Progress made towards the development of a CMV peptide vaccine

Profiling Human CMV-specific T cell responses reveals novel immunogenic ORFs

Despite the prevalence and medical significance of human cytomegalovirus (HCMV) infections, a systematic analysis of the targets of T cell recognition in humans that spans the entire genome and includes recently described potential novel ORFs is not available. Here, we screened a library of epitopes predicted to bind HLA class II that spans over 350 different HCMV ORFs and includes ∼150 previously described and ∼200 recently described potential novel ORFs using an ex vivo IFNγ fluorospot assay. We identified 235 unique HCMV specific epitopes derived from 100 ORFs, some previously described as immunodominant and others that were not previously described to be immunogenic. Of those, 41 belong to the set of recently reported novel ORFs, thus providing evidence that at least some of these are actually expressed in vivo in humans. These data reveal that the breadth of the human T cell response to HCMV is much greater than previously thought. The ORFs and epitopes identified will help elucidate how T cell immunity relates to HCMV pathogenesis and instruct ongoing HCMV vaccine research. Importance To understand the crucial role of adaptive immunity in controlling cytomegalovirus infection and disease, we systematically analyzed the CMV 'ORFeome' to identify new CMV epitopes targeted primarily by CD4 T cells in humans. Our study identified >200 new T cell epitopes derived from both canonical and novel ORFs, highlighting the substantial breadth of anti-CMV T cell response and providing new targets for vaccine design.

Battle between Host Immune Cellular Responses and HCMV Immune Evasion

Human cytomegalovirus (HCMV) is ubiquitously prevalent. HCMV infection is typically asymptomatic and controlled by the immune system in healthy individuals, yet HCMV can be severely pathogenic for the fetus during pregnancy and in immunocompromised persons, such as transplant recipients or HIV infected patients. HCMV has co-evolved with the hosts, developed strategies to hide from immune effector cells and to successfully survive in the human organism. One strategy for evading or delaying the immune response is maintenance of the viral genome to establish the phase of latency. Furthermore, HCMV immune evasion involves the downregulation of human leukocyte antigens (HLA)-Ia molecules to hide infected cells from T-cell recognition. HCMV expresses several proteins that are described for downregulation of the HLA class I pathway via various mechanisms. Here, we review the wide range of immune evasion mechanisms of HCMV. Understanding the mechanisms of HCMV immune evasion will contribute to the development of new customized therapeutic strategies against the virus.

Off-the-Shelf Virus-Specific T Cells to Treat BK Virus, Human Herpesvirus 6, Cytomegalovirus, Epstein-Barr Virus, and Adenovirus Infections After Allogeneic Hematopoietic Stem-Cell Transplantation

Purpose Improvement of cure rates for patients treated with allogeneic hematopoietic stem-cell transplantation (HSCT) will require efforts to decrease treatment-related mortality from severe viral infections. Adoptively transferred virus-specific T cells (VSTs) generated from eligible, third-party donors could provide broad antiviral protection to recipients of HSCT as an immediately available off-the-shelf product. Patient and Methods We generated a bank of VSTs that recognized five common viral pathogens: Epstein-Barr virus (EBV), adenovirus (AdV), cytomegalovirus (CMV), BK virus (BKV), and human herpesvirus 6 (HHV-6). The VSTs were administered to 38 patients with 45 infections in a phase II clinical trial. Results A single infusion produced a cumulative complete or partial response rate of 92% (95% CI, 78.1% to 98.3%) overall and the following rates by virus: 100% for BKV (n = 16), 94% for CMV (n = 17), 71% for AdV (n = 7), 100% for EBV (n = 2), and 67% for HHV-6 (n = 3). Clinical benefit was achieved in 31 patients treated for one infection and in seven patients treated for multiple coincident infections. Thirteen of 14 patients treated for BKV-associated hemorrhagic cystitis experienced complete resolution of gross hematuria by week 6. Infusions were safe, and only two occurrences of de novo graft-versus host disease (grade 1) were observed. VST tracking by epitope profiling revealed persistence of functional VSTs of third-party origin for up to 12 weeks. Conclusion The use of banked VSTs is a feasible, safe, and effective approach to treat severe and drug-refractory infections after HSCT, including infections from two viruses (BKV and HHV-6) that had never been targeted previously with an off-the-shelf product. Furthermore, the multispecificity of the VSTs ensures extensive antiviral coverage, which facilitates the treatment of patients with multiple infections.

Enhanced Induction of T Cell Immunity Using Dendritic Cells Pulsed with HIV Tat and HCMV-pp65 Fusion Protein In Vitro

Background

Cytotoxic T lymphocytes (CTLs) appear to play an important role in the control and prevention of human cytomegalovirus (HCMV) infection. The pp65 antigen is a structural protein, which has been defined as a potential target for effective immunity against HCMV infection. Incorporation of an 11 amino acid region of the HIV TAT protein transduction domain (Tat) into protein facilitates rapid, efficient entry into cells.

Methods

To establish a strategy for the generation of HCMV-specific CTLs in vitro, recombinant truncated N- and C-terminal pp65 protein (pp65 N&C) and N- and C-terminal pp65 protein fused with Tat (Tat/pp65 N&C) was produced in E.coli system. Peripheral blood mononuclear cells were stimulated with dendritic cells (DCs) pulsed with pp65 N&C or Tat/pp65 N&C protein and immune responses induced was examined using IFN-γ ELISPOT assay, cytotoxicity assay and tetramer staining.

Results

DCs pulsed with Tat/pp65N&C protein could induce higher T-cell responses in vitro compared with pp65N&C. Moreover, the DCs pulsed with Tat/pp65 N&C could stimulate both of CD8⁺ and CD4⁺ T-cell responses. The T cells induced by DCs pulsed with Tat/pp65 N&C showed higher cytotoxicity than that of pp65-pulsed DCs against autologous lymphoblastoid B-cell line (LCL) expressing the HCMV-pp65 antigen.

Conclusion

Our results suggest that DCs pulsed with Tat/pp65 N&C protein effectively induced pp65-specific CTL in vitro. Tat fusion recombinant protein may be useful for the development of adoptive T-cell immunotherapy and DC-based vaccines.

Hematopoietic stem cell transplantation

More than 25,000 hematopoietic stem cell transplantations (HSCTs) are performed each year for the treatment of lymphoma, leukemia, immune-deficiency illnesses, congenital metabolic defects, hemoglobinopathies, and myelodysplastic and myeloproliferative syndromes. Before transplantation, patients receive intensive myeloablative chemoradiotherapy followed by stem cell “rescue.” Autologous HSCT is performed using the patient’s own hematopoietic stem cells, which are harvested before transplantation and reinfused after myeloablation. Allogeneic HSCT uses human leukocyte antigen (HLA)-matched stem cells derived from a donor. Survival after allogeneic transplantation depends on donor–recipient matching, the graft-versus-host response, and the development of a graft versus leukemia effect. This article reviews the biology of stem cells, clinical efficacy of HSCT, transplantation procedures, and potential complications.

A HCMV pp65 polypeptide promotes the expansion of CD4+ and CD8+ T cells across a wide range of HLA specificities

Human cytomegalovirus (HCMV) can cause life-threatening disease in infected hosts. Immunization with human leukocyte antigen (HLA)-restricted immunodominant synthetic peptides and adoptive transfer of epitope-specific T cells have been envisaged to generate or boost HCMV-specific cellular immunity, thereby preventing HCMV infection or reactivation. However, induction or expansion of T cells effective against HCMV are limited by the need of utilizing peptides with defined HLA restrictions. We took advantage of a combination of seven predictive algorithms to identify immunogenic peptides of potential use in the prevention or treatment of HCMV infection or reactivation. Here we describe a pp65-derived peptide (pp65(340-355), RQYDPVAALFFFDIDL: RQY16-mer), characterized by peculiar features. First, RQY-16mer is able to stimulate HCMV pp65 specific responses in both CD4(+) and CD8(+) T cells, restricted by a wide range of HLA class I and II determinants. Second, RQY-16mer is able to induce an unusually wide range of effector functions in CD4(+) T cells, including proliferation, killing of autologous HCMV-infected target cells and cytokine production. Third, and most importantly, the RQY-16mer is able to stimulate CD4(+) and CD8(+) T-cell responses in pharmacologically immunosuppressed patients. These data suggest that a single reagent might qualify as synthetic immunogen for potentially large populations exposed to HCMV infection or reactivation.

The prevention and treatment of cytomegalovirus infection in haematopoietic stem cell transplantation

Allogeneic haematopoietic stem cell transplantation (HSCT) is an intensive medical treatment involving myeloablative chemo-radiotherapy followed by stem cell rescue using allogeneic haematopoietic stem cells harvested from HLA-matched donors, which is primarily used for the treatment of haematological malignancies. Cytomegalovirus (CMV) infection is one of the major causes of morbidity and death after HSCT. This focused research review highlights the advances made with research into CMV in the HSCT setting. It provides the reader with an overview of current CMV research into the prevention and management of CMV infection.

Using hydroxymethylphenoxy derivates with the SPOT technology to generate peptides with authentic C-termini

The SPOT technology can fulfill most requirements for highly parallel, multiple peptide synthesis of soluble peptides within the upper microgram range. Here, we report on an improved method using hydroxymethylphenoxyacetic acid (HMPA) for 19 amino acids and 4-(4-hydroxymethyl-3-methoxyphenoxy)-butyric acid (HMPB) for proline as acidic labile linkers in SPOT synthesis. Using this approach we could reduce side-chain reactions normally occurring during conventional alkaline peptide cleavage from cellulose membranes. All synthesis steps were adapted to fully-automated SPOT synthesis and therefore represent a time- and cost-saving procedure. Furthermore, the improved cleavage and washing steps resulted in peptides with authentic C-termini in a purity range of 60-95%. Our improved method is ideal for synthesizing many thousand different peptides subsequently used directly for different biological assays requiring authentic C-termini, such as CD8 T-cell epitope screening, vaccine immunization, or tumor imaging.

Antigenic properties of HCMV peptides displayed by filamentous bacteriophages vs. synthetic peptides

Several efforts have been invested in the identification of CTL and Th epitopes, as well as in the characterization of their immunodominance and MHC restriction, for the generation of a peptide-based HCMV vaccine. Small synthetic peptides are, however, poor antigens and carrier proteins are important for improving the efficacy of synthetic peptide vaccines. Recombinant bacteriophages appear as promising tools in the design of subunit vaccines. To investigate the antigenicity of peptides carried by recombinant bacteriophages we displayed different HCMV MHCII restricted peptides on the capsid of filamentous bacteriophage (fd) and found that hybrid bacteriophages are processed by human APC and activate HCMV-specific CD4 T-cells. Furthermore we constructed a reporter T-cell hybridoma expressing a chimeric TCR comprising murine alphabeta constant regions and human variable regions specific for the HLA-A2 restricted immunodominant NLV peptide of HCMV. Using the filamentous bacteriophage as an epitope carrier, we detected a more robust and long lasting response of the reporter T-cell hybridoma compared to peptide stimulation. Our results show a general enhancement of T-cell responses when antigenic peptides are carried by phages.

Cytomegalovirus infection after solid-organ transplantation, its risk factors, direct and indirect effects and prevention strategies

A humán populációban szélesen elterjedt cytomegalovírus által okozott infekció egyike a leggyakrabban előforduló szervátültetést követő virális eredetű fertőzéseknek, amely befolyásolja a transzplantált szerv és a beteg túlélését is. Leggyakrabban a súlyos tünetekkel járó fertőzés olyan transzplantáltaknál alakul ki, akik cytomegalovírus-szeronegatívak az átültetés idejében, és a szervet szeropozitív donortól kapják. A fertőzés előfordulását és súlyosságát egyéb rizikótényezők is befolyásolják: az immunszuppresszió intenzitása, a beültetett szerv típusa, a graftkilökődés és/vagy ennek kezelése, a donor és recipiens közötti „HLA-mismatch”, a recipiens egyes HLA-típusai, női nem stb. A már kialakult cytomegalovírus-infekciónak direkt (tünetek) és indirekt (szövetkárosító és immunmoduláló) hatásai vannak, mindkettő befolyásolja a beteg életminőségét és a további állapot alakulását. Ezért speciális kezelési sémákat és a megelőzésre irányuló intézkedéseket dolgoztak ki, amelyek segítségével a cytomegalovírus károsító hatása csökkenthető vagy elkerülhető. Számos preventív lehetőség közül a gyakorlatban két megelőzési stratégia alkalmazható hatékonyan: az univerzális profilaxis (részét képezi a szelektív profilaxis) és a preemptív terápia. A szerzők – saját és külföldi tapasztalatok alapján – összefoglalják a prevenciós lehetőségeket, összehasonlítják az alkalmazott protokollok előnyeit és hátrányait. Az Amerikai és Kanadai Transzplantációs Társaságok ajánlása alapján a legtöbb amerikai, de sok európai transzplantációs központban is a betegeket három csoportba sorolják: magas, közepes és alacsony rizikójú csoportok; a besorolásnak megfelelően választható a profilaxis. A magas rizikójú betegcsoportoknál (R–/D+ betegek és tüdőtranszplantáltak) nélkülözhetetlen az univerzális profilaxis. Azoknál a betegeknél, akik antilymphocyta-ellenanyagot (ATG, ALG vagy OKT3) kapnak, szükséges az ún. szelektív profilaxis alkalmazása. A közepes rizikójú betegcsoportoknál (R+/D+ vagy R+/D–) lehet választani az univerzális profilaxis és a preemptív terápia között a klinika adottságait figyelembe véve. A nagy forgalmú ambulanciákon, a szoros monitorozás nehézségei és a költséges laboratóriumi vizsgálatok miatt, továbbá a CMV-fertőzés indirekt hatásainak kiküszöbölése érdekében az ajánlások az univerzális profilaxis alkalmazását javasolják. Az alacsony rizikójú csoportban (R–/D–) vese-, máj-, hasnyálmirigy-, szívtranszplantáció esetén a megelőzés szükségességét a transzplantációs centrum dönti el.

The immunoinformatics of cancer immunotherapy

We review here the developments in the field of immunoinformatics and their present and potential applications to the immunotherapeutic treatment of cancer. Antigen presentation plays a central role in the immune response, and as a result in immunotherapeutic methods such as adoptive T-cell transfer and antitumor vaccination. We therefore extensively review the current technologies of antigen presentation prediction, including the next generation predictors, which combine proteasomal processing, transporter associated with antigen processing and major histocompatibility complex (MHC)-binding prediction. Minor histocompatibility antigens are also relevant targets for immunotherapy, and we review the current systems available, SNEP and SiPep. Here, antigen presentation plays a key role, but additional types of data are also incorporated, such as single nucleotide polymorphism data and tissue/cell-type expression data. Current systems are not capable of handling the concept of immunodominance, which is critical to immunotherapy, but efforts have been made to model general aspects of the immune system. Although tough challenges lie ahead, when measuring the field of immunoinformatics on its contributions thus far, one can expect fruitful developments in the future.

Vaccine strategies against human cytomegalovirus infection

Human cytomegalovirus (HCMV) disease is a major cause of morbidity and mortality in neonates and immunocompromised populations, such as transplant recipients and HIV-infected patients. The development of a vaccine to prevent HCMV infection or disease has been assigned the highest priority by the US Institute of Medicine. Although, after 30 years of intensive study, a clinically licensed vaccine is still not available, significant progress has been made in the field of HCMV vaccine development, along with greater understanding of HCMV immunology, molecular biology and pathology. In recent years, new vaccine strategies have been developed that have shown promising results in preclinical studies and are able to induce HCMV-specific immune responses in clinical studies, although efficacy data are not yet available. Here we review the history of HCMV vaccine development and the current strategies in the development of new HCMV vaccines. We propose that research should focus on the development of a vaccine to prevent or control HCMV-related disease rather than to prevent infection, and that discerning strategies should be used for targeting HCMV disease in different clinical settings.

Production of Monoclonal Antibodies Against Phosphoprotein 65 from Human Cytomegalovirus

Human cytomegalovirus (HCMV) has a very high infection rate in the normal population. Early diagnosis is of great value, especially in immunosuppressed individuals. HCMV phosphoprotein 65 (pp65) is the most widely used antigen for diagnosis. In this report, we prepared a monoclonal antibody against pp65, which could be used for both immunohistochemistry and Western blot diagnosis of HCMV infection.

Sorting and pooling strategy: A novel tool to map a virus proteome for CD8 T-cell epitopes

Human cytomegalovirus (CMV) is a major cause of morbidity in immunocompromised individuals. However, no efficient vaccine has been developed to date. Identification of T-cell target proteins and epitopes is crucial not only for developing a successful immunization strategy, but also for new approaches using adoptive transfer of antigen-specific T-cells. The CMV genome has more than 200 open reading frames potentially coding for as many proteins. Here, we describe a robust, fast, and simple SPOT synthesis strategy, which allowed us to micro-synthesize every possible CD8 T-cell epitope in the entire potential CMV proteome. So far, 9069 of these peptides have been tested in an ex vivo T-cell stimulation assay. As well as confirming a number of previously known epitopes, we identified several new ones.

Progress toward an elusive goal: current status of cytomegalovirus vaccines

Although infection with human cytomegalovirus (CMV) is ubiquitous and generally asymptomatic in most individuals, certain patient populations are at high risk for CMV-associated disease. These include HIV-infected individuals with AIDS, transplant patients, and newborn infants with congenital CMV infection. Immunity to CMV infection, both in the transplant setting and among women of childbearing age, plays a vital role in the control of CMV-induced injury and disease. Although immunity induced by CMV infection is not completely protective against reinfection, there is nevertheless a sound basis on which to believe that vaccination could help control CMV disease in high-risk patient populations. Evidence from several animal models of CMV infection indicates that a variety of vaccine strategies are capable of inducing immune responses sufficient to protect against CMV-associated illness following viral challenge. Vaccination has also proven effective in improving pregnancy outcomes following CMV challenge of pregnant guinea pigs, providing a 'proof-of-principle' relevant to human clinical trials of CMV vaccines. Although there are no licensed vaccines currently available for human CMV, progress toward this goal has been made, as evidenced by ongoing clinical trial testing of a number of immunization strategies. CMV vaccines currently in various stages of preclinical and clinical testing include: protein subunit vaccines; DNA vaccines; vectored vaccines using viral vectors, such as attenuated pox- and alphaviruses; peptide vaccines; and live attenuated vaccines. This review summarizes some of the obstacles that must be overcome in development of a CMV vaccine, and provides an overview of the current state of preclinical and clinical trial evaluation of vaccines for this important public health problem.

Self HSP60 peptide serves as an immunogenic carrier for a CTL epitope against persistence of murine cytomegalovirus in the salivary gland

Murine cytomegalovirus (MCMV) infection is associated with persistence of virus in the salivary glands, despite relatively rapid clearance of virus from the spleen. An effective immunization against MCMV should prevent such viral persistence. We previously reported that a peptide (p458) from the sequence of the 60 kDa heat shock protein (HSP60) molecule in a conjugate vaccine can provide T cell help for the induction of protecting antibody against bacterial capsular polysaccharides. We now report that the p458 peptide as a carrier peptide can also enhance the immunogenicity of a dominant CTL epitope of the MCMV pp89 antigen-89pep. We synthesized a linear combined peptide: chimeric p458-89pep. We immunized young BALB/c mice and challenged them with MCMV. We found that the p458-89pep chimeric peptide was more effective than the 89pep in inducing 89pep-specific IFN(gamma) secretion and specific CTL activity. Moreover, the p458-89pep chimeric peptide induced sustained IFN(gamma) secretion in the salivary gland specific to 89pep and only this immunization was associated with clearance of virus from the salivary gland. These results suggest that a peptide epitope of HSP60 may be advantageous as a T cell carrier peptide in the induction of specific T cell immunity against infectious agents.

Selection of CMV-specific CD8+ and CD4+ T cells by mini-EBV-transformed B cell lines

Efficient protocols to generate cytomegalovirus (CMV)-specific T cells are required for adoptive immunotherapy. Recombinant Epstein-Barr virus (EBV) vectors called mini-EBV can be used to establish permanent B cell lines in a single step, which present the CMV antigen pp65 in a constitutive manner. These B cell lines, coined pp65 mini-LCL, were successfully used to reactivate and expand CMV-specific cytotoxic T cells. Here we evaluate this pp65 mini-EBV system in closer detail, focusing on (1) the quantification of T cells with specific effector function and (2) the identification of CMV-specific CD4(+) helper T cells. The co-expansion of various functional CMV epitope specificities was demonstrated by IFN-gamma enzyme-linked immunospot assay (ELISPOT) assays and HLA-peptide tetramer staining. Single-cell cloning resulted in both CD4(+) and CD8(+) T cell clones, the majority of which was CMV specific. Thus, mini-LCL present the pp65 antigen on HLA class I and II, mobilizing both arms of the T cell response. Using a peptide library covering the pp65 sequence for further analysis of T cell clones, we identified new pp65 CD8(+) and CD4(+) T cell epitopes.

Long-term cytomegalovirus infection leads to significant changes in the composition of the CD8+ T-cell repertoire, which may be the basis for an imbalance in the cytokine production profile in elderly persons

In spite of the present belief that latent cytomegalovirus (CMV) infection drives CD8+ T-cell differentiation and induces premature immune senescence, no systematic studies have so far been performed to compare phenotypical and functional changes in the CD8+ T-cell repertoire in CMV-infected and noninfected persons of different age groups. In the present study, number, cytokine production, and growth potential of naive (CD45RA+ CD28+), memory (CD45RA- CD28+), and effector (CD45RA+ CD28- or CD45RA- CD28-) CD8+ T cells were analyzed in young, middle-aged, and elderly clinically healthy persons with a positive or negative CMV antibody serology. Numbers and functional properties of CMVpp65(495-503)-specific CD8+ T cells were also studied. We demonstrate that aging as well as CMV infection lead to a decrease in the size of the naive CD8+ T-cell pool but to an increase in the number of CD8+ effector T cells, which produce gamma interferon but lack substantial growth potential. The size of the CD8+ memory T-cell population, which grows well and produces interleukin-2 (IL-2) and IL-4, also increases with aging, but this increase is missing in CMV carriers. Life-long latent CMV infection seems thus to diminish the size of the naive and the early memory T-cell pool and to drive a Th1 polarization within the immune system. This can lead to a reduced diversity of CD8 responses and to chronic inflammatory processes which may be the basis of severe health problems in elderly persons.