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

The relevance of HLA class II genes in JAK2 V617F-positive myeloproliferative neoplasms

In the present study we analyzed the relevance of HLA class II in JAK2 V617F-positive (JAK2 V617F+) myeloproliferative neoplasms (MPNs) focusing on genotype diversity, associations with specific alleles and haplotypes and the level of gene expression. One hundred and thirty-nine JAK2 V617F+ MPN patients and 1083 healthy controls, typed by Next generation sequencing (NGS) were included in the study. Multivariate generalized linear models with age as a covariate were applied for analysis of HLA-II allele and haplotype associations. Publicly available gene expression datasets were used to analyze HLA-II pathway genes expression in CD34+ stem cells (SCs) from MPN patients and healthy controls. We did not observe differences in HLA evolutionary divergence (HED) between JAK2 V617F+ MPNs and healthy controls. Two alleles: HLA-DPB1*03:01, DQB1*04:02 and 4 haplotypes: DPB1*02:01-DQA1*05:05-DQB1*03:01-DRB1*11:01, DPB1*04:02-DQA1*05:05-DQB1*03:01-DRB1*11:03, DPB1*02:01-DQA1*01:04-DQB1*05:03-DRB1*14:04, and DPB1*04:01-DQA1*03:01-DQB1*03:02-DRB1*04:01 had significantly lower frequency in MPN patients compared to controls. Additionally, we observed HLA-II alleles and haplotypes with statistically higher frequencies in JAK2 V617F+ patients. Differential gene expression analysis showed down-regulation of HLA-DRB1, -DRA, -DMA, -DMB, -DOA,-DRB4, CIITA, and CD74 genes in JAK2 V617F+ MPN CD34+ SCs as compared to normal CD34 + SCs. In conclusion, this study provides evidence for the pleiotropic effects of HLA-II genes in JAK2 V617F-driven MPNs.

Tnfrsf4-expressing regulatory T cells promote immune escape of chronic myeloid leukemia stem cells

Leukemia stem cells (LSCs) promote the disease and seem resistant to therapy and immune control. Why LSCs are selectively resistant against elimination by CD8⁺ cytotoxic T cells (CTLs) is still unknown. In this study, we demonstrate that LSCs in chronic myeloid leukemia (CML) can be recognized and killed by CD8⁺ CTLs in vitro. However, Tregs, which preferentially localized close to CD8⁺ CTLs in CML BM, protected LSCs from MHC class I–dependent CD8⁺ CTL–mediated elimination in vivo. BM Tregs in CML were characterized by the selective expression of tumor necrosis factor receptor 4 (Tnfrsf4). Stimulation of Tnfrsf4 signaling did not deplete Tregs but reduced the capacity of Tregs to protect LSCs from CD8⁺ CTL–mediated killing. In the BM of newly diagnosed CML patients, TNFRSF4 mRNA levels were significantly increased and correlated with the expression of the Treg-restricted transcription factor FOXP3. Overall, these results identify Tregs as key regulators of immune escape of LSCs and TNFRSF4 as a potential target to reduce the function of Tregs and boost antileukemic immunity in CML.

Chronic myeloid leukemia: the concepts of resistance and persistence and the relationship with the BCR-ABL1 transcript type

Chronic myeloid leukemia is driven by a hybrid gene, BCR-ABL1, that codes for a leukemogenic tyrosine kinase (TK) protein of 210 KDa (p210^BCR-ABL1). Resistance to TK inhibitor (TKI) therapy occurs in relatively few patients, no more than 10%, while persistence of minimal residual disease during TKI therapy occurs in the great majority of patients. Resistance is a cause of death, persistence is compatible with a fairly normal length and quality of life, but may require lifelong treatment. The causes of resistance are heterogeneous, including the development of other genomic abnormalities or the altered expression of other genes, requiring different treatments. The causes of persistence may not be the same as those of resistance. We hypothesize that the variability in breakpoint position within the Major-breakpoint cluster region (M-bcr), resulting in two different messenger RNAs that may or may not include exon 14 of BCR (e13a2 and e14a2, respectively), and, as a consequence, in two p210^BCR-ABL1 proteins that differ by 25 amino acids, may be a cause of persistence. The hypothesis is based on a critical review of the relationships between the BCR-ABL1 transcript types, the response to TKIs, the outcome of treatment, and the immune response, suggesting that the e14a2 transcript is associated with more and deeper molecular responses, hence with a higher probability of achieving treatment-free remission (TFR). Investigating this putative cause of persistence may help bringing more patients into stable TFR.

The proportion of different BCR-ABL1 transcript types in chronic myeloid leukemia. An international overview

There are different BCR-ABL1 fusion genes that are translated into proteins that are different from each other, yet all leukemogenic, causing chronic myeloid leukemia (CML) or acute lymphoblastic leukemia. Their frequency has never been systematically investigated. In a series of 45503 newly diagnosed CML patients reported from 45 countries, it was found that the proportion of e13a2 (also known as b2a2) and of e14a2 (also known as b3a2), including the cases co-expressing e14a2 and e13a2, was 37.9% and 62.1%, respectively. The proportion of these two transcripts was correlated with gender, e13a2 being more frequent in males (39.2%) than in females (36.2%), was correlated with age, decreasing from 39.6% in children and adolescents down to 31.6% in patients ≥ 80 years old, and was not constant worldwide. Other, rare transcripts were reported in 666/34561 patients (1.93%). The proportion of rare transcripts was associated with gender (2.27% in females and 1.69% in males) and with age (from 1.79% in children and adolescents up to 3.84% in patients ≥ 80 years old). These data show that the differences in proportion are not by chance. This is important, as the transcript type is a variable that is suspected to be of prognostic importance for response to treatment, outcome of treatment, and rate of treatment-free remission.

Antigen Discovery and Therapeutic Targeting in Hematologic Malignancies

Historically, immune-based therapies have played a leading role in the treatment of hematologic malignancies, with the efficacy of stem cell transplantation largely attributable to donor immunity against malignant cells. As new and more targeted immunotherapies have developed, their role in the treatment of hematologic malignancies is evolving and expanding. Herein, we discuss approaches for antigen discovery and review known and novel tumor antigens in hematologic malignancies. We further explore the role of established and investigational immunotherapies in hematologic malignancies, with a focus on personalization of treatment modalities such as cancer vaccines and adoptive cell therapy. Finally, we identify areas of active investigation and development. Immunotherapy is at an exciting crossroads for the treatment of hematologic malignancies, with further investigation aimed at producing effective, targeted immune therapies that maximize antitumor effects while minimizing toxicity.

Immunotherapeutic approaches to improve graft-versus-tumor effect and reduce graft-versus-host disease

The therapeutic efficacy of allogeneic stem cell transplantation is mainly based on the alloreactive immune response of the graft against the host. However, the graft-versus-host process can be viewed as a double-edged sword since it is responsible for both the beneficial graft-versus-tumor effect and the deleterious graft-versus-host disease. During the last two decades, intensive research has been focused on the development of novel immunotherapeutic methods aimed to dissociate graft-versus-host disease from graft-versus-tumor effect. A brief description of these efforts is discussed in this review.

Meta-analysis of human leukocyte antigen genetic polymorphisms and susceptibility to chronic myelogenous leukemia in Chinese population

Human leukocyte antigen (HLA) genetic polymorphisms are assumed to be correlated to the risk of chronic myelogenous leukemia (CML) in various ethnicities. Up to now, no clear consensus has been reached. Our goal is to address this issue in Chinese population. By searching the data in PubMed, Embase and four Chinese databases (prior to July 2010), the association of HLA genetic polymorphisms with CML has been fixed as the research objective. We studied a totality of 12 studies, comprising 2281 CML cases and 41000 health controls. The data demonstrated that HLA-A*11, A*74, HLA-B*40, B*47, B*55 and B*81 alleles were correlated with the increasing risk of CML. Nevertheless, HLA-DRB1*13 allele seemed to contribute to the genetic protection to CML. Conclusively we suggested that certain HLA alleles might be in association with the pathogenesis of CML in Chinese population. Due to little statistical scale, larger studies and particularly in a mono-people background, our hypothesis need to be further investigated in the future.

Usage of cancer associated autoantibodies in the detection of disease

Efforts toward deciphering the complexity of the tumor specific proteome by profiling immune responses generated against tumor associated antigens (TAAs) holds great promise for predicting the presence of cancer long before the development of clinical symptoms. The immune system is capable of sensing aberrant expression of certain cellular components involved in tumorigenesis and the resultant autoantibody response provides insights to the targets that are responsible for eliciting immunogenicity to these cellular components. Analysis of the cancer-specific humoral immune response has led to panels of biomarkers that are specific and sensitive biomarkers of disease. Using multianalyte-based in vitro analytical discovery platforms which can be easily adapted into clinical diagnostic screening tests, body fluids such as serum, plasma saliva, or urine can be interrogated to detect autoantibodies against natural or recombinant antigens, which may possess etiologic significance to cancer. Non-invasive screening tests exhibiting high specificity and sensitivity to detect early stage cancer in the heterogeneous population of cancer patients potentially have the greatest impact in decreasing mortality rates. Overall, this review summarizes different experimental approaches in the development of diagnostic screening tests for the early detection of cancer and their implementation in the development of clinical multianalyte biomarker assays.

BCR/ABL-specific CD8+ T cells can be detected from CML patients, but are only expanded from healthy donors

The BCR/ABL p210 fusion protein has long been considered an ideal target antigen for the development of immunotherapeutic strategies in chronic myeloid leukaemia (CML) due to its central role in malignant transformation and to its unique novel amino acid sequence solely expressed in leukaemia cells. However, the feasibility to expand BCR-ABL-specific T cells remains still controversial. Using BCR/ABL peptide/MHC tetramers, significantly higher frequencies of tetramer positive cells were detected in the peripheral blood of HLA-A*0301 (mean 0.38%) and HLA-B*0801 (mean 0.28%) CML patients than in healthy donors (P = 0.0025 and 0.0026, respectively). However, following stimulation with autologous peptide-pulsed DCs, BCR/ABL-specific T cells were only expanded from some healthy donors, suggesting that CML patients may have a specific immune deficit with respect to the BCR/ABL antigen.

Synthetic tumor-specific breakpoint peptide vaccine in patients with chronic myeloid leukemia and minimal residual disease: a phase 2 trial

BACKGROUND

Imatinib is the current standard frontline therapy for chronic myelogenous leukemia (CML). In the majority of patients, imatinib induces a complete cytogenetic response (CCyR); however, complete molecular responses are infrequent. The Bcr-Abl fusion creates a unique sequence of amino acids that could constitute a target for immunomodulation.

METHODS

A mixture of heteroclitic and native peptides derived from both b3a2 and b2a2 sequences was used to vaccinate patients with CML in CCyR who were receiving imatinib therapy and who had stable Bcr-Abl transcript levels.

RESULTS

Ten patients were enrolled, all with b2a2 transcripts (including 2 patients who had coexpression of b2a2 and b3a2). Patients had received imatinib for a median of 62 months. Three of 10 patients achieved 1-log reduction in Bcr-Abl transcript levels, including the 2 patients who had received previous interferon therapy, and 3 other patients achieved a major molecular response. The vaccine was tolerated well, and there were no grade > or =3 adverse events. Vaccination did not affect the leukocyte profiles in peripheral blood except for regulatory T cells, which were down-regulated briefly during the late stage of vaccination in patients who achieved approximately 1-log reduction in Bcr-Abl transcript levels.

CONCLUSIONS

The current data suggested that vaccination-related transient disruption of immune tolerance may contribute to the reduction in Bcr-Abl transcripts. Clinically, this Bcr-Abl peptide vaccine may transiently improve the molecular response in a subset of patients with CML.

Vector prime protein boost vaccination in the setting of myeloablative-induced lymphopenia suppresses growth of leukemia and solid tumors

We have developed a vaccine, which is designed to induce tumor-associated antigen (TAA)-specific T cells and antibodies in the setting of profound lymphopenia induced by myeloablative therapy and T-cell-depleted bone marrow transplantation. Test mice were injected subcutaneously (sc) with the 32DP210Bcr-Abl cell line, which is positive for the p210Bcr-Abl protein (Group 1). In Group 2, 7 days after injection of the 32DP210Bcr-Abl positive cell line, the mice received 900 cGy total body irradiation (TBI) followed in 1 h by the intravenous infusion of 10 million T-cell-depleted syngeneic bone marrow cells (TCDBMT) (Group 2). The leukemia-bearing group received an intravenous injection of 10 million spleen cells (donor lymphocyte infusions) from unvaccinated (Group 3) and TAA/ecdCD40L-vaccinated (Group 4) syngeneic mice 3 days after completion of the TBI and TCDBMT. Groups 3 and 4 mice received three additional sc vaccinations at 7-day intervals with the TAA/ecdCD40L vaccine, in which the TAA was taken from the junctional peptide of the P210bcr-Abl protein. The survival of Groups 3 and 4 mice was significantly longer than that in Groups 1 and 2 mice. Vaccinated mice from Group 4, which developed complete responses, survived up to 350 days post-injection of the leukemia cells without any evidence of leukemia regrowth.

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.

Immunotherapeutic strategies in chronic myeloid leukemia

Several clinical observations demonstrate that immunologic effects are important in chronic myeloid leukemia (CML). The characteristic BCR-ABL fusion protein is a leukemia-specific antigen, and it has therefore received much immunologic attention, especially regarding the amino acid sequences that span the e14a2 junction. Other attractive targets are the Wilms' tumor 1 antigen and the PR1 epitope from proteinase 3, a granule protein overexpressed in CML. Imatinib may modulate several components of the immune response, although the clinical relevance of this effect is uncertain. In clinical trials, peptide vaccination appears safe and undoubtedly produces clinical effects, but randomized trials are now required to see if these are distinct from the effects of other concurrent therapy. These trials will be difficult to orchestrate in the competitive environment of novel therapies for CML.

Vaccination with autologous non-irradiated dendritic cells in patients with bcr/abl+ chronic myeloid leukaemia

In chronic myeloid leukaemia (CML), dendritic cells (DC) and leukaemic cells share a common progeny, leading to constitutive expression of putative tumour antigens, such as bcr/abl, in DC. In this phase-I/II study, autologous DC were used as a vaccine in patients with chronic phase bcr/abl+ CML, who had not achieved an adequate cytogenetic response after treatment with alpha-interferon or imatinib. Ten patients were enrolled, DC were generated from peripheral blood monocytes and vaccination consisted of four subcutaneous injections of increasing numbers of DC (1-50 x 10(6) cells per injection) on days 1, 2, 8 and 21. Vaccination was feasible and safe. Improvement of the cytogenetic/molecular response, as detected by fluorescence in situ hybridization of peripheral blood mononuclear cells (PBMC), was possibly related to vaccination in four of 10 patients. In three of these patients, T cells recognizing leukaemia-associated antigens became detectable. The proliferative capacity of PBMC in response to autologous DC increased after vaccination in all evaluable patients. We conclude that vaccination with autologous, non-irradiated 'leukaemic' DC is feasible, safe and induces anti-leukaemic T-cell responses in some CML patients. DC vaccination might be useful in CML as postremission therapy, i.e. after treatment with tyrosine kinase inhibitors.

Evidence that a BCR-ABL fusion peptide does not induce lymphocyte proliferation or cytokine production in vitro

The BCR-ABL fusion protein is characteristic of chronic myeloid leukaemia and may be an effective tumour-specific antigen. CD8+ T cell responses to BCR-ABL fusion peptides have been reported in normal subjects and CML patients but CD4+ T cell responses have been less well characterised. Here, the 23-mer e14a2 fusion peptide VHSATGFKQSSKALQRPVASDFE has been used to stimulate T cell responses. Most normal subjects and CML patients showed no proliferative responses to this peptide, with stimulation indices not significantly greater than 1.0. Following a second stimulation with the same peptide, small proliferative responses were obtained in normal subjects but not CML patients. These responses were not improved following a third stimulation with 23-mer peptide, nor by using mature autologous dendritic cells to present the peptide. Intracellular interferon-gamma production by CD4+ T cells was also not induced by the 23-mer e14a2 peptide. Hence, this e14a2 peptide does not stimulate CD4+ T cell proliferation in vitro in most normal subjects or CML patients. The precise sequence of amino acids may be critical in defining immunogenicity for CD4+ T cell responses against BCR-ABL peptides.

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.

Combinational adenovirus-mediated gene therapy and dendritic cell vaccine in combating well-established tumors

Recent developments in tumor immunology and biotechnology have made cancer gene therapy and immunotherapy feasible. The current efforts for cancer gene therapy mainly focus on using immunogenes, chemogenes and tumor suppressor genes. Central to all these therapies is the development of efficient vectors for gene therapy. By far, adenovirus (AdV)-mediated gene therapy is one of the most promising approaches, as has confirmed by studies relating to animal tumor models and clinical trials. Dendritic cells (DCs) are highly efficient, specialized antigen-presenting cells, and DC-based tumor vaccines are regarded as having much potential in cancer immunotherapy. Vaccination with DCs pulsed with tumor peptides, lysates, or RNA, or loaded with apoptotic/necrotic tumor cells, or engineered to express certain cytokines or chemokines could induce significant antitumor cytotoxic T lymphocyte (CTL) responses and antitumor immunity. Although both AdV-mediated gene therapy and DC vaccine can both stimulate antitumor immune responses, their therapeutic efficiency has been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or to growth inhibition of small tumors. However, this approach has been unsuccessful in combating well-established tumors in animal models. Therefore, a major strategic goal of current cancer immunotherapy has become the development of novel therapeutic strategies that can combat well-established tumors, thus resembling real clinical practice since a good proportion of cancer patients generally present with significant disease. In this paper, we review the recent progress in AdV-mediated cancer gene therapy and DC-based cancer vaccines, and discuss combined immunotherapy including gene therapy and DC vaccines. We underscore the fact that combined therapy may have some advantages in combating well-established tumors vis-a-vis either modality administered as a monotherapy.

Professional type I interferon-producing cells--a unique subpopulation of dendritic cells

Dendritic cells (DC) represent a rare but multifunctional population of cells with the capacity to prime and orchestrate antigen-specific immune responses. Both human and mouse DC are classified to myeloid and plasmacytoid DC (pDC) with distinct functional activities. These DC subsets can be found in the peripheral blood and tissues as resting cells and act as sensors of environmental changes. Activation of DC by various stimuli induces morphological and functional changes and transforms these cells to potent antigen presenting and secretory cells. A newly identified precursor subset of human DC has recently been identified as professional type I interferon producing cells (IPC) with multiple functional activities. Interferon-producing cells, also referred as pDC act as a link between innate and adaptive immunity and possess the capacity to instruct and regulate pathogen- and tumor-specific immune responses. The role of IPC/pDC--partly mediated by type I interferons--has also been demonstrated in the pathogenesis of various diseases and could be used as a target for modulating immune responses.

Interferon alpha and T-cell responses in chronic myeloid leukemia

Chronic myelogenous leukemia (CML) was the first human malignancy where a consistent chromosomal abnormality, the BCR-ABL translocation, was identified as the causative genetic aberration. There is a mounting body of evidence suggesting that CML cells are particularly good targets for immunological surveillance mechanisms, the most intriguing being the curative effect of allogeneic donor lymphocyte infusion given in relapsed disease after allogeneic bone marrow transplantation. Likewise, interferon alpha (IFN alpha), which has long been considered as the standard conservative therapy in CML, may exert its life-prolonging effect by activating immunological effector functions. This review will focus on the recent advances in the understanding of the contribution of IFN alpha in eliciting T-cell responses against self-antigens in CML.

Growth factors in haematological cancers

Since their discovery just under a century ago, growth factors (GFs) have been used almost ubiquitously in haematology. Many haematological cancers are associated with bone marrow failure, either as a direct consequence of the disease or its treatment. Colony stimulating factors (CSFs) have been used to address the problems associated with the resulting cytopenias, however, concerns about the potential leukaemogenic effects of some of these CSFs led to a degree of initial hesitancy in usage, particularly in the management of acute myeloid leukaemia (AML). This has now been largely overcome. Other limitations have included cost and side effect profiles (the latter particularly with the multilineage factors). There has been wide variation locally, nationally and internationally in the usage of GFs. The American Society of Clinical Oncologists (ASCO) attempted to rationalise the usage of GFs by producing a consensus document enumerating the evidence-based indications for use of GFs. There is little information on cost effectiveness, this remains an important issue for the future. Peripheral blood stem cell transplantation (PBSCT) has revolutionised the management of many malignant conditions and has contributed to the increased use of growth factors. Many other indications are emerging for GFs used singly or in combination. Current clinical applications of GFs include: i) amelioration of cytopenias following chemotherapy and stem cell transplantation, ii) chemotherapy dose maintenance and escalation, iii) chemosensitisation and modification of disease states, iv) optimisation of methods for mobilisation of progenitor stem cells, v) immunotherapy, and vi) as therapeutic targets for treatment of haematolgical malignancies.

Effect of a p210 multipeptide vaccine associated with imatinib or interferon in patients with chronic myeloid leukaemia and persistent residual disease: a multicentre observational trial

BACKGROUND

Although imatinib is the standard treatment for chronic myeloid leukaemia, not all patients reach complete cytogenetic remission (CCR) and most maintain detectable disease at the molecular level. We investigated whether a vaccine targeting the BCR-ABL-derived p210 fusion protein was an active and specific immunotherapy.

METHODS

We recruited 16 patients who had chronic myeloid leukaemia (with the b3a2 fusion point of p210), stable residual disease, a minimum treatment of 12 months of imatinib or 24 months of interferon alfa, and no further reduction of residual disease for at least 6 months preceding enrollment. They were given six vaccinations with a peptide vaccine derived from the sequence p210-b3a2 plus molgramostim and QS-21 as adjuvants (CMLVAX100) before assessment of immunological and disease response, which included detecting amounts of b3a2 transcripts by standardised quantitative real-time reverse-transcriptase PCR.

RESULTS

Of ten patients on imatinib, nine started CMLVAX100 having had a median of 10 months' stable cytogenetic disease (median 10% Philadelphia-chromosome-positive metaphases), whereas one started in stable CCR. All patients' cytogenetic responses improved after six vaccinations, with five reaching CCR. Notably, three of these five patients also had undetectable amounts of b3a2 transcript (BCR-ABL:beta2 microglobulin ratio <0.00001). Six patients on interferon alfa treatment with a median of 17 months' stable residual disease (median 13% Philadelphia-chromosome-positive cells) were also vaccinated. All but one had improved cytogenetic responses, and two reached CCR. Overall, we recorded peptide-specific delayed-type hypersensitivity (in 11 of 16 patients), CD4 cell proliferation (13 of 14 assessed), and interferon gamma production (five of five assessed).

INTERPRETATION

Addition of CMLVAX100 to conventional treatment in patients with chronic myeloid leukaemia might favour further reduction of residual disease and increase the number of patients reaching a molecular response.

Myeloma Cells Are Highly Sensitive to the Granule Exocytosis Pathway Mediated by WT1-Specific Cytotoxic T Lymphocytes

PURPOSE

Because WT1 is a universal tumor antigen, we examined the sensitivity of myeloma cells to WT1-specific cytotoxic T lymphocyte (CTL)-mediated cytotoxicity.

EXPERIMENTAL DESIGN

WT1 expression in hematologic malignant cells was examined by quantitative reverse transcription-polymerase chain reaction. The cytotoxicity of a WT1-specific CTL clone against hematologic malignant cells, including myeloma cells, was examined by standard chromium-51 release assays. The extent of membrane damage induced by purified perforin was examined. Induction of WT1-specific CTLs from the patients with multiple myeloma (MM) was attempted, and we examined their function against myeloma cells.

RESULTS

The expression levels of WT1 mRNA in myeloma and lymphoma cells were significantly lower than that in acute leukemia cells. Although the WT1 expression levels in myeloma and lymphoma cells were almost same, only myeloma cells were lysed efficiently by WT1-specific CTLs in a HLA-restricted manner. The amounts of interferon-gamma produced by WT1-specific CTLs in response to stimulation with myeloma cells and with lymphoma cells were almost the same, suggesting that WT1 protein is processed and expressed in the context of HLA class I molecules similarly on both myeloma and lymphoma cells. The extent of membrane damage induced by purified perforin appeared to be significantly higher in myeloma cells than in lymphoma cells. WT1-specific CTLs appeared to be present in patients with MM.

CONCLUSIONS

The present study has shown that susceptibility of membranes to perforin is an important factor determining the sensitivity of target cells to CTL-mediated cytotoxicity and that WT1 is an ideal target antigen for cellular immunotherapy of MM.

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.

IFN-α promotes the rapid differentiation of monocytes from patients with chronic myeloid leukemia into activated dendritic cells tuned to undergo full maturation after LPS treatment

Chronic myelogenous leukemia (CML) is a malignant myeloproliferative disease arising from the clonal expansion of a stem cell expressing the bcr/abl oncogene. CML patients frequently respond to treatment with interferon-α (IFN-α), even though the mechanisms of the response remain unclear. In the present study, we evaluated the role of IFN-α in differentiation and activity of monocyte-derived dendritic cells (DCs) from CML patients as well as in modulation of the cell response to lipopolysaccharide (LPS). Treatment of CML monocytes with IFN-α and granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in the rapid generation of activated DCs (CML-IFN-DCs) expressing interleukin-15 (IL-15) and the antiapoptotic bcl-2 gene. These cells were fully competent to induce IFN-γ production by cocultured autologous T lymphocytes and expansion of CD8+ T cells. LPS treatment of CML-IFN-DCs, but not of immature DCs generated in the presence of IL-4/GM-CSF, induced the generation of CD8+ T cells reactive against autologous leukemic CD34+ cells. Altogether, these results suggest that (1) the generation of highly active monocyte-derived DCs could be important for the induction of an antitumor response in IFN-treated CML patients and (2) IFN-α can represent a valuable cytokine for the rapid generation of active monocyte-derived DCs to be utilized for vaccination strategies of CML patients. (Blood. 2004;103:980-987)

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.

HLA system affects the age-at-onset in chronic myeloid leukemia

Chronic myeloid leukemia (CML) occurs from childhood to old age. The adult form is characterized by the presence of Philadelphia chromosome resulting from bcr/abl translocation. The BCR-ABL fusion proteins are immunogenic, and the junctional sequences show unique HLA class I and class II restriction patterns in vitro. A previous study in the west of Scotland showed an influence of several HLA genotypes on the age-at-onset of CML. In the present study, we examined the HLA-A, -B, and -DRB1/3/4/5 allele and haplotype distributions in Turkish CML patients diagnosed in a single center where they are routinely HLA-typed by PCR-SSP analysis as a preparation for stem cell transplantation. The patients were 169 subjects of age 17-60 years. The older patients were not HLA typed and missing from the study group. The age-matched control group (n = 213) was healthy blood donors from the same geographical area. HLA-B*37 showed a risk association with CML [P = 0.02; odds ratio (OR) = 5.35]. The DRB1*10 association at similar magnitude was due to its linkage disequilibrium (LD) with B*37. HLA-B*35 and DRB1*11 showed independent protective effects (P = 0.007 and 0.017; OR = 0.54 and 0.60, respectively). The protective association of DRB1*11 may be due to its involvement in the presentation of the common (b3a2) fusion gene. HLA-B*14 and DRB1*01 showed strong LD, and all 5 patients who were positive for the presumed haplotype B*14-DRB1*01 were of age 43 years old or older (P = 0.003), suggesting a delay effect. We also examined the influence of homozygosity for DRB3 (DR52) and DRB4 (DR53) haplotypes on susceptibility. As previously shown in CML and CLL, DRB4 homozygosity was a risk marker (P = 0.01; OR = 3.36), and DRB3 homozygosity was protective (P = 0.007; OR = 0.51). Despite the lack of elderly patients in the study group, the opposite accelerating (DRB4) and delaying (DRB3) effects of homozygous genotypes on the age-at-onset were evident. Besides replicating previously found associations in a different population, this study also suggested new, and probably population-specific associations in CML. The mechanisms by which the HLA system modifies susceptibility to CML are unknown, likely to include immune and nonimmune ones, and worthy of further studies.

Minor histocompatibility antigens on canine hemopoietic progenitor cells

Adoptive immunotherapy with CTL against minor histocompatibility Ags (mHA) provides a promising way to treat leukemia relapse in allogeneic chimeras. Here we describe the in vitro generation of CTL against mHA in the dog. We tested their inhibitory effect on the growth of hemopoietic progenitor cells stimulated by hemopoietic growth factors in a 4-day suspension culture. CTL were produced by coculture of donor PBMC with bone marrow-derived dendritic cells (DCs). These DCs were characterized by morphology, high expression of MHC class II and CD1a, and the absence of the monocyte-specific marker CD14. Characteristically these cells stimulated allogeneic lymphocytes (MLR) and, after pulsing with a foreign Ag (keyhole limpet hemocyanin), autologous T cells. CTL were generated either ex vivo by coculture with DCs of DLA-identical littermates or in vivo by immunization of the responder with DCs obtained from a DLA-identical littermate. In suspension culture assays the growth of hemopoietic progenitor cells was inhibited in 53% of DLA-identical littermate combinations. In canine families mHA segregated with DLA as restriction elements. One-way reactivity against mHA was found in five littermate combinations. In two cases mHA might be Y chromosome associated, in three cases autosomally inherited alleles were detected. We conclude that CTL can be produced in vitro and in vivo against mHA on canine hemopoietic progenitor cells using bone marrow-derived DCs.

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.

Adoptive cellular therapy: a therapeutic reality?

The past decade has seen numerous lines of evidence emerging that suggest human malignancies may be sensitive to the effects of cellular immunotherapy. An increasing understanding of the nature of the effector cells and their target antigens is now leading to more focused efforts to harness these responses for therapeutic benefit. However, clinical application has proven more challenging than initially envisaged. Advances in the setting of allogeneic stem cell transplantation now allow attempts to augment both immunological recovery and anti-tumour activity. Some of the most attractive targets here are allospecific rather than truly tumour-specific. Application outside of this setting is based on attempts to delineate further tumour-specific or, increasingly, tumour-selective targets. This review summarizes these developments and highlights some of the issues that remain to be resolved.

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.