A BCR-ABL Oncoprotein p210b2a2 Fusion Region Sequence Is Recognized by HLA-DR2a Restricted Cytotoxic T Lymphocytes and Presented by HLA-DR Matched Cells Transfected With an Iib2a2 Construct

Therapeutic Cancer Vaccines—Antigen Discovery and Adjuvant Delivery Platforms

For decades, vaccines have played a significant role in protecting public and personal health against infectious diseases and proved their great potential in battling cancers as well. This review focused on the current progress of therapeutic subunit vaccines for cancer immunotherapy. Antigens and adjuvants are key components of vaccine formulations. We summarized several classes of tumor antigens and bioinformatic approaches of identification of tumor neoantigens. Pattern recognition receptor (PRR)-targeting adjuvants and their targeted delivery platforms have been extensively discussed. In addition, we emphasized the interplay between multiple adjuvants and their combined delivery for cancer immunotherapy.

Immunology of chronic myeloid leukemia: current concepts and future goals

Although chronic myeloid leukemia is a rare malignancy, it has developed into a model system for the study of a variety of aspects of cancer biology and immunology. The introduction of tyrosine kinase inhibitors has resulted in a significant prolongation of the survival rates of chronic myeloid leukemia patients but has not resulted in a cure. There is a growing conviction that this aim can be achieved through immunotherapy. For this concept to be successful, a considerable increase in the present understanding of chronic myeloid leukemia immunology is required. The authors attempt to review and evaluate the current findings that demonstrate a number of immunological aberrations in patients prior to the start of any therapy and their normalization after achieving remission. They also discuss the recent clinical trials with experimental therapeutic vaccines and then present their own strategy on how to address the problem.

Development and immunological evaluation of HLA-specific chronic myeloid leukemia polyepitope vaccine in Chinese population

BACKGROUND

BCR/ABL and Wilms' tumor 1 (WT1) are an ideal tumor associated antigens which can be used to develop a potential chronic myeloid leukemia (CML) dentritic cell (DC) vaccine. Here, we constructed a novel polyepitope vaccine which used recombinant lentiviral vector carrying BCR/ABL and WT1 genes, and determined the immunological effects of this vaccine in vitro.

METHODS

The DC vaccine was constructed using lentiviral vector transduced DCs. T lymphocytes were stimulated with DC vaccine and then co-cultured in vitro with peripheral blood mononuclear cells (PBMCs) from CML or ALL patients, respectively. The cytotoxicity of proliferous cytotoxic T lymphocytes (CTLs) was determined by the LDH assay. The IFN-γ production of CTLs was detected using ELISPOT assay.

RESULTS

We constructed an lentiviral vector encoding 50 different epitopes from BCR/ABL and WT1 antigens, and transferred it into DCs to prepare the DC vaccine successfully. The in vivo stimulation of CTLs with this DC vaccine were proved to show strong cytotoxicity and produce high level of IFN-γ.

CONCLUSIONS

The novel recombinant lentiviral polyepitope DC vaccine is a promising candidate for clinical trials and may be an effective approach for CML immunotherapy.

Vaccination strategies in lymphomas and leukaemias: recent progress

The successful identification of a range of leukaemia-specific and lymphoma-specific antigens in recent years has stimulated efforts to develop therapeutic vaccination strategies. A number of clinical trials have established the safety and immunogenicity of vaccination against tumour antigens, although there are limited data on the clinical efficacy of this approach in haematological malignancies. After encouraging results of phase I/II trials using idiotype vaccines in lymphoma, the outcome of the three phase III trials has been somewhat disappointing. Several other promising strategies are currently being developed to improve these results, including optimization of antigen delivery. In myeloid leukaemias, clinical trials of vaccination with peptides derived from a number of leukaemia antigens, including WT1, PR1, RHAMM and BCR-ABL, have shown evidence of immunogenicity, but limited data are available on the clinical efficacy of this approach. In this review, we focus on the results of clinical trials of vaccination in leukaemia and lymphoma, and discuss potential strategies to enhance the efficacy of immunotherapy in the future.

Characterization of a monoclonal antibody specific for novel Bcr/Abl out-of-frame fusion proteins

The new tumor-specific antigens Bcr/Abl-OOF, identified in Philadelphia chromosome (Ph)-positive leukemia cells, are derived from an alternative splicing event involving BCR exons 1, 13, or 14 and ABL exons 4 and 5. The COOH-terminus of these transcription products contain an amino acid portion derived from an out-of-frame (OOF) reading of the ABL gene; these variants are expressed in Ph-positive chronic myelogenous leukemia (CML) and acute lymphocytic leukemia patients. Previously, we confirmed the presence of out-of-frame peptide-specific T cells in the peripheral blood of CML patients with the ability to lyse primary autologous CML cells. We also demonstrated that the out-of-frame Abl portion was immunogenic in HLA-A2.1 transgenic mice. Here we describe the production and characterization of monoclonal antibody 1D8G8, a new tool for localization and functional studies of the tumor antigen Bcr/Abl-OOF. This antibody recognizes the out-of-frame protein portion of the native full-length Bcr/Abl-OOF protein expressed in cells transiently transfected, as demonstrated by immunoprecipitation and immunofluorescence, and binds to a specific epitope of this antigen presented in association with HLA-A2.1 molecules at the surface of these cells, as demonstrated by flow cytometry. Thus this MAb could be useful to better understand how this new protein presents in Ph-positive cells beside the canonical Bcr/Abl fusion proteins.

The biological basis for immunotherapy in patients with chronic myelogenous leukemia

BACKGROUND

Chronic myelogenous leukemia (CML) has long been recognized as an entity responsive to immunotherapeutic interventions. Despite the success of the tyrosine kinase inhibitors (TKIs) in this disease, CML remains incurable. Only allogeneic bone marrow transplantation can provide long-term eradication of CML.

METHODS

This review summarizes the recent advances in the field of immunology in CML, specifically in tumor antigen discovery, that have been incorporated into the design of new clinical trials.

RESULTS

Multiple vaccine approaches are currently under clinical investigation. Recent laboratory and clinical data also point to a unique interaction of TKIs with the immune system.

CONCLUSIONS

A better understanding of these interactions combined with advances in the field of immunotherapy will likely lead to incorporation of TKIs in future therapeutic interventions to develop a cure for this disease.

Peptide vaccines for myeloid leukaemias

The development of cancer vaccines directed against myeloid leukaemias has been a research area of intense interest in the past decade. Both human studies in vitro and mouse models in vivo have demonstrated that leukaemia-associated antigens (LAAs), such as the fusion protein BCR-ABL, Wilms' tumour protein and proteinase 3, may serve as effective targets for cellular immunotherapy. Peptide-based vaccines are able to induce cytotoxic T-lymphocyte responses that kill leukaemia cells. Based on these results, pilot clinical trials have been initiated in chronic and acute myeloid leukaemia and other haematological malignancies, which include vaccination of patients with synthetic peptides derived from these LAAs. Results from these trials show that peptide vaccines are able to induce immune responses that are sometimes associated with clinical benefit. These early clinical results are promising and provide valuable information for future improvement of the vaccines. This chapter will focus mainly on discussing the preclinical studies of peptide vaccines in human systems, the results from clinical trials and the future prospects for vaccine therapy for myeloid leukaemia.

Leukemia-associated antigens are critical for the proliferation of acute myeloid leukemia cells

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. With intensive induction therapy, most patients younger than 60 years achieve complete remission. However, even if these younger patients were treated intensively, more than 50% will relapse. Clinical results of patients older than 60 years are more unfavorable. Therefore, in all patients with AML, the overall survival is still low. In the past decade, several leukemia-associated antigens (LAA) have been identified in patients with acute myeloid leukemia. BAGE, BCL-2, OFA-iLRP, FLT3-ITD, G250, hTERT, PRAME, proteinase 3, RHAMM, survivin, and WT-1 are all LAAs that have been shown to induce CD8+ T-cell recognition and for some antigens also humoral immune responses. Interestingly, most of these LAAs are linked to cell cycle or proliferation. This article discusses the balance between LAA-driven leukemia cell expansion and the elimination of these cells through attacks on LAAs by the immune system. Current knowledge of the function and CD8+ T-cell recognition of LAAs is reviewed and an outlook is given on how to improve T-cell responses to LAAs in acute myeloid leukemia cells.

PR1 vaccination in myeloid malignancies

The graft-versus-leukemia (GVL) effect following allogeneic stem cell transplantation is testament to the effectiveness of the immune system in recognizing and eliminating leukemia cells. The successful identification of a range of leukemia-associated antigens (LAAs) that drive the GVL response in recent years has stimulated research in the development of vaccines to treat hematological malignancies. Here, we review the current experience with the PR1 vaccine. PR1 is a nine amino acid, HLA-A(*)0201-restricted peptide, shared by two myeloid LAAs, proteinase (PR)3 and neutrophil elastase (NE). PR3 and NE are found in the primary (azurophil) granule proteins of normal granulocytes and are overexpressed in myeloid leukemia cells. PR1 induces powerful HLA-A(*)0201-restricted CD8+ T-cell responses that selectively kill myeloid leukemia cells in vitro. The detection of low frequencies of PR1-specific CD8+ T cells in patients with chronic myeloid leukemia and at higher frequencies in patients entering molecular remission after allogeneic stem cell transplantation supports the concept that there is natural immunity to PR1, which can be boosted further by vaccination to enhance immunity to leukemia. Preliminary reports indicate that PR1 peptide vaccination induces significant increases in PR1-specific CD8+ T cells, with rapid and durable remissions in some patients with myeloid leukemia. These promising early results point the way to optimizing the administration of peptide vaccines to improve the treatment of otherwise refractory myeloid leukemias.

Characterizing and optimizing immune responses to leukaemia antigens after allogeneic stem cell transplantation

Allogeneic stem cell transplantation remains a curative treatment for haematological malignancies resistant to other treatment approaches through the unique graft-versus-leukaemia effect (GvL). However, the lack of specificity of this response results in the targeting of normal tissue, and the morbidity and mortality associated with graft-versus-host disease (GvHD). Further improvements in exploiting the GvL effect to prevent relapse in high-risk leukaemias while minimizing toxicity have focused on the use of targeted anti-leukaemic immunotherapy. These strategies include the use of vaccines against minor histocompatibility antigens (HA-1, HA-2 and H-Y) and leukaemia-specific antigens (proteinase 3, Wilms' tumour 1 and BCR-ABL), and the adoptive transfer of leukaemia-specific T cells. The unique post-transplant milieu, which is characterized by lymphopenia, regulatory T-cell depletion and the release of growth factors, offers the opportunity to promote the expansion of engrafted T cells and enhance the specific GvL response. Techniques to reduce regulatory T-cell control over T-cell responses to leukaemia antigens could further enhance GvL reactivity. Finally, these approaches to increase GvL effects would be facilitated by transplant approaches to deplete GvHD alloresponses selectively while preserving GvL reactivity.

Review of current knowledge on HPV vaccination: an appendix to the European Guidelines for Quality Assurance in Cervical Cancer Screening

The recognition of a strong etiological relationship between infection with high-risk human papillomavirusses and cervical cancer has prompted research to develop and evaluate prophylactic and therapeutic vaccines. One prophylactic quadrivalent vaccine using L1 virus-like particles (VLP) of HPV 6, 11, 16 and 18 is available on the European market since the end of 2006 and it is expected that a second bivalent vaccine containing VLPs of HPV16 and HPV18 will become available in 2007. Each year, HPV16 and HPV18 cause approximately 43,000 cases of cervical cancer in the European continent. Results from the phase-IIb and III trials published thus far indicate that the L1 VLP HPV vaccine is safe and well-tolerated. It offers HPV-naive women a very high level of protection against HPV persistent infection and cervical intra-epithelial lesions associated with the types included in the vaccine. HPV vaccination should be offered to girls before onset of sexual activity. While prophylactic vaccination is likely to provide important future health gains, cervical screening will need to be continued for the whole generation of women that is already infected with the HPV types included in the vaccine. Phase IV studies are needed to demonstrate protection against cervical cancer and to verify duration of protection, occurrence of replacement by non-vaccine types and to define future policies for screening of vaccinated cohorts. The European Guidelines on Quality Assurance for Cervical Cancer Screening provides guidance for secondary prevention by detection and management of precursors lesions of the cervix. The purpose of the appendix on vaccination is to present current knowledge. Developing guidelines for future use of HPV vaccines in Europe, is the object of a new grant offered by the European Commission.

Emerging drugs in chronic myelogenous leukaemia

Chronic myelogenous leukaemia (CML) is characterised by a t(9;22)(q34;q11) translocation, which produces a fusion BCR-ABL protein with constitutive tyrosine kinase activity that is central to the pathogenesis of CML representing an ideal target for therapeutic intervention. Targeting BCR-ABL by imatinib has revolutionised the clinical course of CML. All patients in early chronic phase treated with imatinib achieve a complete haematological response, with 80-90% achieving a complete cytogenetic response. However, BCR-ABL transcripts remain detectable in the great majority of them, and approximately 16% chronic phase CML patients are resistant to or relapse after imatinib treatment, mainly through pre-existing or acquired point mutations in the binding pocket. Thus, other targeted approaches are being developed to overcome imatinib resistance. These include two novel tyrosine kinase inhibitors (nilotinib and dasatinib) that are producing clinical responses in different clinical settings, while other similar compounds are under evaluation in preclinical studies. Furthermore, additive immunotherapeutic strategies are emerging to synergise with imatinib in the elimination of molecular residual disease. This paper reviews the current details regarding these approaches and their developments.

A listing of human tumor antigens recognized by T cells: March 2004 update

The technological advances occurred in the last few years have led to a great increase in the number of tumor associated antigens (TAA) that are currently available for clinical applications. In this review we provide a comprehensive list of human tumor antigens as reported in the literature updated at February 2004. The list includes all T cell-defined epitopes, while excluding analogs or artificially modified epitopes, as well as virus-encoded and antibodies-recognized antigens. TAAs are listed in alphabetical order along with the epitope sequence and the HLA allele which restricts recognition by T cells. Data on the tissue distribution of each antigen are also provided together with an extensive bibliography that allows a rapid search for any additional information may be needed on each single antigen or epitope. Overall, the updated list is a database tool for clinicians, scientists and students who have an interest in the field of tumor immunology and immunotherapy.

Association of HLA Class I and Class II genes with bcr-abl transcripts in leukemia patients with t(9;22) (q34;q11)

Background

Based on the site of breakpoint in t(9;22) (q34;q11), bcr-abl fusion in leukemia patients is associated with different types of transcript proteins. In this study we have seen the association of HLA genes with different types of bcr-abl transcripts. The association could predict the bcr-abl peptide presentation by particular HLA molecules.

Methods

The study included a total of 189 patients of mixed ethnicity with chronic myelogenous leukemia and acute lymphocytic leukemia who were being considered for bone marrow transplantation. Typing of bcr-abl transcripts was done by reverse transcriptase PCR method. HLA typing was performed by molecular methods. The bcr-abl and HLA association was studied by calculating the relative risks and chi-square test.

Results

Significant negative associations (p < 0.05) were observed with HLA-A*02 (b2a2, e1a2), -A*68 (b2a2, b3a2, e1a2), -B*14 (b2a2, b3a2, e1a2), -B*15 (b2a2, b3a2), -B*40 (b2a2), -DQB1*0303 (b2a2, b3a2), -DQB1*0603 (b2a2), -DRB1*0401 (e1a2), -DRB1*0701 (b3a2), and -DRB1*1101 (b2a2).

Conclusions

The negative associations of a particular bcr-abl transcript with specific HLA alleles suggests that these alleles play a critical role in presenting peptides derived from the chimeric proteins and eliciting a successful T-cell cytotoxic response. Knowledge of differential associations between HLA phenotypes and bcr-abl fusion transcript types would help in developing better strategies for immunization with the bcr-abl peptides against t(9;22) (q34;q11)-positive leukemia.

Identification of new MHC-restriction elements for presentation of the p210(BCR-ABL) fusion region to human cytotoxic T lymphocytes

Chronic myelogenous leukemia (CML) is characterized by a t(9;22) translocation resulting in expression of BCR-ABL fusion oncoproteins which are unique to the leukemic cells, necessary for oncogenesis, and potentially immunogenic. We have previously shown that human dendritic cells transduced with an adeno-associated virus vector encoding the fusion region of the b3a2 splice variant (p210(b3a2)) of the BCR-ABL oncoprotein elicit specific T-cell responses in vitro. Two cytotoxic T lymphocyte (CTL) clones generated in this fashion displayed restriction with previously unreported HLA alleles. The first, T1/B9, was CD4(+) and restricted by DRB5*0101 (autologous) or DRB1*1101 (allogeneic). The minimum cytotoxic epitope (MCE) binding to DRB5*0101 for this clone was identified as FKQSSKALQ, overlapping the p210(b3a2) fusion point (boldface). The MCE of DRB1*1101 for this clone differed from DRB5*0101, but also included the fusion point. The clonality of CTL T1/B9 was verified by analyses of TCRalpha/beta chain usage and DNA sequence analyses. To our knowledge, this is the first description of a single clone recognizing both DRB5*0101 and DRB1*1101. The other CTL clone, T1/33, was CD8+ and recognized HLA-B*3501 or B*3503 complexed with an MCE, RPVASDFEP, derived from the c-abl sequence in proximity to the p210(b3a2) fusion point. K562 cells transfected with plasmids encoding HLA-DRA + B5*0101, B*3501, or B*3503 but not controls expressing DRA + DRB1*1501 were lysed by cognate CTL clones, confirming that DRB5*0101 and B*3501/3 could present p210(b3a2) joining region epitopes via endogenous processing. The identification of three additional HLA alleles (DRB5*0101, B*3501, and B*3503) presenting the p210(b3a2) fusion-region antigen will broaden the application of vaccine strategies for targeting CML cells. The findings of single CTL clones cross-recognizing autologous (DRB5*0101 or B*3501) and allogeneic (DRB1*1101 or B*3503) HLA alleles presenting BCR-ABL fusion-region epitopes implies the potential separation of graft-versus-leukemia from graft-versus-host effects.

A multivalent bcr-abl fusion peptide vaccination trial in patients with chronic myeloid leukemia

A tumor-specific, bcr-abl-derived fusion peptide vaccine can be safely administered to patients with chronic myelogenous leukemia (CML) and can elicit a bcr-abl peptide-specific T-cell immune response. In the present phase 2 trial, 14 patients with CML in chronic phase were vaccinated with 6 fusion peptides mixed with Quillaja saponaria (QS-21). No significant toxic effects were observed. In 14 of 14 patients, delayed-type hypersensitivity (DTH) and/or CD4 proliferative responses developed after beginning vaccinations, and 11 of 14 patients showed interferon-gamma (IFN-gamma) release by CD4 enzyme-linked immunospot (ELISPOT) at one or more time points. These responses were CD4(+)CD45RO(+). A peptide-specific CD8(+) interferon-gamma ELISPOT was found in 4 patients. Four patients in hematologic remission had a decrease in Philadelphia chromosome (Ph) percentage (3 concurrently receiving interferon-alpha and 1 on imatinib mesylate), and 3 patients in molecular relapse after allogenic transplantation became transiently polymerase chain reaction (PCR) negative after vaccination; 2 of these patients received concurrent donor lymphocyte infusion (DLI). All 5 patients on IFN-alpha ultimately reached a complete cytogenetic remission. In conclusion, a tumor-specific bcr-abl breakpoint peptide-derived vaccine can be safely administered and can reliably elicit measurable peptide-specific CD4 immune responses, including in patients after bone marrow transplantation, on interferon, or on imatinib mesylate. A relationship between the clinical responses and vaccination cannot be determined from this trial.

The abl/bcr gene product as a novel leukemia-specific antigen: peptides spanning the fusion region of abl/bcr can be recognized by both CD4+ and CD8+ T lymphocytes

Chronic myelogenous leukemia (CML) is characterized by a reciprocal translocation leading to the Philadelphia chromosome. Two fusion genes are created by this translocation: bcr/abl and abl/bcr. The fusion regions of both translocation products are unique and strictly limited to leukemia cells, giving rise to potential tumor-specific antigens. Although several studies on the immunogenicity of peptides spanning the bcr/abl fusion region have been reported, little is known about the corresponding reciprocal translocation product abl/bcr. Here we report that synthetic peptides representing the fusion region of the abl/bcr forms a1bb3 and a1bb4 can be specifically recognized by HLA-A2-restricted cytotoxic T lymphocytes from healthy donors. Furthermore, HLA-matched a1bb3-expressing CML cells can be recognized by a1bb3-specific HLA-A2-restricted T cells, indicating natural processing and presentation of abl/bcr protein by leukemia cells. Moreover, a 19-mer peptide encompassing this class I-binding sequence also elicited a1bb3-specific class II-restricted T-cell responses. Thus, both class I- and class II-restricted T-cell responses can be stimulated in healthy donors by abl/bcr peptides in vitro. Because abl/bcr is expressed in the majority of CML patients, it may represent a highly leukemia-specific antigen with potential use in immunotherapy.

Leukemia-associated fusion proteins, dek-can and bcr-abl, represent immunogenic HLA-DR-restricted epitopes recognized by fusion peptide-specific CD4+ T lymphocytes

Although CD4(+) helper T lymphocytes have been demonstrated to play an important role in antitumor immune response, only a few epitopes of tumor-associated antigens recognized by HLA class II-restricted CD4(+) T lymphocytes have been identified. In the present study, we addressed the question of whether leukemia-associated fusion proteins are recognized by CD4(+) T lymphocytes. Immature dendritic cells (DCs) were loaded with necrotic or apoptotic leukemia cells with t(6;9) or t(9;22) and then cocultured with the dek-can fusion peptide-specific or the bcr-abl fusion peptide-specific CD4(+) T lymphocyte clone. The dek-can peptide-specific and bcr-abl peptide-specific CD4(+) T lymphocyte clones produced interferon-gamma (IFN-gamma) when they were cocultured with HLA-DR-matched but not with mismatched DCs which had been loaded with apoptotic as well as necrotic leukemia cells with t(6;9) and t(9;22), respectively. IFN-gamma production by CD4(+)T lymphocyte clones in response to stimulation with DCs loaded with leukemia cells was inhibited by the anti-HLA-DR monoclonal antibody. These data indicate that the acute myelogenous leukemia-associated fusion protein, dek-can, and chronic myelogenous leukemia-associated fusion protein, bcr-abl, are both processed and presented by DCs to the fusion peptide-specific CD4(+) T lymphocytes.

Donor-derived b2a2-specific T cells for immunotherapy of patients with chronic myeloid leukemia

The BCR-ABL fusion proteins, b2a2 and b3a2, are potential targets for a beneficial graft-versus-leukemia (GVL) effect after allogeneic stem cell transplantation for chronic myeloid leukemia (CML). This study demonstrates that CD4+ T cells specific to the b2a2 peptide can be generated from a normal allogeneic stem cell transplant donor after stimulation with monocyte-derived dendritic cells (Mo-DC) using culture conditions applicable to clinical use. Stimulation of donor T-cell enriched mononuclear cells (MNC) with b2a2-pulsed Mo-DC produced approximately 3 x 10(9) b2a2-specific CD4+ T cells. The CD4+ T cells were HLA-DR7 restricted. These results confirm that the generation of donor derived b2a2-specific T cells for clinical use is feasible and warrants clinical testing after stem cell transplantation.

Innovative cancer vaccine strategies based on the identification of tumour-associated antigens

The identification of tumour-associated antigens has opened up new approaches to cancer immunotherapy. While past research focused on CD8+ cytotoxic T-cell responses, accumulating evidence suggests that CD4+ T cells also play an important role in orchestrating the host immune response against cancer. In this article, we summarise new strategies for the identification of major histocompatibility complex (MHC) class II-associated tumour antigens and discuss the importance of engaging both CD4+ and CD8+ T cells in cancer immunotherapy. The cloning of MHC class I- or class II-associated antigens has made it possible to develop synthetic and recombinant cancer vaccines that express specific tumour antigens. There are three major types of synthetic and recombinant cancer vaccines: recombinant viral and bacterial vaccines; naked DNA or RNA vaccines; and recombinant protein and peptide vaccines. In this article, we also discuss a new generation of recombinant cancer vaccines, 'self-replicating' DNA and RNA vaccines. Studies on the mechanisms of 'self-replicating' nucleic acid vaccines revealed that the enhanced immunogenicity was not due to an enhanced antigen expression, suggesting that the quantitative difference may not be as important as the qualitative difference in antigen presentation. The presence of the RNA replicase in the 'self-replicating' nucleic acid vaccines mimics alphavirus infection, which triggers the innate antiviral pathways of the host cells. Studies on how viral and cellular modulators of the innate antiviral pathways affect vaccine function should provide molecular insights crucial to future vaccine design.

Generation of Fas-independent CD4+ cytotoxic T-cell clone specific for p190 minor bcr-abl fusion peptide

In the majority of Ph+ALL patients, p190 bcr-abl fusion protein is generated in the Philadelphia chromosome. The fusion protein may serve as a leukemia antigen because it is not expressed in normal cells and hardly in any other malignancy. From a healthy donor, we have established a p190 bcr-abl fusion peptide-specific CD4+ cytotoxic T-cell clone, activation of which depends on HLA-DRB1*1501. This T-cell clone has a strong cytotoxic activity against autologus MoDCs pulsed with e1a2 peptide and its cytotoxicity is not mediated by Fas/Fas ligand or perforin pathway. Success in establishment of the p190 bcr-abl fusion peptide-specific T-cell clone encourages us to develop a new approach to an effective immunotherapy for Ph+ALL.

T-cell therapy of leukemia

BACKGROUND

The demonstration that immune-mediated elimination of leukemia contributes to the success of allogeneic hematopoietic stem cell transplantation (HSCT) has renewed interest in the development of immune-based therapies that might be used to augment the antileukemic effect of HSCT or in patients who are not receiving HSCT.

METHODS

The authors reviewed studies that have analyzed the mechanisms that may be operative in T-cell recognition of leukemia after allogeneic HSCT, identified candidate target antigens for immunotherapy of leukemia in transplant and nontransplant patients, and evaluated expression of candidate antigens on leukemic progenitors.

RESULTS

A large number of potential targets for T-cell therapy or vaccination have now been identified in human leukemia. Studies to evaluate novel immune-based therapies are now being initiated.

CONCLUSIONS

The rapid pace of progress in cellular and molecular immunology has identified new opportunities for developing T-cell therapy or vaccination for leukemia. Obstacles must be addressed before these approaches can be applied broadly, but the promising results of preclinical studies suggest continued efforts in this area will result in the establishment of immunotherapy as a useful modality in clinical practice.

BCR-ABL as a target for novel therapeutic interventions

The BCR-ABL oncogene is the result of a reciprocal translocation between the long arms of chromosome 9 and 22 t(9; 22). There is good experimental evidence demonstrating that BCR-ABL is the single causative abnormality in chronic myeloid leukaemia (CML), making it a unique model for the development of molecular targets. In addition to CML, BCR-ABL transcripts can be found in a minority of acute lymphoblastic leukaemias and very rarely in acute myeloid leukaemia (AML). Elucidating the molecular mechanisms and downstream pathways of BCR-ABL has led to the design of several novel therapeutic approaches. In this review, molecular targeting of BCR-ABL will be discussed based on the inhibition of protein tyrosine kinase activity, antisense strategies and immunomodulation.

Hematopoietic system-specific antigens as targets for cellular immunotherapy of hematological malignancies

Allogeneic stem cell transplantation (SCT) is the treatment of choice for many hematological malignancies. Its curative graft-versus-leukemia (GvL) effect is mainly mediated by donor-derived alloreactive T cells. However, if the donor T cells are not selected for their reactivity against leukemic cells, the GvL effect is often associated with graft-versus-host disease (GvHD), a major complication of SCT. Here we summarize our current knowledge on leukemia-associated antigens and discuss strategies to apply minor and major histocompatibility antigens for cellular immunotherapy of hematological malignancies with a low risk of GvHD.

Expression of co-stimulatory and adhesion molecules and chemokine or apoptosis receptors on acute myeloid leukaemia: high CD40 and CD11a expression correlates with poor prognosis

The expression of adhesion and co-stimulatory molecules, and chemokine and death receptors such as tumour necrosis factor (TNF) and FAS on acute myeloid leukaemia (AML) may influence the biology of the disease and response to chemotherapy and immunotherapy. In this study, we analysed the expression of these molecules in 99 AML patients using monoclonal antibodies and flow cytometry, and correlated the expression with French-American-British (FAB) classification and survival. The following molecules were studied: the co-stimulatory molecules CD80, CD86 and CD40; the adhesion molecules CD11a-c, CD31, CD43, CD50, CD54, CD102, CD58 and CD62L; the chemokine receptor CXCR4; and the death receptors TNFR1 and TNFR2 and FAS. The expression of all molecules was significantly higher in the M4/M5 FAB subgroups except for CD80, CD43, CD54 and CD62L. The AML M3 subgroup had a significant lower expression of CD11a (P = 0.02) and CD11c (P = 0.03). Five-year survival was significantly shorter in cases of high CD40 expression [> 20% positive cells, relative risk (RR) 2.56, P = 0.02] or high CD11a expression (> 80% positive cells, RR 2.6, P = 0.03). This effect was most prominently present in the AML M4/M5 FAB subgroups. We conclude that the expression levels of adhesion and co-stimulatory molecules, CXCR4 and apoptosis-receptors are predominantly FAB subtype-related with high CD40 and CD11a expression as poor prognostic factors.

BCR-ABL fusion peptides and cytotoxic T cells in chronic myeloid leukaemia

The BCR-ABL gene that arises in chronic myeloid leukaemia (CML) is a neoantigen. Peptides derived from the BCR-ABL fusion junction may therefore be immunogenic, if appropriately presented to the immune system. This article reviews data demonstrating that certain junctional peptides will bind to HLA molecules, and that these peptides will elicit specific T-lymphocyte responses in vitro, in both normal subjects and in CML patients. The clinical relevance of these observations is discussed.

HLA class II-restricted antigen presentation of endogenous bcr-abl fusion protein by chronic myelogenous leukemia-derived dendritic cells to CD4(+) T lymphocytes

Bcr-abl fusion peptide-specific CD4+ T-lymphocyte clones have recently been shown to augment colony formation by chronic myelogenous leukemia (CML) cells in a bcr-abl type-specific and HLA class II-restricted manner without addition of exogenous antigen. These findings suggest that CML cells can naturally process and present endogenous bcr-abl fusion protein to CD4+ T lymphocytes in the context of HLA class II molecules. To verify this possibility, the ability of CML-derived dendritic cells (DCs) to present endogenous bcr-abl fusion protein to bcr-abl fusion peptide-specific CD4+ T-lymphocyte clones was investigated. The bcr-abl b3a2 peptide-specific and HLA-DRB1*0901-restricted CD4+ T-lymphocyte clones produced interferon-gamma in response to stimulation with monocyte-derived DCs from HLA-DRB1*0901+ patients with b3a2 type CML. In contrast, DCs from patients with HLA-DRB1*0901- or b2a2 type CML and those from healthy individuals did not exert stimulatory activity on bcr-abl-specific CD4+ T-lymphocyte clones. The response of CD4+ T-lymphocyte clones to CML-derived mature DCs was higher than that to immature DCs and was inhibited by anti-HLA-DR monoclonal antibody. These data suggest that CML-derived DCs can process and present endogenous bcr-abl fusion protein to CD4+ T lymphocytes.

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

A CD4+ T CELL CLONE SELECTED FROM A CML PATIENT AFTER DONOR LYMPHOCYTE INFUSION RECOGNIZES BCR-ABL BREAKPOINT PEPTIDES BUT NOT TUMOR CELLS1

BACKGROUND

In patients with chronic myelocytic leukemia (CML), the breakpoint cluster region and fusion between the BCR and the c-ABL genes (BCR-ABL) oncogen product is a potential tumor-specific antigen. Previous studies have shown that T cells specific for the junctional region peptides of the BCR-ABL oncoprotein can be detected in healthy individuals as well as in patients with CML in chronic phase. We assessed whether BCR-ABL- specific T cells could be found in a patient achieving a complete cytogenetic remission after CD4+ donor lymphocyte infusion.

METHODS

Using dendritic cells pulsed with BCR-ABL breakpoint peptides as antigen-presenting cells, we stimulated patient peripheral blood lymphocytes to isolate peptide-specific T cell clones present at the time of the cytogenetic response. T cell clones were isolated and the cellular specificity of these cells was examined.

RESULTS

A CD3+ CD4+ T cell clone (1F7) that recognizes overlapping p210 junctional peptides presented by HLA-DR molecules was identified and expanded in vitro. Clone 1F7 failed to recognize autologous tumor cells as well as dendritic cells derived from patient CML cells. Clone 1F7 did not inhibit the growth and differentiation of CML precursor cells in a standard colony formation assay. Finally, using a clone-specific probe, 1F7 cells could not be detected in patient peripheral blood at the time of the donor lymphocyte infusion response.

CONCLUSIONS

These results suggest that clone 1F7 was selected in vitro using highly potent peptide pulsed dendritic cells but was not representative of the anti-leukemia immune response in vivo. Based on these findings, CD4+ T cells with BCR-ABL specificity do not appear to be mediators of the anti-leukemia response in vivo after donor lymphocyte infusion.

Advances in immunotherapy of hematologic malignancies: cellular and humoral approaches

Monoclonal antibodies have become an important modality for cancer therapy. Genetically engineered chimeric and humanized antibodies have demonstrated activity against overt lymphoma and leukemia, as well as minimal residual disease. Radioimmunotherapy in both nonmyeloablative and myeloablative regimens has produced significant responses and also minimized radiation exposure to normal tissues. Targeted alpha-particle therapy offers the possibility of selective tumor cell kill. Antibody-drug conjugates have produced remissions in acute leukemia. Many proteins potentially act as leukemia or lymphoma-specific antigens for major histocompatibility complex-restricted T cell cytotoxicity. These include the idiotype proteins, breakpoint cluster region (bcr)-abl and other fusion oncoproteins, myeloid-specific differentiation antigens and minor histocompatibility antigens. Clinical trials exploiting the new understanding of the T cell immunology are underway.

BCR-ABL directed immunotherapy: a virtual reality?

Nearly ten years of research on the feasibility of specific immunotherapy targeting the junctional regions of BCR-ABL has considerably increased our knowledge of which MHC alleles might present BCR-ABL peptides, yet has failed to provide us with definite proof of appropriate processing of the hybrid oncoprotein into such antigenic peptides. This paper intends to provide an overview of the current state of affairs as well as to delineate limitations and future directions of this line of research.

CML vaccines as a paradigm of the specific immunotherapy of cancer

T cells are implicated in the effective control of chronic myeloid leukemia (CML). Recently, several clinical observations supported by laboratory data, indicate the presence of CML-specific T cells. Many proteins potentially act as leukemia-specific antigens for MHC-restricted cytotoxicity in CML. These include the bcr-abl fusion protein, myeloid-specific differentiation antigens and minor histocompatibility antigens. There is recent evidence to suggest that bcr-abl junctional peptides are capable of eliciting both CD4 and CD8 responses in normal healthy donors and in patients with CML. Moreover, T cell lines can be generated that react with autologous or HLA-matched fresh CML cells, suggesting that the bcr-abl fusion protein can be processed and expressed in the MHC cell surface molecules. Clinical trials exploiting the new understanding of the immunology of CML are underway.

Role of interferon-alpha and clonally expanded T cells in the immunotherapy of chronic myelogenous leukemia

Twenty five percent of patients in the chronic phase of chronic myelogenous leukemia (CML) are treated with interferon-alpha (IFN-alpha) to induce a cytogenic remission. In addition to its direct effects on leukemic cells, IFN-alpha has been shown to induce immunologic alterations, including upregulation of the expression of major histocompatibility (MHC) antigens in antigen-presenting cells (APCs), as well as augmentation of the activity of the lymphocytes against tumor cells. However, there has been little direct evidence supporting a causal interaction between cellular immunoreactivity and clinical responsiveness to IFN-alpha. We have shown that one approach to elucidate the immunological mechanisms by which IFN-alpha exerts its anti-CML activity is by analyzing therapy-induced modulation in T-cell receptor (TCR) Vbeta chain usage, using the reverse transcription-polymerase chain reaction (RT-PCR) followed by single-strand conformation (SSCP) analysis. This method is particularly attractive, since it provides an index of antigen-specific T cell expansion, but does not require the extraction and purification of the antigens involved in the T-cell response. T cell clones that express the Vbeta 10, 12, and 14 families predominate in the peripheral blood (PB) of CML patients. The enhanced expression of the Vbeta 9 and 20 families has been detected in IFN-alpha responsive patients but not patients who are poorly responsive to this agent. This suggests that expansion of T cells expressing these TCR Vbeta gene families may serve as a prognostic factors of the clinical responsiveness of CML patients to IFN-alpha. In addition, since T cell clones that express certain Vbeta families may react with a discrete set of antigenic peptides presented on the surface of malignant cells, a better understanding of the immunobiology of T cells in CML may allow for the design of increasing efficacious immune therapy for this disease.

Generation of HLA-DRB1*1501-restricted p190 minor bcr-abl (e1a2)-specific CD4+ T lymphocytes

A small population of cells in acute lymphoblastic leukaemia is characterized by a specific translocation of the c-abl oncogene on chromosome 9 to the break point cluster lesion (bcr) on chromosome 22, t(9; 22)(q34; q11) (e1a2). Theoretically, the junction-spanning sequences of oncogene fusion proteins might be ideal targets for immunotherapy because these are not present in normal cells. In this study, we show for the first time that in vitro immunization with a 17-mer e1a2 peptide representing the p190 minor bcr-abl fusion protein resulted in HLA-DRB1*1501-restricted peptide-specific proliferative CD4+ T lymphocytes, using peptide-pulsed monocyte-derived dendritic cells as the antigen-presenting cells.

Transfusion Medicine: New Clinical Applications of Cellular Immunotherapy

There is now clear clinical evidence that adoptive cellular immunotherapy can eradicate hematologic malignancy and cure otherwise lethal viral infections. With this knowledge comes the challenge of improving the effectiveness and safety of the approach and of simplifying the methodologies required whilst still meeting appropriate federal regulatory guidelines. This review provides an overview of the current status of cellular immunotherapies and addresses how they may be implemented and the future directions they are likely to take.

In Section I, Dr. Brenner with Drs. Rossig and Sili reviews the clinical experience to date with adoptive transfer of viral antigen-specific T cells for the successful treatment of Epstein-Barr virus-associated malignancies as well as viral infectious diseases. Genetic modification of the T cell receptor of the infused cells to potentiate such T cells as well as modifications to improve safety of the infusions are described.

In Section II, Dr. Young describes the hematopoietic lineages of human dendritic cells and some of their immunotherapeutic applications. The critical importance of dendritic cells to T cell immunity and the capacity to generate dendritic cells in large numbers has spawned enormous interest in the use of these specialized leukocytes to manipulate cellular immunity. Successful cytokine-driven differentiation of dendritic cells reveal two types, myeloid- and plasmacytoid or lymphoid-related dendritic cells. The effects of maturation on phenotype and function of the dendritic cells and their use as immune adjuvants in dendritic cell vaccines to elicit antitumor and antiviral immunity are reviewed.

In Section III, Professor Goulmy illustrates some current and future approaches towards tumor-specific cellular therapy of hematopoietic malignancy. Minor histocompatibility antigen (mHag) disparities between HLA-matched bone marrow donor and recipient can induce allo-responses that may participate in post bone marrow transplantation (BMT) graft-versus-leukemia (GVL) reactivities. A lack of such allo-reactivity may result in relapse of leukemia after BMT. In these patients, adoptive immunotherapy with cytotoxic T cells (CTLs) specific for hematopoietic system-restricted mHags may be used as an extension of current efforts using immunotherapy with donor lymphocyte infusions. Adoptive immunotherapy with CTLs specific for the hematopoietic system-restricted mHags, however, offers the prospect of greater and more predictable effectiveness in the absence of graft-versus-host disease.

Transfusion Medicine: New Clinical Applications of Cellular Immunotherapy

There is now clear clinical evidence that adoptive cellular immunotherapy can eradicate hematologic malignancy and cure otherwise lethal viral infections. With this knowledge comes the challenge of improving the effectiveness and safety of the approach and of simplifying the methodologies required whilst still meeting appropriate federal regulatory guidelines. This review provides an overview of the current status of cellular immunotherapies and addresses how they may be implemented and the future directions they are likely to take.

In Section I, Dr. Brenner with Drs. Rossig and Sili reviews the clinical experience to date with adoptive transfer of viral antigen-specific T cells for the successful treatment of Epstein-Barr virus-associated malignancies as well as viral infectious diseases. Genetic modification of the T cell receptor of the infused cells to potentiate such T cells as well as modifications to improve safety of the infusions are described.

In Section II, Dr. Young describes the hematopoietic lineages of human dendritic cells and some of their immunotherapeutic applications. The critical importance of dendritic cells to T cell immunity and the capacity to generate dendritic cells in large numbers has spawned enormous interest in the use of these specialized leukocytes to manipulate cellular immunity. Successful cytokine-driven differentiation of dendritic cells reveal two types, myeloid- and plasmacytoid or lymphoid-related dendritic cells. The effects of maturation on phenotype and function of the dendritic cells and their use as immune adjuvants in dendritic cell vaccines to elicit antitumor and antiviral immunity are reviewed.

In Section III, Professor Goulmy illustrates some current and future approaches towards tumor-specific cellular therapy of hematopoietic malignancy. Minor histocompatibility antigen (mHag) disparities between HLA-matched bone marrow donor and recipient can induce allo-responses that may participate in post bone marrow transplantation (BMT) graft-versus-leukemia (GVL) reactivities. A lack of such allo-reactivity may result in relapse of leukemia after BMT. In these patients, adoptive immunotherapy with cytotoxic T cells (CTLs) specific for hematopoietic system-restricted mHags may be used as an extension of current efforts using immunotherapy with donor lymphocyte infusions. Adoptive immunotherapy with CTLs specific for the hematopoietic system-restricted mHags, however, offers the prospect of greater and more predictable effectiveness in the absence of graft-versus-host disease.

Chronic Myelogenous Leukemia: Disease Biology and Current and Future Therapeutic Strategies

Over the last 2 decades, four major therapeutic approaches have drastically changed the prognosis in chronic myelogenous leukemia (CML): 1) allogeneic stem cell transplant (SCT); 2) interferon alpha (IFN-α) based regimens; 3) donor lymphocyte infusions (DLI); and 4) and the revolutionary BCR-ABL tyrosine kinase inhibitors such as STI571 (signal transduction inhibitor 571). Each modality has exploited and targeted different aspects of CML biology, and is associated with different risk-benefit ratios.

In Section I of this review, Dr. Melo reviews the molecular pathophysiology of CML and potential new targets for therapy including anti-sense strategies to disrupt the BCR-ABL gene and inhibition of the BCR-ABL tyrosine kinase activity.

In Section II, Dr. Tura, addresses important questions in the use of IFN-α for the treatment of CML, including the mechanism of action and the development of resistance, the optimal dose and duration of therapy and the prediction of response based on clinical features. An approach to the choice of therapy based on the predicted mortality is presented.

In Section III Dr. Giralt presents an update on the results of unrelated donor transplantion, donor lymphocyte infusions (DLI) and non-ablative stem cell transplantation (NST) in CML. The roles of CD8-depletion, dose escalation and the transduction of suicide genes in treatment with DLI are addressed. Early results of NST in CML show that it is feasible and can result in long-term disease control.

In Section IV Drs. Kantarjian and Talpaz review the results of IFN-α plus low-dose cytosine arabinoside and other promising modalities for CML including homoharringtonine, decitabine, and polyethylene glycol-interferon. In Section V they present an update on the recent experience with STI571. Objective but transient responses have been seen in 40% to 50% of patients in CML blastic phase. In accelerated phase, the response rate with STI571 exceeds 70%, and these responses are durable. In chronic phase CML, STI571 at 300 mg daily in patients who failed IFN-α produces a complete hematologic response (CHR) in over 90% of patients. Early results suggest cytogenetic response rates of approximately 50%, which may be major in approximately 30%. The maturing results with STI571 may soon change current recommendations regarding the relative roles of established modalities such as allogeneic SCT and IFN-α. Important questions include 1) whether STI571 therapy alone may be sufficient to induce long-term survival and event-free survival in CML, or whether it needs to be combined simultaneously or sequentially with IFN-α and cytosine arabinoside; and 2) what should the indications for frontline allogeneic SCT be in relation to STI571 therapy.

Chronic Myelogenous Leukemia: Disease Biology and Current and Future Therapeutic Strategies

Over the last 2 decades, four major therapeutic approaches have drastically changed the prognosis in chronic myelogenous leukemia (CML): 1) allogeneic stem cell transplant (SCT); 2) interferon alpha (IFN-α) based regimens; 3) donor lymphocyte infusions (DLI); and 4) and the revolutionary BCR-ABL tyrosine kinase inhibitors such as STI571 (signal transduction inhibitor 571). Each modality has exploited and targeted different aspects of CML biology, and is associated with different risk-benefit ratios.

In Section I of this review, Dr. Melo reviews the molecular pathophysiology of CML and potential new targets for therapy including anti-sense strategies to disrupt the BCR-ABL gene and inhibition of the BCR-ABL tyrosine kinase activity.

In Section II, Dr. Tura, addresses important questions in the use of IFN-α for the treatment of CML, including the mechanism of action and the development of resistance, the optimal dose and duration of therapy and the prediction of response based on clinical features. An approach to the choice of therapy based on the predicted mortality is presented.

In Section III Dr. Giralt presents an update on the results of unrelated donor transplantion, donor lymphocyte infusions (DLI) and non-ablative stem cell transplantation (NST) in CML. The roles of CD8-depletion, dose escalation and the transduction of suicide genes in treatment with DLI are addressed. Early results of NST in CML show that it is feasible and can result in long-term disease control.

In Section IV Drs. Kantarjian and Talpaz review the results of IFN-α plus low-dose cytosine arabinoside and other promising modalities for CML including homoharringtonine, decitabine, and polyethylene glycol-interferon. In Section V they present an update on the recent experience with STI571. Objective but transient responses have been seen in 40% to 50% of patients in CML blastic phase. In accelerated phase, the response rate with STI571 exceeds 70%, and these responses are durable. In chronic phase CML, STI571 at 300 mg daily in patients who failed IFN-α produces a complete hematologic response (CHR) in over 90% of patients. Early results suggest cytogenetic response rates of approximately 50%, which may be major in approximately 30%. The maturing results with STI571 may soon change current recommendations regarding the relative roles of established modalities such as allogeneic SCT and IFN-α. Important questions include 1) whether STI571 therapy alone may be sufficient to induce long-term survival and event-free survival in CML, or whether it needs to be combined simultaneously or sequentially with IFN-α and cytosine arabinoside; and 2) what should the indications for frontline allogeneic SCT be in relation to STI571 therapy.

Get into the groove! Targeting antigens to MHC class II

The activation of MHC class II-restricted helper T cells is paramount to adaptive immune responses. Vaccine development could therefore benefit from improved ways of targeting antigens into MHC class II molecules. In recent years, the natural pathways of MHC class II antigen presentation have been exploited to achieve this goal. First, antigenic proteins and peptides have been modified to facilitate receptor-mediated uptake by professional antigen-presenting cells. Second, DNA constructs containing specific targeting sequences have been used to direct endogenously synthesized antigens to the MHC class II compartments. Both strategies proved to be highly effective. We review these data and describe how this knowledge is currently applied to the design of vaccines that activate helper T cells in vivo.