Antileukemic HLA-Restricted T-Cell Clones Generated With Naturally Processed Peptides Eluted From Acute Myeloblastic Leukemia Blasts

Dendritic cells pulsed with leukemia cell-derived exosomes more efficiently induce antileukemic immunities

Dendritic cells (DCs) and tumor cell-derived exosomes have been used to develop antitumor vaccines. However, the biological properties and antileukemic effects of leukemia cell-derived exosomes (LEXs) are not well described. In this study, the biological properties and induction of antileukemic immunity of LEXs were investigated using transmission electron microscopy, western blot analysis, cytotoxicity assays, and animal studies. Similar to other tumor cells, leukemia cells release exosomes. Exosomes derived from K562 leukemia cells (LEX_K562) are membrane-bound vesicles with diameters of approximately 50–100 μm and harbor adhesion molecules (e.g., intercellular adhesion molecule-1) and immunologically associated molecules (e.g., heat shock protein 70). In cytotoxicity assays and animal studies, LEXs-pulsed DCs induced an antileukemic cytotoxic T-lymphocyte immune response and antileukemic immunity more effectively than did LEXs and non-pulsed DCs (P<0.05). Therefore, LEXs may harbor antigens and immunological molecules associated with leukemia cells. As such, LEX-based vaccines may be a promising strategy for prolonging disease-free survival in patients with leukemia after chemotherapy or hematopoietic stem cell transplantation.

Dramatic efficacy improvement of a DC-based vaccine against AML by CD25 T cell depletion allowing the induction of a long-lasting T cell response

Dendritic cell (DC)-based vaccination is a promising approach to enhance anti-tumor immunity that could be considered for acute myeloid leukemia (AML) patients with high-risk of relapse. Our purpose was to study the efficiency and to optimize the immunogenicity of a DC-based vaccine in a preclinical AML murine model. In this report, C57BL6 mice were vaccinated with DC pulsed with peptides eluted (EP) from the syngeneic C1498 myelomonocytic leukemic cell line in a prophylactic setting. In this model, a natural antileukemic immunity mediated by NK cells was observed in the control unloaded DC-vaccinated group. On the other hand, we showed that the cytotoxic antileukemic immune response induced by vaccination with eluted peptides pulsed-DC (DC/EP), in vitro and in vivo, was mainly mediated by CD4(+) T cells. Treatment with anti-CD25 antibody to deplete CD4(+) CD25(+) regulatory T cells before DC-vaccination dramatically improved the antileukemic immune response induced by immunization, and allowed the development of long-lasting immune responses that were tumor protective after a re-challenge with leukemic cells. Our results suggest that this approach could be successful against weakly immunogenic tumors such as AML, and could be translated in human.

DC-based vaccine loaded with acid-eluted peptides in acute myeloid leukemia: the importance of choosing the best elution method

Tumor-associated peptides isolated by acid elution are frequently used for therapeutic immunization against various tumors both in mice and in humans. In acute myeloid leukemia (AML), the frequent accessibility of a large tumor burden allows for extraction of peptides from leukemia cells by using either citrate-phosphate (CP) or trifluoroacetic acid (TFA) buffer. To develop an optimal immunotherapeutic protocol for AML patients, we evaluated both in mice and in humans, the immunogenicity of peptides eluted from leukemia cells with the two acids (TFA or CP). Although ex vivo studies in mice showed that both prophylactic immunizations with mature dendritic cells (DC) loaded with TFA-peptides (DC/TFA), or CP-peptides (DC/CP), were able to stimulate specific antileukemia immune responses, only vaccination with DC/TFA was able to prevent leukemia outgrowth. Moreover, in humans, only DC/TFA generated significant antileukemia CD4(+) and cytotoxic CD8(+) T cell responses in vitro. In summary, these data demonstrate that the choice of the acid elution procedure to isolate immunogenic peptides strongly influences the efficacy of the antileukemia immune responses. These finding raise essential considerations for the development of immunotherapeutic protocols for cancer patients. In our model, our results argue for the use of the TFA elution method to extract immunogenic AML-associated peptides.

Proteasome-inhibited dendritic cells demonstrate improved presentation of exogenous synthetic and natural HLA-class I peptide epitopes

The design and successful clinical implementation of cancer vaccines targeting the induction of T-cell mediated immunity is a rapidly evolving field that is hampered by an empirical selection of antigen and adjuvant. In particular, vaccines using defined tumor-associated peptide epitopes elicit only a restricted T-cell repertoire in a minority of patients. In this regard, vaccines comprising the whole spectrum of antigens presented by individual autologous tumors would be advantageous. In an in vitro model, we evaluated the capacity of naturally processed Epstein-Barr virus-transformed B-lymphoblastoid-cell line (LCL)-derived peptides to activate virus-specific CD8+ T cells of seropositive healthy individuals. While bulk peptides obtained by mild acid elution from LCL contained multiple T-cell epitopes, this complex mixture of peptides was poorly immunogenic, even when presented by mature dendritic cells (DC). Pretreatment of DC with proteasome inhibitors strongly enhanced the immunogenicity of single viral synthetic as well as bulk LCL peptides. This was most likely achieved by facilitating the loading of exogenous epitopes onto DC-associated HLA-class I complexes in the face of significant inter-peptide competition for such loading. Our results suggest that proteasome inhibitors may be used to increase the antigenicity of mature DC pulsed with exogenous synthetic or naturally processed peptide epitopes in vaccination trials.

Ex Vivo Characterization of Multiepitopic Tumor-Specific CD8 T Cells in Patients with Chronic Myeloid Leukemia: Implications for Vaccine Development and Adoptive Cellular Immunotherapy

Identification of tumor-associated Ags is a prerequisite for vaccine-based and adoptive immune therapies. Some tumor-associated Ags elicit specific CD8 T cells in patients with chronic myeloid leukemia (CML). Here, we characterized ex vivo responses of CD8 T cells from CML patients to extrajunction bcr-abl peptides and telomerase 540-548 hTert, PR1, and WT1 peptides. CML-specific CD8 T cells were present in most treated patients and were usually multiepitopic: WT1, hTert, PR1, and bcr74 tetramer(+) cells were detected in 85, 82, 67, and 61% of patients, respectively. The breadth and magnitude of these responses did not differ significantly according to treatment or disease status. CML-specific tetramer(+) CD8 T cells had a predominantly memory phenotype, an intermediate perforin content, and low intracellular IFN-gamma accumulation in the presence of the relevant peptide. However, in short-term culture with HLA-matched leukemia cells, the patients' memory T cells were specifically reactivated to become IFN-gamma-producing effector cells, suggesting that CD8 T cell precursors with lytic potential are present in vivo and can be activated by appropriate stimulation. In conclusion, this study shows that multiepitopic tumor-specific CD8 T cell responses occur naturally in most CML patients, opening the way to new strategies for enhancing anti-CML immunity, in particular in patients with minimal residual disease.

The clinical implications of mixed lymphocyte reaction with leukemic cells

To evaluate the clinical implications of a mixed lymphocyte reaction between leukemic cells and lymphocytes from HLA-matched sibling donors, we attempted to generate donor-derived, graft-versus-leukemia-effective cells and to define their characteristics. We studied 8 patients with chronic myelogenous leukemia (CML), including 5 patients in the chronic phase (CP), 3 patients in the accelerated phase (AP), and 2 patients with acute myelogenous leukemia (AML) in their first complete remission. Cells from these patients were used as stimulators in a mixed lymphocyte reaction.The effects of natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) were separated by observing tests for cytotoxicity to target cells, including K562 cells, the patient's leukemic cells, and phytohemagglutinin (PHA) blasts. Donor-derived antileukemic CTLs againstthe patient's own leukemic cells are productive in vitro. The efficacy of generating CTLs against leukemic target cells was (in decreasing order) AML, CML-CP, and CML-AP. Cytotoxic activity against leukemic targets was prominent in 4 cases--2 CML-CP and the 2 AML cases. On the contrary, the 3 cases of CML-AP showed low CTL activity. In cases showing 1 positive result among 3 targets (K562 cells, the patient's leukemic cells, and PHA blasts), the relapse rate was significantly lower (P = .022) on follow-up (median, 33 months; 7-40 months) after hematopoietic stem cell transplantation. By a combined analysis of the cytotoxicity effects for all 3 target cells, we were able to demonstrate a correlation between leukemic relapse and the variable degree of the cytotoxicity test results. Although the total sample numbers for this study were low, we speculate that these results may come from differences in the individual characteristics of the leukemic cells that are in line with their clinical disease status.

Immunological weapons against acute myeloid leukaemia

A better understanding of the biology of malignant cells and of the host immune system together with dramatic advances in technology have led to the design of innovative immune-mediated approaches to control neoplastic clones, including various haematological malignancies. One of the major problems with conventional cancer therapies is their inability to eradicate residual cancer cells that are resistant to therapy, hence immune intervention might improve the clinical outcome of patients. This mini-review will focus mainly on immunological approaches to the therapy of acute myeloid leukaemia (AML), a subset of a much larger family of leukaemias. Immune-mediated approaches ranging from allogeneic lymphocyte transplants to cytokine therapy, immune-gene therapy and vaccination by dendritic-cell-based vaccines will be discussed.

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

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

Biological treatment in acute myelogenous leukaemia: how should T-cell targeting immunotherapy be combined with intensive chemotherapy?

T-cell targeting immunotherapy is now considered as a possible strategy in the treatment of acute myelogenous leukaemia (AML). Clinical importance of antileukaemic T-cell reactivity after allogeneic stem cell transplantation (SCT) is well established and the early experience from IL-2 therapy suggests that even autologous T-cells can mediate antileukaemic reactivity. The clinical experience also indicates that immunotherapy should begin when the leukaemia cell burden is minimal, and the detection of an operative cellular immune system, even in patients with chemotherapy-induced cytopenia, further suggests that it is possible to begin T-cell targeting therapy early after chemotherapy while patients are still cytopenic. However, adult patients in particular have a T-cell defect after chemotherapy that may last for several months. For this reason immunotherapy should probably be continued or repeated until a maximal effect is achieved when the patients no longer have a T-cell defect. This treatment approach may also be considered in combination with autologous SCT. T-cell targeting regimens should include, if possible, several therapeutic components. Firstly, native AML blasts can function as accessory cells during T-cell activation and in vivo therapy with T-cell growth factors (e.g., IL-2, IL-15) may then enhance antileukaemic reactivity or non-specific cytotoxicity against the AML cells; and secondly, a further enhancement of AML-specific reactivity may be achieved by vaccination with AML-specific peptides, immunisation with AML-blasts expressing a dendritic cell phenotype, or exposure to normal antigen-presenting cells (APC) pulsed with or expressing AML-specific peptide sequences.

Developmental approaches in immunological control of acute myelogenous leukaemia

After many years of hope and disillusionment, the possibility of utilizing immune-mediated approaches to control neoplastic clones has become a reality in various haematological malignancies. This is largely a consequence of the continuous advances in knowledge and the progressive development of more refined technologies that have led to a better understanding of the biology of the malignant cells and of the host immune system, to a more precise definition of disease entities and to the design of innovative therapeutic programmes. In this chapter, we will review different immunological strategies that have reached clinical practice in patients with acute myelogenous leukaemia (AML), the focus of this volume, and discuss pre-clinical developments that may in the near future translate into the design of new immunotherapeutic protocols for the management of AML. Treatment of AML with antibody directed therapy will also be discussed.

Functional and selective targeting of adenovirus to high-affinity Fcgamma receptor I-positive cells by using a bispecific hybrid adapter

Adenovirus (Ad) efficiently delivers its DNA genome into a variety of cells and tissues, provided that these cells express appropriate receptors, including the coxsackie-adenovirus receptor (CAR), which binds to the terminal knob domain of the viral capsid protein fiber. To render CAR-negative cells susceptible to Ad infection, we have produced a bispecific hybrid adapter protein consisting of the amino-terminal extracellular domain of the human CAR protein (CARex) and the Fc region of the human immunoglobulin G1 protein, comprising the hinge and the CH2 and CH3 regions. CARex-Fc was purified from COS7 cell supernatants and mixed with Ad particles, thus blocking Ad infection of CAR-positive but Fc receptor-negative cells. The functionality of the CARex domain was further confirmed by successful immunization of mice with CARex-Fc followed by selection of a monoclonal anti-human CAR antibody (E1-1), which blocked Ad infection of CAR-positive cells. When mixed with Ad expressing eGFP, CARex-Fc mediated an up to 250-fold increase of transgene expression in CAR-negative human monocytic cell lines expressing the high-affinity Fcgamma receptor I (CD64) but not in cells expressing the low-affinity Fcgamma receptor II (CD32) or III (CD16). These results open new perspectives for Ad-mediated cancer cell vaccination, including the treatment of acute myeloid leukemia.

Cytokine-driven differentiation of blasts from patients with acute myelogenous and lymphoblastic leukemia into dendritic cells

We investigated the ability of both acute myelogenous leukemia (AML) and acute lymphoblastic leukemia (ALL) blasts to differentiate into dendritic cells (DC) in vitro. Cytokine-supplemented suspension cultures of leukemic blasts in 98 patients with AML and five patients with ALL (normal karyotype, n = 2; BCR/ABL, n = 3) were performed. Mononuclear cells out of peripheral blood or bone marrow containing between 60% and 90% leukemic blasts were cultured for eight days using different growth factor combinations. The highest yield of CD1a(+)/CD14(-) cells could be obtained with stem cell factor, transforming growth factor-beta, tumor necrosis factor-alpha, GM-CSF, and FLT-3-ligand. In the AML samples the median content of CD1a(+)/CD14(-) cells after eight days of culture was 3.5% (r = 0%-82%). In five informed patients CD1a(+)/CD14(-) cells were sorted by fluorescence-activated cell sorting or immunomagnetic separation. Cytogenetic and polymerase chain reaction analyses showed known primary chromosomal aberrations (monosomy 7 and inversion 16) in the sorted fractions, respectively. Dendritic cells (DC) could be generated out of leukemic blasts in 68% of AML patients. Leukemic DC showed no phagocytosis of latex beads, but stimulated allogeneic naive cord blood-derived T cells more efficiently than did uncultured blasts. In ALL patients the median percentage of CD1a(+)/CD14(-) cells was 1.2% (r = 0.7%-3.8%) after culture. The sorted CD1(+)/CD14(-) fractions were BCR/ABL-negative when analyzed with fluorescence in situ hybridization, indicating their nonleukemic origin. Leukemic DC can be generated out of leukemic progenitors in patients with AML. These cells might become relevant for autologous and allogeneic immunotherapy in selected patients. BCR/ABL-positive lymphoblasts could not be transformed into cells with an early dendritic phenotype with the cytokines used in our experiments.

Transfusion Medicine: New Clinical Applications of Cellular Immunotherapy

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

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

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

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

Transfusion Medicine: New Clinical Applications of Cellular Immunotherapy

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

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

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

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