss some of the issues surrounding the planning and implementation of trial protocols incorporating these products, and the techniques necessary for monitoring the fate of the infused cells and their efficacy. Finally, we review the preliminary data that is available on the newer generation of clinical trials that are ongoing in this field.

DISCUSSION

Extensive characterization of many different systems used to culture CMV-specific cells has now been performed. These suggest that it is now possible to generate T cells with specificity for a number of different CMV-specific target antigens (most commonly the lower matrix protein pp65). Clinical trials using these products within the current regulatory guidelines ares till in their infancy. However, preliminary results are beginning to suggest that the newer generation of CMV-specific T cell products can be administered with a relatively low risk of graft-versus-host disease, and that antiviral activity can be demonstrated following infusion.

Longitudinal analysis of the T-cell receptor (TCR)-VA and -VB repertoire in CD8+ T cells from individuals immunized with recombinant hepatitis B surface antigen

Recent studies have suggested that vaccination induces alterations in the T cell receptor (TCR) repertoire. We investigate the diversity of the TCR repertoire after immunization with a recombinant hepatitis B surface vaccine in seven healthy subjects in CD8+ T cells in peripheral blood lymphocytes. Cellular immune responses were monitored over time by sorting CD8 T cells followed by TCR-VA and -VB complementarity determining region 3 (CDR3) analysis. Frequency of individual VB families was determined by flow cytometry. TCR-VA/VB repertoires obtained from CD8+ T cells drawn after vaccination were compared to the TCR repertoire determined prior to vaccination. Monoclonal TCR transcripts could be detected exclusively in CD8+, but not in CD4+ T cells. Such monoclonal TCR transcripts were either stable in some individuals, or could only be detected at certain time points after vaccination. Sorting of monoclonal TCR-VB3+ T cells, which constituted up to 5% of the CD8+ T cell population from one individual, revealed that this T cell clone recognizes an epitope provided by the recombinant hepatitis B vaccine presented by MHC-class I on autologous antigen-presenting cells. Examination of the structural anatomy, defined by the TCR, and the frequency of T cells responding to the immunizing antigen may be helpful to provide surrogate markers to monitor cellular immune responses induced by protein antigens utilized for vaccination.

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.