T cells recognizing leukemic CD34(+) progenitor cells mediate the antileukemic effect of donor lymphocyte infusions for relapsed chronic myeloid leukemia after allogeneic stem cell transplantation

Allogeneic Tumor Antigen-Specific T Cells for Broadly Applicable Adoptive Cell Therapy of Cancer

T cells specific for major histocompatibility complex (MHC)-presented tumor antigens are capable of inducing durable remissions when adoptively transferred to patients with refractory cancers presenting such antigens. When such T cells are derived from healthy donors, they can be banked for off-the-shelf administration in appropriately tissue matched patients. Therefore, tumor antigen-specific, donor-derived T cells are expected to be a mainstay in the cancer immunotherapy armamentarium. In this chapter, we analyze clinical evidence that tumor antigen-specific donor-derived T cells can induce tumor regressions when administered to appropriately matched patients whose tumors are refractory to standard therapy. We also delineate the landscape of MHC-presented and unconventional tumor antigens recognized by T cells in healthy individuals that have been targeted for adoptive T cell therapy, as well as emerging antigens for which mounting evidence suggests their utility as targets for adoptive T cell therapy. We discuss the growing technological advancements that have facilitated sequence identification of such antigens and their cognate T cells, and applicability of such technologies in the pre-clinical and clinical settings.

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.

Beyond tyrosine kinase inhibitors: Combinations and other agents

The modern therapeutic strategy for patients with chronic myeloid leukemia (CML) has been successfully altered by first and subsequently second generation tyrosine kinase inhibitors. However, despite high rate of molecular response, minimal residual disease persists in the majority of patients. Thus other approaches are warranted in order to eliminate the leukemia stem cells. Targeting CML stem cells could be of clinical benefit and a number of new agents are currently tested in phase I/II trials. Also immunological approaches with vaccination strategies and combination of tyrosine kinase inhibitors with various form of interferons are actively ongoing.

Treatment of Lymphoid Malignancies with Non-myeloablative Stem Cell Transplantation

The traditional approach to allogeneic hematopoietic stem cell transplantation involves the administration of myeloablative preparative regimens. This form of conditioning is associated with a relatively high incidence of regimen-related toxicity. As a result, candidates for allogeneic stem cell transplantation may be excluded owing to advanced age or co-morbid medical illness. Recently, so-called "non-myeloablative" regimens have been introduced, where less intense conditioning therapy is used in an attempt to reduce regimen-related toxicity. In addition, non-myeloablative transplantation takes advantage of the graft-versus-tumour effect that is characteristic of allogeneic stem cell transplantation. We review the background, available clinical data, and future directions in non-myeloablative stem cell transplantation, and focus on its potential use in the treatment of lymphoid malignancies.

Developing strategies in the immunotherapy of leukemias

BACKGROUND

In the current treatment paradigms for leukemias, hematopoietic stem cell transplant (HSCT) is considered the best option with a curative potential although more often than not it simply delays disease progression. Advances are needed, both in current therapies and in the development of new strategies. Partly from studying the nuances of the curative potential of stem cell transplant, we have come to appreciate the relevance of the immune response and the potential of immunotherapy.

METHODS

This review article summarizes the recent advances in the field of immunology and immunotherapy for leukemia.

RESULTS

In passive immunotherapy, recent progress in chimeric T-cell antigen receptor technology has been encouraging. In active immunotherapy, a cancer vaccine may potentially enhance HSCT. An overview of various clinical studies of peptide vaccination strategies focusing on molecular targets such as the Wilms' tumor gene 1 (WT1), proteinase 3 (PR3), and receptor for hyaluronan acid-mediated motility (RHAMM) is provided. Cell-based vaccination strategies are also briefly explored.

CONCLUSIONS

The immune system clearly has the capacity to recognize and react to leukemic cells, and recent evidence directs our attention to the importance of mounting inflammatory and CD4 T-cell responses to complement and support the cytotoxic activity elicited by peptide vaccines.

Reduced efficacy of mesenchymal stromal cells in preventing graft-versus-host disease in an in vivo model of haploidentical bone marrow transplant with leukemia

Mesenchymal stromal cell (MSC) immunosuppressive properties have been applied to treat graft-versus-host disease (GVHD) in allogeneic hematopoietic stem cell transplants (HSCTs). We have previously demonstrated that MSC infusions early after haplo-HSCT prevent GVHD in a haploidentical-HSCT mouse model. Now, we investigated the impact that MSCs' immunosuppressive properties have on the graft-versus-leukemia (GVL) effect. First, to mimic a chronic myeloid leukemia (CML) relapse after a haploidentical HSCT, lethally irradiated mice were coinfused with haploidentical donor bone marrow cells plus syngenic hematopoietic progenitors transduced with a retroviral vector encoding both the BCR/ABL oncogene and the ΔNGFR marker gene. As expected, a CML-like myeloproliferative syndrome developed in all the recipient animals. The addition of haploidentical splenocytes to the transplanted graft prevented CML development by a GVL effect, and all transplanted recipients died of GVHD. This GVL mouse model allowed us to investigate the impact of MSCs infused to prevent GVHD on days 0, 7, and 14 after HSCT, on the GVL effect, expecting an increase in leukemic relapse. Strikingly, a high mortality of the recipients was observed, caused by GVHD, and only few leukemic cells were detected in the recipient animals. In contrast, GVHD prevention by MSCs in the absence of BCR/ABL leukemic cells resulted in a significant survival of the recipients. In vitro data pointed to an inability of MSCs to control strong CTLs responses against BCR/ABL. Our results show that, although an evident increase in leukemic relapses induced by MSCs could not be detected, they showed a reduced efficacy in preventing GVHD that precluded us to draw clear conclusions on MSCs' impact over GVL effect.

A novel nonradioactive CFDA assay to monitor the cellular immune response in myeloid leukemia

BACKGROUND

Donor lymphocyte transfusion (DLT) may induce the graft-versus-leukemia (GVL) effect for patients with AML relapsed after transplant. However, AML is a highly diverse disease and the limited overall efficacy of DLT in clinical practice emphasizes the importance of identifying a specific subgroup of patients who might benefit from this treatment approach.

OBJECTIVE

To monitor the cellular immune response after DLT, we developed an active specific immunization strategy using in vitro generated AML-trained T cells to induce a highly specific antileukemic T-cell response and thus established a novel nonradioactive assay system to assess the antileukemia immunity by flow cytometry, correlated with [3H]-thymidine uptake.

METHODS

The myeloid blasts derived from five patients with AML relapsed post-allogeneic hematopoietic stem cell transplantation (allo-HSCT) were first labeled with CFDA (5,6-carboxyfluorescein diacetate succinimidyl ester). To analyze the growth inhibitory potential of the donor T cells trained by AML progenitor cells, the myeloid blasts were induced to proliferate by means of a cytokine cocktail (50ng/mL of SCF; 25ng/mL of IL-3; 100ng/mL of GM-CSF; 100ng/mL of G-CSF; 2U/mL of EPO; 0.47g/L of transferrin; and 5×10(-5)mmol/L of 2-ME). The T cell mediated growth inhibitory potential was detected after 5 days by flow cytometry and correlated with [3H]-thymidine uptake. The simultaneous use of TO-PRO-dye and calibrate beads allowed not only the cell viability to be known but also allowed quantification of the effector function.

RESULTS

Here, we applied a CFDA dye to track the proliferation and expansion of AML blasts in response to the cytokine cocktail in vitro. AML-trained T cells, expressed high levels of the activation markers CD25 and CD69, and were generated to recognize the leukemic progenitor cells and inhibit cytokine-induced leukemic cell proliferation, which is an active specific immunization strategy circumventing the identification of leukemia-associated antigens. The capability of proliferation inhibition of AML-trained T cells evaluated with our nonradioactive, CFDA-based assay provided comparable results with the classic [3H]-thymidine assay with an even lower ratio of effector to target cells.

CONCLUSION

Taken together, the novel, nonradioactive, CFDA-based assay was a robust tool to monitor the antileukemic immune response after DLT in myeloid leukemias.

Chronic myeloid leukemia lysate-loaded dendritic cells induce T-cell responses towards leukemia progenitor cells

Treatment of chronic myeloid leukemia with tyrosine kinase inhibitors, such as imatinib mesylate, dasatinib and nilotinib, results in high rates of cytogenetic and molecular responses. However, in many patients, minimal residual disease is detected by molecular techniques. Since chronic myeloid leukemia cells are particularly good targets for immune surveillance mechanisms, we explored active specific immunotherapy using leukemia lysate-loaded dendritic cells in vitro. Our data show the potency of dendritic cell-based vaccination strategies for the induction of T cell-mediated responses to eradicate minimal residual disease.

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.

Myeloid leukemic progenitor cells can be specifically targeted by minor histocompatibility antigen LRH-1–reactive cytotoxic T cells

CD8+ T cells recognizing minor histocompatibility antigens (MiHAs) on leukemic stem and progenitor cells play a pivotal role in effective graft-versus-leukemia reactivity after allogeneic stem cell transplantation (SCT). Previously, we identified a hematopoiesis-restricted MiHA, designated LRH-1, which is presented by HLA-B7 and encoded by the P2X5 purinergic receptor gene. We found that P2X5 is significantly expressed in CD34+ leukemic subpopulations from chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) patients. Here, we demonstrate that LRH-1–specific CD8+ T-cell responses are frequently induced in myeloid leukemia patients following donor lymphocyte infusions. Patients with high percentages of circulating LRH-1–specific CD8+ T cells had no or only mild graft-versus-host disease. Functional analysis showed that LRH-1–specific cytotoxic T lymphocytes (CTLs) isolated from 2 different patients efficiently target LRH-1–positive leukemic CD34+ progenitor cells from both CML and AML patients, whereas mature CML cells are only marginally lysed due to down-regulation of P2X5. Furthermore, we observed that relative resistance to LRH-1 CTL-mediated cell death due to elevated levels of antiapoptotic XIAP could be overcome by IFN-γ prestimulation and increased CTL-target ratios. These findings provide a rationale for use of LRH-1 as immunotherapeutic target antigen to treat residual or persisting myeloid malignancies after allogeneic SCT.

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.

Primitive quiescent CD34+ cells in chronic myeloid leukemia are targeted by in vitro expanded natural killer cells, which are functionally enhanced by bortezomib

Primitive quiescent CD34(+) chronic myeloid leukemia (CML) cells are more biologically resistant to tyrosine kinase inhibitors than their cycling counterparts; however, graft-versus-leukemia (GVL) effects after allogeneic stem cell transplantation (SCT) probably eliminate even these quiescent cells in long-term surviving CML transplant recipients. We studied the progeny of CD34(+) cells from CML patients before SCT, which were cultured 4 days in serum-free media with hematopoietic growth factors. BCR-ABL expression was similar in both cycling and quiescent noncycling CD34(+) populations. Quiescent CD34(+) cells from CML patients were less susceptible than their cycling CD34(+) and CD34(-) counterparts to lysis by natural killer (NK) cells from their HLA-identical sibling donors. Compared with cycling populations, quiescent CD34(+) CML cells had higher surface expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR4 and DR5. Bortezomib up-regulated TRAIL receptor expression on quiescent CD34(+) CML cells, and further enhanced their susceptibility to cytotoxicity by in vitro expanded donor NK cells. These results suggest that donor-derived NK cell-mediated GVL effects may be improved by sensitizing residual quiescent CML cells to NK-cell cytotoxicity after SCT. Such treatment, as an adjunct to donor lymphocyte infusions and pharmacologic therapy, may reduce the risk of relapse in CML patients who require treatment by SCT.

Hematopoietic stem cells and progenitors of chronic myeloid leukemia express leukemia-associated antigens: implications for the graft-versus-leukemia effect and peptide vaccine-based immunotherapy

The cure of chronic myeloid leukemia (CML) patients following allogeneic stem cell transplantation (SCT) is attributed to graft-versus-leukemia (GVL) effects targeting alloantigens and/or leukemia-associated antigens (LAA) on leukemia cells. To assess the potential of LAA-peptide vaccines in eliminating leukemia in CML patients, we measured WT1, PR3, ELA2 and PRAME expression in CD34+ progenitor subpopulations in CML patients and compared them with minor histocompatibility antigens (mHAgs) HA1 and SMCY. All CD34+ subpopulations expressed similar levels of mHAgs irrespective of disease phase, suggesting that in the SCT setting, mHAgs are the best target for GVL. Furthermore, WT1 was consistently overexpressed in advanced phase (AdP) CML in all CD34+ subpopulations, and mature progenitors of chronic phase (CP) CML compared to healthy individuals. PRAME overexpression was limited to more mature AdP-CML progenitors only. Conversely, only CP-CML progenitors had PR3 overexpression, suggesting that PR1-peptide vaccines are only appropriate in CP-CML. Surface expression of WT1 protein in the most primitive hematopoietic stem cells in AdP-CML suggest that they could be targets for WT1 peptide-based vaccines, which in combination with PRAME, could additionally improve targeting differentiated progeny, and benefit patients responding suboptimally to tyrosine kinase inhibitors, or enhance GVL effects in SCT patients.

High PR3 or ELA2 expression by CD34+ cells in advanced-phase chronic myeloid leukemia is associated with improved outcome following allogeneic stem cell transplantation and may improve PR1 peptide-driven graft-versus-leukemia effects

The primary granule proteins elastase (ELA2) and proteinase 3 (PR3) both contain the nonapeptide PR1, which can induce cytotoxic T lymphocyte (CTL) responses against chronic myeloid leukemia (CML) cells. To investigate whether eradication of CML after allogeneic stem cell transplantation (SCT) was influenced by PR3 and ELA2 gene expression or PR1-specific CTL responses, we studied cells from 87 CML patients and 27 HLA-A*0201(+) donors collected prior to T-cell-depleted HLA-identical sibling SCT. For patients in advanced phase (AdP), a higher expression of both PR3 and ELA2 in CD34(+) progenitors before SCT was associated with a lower incidence of relapse-related death, improved leukemia-free survival (LFS), and overall survival (OS); in chronic phase patients, no differences were observed. PR1-CTL responses were detected in 7 of 27 HLA-identical sibling donors, and associated with improved LFS and OS after SCT on follow-up. PR1-CTL responses detected in 7 of 28 CML patients before transplantation were not predictive of outcome and correlated inversely with PR3 and ELA2 expression. These findings suggest that assessment of PR3 and ELA2 expression in leukemic progenitors is useful for predicting posttransplantation outcome in AdP patients undergoing SCT. The presence of a donor immune response against PR1 may be advantageous and could be exploited therapeutically.

Response to donor lymphocyte infusions for chronic myeloid leukemia is dose-dependent: the importance of escalating the cell dose to maximize therapeutic efficacy

Donor lymphocyte infusions (DLI) are an effective treatment for patients with chronic myeloid leukemia (CML) in relapse after allografting but the optimal cell dose has yet to be identified. To address this question, we investigated the factors affecting the dose required to achieve remission (effective cell dose, (ECD)) in 81 patients treated with an escalating dose regimen. The overall proportion of patients who achieved a molecular remission was 88%. The cumulative proportion of remitters increased significantly at each dose level. With a CD3(+) cell dose < or =10(7)/kg, 56% of patients in molecular/cytogenetic relapse obtained molecular remission, whereas only 20% of those in hematologic relapse did so. At the same cell dose, 58% of patients who received lymphocytes from volunteer unrelated donors achieved remission, as compared to 29% of those who received DLI from sibling donors. We conclude that the response to DLI is dose-dependent and that the ECD is influenced by the quantity and phase of CML at relapse and degree of donor/recipient histocompatibility.

Lentiviral PU.1 overexpression restores differentiation in myeloid leukemic blasts

PU.1, a transcription factor of the ETS family, plays a pivotal role in normal hematopoiesis, and particularly in myeloid differentiation. Altered PU.1 function is possibly implicated in leukemogenesis, as PU.1 gene mutations were identified in some patients with acute myeloid leukemia (AML) and as several oncogenic products (AML1-ETO, promyelocytic leukemia-retinoic acid receptor alpha, FMS-like receptor tyrosine kinase 3 internal tandem duplication) are associated with PU.1 downregulation. To demonstrate directly a role of PU.1 in the blocked differentiation of leukemic blasts, we transduced cells from myeloid cell lines and primary blasts from AML patients with a lentivector encoding PU.1. In NB4 cells we obtained increases in PU.1 mRNA and protein, comparable to increases obtained with all-trans retinoic acid-stimulation. Transduced cells showed increased myelomonocytic surface antigen expression, decreased proliferation rates and increased apoptosis. Similar results were obtained in primary AML blasts from 12 patients. These phenotypic changes are characteristic of restored blast differentiation. PU.1 should therefore constitute an interesting target for therapeutic intervention in AML.

Molecular persistence of chronic myeloid leukemia caused by donor T cells specific for lineage-restricted maturation antigens not recognizing immature progenitor-cells

Although donor lymphocyte infusion (DLI) induces complete remissions in 70% of patients with relapsed chronic myeloid leukemia (CML) after allogeneic stem-cell transplantation (SCT), some patients are refractory to DLI by showing disease persistence. In a patient who received DLI for relapsed CML, we observed persisting molecular disease despite a hematological and cytogenetic remission in the absence of graft-versus-host disease (GVHD). To determine the nature of this immune response, we isolated leukemia-reactive donor T-cell clones from the bone marrow (BM) of the patient at the time of clinical response. Four different types of CD8+ HLA class I restricted T-cell clones were obtained that were cytotoxic against Ebstein-Barr virus-transformed B-cell lines (EBV-LCL) of the patient, but not the donor, indicating recognition of minor histocompatibility antigens (mHags). By using survival studies with CFSE labelled BM cells populations, a hematopoietic progenitor cell inhibition assay and direct morphological examination we showed that the T-cell clones recognized mature monocytic and myeloid cells, whereas immature BM progenitor cells were insufficiently lysed. This patient's refractoriness for DLI appears to be caused by inadequate lysis of progenitor cells by these cytotoxic T cells. These findings support the hypothesis that for eradication of CML a cytotoxic T-cell response against leukemic progenitor cells is essential.

Responses to donor lymphocyte infusion for acute lymphoblastic leukemia may be determined by both qualitative and quantitative limitations of antileukemic T-cell responses as observed in an animal model for human leukemia

OBJECTIVE

Donor lymphocyte infusion (DLI) after allogeneic stem cell transplantation is largely unsuccessful in the treatment of acute lymphoblastic leukemia (ALL). To allow identification of the causes of this failure, we established an animal model of DLI in human ALL.

METHODS

NOD/scid mice were inoculated with primary human ALL cells. Cells from five different patients were studied. After engraftment, DLI was performed by infusion of human leukocyte antigen (HLA)-identical donor T cells or HLA-disparate donor T cells.

RESULTS

DLI resulted in expansion of activated, leukemia-reactive T cells in all donor-patient combinations. After 40 days of expansion, T cells abruptly declined in numbers and displayed loss of cytotoxicity. At this moment, remissions were observed in three of five donor-patient combinations. In animals engrafted with the two unresponsive ALL, remissions could be achieved when HLA-disparate DLI was given.

CONCLUSION

Our results indicate that the inefficacy of DLI in ALL may be due to the limitation of the proliferative capacity of ALL-reactive T cells and that the antileukemic efficacy during the limited time span of proliferation depends on the antigenic disparity between the donor and the patient. The model can be used to study whether alternative strategies may result in more sustained antileukemic responses after DLI in ALL.

Graft-versus-leukemia target antigens in chronic myelogenous leukemia are expressed on myeloid progenitor cells

PURPOSE

Donor lymphocyte infusion (DLI) reliably induces durable remission in 75% to 80% of patients with relapsed chronic myelogenous leukemia (CML) following allogeneic bone marrow transplantation. We previously reported the identification of a high titer-specific immunoglobulin G response against two novel leukemia-associated antigens, CML28 and CML66, which correlated with immune-induced remission. The present studies characterize expression of CML28 and CML66 in primary hematopoietic tissues.

EXPERIMENTAL DESIGN

Specific monoclonal antibodies to CML28 and CML66 were developed and used to detect antigen expression in leukemia cell lines and primary leukemia tissue on Western blot and immunohistochemistry. Expression patterns were confirmed by antigen-specific real-time PCR.

RESULTS

Both CML28 and CML66 were highly expressed in leukemic blasts from patients with acute myelogenous leukemia and CML blast crisis but barely detectable in normal bone marrow, normal peripheral blood, or leukemic cells from patients with stable-phase CML. In contrast, purified CD34+ progenitors from normal individuals and patients with stable-phase CML expressed high levels of CML28 and CML66 transcript and protein. Immunohistochemical staining for CML66 confirmed rare staining of myeloid precursors in normal marrow and diffuse staining of myeloblastic cells in acute myelogenous leukemia and blast crisis CML marrows.

CONCLUSIONS

The expression patterns of CML28 and CML66 are strikingly similar and suggest that antigen expression may play a role in shaping the post-DLI antibody repertoire. The CD34+ restricted pattern of expression of CML28 and CML66 is particularly relevant in light of the notion that DLI likely exerts its curative effect by targeting antigens present in self-renewing malignant progenitor populations in CML.

Heteroclitic CD33 peptide with enhanced anti-acute myeloid leukemic immunogenicity

The goal of these studies was to engineer a synthetic CD33 peptide with enhanced immunogenicity for the induction of acute myeloid leukemia (AML)-specific CTLs. Eight modified CD33 peptides YLISGDSPV, YIGSGDSPV, YIIIGDSPV, YIILGDSPV, YIISGISPV, YIISGDLPV, YIISGDSWV and YIISGDSPL were designed for increased HLA-A2.1 or T cell receptor affinity and compared with the native CD33(65-73) peptide, AIISGDSPV, for enhanced immunogenicity. The YLISGDSPV peptide was found to be the most immunogenic epitope producing highly cytolytic CTLs against AML target cells. The CTLs generated withYLISGDSPV peptide showed CD33 peptide-specificity through targeting of both native (AIISGDSPV) and modified (YLISGDSPV) peptide presenting EBV-BLCL. The CTL cultures displayed a distinct phenotype consisting of a high percentage of activated memory (CD69(+)/CD45RO(+))-CD8(+)and a low percentage of naive (CD45RA(+)/CCR7(+))-CD8(+)cells. In addition, T-cell clones specific to the YLISGDSPV peptide were isolated and characterized to target AML cells. The clones exhibited both HLA-A2.1-restricted and AML cell-specific cytotoxicity that was mediated through a granule-dependent pathway. More importantly, the CTL clones did not lyse or inhibit the proliferation of normal CD34(+) progenitor cells. In conclusion, we report on the identification of a highly immunogenic heteroclitic YLISGDSPV CD33 epitope that is a promising candidate for immunotherapy targeting AML.

Chronic myeloid leukemia: current application of cytogenetics and molecular testing for diagnosis and treatment

Chronic myeloid leukemia provides an illustrative disease model for both molecular pathogenesis of cancer and rational drug therapy. Chronic myeloid leukemia is a clonal stem cell disease caused by an acquired somatic mutation that fuses, through chromosomal translocation, the abl and bcr genes on chromosomes 9 and 22, respectively. The bcr/abl gene product is an oncogenic protein that localizes to the cytoskeleton and displays an up-regulated tyrosine kinase activity that leads to the recruitment of downstream effectors of cell proliferation and cell survival and consequently cell transformation. Such molecular information on pathogenesis has facilitated accurate diagnosis, the development of pathogenesis-targeted drug therapy, and most recently the application of molecular techniques for monitoring minimal residual disease after successful therapy. These issues are discussed within the context of clinical practice.

A novel approach to identify antigens recognized by CD4 T cells using complement-opsonized bacteria expressing a cDNA library

In patients with hematological malignancies receiving HLA-matched stem cell transplantation, T cells specific for minor histocompatibility antigens play a major role in graft rejection, induction of graft-versus-host disease and beneficial graft-versus-leukemia reactivity. Several human minor histocompatibility antigens recognized by T cells have been identified, but only two are presented by HLA class II molecules. In search of an efficient approach to identify antigenic peptides processed through the HLA class II pathway, we constructed a cDNA library in bacteria that were induced to express proteins. Bacteria were opsonized with complement to enforce receptor-mediated uptake by Epstein-Barr virus immortalized B cells that were subsequently used as antigen-presenting cells. This approach was validated with an HLA class II-restricted antigen encoded by gene DBY. We were able to identify bacteria expressing DBY diluted into a 300-fold excess of bacteria expressing a nonrelevant gene. Screening of a bacterial library using a DBY-specific CD4 T cell clone resulted in the isolation of several DBY cDNAs. We propose this strategy for a rapid identification of HLA class II-restricted antigenic peptides recognized by CD4 T cells.

Minor histocompatibility antigen-specific T cells with multiple distinct specificities can be isolated by direct cloning of IFNγ-secreting T cells from patients with relapsed leukemia responding to donor lymphocyte infusion

Graft-vs-leukemia reactivity after donor lymphocyte infusion (DLI) can be mediated by donor T cells recognizing minor histocompatibility antigens (mHags) on recipient hematopoietic cells. To study the diversity of cells involved in this immune response, hematopoietic cell reactive T cells were directly clonally isolated from peripheral blood of patients entering complete remission after DLI. T cells were briefly stimulated with bone marrow cells from patients pretransplant, and IFNgamma-secreting T cells were directly clonally isolated, and expanded. Cytotoxic T-lymphocyte (CTL) clones from individual patients used multiple distinct HLA-restricting molecules and varied in reactivity against patient-derived normal and/or malignant hematopoietic cells. For each patient, CTL clones specific for known immunodominant mHags as well as distinct unknown mHags were found. Within individual patients, CTL clones using the same HLA-restricting element could show differential recognition patterns, indicating further diversity in mHag reactivity. CTL clones from individual patients exhibiting identical specificities could show oligoclonal origin. In conclusion, the direct cloning technique shows that the response to hematopoietic cells after DLI is directed against multiple distinct mHags, including but not limited to known immunodominant mHags, implying that immunotherapy with T cells against multiple mHag specificities may be more effective in eradicating malignant cells.

Direct cloning of leukemia-reactive T cells from patients treated with donor lymphocyte infusion shows a relative dominance of hematopoiesis-restricted minor histocompatibility antigen HA-1 and HA-2 specific T cells

Donor T cells recognizing hematopoiesis-restricted minor histocompatibility antigens (mHags) HA-1 and HA-2 on malignant cells play a role in the antileukemia effect of donor lymphocyte infusion (DLI) in patients with relapsed leukemia after allogeneic stem cell transplantation. We quantified the contribution of HA-1 and HA-2 specific T cells to the total number of leukemia-reactive T cells in three HA-2 and/or HA-1 positive patients responding to DLI from their mHag negative donors. Clinical responses occurring 5-7 weeks after DLI were accompanied by an increase in percentages HLA-DR expressing T cells within the CD8+ T cell population. To clonally analyze the leukemia-reactive immune response, T cells responding to the malignancy by secreting IFNgamma were isolated from peripheral blood, directly cloned, and expanded. Tetramer analysis and specific lysis of peptide-pulsed target cells showed that 3-35% of cytotoxic T lymphocyte (CTL) clones isolated were specific for HA-1 or HA-2. TCR VB analysis showed oligoclonal origin of the HA-1 and HA-2 specific CTL clones. The HA-1 and HA-2 specific CTL clones inhibited leukemic progenitor cell growth in vitro. The relatively high frequency of HA-1 and HA-2 specific T cells within the total number of tumor-reactive T cells illustrates relative immunodominance of mHags HA-1 and HA-2.

Reprogramming of virus-specific T cells into leukemia-reactive T cells using T cell receptor gene transfer

T cells directed against minor histocompatibility antigens (mHags) might be responsible for eradication of hematological malignancies after allogeneic stem cell transplantation. We investigated whether transfer of T cell receptors (TCRs) directed against mHags, exclusively expressed on hematopoietic cells, could redirect virus-specific T cells toward antileukemic reactivity, without the loss of their original specificity. Generation of T cells with dual specificity may lead to survival of these TCR-transferred T cells for prolonged periods of time in vivo due to transactivation of the endogenous TCR of the tumor-reactive T cells by the latent presence of viral antigens. Furthermore, TCR transfer into restricted T cell populations, which are nonself reactive, will minimize the risk of autoimmunity. We demonstrate that cytomegalovirus (CMV)-specific T cells can be efficiently reprogrammed into leukemia-reactive T cells by transfer of TCRs directed against the mHag HA-2. HA-2-TCR–transferred CMV-specific T cells derived from human histocompatibility leukocyte antigen (HLA)-A2⁺ or HLA-A2⁻ individuals exerted potent antileukemic as well as CMV reactivity, without signs of anti–HLA-A2 alloreactivity. The dual specificity of these mHag-specific, TCR-redirected virus-specific T cells opens new possibilities for the treatment of hematological malignancies of HLA-A2⁺ HA-2–expressing patients transplanted with HLA-A2–matched or –mismatched donors.

Cellular immunotherapy after allogeneic stem cell transplantation in hematologic malignancies

PURPOSE OF REVIEW

The chimeric state after allogeneic stem cell transplantation provides an ideal platform for adoptive immunotherapy of hematologic malignancies using donor-derived cells. The present review aims to summarize recent results of the transfusion of donor-derived cells with regard to the diseases treated, the cells used for treatment, and the origin of these cells.

RECENT FINDINGS

The transfusion of donor lymphocytes has been studied widely, not only in patients with recurrent disease, persistent disease, and mixed chimerism but also in a variety of hematologic malignancies. Donors of lymphocytes and hematopoietic stem cells have been HLA-identical siblings, HLA-matched unrelated donors, and HLA-different haploidentical family members. A variety of cells have been used for adoptive immunotherapy, including plain lymphocytes, selected T cells, T cell lines, and T cell clones. The possible therapies have been expanded by natural killer cells and natural killer T cells as well as antibodies directing the effector cells toward the malignancy.

SUMMARY

Adoptive immunotherapy in chimeras has become not only a routine form of treatment of recurrent hematologic malignancy but also a prophylactic measure in high-risk leukemia and lymphoma.

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

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

New CFSE-based assay to determine susceptibility to lysis by cytotoxic T cells of leukemic precursor cells within a heterogeneous target cell population

For the clinical evaluation of the efficacy of cellular immunotherapy it is necessary to analyze the effector functions of T cells against primary leukemic target cell populations which are usually considerably heterogeneous caused by differential maturation stages of the leukemic cells. An appropriate assay should not only allow the quantitative analysis of rapid cell death induction as measured by the conventional 51Cr release assay but also of the more slowly executing pathways of T-cell-induced apoptosis occurring within days instead of hours which cannot be measured using this method. Furthermore, it should dissect the differential susceptibility to T-cell-induced cell death of various target cell subpopulations and characterize the malignant precursor cells capable of producing malignant progeny. To fulfill these requirements we developed a new assay based on carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling of the target cell population combined with antibody staining of specific cell populations and addition of fluorescent microbeads to quantitatively monitor target cell death occurring within a longer time frame up to at least 5 days. This new assay facilitates the analysis of differential recognition of distinct cell types within a heterogeneous target cell population and allows simultaneously evaluation of the proliferative status of surviving target cells in response to relevant cytokines.

Redirection of antileukemic reactivity of peripheral T lymphocytes using gene transfer of minor histocompatibility antigen HA-2-specific T-cell receptor complexes expressing a conserved alpha joining region

Donor-derived T lymphocytes directed against minor histocompatibility antigens (mHags) exclusively expressed on cells of the hematopoietic lineages can eliminate hematologic malignancies. Transfer of T-cell receptors (TCRs) directed against these mHags into T lymphocytes may provide a strategy to generate antileukemic T cells. To investigate the feasibility of this strategy the TCR usage of mHag HA-2-specific T-cell clones was characterized. Thirteen different types of HA-2-specific T-cell clones were detected, expressing TCRs with diversity in TCR alpha- and beta-chain usage, however, containing in the TCR alpha chain a single conserved gene segment J alpha 42, indicating that J alpha 42 is involved in HA-2-specific recognition. We transferred various HA-2 TCRs into T lymphocytes from HLA-A2-positive HA-2-negative individuals resulting in T cells with redirected cytolytic activity against HA-2-expressing target cells. Transfer of chimeric TCRs demonstrated that the HA-2 specificity is not only determined by the J alpha 42 region but also by the N-region of the alpha chain and the CDR3 region of the beta chain. Finally, when HA-2 TCRs were transferred into T cells from HLA-A2-negative donors, the HA-2 TCR-modified T cells exerted potent antileukemic reactivity without signs of anti-HLA-A2 alloreactivity. These results indicate that HA-2 TCR transfer may be used as an alternative strategy to generate HA-2-specific T cells to treat hematologic malignancies of HLA-A2-positive, HA-2-expressing patients that received transplants from HLA-A2-matched or -mismatched donors.

The progenitor cell inhibition assay to measure the anti-leukemic reactivity of T cell clones against acute and chronic myeloid leukemia

Adoptive immunotherapy with donor T lymphocytes may be used as a treatment for relapsed leukemia after allogeneic hematopoietic stem cell transplantation (SCT). In vitro selected and expanded anti-leukemic T cells may be more effective in inducing a response in vivo. To identify the anti-leukemic reactivity of in vitro generated T cells, standard target cell read-out assays like the 51Cr-release assay are not always appropriate. We developed an assay in which the ability of T cells to antigen specifically inhibit the in vitro growth of leukemic progenitor cells in the presence of cytokines can be measured. This assay allows the evaluation of the cytolytic or suppressive potential of leukemia reactive T cells for prolonged periods of time. The assay is based on inhibition of [3H]thymidine incorporation by the leukemic progenitor cells induced by multiple hematopoietic growth factors. T cell clones with a known specificity were used to compare the analytic potential of the new assay with those of other cytotoxicity assays. Based on the results of the T cell clones, a modification of a limiting dilution assay was developed to identify anti-leukemic allogeneic T cells in HLA identical donor-recipient combinations selected on their ability to inhibit the in vitro growth of CML or AML progenitor cells, to be used for the generation of leukemia-reactive CTL lines for clinical use.

Allogeneic hematopoietic stem cell transplantation for myeloproliferative disorders and myelodysplastic syndromes

Allogeneic SCT is the most effective method to achieve cure in patients with MPD and MDS. This approach is associated with significant risk of morbidity (eg, GVHD) and TRM, although the incidence and severity vary based on donor and recipient characteristics. For young patients with HLA-matched donors, SCT is the preferred therapy. Efforts to improve outcome for older patients and for patients with alternative donors have led to decreased treatment-associated complications with associated better long-term DFS.

Minimal GVHD following in-vitro Tcell–depleted allogeneic stem cell transplantation with reduced-intensity conditioning allowing subsequent infusions of donor lymphocytes in patients with hematological malignancies and solid tumors

OBJECTIVE

Allogeneic stem cell transplantation (alloSCT) following reduced-intensity conditioning offers a relatively nontoxic regimen while preserving rapid and sustained engraftment. Acute and chronic graft-vs-host disease (GVHD) is, however, a significant cause of severe morbidity. To reduce the incidence of GVHD, we treated a group of high-risk patients with a reduced-intensity conditioning regimen followed by in vitro T-cell-depleted alloSCT using Campath 1-H incubation.

PATIENTS AND METHODS

Eighteen patients were treated with fludarabine (6 x 30 mg/m(2)), busulphan (2 x 3.2 mg/kg), and ATG (4 x 10 mg/kg) followed by the infusion of high-dose T-cell-depleted peripheral stem cells from sibling donors. No posttransplant GVHD prophylaxis was administered. At 6 months after alloSCT, low-dose donor lymphocyte infusion (DLI) was administered.

RESULTS

All patients had sustained engraftment of donor cells with a median of 95% donor cells at 3 months after alloSCT. Minimal acute and no chronic GVHD was observed after alloSCT. A high incidence of cytomegalovirus (CMV) reactivation but no CMV disease was observed. Eleven patients received DLI at a median of 6.5 months after alloSCT. Acute GVHD grade II-III developed in 6 patients. All patients showed improvement of donor chimerism after DLI. With a median follow-up of 211 days, 11 patients are alive. Particular in patients with chronic lymphocytic leukemia and acute myeloid leukemia, a significant graft-vs-tumor effect was observed.

CONCLUSIONS

In vitro T-cell-depleted alloSCT following reduced-intensity conditioning leads to durable donor engraftment without GVHD. The high levels of donor chimerism allow the subsequent use of cellular immunotherapy to treat residual disease.

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.

HLA-DRB1*16-restricted recognition of myeloid cells, including CD34+ CML progenitor cells

The therapeutic effect of a human leucocyte antigen (HLA)-identical allogeneic stem cell transplantation (allo-SCT) for the treatment of haematological malignancies is mediated partly by the allogeneic T cells that are administered together with the stem cell graft. Chronic myeloid leukaemia (CML) is particularly sensitive to this graft-versus-leukaemia (GVL) effect. Several studies have shown that in allogeneic responses both CD4 and CD8 cells are capable of strong antigen-specific growth inhibition of leukaemic progenitor cells, but that CD4 cells mainly exert the GVL effect against CML. Efficient activation of allogeneic CD4 cells, as well as CD8 cells, may explain the sensitivity of CML cells to elimination by allogeneic T cells. Identification of the antigens recognized by CD4 cells is crucial in understanding the mechanism through which CML cells are so successful in activating allogeneic T cells. In the present report, we describe the characterization of an allogeneic CD4 T-cell clone, DDII.4.4. This clone was found to react against an antigen that is specifically expressed in myeloid cells, including CD34+ CML cells. The antigen recognition is restricted by HLA-DRB1*16. To our knowledge, this is only the second report on an allogeneic CD4 T-cell clone that reacts with early CD34+ myeloid progenitor cells.

Hematopoiesis-restricted minor histocompatibility antigens HA-1- or HA-2-specific T cells can induce complete remissions of relapsed leukemia

Donor lymphocyte infusion (DLI) into patients with a relapse of their leukemia or multiple myeloma after allogeneic stem cell transplantation (alloSCT) has been shown to be a successful treatment approach. The hematopoiesis-restricted minor histocompatibility antigens (mHAgs) HA-1 or HA-2 expressed on malignant cells of the recipient may serve as target antigens for alloreactive donor T cells. Recently we treated three mHAg HA-1- and/or HA-2-positive patients with a relapse of their disease after alloSCT with DLI from their mHAg HA-1- and/or HA-2-negative donors. Using HLA-A2HA-1 and HA-2 peptide tetrameric complexes we showed the emergence of HA-1- and HA-2-specific CD8(+) T cells in the blood of the recipients 5-7 weeks after DLI. The appearance of these tetramer-positive cells was followed immediately by a complete remission of the disease and restoration of 100% donor chimerism in each of the patients. Furthermore, cloned tetramer-positive T cells isolated during the clinical response specifically recognized HA-1 and HA-2 expressing malignant progenitor cells of the recipient and inhibited the growth of leukemic precursor cells in vitro. Thus, HA-1- and HA-2-specific cytotoxic T lymphocytes emerging in the blood of patients after DLI demonstrate graft-versus-leukemia or myeloma reactivity resulting in a durable remission. This finding implies that in vitro generated HA-1- and HA-2-specific cytotoxic T lymphocytes could be used as adoptive immunotherapy to treat hematological malignancies relapsing after alloSCT.

High susceptibility of human leukemic cells to Fas-induced apoptosis is restricted to G1 phase of the cell cycle and can be increased by interferon treatment

In this study, we analyzed the influence of cell cycle status manipulations of leukemic cells on Fas-mediated apoptosis using the GM-CSF-dependent human myeloid leukemia cell line AML-193 as a model. GM-CSF and long-term treatment with interferon-gamma (IFN-gamma) or interferon-alpha (IFN-alpha) were used to manipulate the cell cycle status. Control cells were GM-CSF deprived, nonproliferating cells. IFN-gamma or IFN-alpha treatment did not induce proliferation in control cells, but resulted in recruitment of cells from resting G(0) phase into activated G(1) phase. Using agonistic anti-Fas antibodies (FAS18), we demonstrated that this shift from G(0) to G(1) was accompanied by a 2.5-fold increase in Fas sensitivity. A similar increase in sensitivity to FAS18 could be obtained by induction of proliferation with GM-CSF. Quantitative FACS analysis of surviving cells after FAS18-induced apoptosis showed deletion of the G(1) compartment, but complete protection of resting G(0) cells. Cells in S or G(2)/M phase were relatively protected against Fas induction. In conclusion, sensitivity to Fas-mediated apoptosis was restricted to cells in G(1) phase of the cell cycle, and can be increased by treatment of cells with interferons. By this mechanism, interferon treatment may render leukemic cells more susceptible to lysis by T cells during immunotherapeutic interventions.

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.

Generation of alloreactive anti-leukemic cytotoxic T lymphocytes with attenuated GVHD properties from haploidentical parents in childhood acute lymphoblastic leukemia

We sought to generate alloreactive leukemia-reactive cytotoxic T lymphocytes from haploidentical parents by culture of peripheral blood mononuclear cells in vitro with irradiated leukemic blasts and IL-2 from children with ALL. After 21 days in culture the mean cytotoxicity of haploidentical lymphocytes against ALL blasts was 38% (n = 11). Cultured parental CTL were not leukemia specific but alloreactive as evidenced by equivalent cytotoxicity against stimulating ALL blasts and ConA-stimulated blasts from the other parent. The cultures yielded primarily CD8(+) T cells (59%). Irradiation of CTL limited proliferation by 96% but had no short-term effects on leukemia reactive cytotoxicity, suggesting a means to limit GVHD potential in vivo. One patient was treated for relapse of ALL post-haploidentical transplant with CTL generated from the original donor. A total of nine infusions were given: the first three were irradiated, while the last six were not due to disease progression. The patient experienced clearance of peripheral blasts, and despite concomitant infusion of IL-2 with the last three CTL infusions, did not experience immediate GVHD reactions. We conclude that ALL blasts are sufficiently immunostimulatory to generate in vitro CTL with provision of exogenous IL-2, and that these CTL could exert an anti-leukemia effect in vivo.

Loss or downregulation of HLA class I expression at the allelic level in acute leukemia is infrequent but functionally relevant, and can be restored by interferon

Human leukocyte antigen (HLA) class I expression at the allelic level was analyzed in 397 acute myeloid leukemia (AML) and 186 acute lymphoid leukemia (ALL) using a complement-dependent cytotoxicity assay. Impaired recognition possibly due to HLA downregulation was observed in 2% of the patients with AML and ALL in complete remission, and in 8%-15% in the groups with blasts. In 15 instances of diminished cytotoxicity, leukemic cells and control PHA blasts from the same patients were further analyzed using flow cytometry. In 4/6 ALL and 4/9 AML patients HLA downregulation or complete loss (2 patients) of cell surface expression could be confirmed. No genomic abnormalities were observed. In addition, 12 AML and 13 ALL patients were tested during relapse using flow cytometry. In 1/12 AML patients and 1/13 ALL patients allelic downregulation of cell surface expression was found. In two patients tested, downregulation or loss of cell surface expression of HLA class I antigens corresponded with impaired T cell mediated lysis by HLA restricted cytotoxic T lymphocyte.Treatment of the cells with alpha- or gamma-interferon could restore HLA class I expression and T-cell recognition. In conclusion, downregulation of cell surface expression of HLA class I expression at the allelic level in AML and ALL is infrequent but functionally relevant. HLA downregulation was reversible and T-cell recognition could be restored by alpha- or gamma-interferon.

Expression of CD86 in acute myelogenous leukemia is a marker of dendritic/monocytic lineage

OBJECTIVE

The aim of this study was to determine whether expression of the CD86 costimulatory molecule in acute myeloid leukemia (AML) can identify blast cells committed to the monocytic/dendritic lineage.

MATERIAL AND METHODS

One hundred ten consecutive AML patients observed at diagnosis were studied by flow cytometry. In selected experiments, in vitro cultures with CD34(+)CD86(+) or CD34(-)CD86(+) blasts were performed in the presence of granulocyte-macrophage colony-stimulating actor (GM-CSF) with or without tumor necrosis factor-alpha (TNF-alpha) or GM-CSF + interleukin-4 (IL-4), respectively, to induce a dendritic differentiation, documented by morphologic and immunophenotypic assays. T-cell alloreactivity to CD86(+) AML cells and leukemic dendritic cells (AML-DC) was tested in mixed leukocyte cultures and anti-leukemic cytotoxic assays.

RESULTS

CD86 was expressed in 54% AML, whereas CD80 and CD1a were only occasionally positive. CD86(+) AML samples included M5 and M4, but also 47% M0-M1 FAB types, and were more frequently CD14(+) (p < 0.00001) and CD34(-) (p = 0.00005) than CD86(-)AML. Six different patterns of CD86(+) AML were identified, according to CD34 or CD14 total or partial coexpression. Four samples enriched in CD34(+)CD86(+) AML cells differentiated into AML-DC CD86(+), CD80(+), CD40(+), CD11c(+), HLA-DR(++), CD14(+/-) that also were CD1a(+) or CD83(+), after 6 days of in vitro culture with GM-CSF +/- TNF-alpha. CD34(-)CD86(+) AML cells differentiated into AML-DC after 3 to 5 days (n = 5 experiments), and trisomy 8 was found in two AML and AML-DC samples by fluorescence in situ hybridization analysis. Finally, AML-DC induced more potent allo-T-cell proliferation, cytokine release, and anti-leukemic cytotoxicity than CD86(+) blasts.

CONCLUSIONS

In AML, CD86 is a marker of monocytic/dendritic lineage. Because CD86(+) blasts may differentiate into DC rapidly, CD86(+)AML patients could be optimal candidates for immunotherapy studies, both in autologous and allogeneic settings.

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.

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.

The peptide-specific alloreactive human T cell repertoire varies largely between individuals and is not extended in HLA-A*0205--anti-HLA-A*0201 pairings

Alloreactive T cells recognize framework or peptide-dependent determinants on foreign MHC molecules. Among the peptide-dependent alloreactive T cells a significant proportion is specific for one particular peptide presented by the allo-MHC molecule as antigen-specific T cells would do. Such alloreactive, peptide-specific T cells are referred to as 'allorestricted'. High-avidity HLA-A*02 allorestricted cytotoxic T lymphocyte (CTL) clones specific for peptide libraries can be generated from HLA-A*02(-) donors. We made use of this technique to study the role of closely related self-HLA molecules on shaping of the alloreactive T cell repertoire. Peripheral blood lymphocytes from HLA-A*0205 individuals were stimulated by HLA-A*0201 targets pulsed with an HLA-A*0201 peptide library. We did not observe a bias towards peptide-specific CTL in the HLA-A*0201-directed alloreactive repertoire of HLA-A*0205 donors as compared to HLA-A*02(-) donors. Comparison of the alloreactive T cell response between two donors having similar HLA haplotypes demonstrated that the allorestricted T cell repertoire is largely different between individuals.

Allogeneic bone marrow cells that facilitate complete chimerism and eliminate tumor cells express both CD8 and T-cell antigen receptor–αβ

Nonmyeloablative host conditioning regimens have been used in clinical allogeneic bone marrow and hematopoietic progenitor transplantation to effectively treat lymphohematopoietic tumors and reduce early toxicity. However, severe graft-versus-host disease (GVHD) remains a major problem. The goal of the current study was to determine whether specific subsets of cells in allogeneic bone marrow transplants can effectively treat the BCL1 B-cell lymphoma in nonmyeloablated BALB/c mouse hosts given a single dose of sublethal (450 cGy) total body irradiation, without inducing severe GVHD. The experimental results show that high doses of whole bone marrow cells from major histocompatiblity complex (MHC)-mismatched donors eliminate both normal and malignant host-type lymphohematopoietic cells without causing injury to nonlymphohematopoietic host tissues. The CD8+T-cell antigen receptor–αβ+(TCRαβ+) T cells within the marrow transplants mediated the killing of the tumor cells via both perforin- and FasL-dependent pathways. Cells present in marrow transplants from either CD8−/− or TCRα−/− donors failed to eliminate malignant and normal host lymphohematopoietic cells. Addition of small numbers of blood mononuclear cells to the marrow inoculum caused lethal GVHD. Thus, the resident allogeneic bone marrow CD8+ TCRαβ+ T cells had the unique capacity to eliminate the host lymphohematopoietic cells without nonlymphohematopoietic tissue injury.

Leukemia vaccines

Leukemia is susceptible to immune-mediated therapies such as allogeneic stem-cell transplantation, donor lymphocyte infusion, and interferon. The clinical effectiveness of these immune-based modalities has encouraged interest in vaccine therapies for leukemia. Substantial progress has recently been made in basic immunology, allowing scientifically based vaccination strategies to be developed. The discovery of leukemia- specific and leukemia-associated antigens will allow antigen-specific therapeutic strategies to be developed. Vaccination with genetically modified leukemia cells and the use of dendritic cells in various vaccination approaches are all promising avenues of study for development of effective leukemia vaccines.

Cutting edge: characterization of allorestricted and peptide-selective alloreactive T cells using HLA-tetramer selection

The vast majority of alloreactive T cells recognize foreign MHC molecules in a peptide-dependent manner. A subpopulation of these peptide-dependent alloreactive T cells is peptide-specific and contains T cells that are of interest for tumor immunotherapy. Allorestricted T cells (i.e., peptide-specific and alloreactive) specific for tumor-associated Ags can be raised in vitro. However, it is technically difficult to distinguish between peptide-specific and peptide-nonspecific alloreactive T cells by functional assays in vitro. Here we show for the first time that allorestricted T cells specifically bind HLA-peptide tetrameric complexes, as nominal Ag-specific T cells would do. In consequence, fluorescent HLA-peptide tetrameric complexes can be used for sorting and cloning of allorestricted CTLs specific for a peptide of interest. We also show by the mean of HLA-peptide tetramers the existence of peptide-selective alloreactive T cells that recognize a conformation on the foreign-MHC brought about by some but not all peptides bound.