Feasibility of clinical dendritic cell vaccination in acute myeloid leukemia

Efficacy of dendritic cell-based immunotherapy produced from cord blood in vitro and in a humanized NSG mouse cancer model

AIM

To produce dendritic cells (DCs) from CD34⁺ stem cells from cord blood and explore their prophylactic and curative effect against tumors by vaccinating humanized NSG mice.

MATERIALS & METHODS

Separated CD34⁺ stem cells from cord blood were cultured for 30 days, and the resultant DCs (CD34-DCs) were collected. The basic function of the CD34-DCs and the cytotoxicity of CD34-cytotoxic-T lymphocytes (CTLs) were tested in vitro, and tumor inhibition in a humanized NSG mouse tumor model was observed.

RESULTS

The number of CD34-DCs reached approximately 9 log. These cells performed functions similar to those of DCs derived from monocytes from peripheral blood (PBMC-DCs). The CTLs of the CD34-DCs (CD34-CTLs) presented a better antitumor effect in vitro. The obvious prophylactic and therapeutic antitumor effects of the CD34-DC vaccine were observed in the humanized NSG mouse models.

CONCLUSION

CD34-DCs from cord blood were sufficient in quantity and quality as a vaccine agent against tumors in vitro and in vivo.

Can Dendritic Cell Vaccination Prevent Leukemia Relapse?

Leukemias are clonal proliferative disorders arising from immature leukocytes in the bone marrow. While the advent of targeted therapies has improved survival in certain subtypes, relapse after initial therapy is a major problem. Dendritic cell (DC) vaccination has the potential to induce tumor-specific T cells providing long-lasting, anti-tumor immunity. This approach has demonstrated safety but limited clinical success until recently, as DC vaccination faces several barriers in both solid and hematological malignancies. Importantly, vaccine-mediated stimulation of protective immune responses is hindered by the aberrant production of immunosuppressive factors by cancer cells which impede both DC and T cell function. Leukemias present the additional challenge of severely disrupted hematopoiesis owing to both cytogenic defects in hematopoietic progenitors and an abnormal hematopoietic stem cell niche in the bone marrow; these factors accentuate systemic immunosuppression and DC malfunction. Despite these obstacles, several recent clinical trials have caused great excitement by extending survival in Acute Myeloid Leukemia (AML) patients through DC vaccination. Here, we review the phenotype and functional capacity of DCs in leukemia and approaches to harness DCs in leukemia patients. We describe the recent clinical successes in AML and detail the multiple new strategies that might enhance prognosis in AML and other leukemias.

Hematologic neoplasms: Dendritic cells vaccines in motion

Dendritic cells (DCs) are bone-marrow-derived immune cells accounted for a key role in cancer vaccination as potent antigen-presenting cells within the immune system. Cancer microenvironment can modulate DCs maturation resulting in their accumulation into functional states associated with a reduced antitumor immune response. In this regard, a successful cancer vaccine needs to mount a potent antitumor immune response able to overcome the immunosuppressive tumor milieu. As a consequence, DCs-based approaches are a safe and promising strategy for improving the therapeutic efficacy in hematological malignancies, particularly in combinations with additional treatments. This review summarizes the most significant evidence about the immunotherapeutic strategies performed to target hematologic neoplasms including the tumoral associated antigens (TAA) pulsed on DCs, whole tumor cell vaccines or leukemia-derived DCs.

Procedures for the expansion of CD14(+) precursors from acute myeloid leukemic cells to facilitate dendritic cell-based immunotherapy

AIMS

Vaccination with acute myeloid leukemia (AML)-derived dendritic cells (DCs) is a promising immunotherapeutic approach to prevent relapse of AML. However, in clinical practice AML-derived DC culture is unfeasible in 40% of cases. Here, we demonstrate that AML cells can be expanded in vitro prior to differentiation with cocktails of cytokines with known myeloid growth-promoting effects.

RESULTS

Nine out of 13 initially CD14(-) samples gain de novo CD14 (>10%) expression (69% increment; p = 0.01) after in vitro expansion. These expanded CD14(+) leukemic cells displayed a high probability (six out of six initially CD14(-) samples tested) to differentiate into DCs upon culture with GM-CSF, TNF-α and IL-4.

CONCLUSION

Induction of CD14 on initially CD14(-) AML cells potentially increases the number of patients eligible for DC-based immunotherapy.

Dendritic cells in myelodysplastic syndromes: from pathogenesis to immunotherapy

Myelodysplastic syndromes (MDS) are clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis leading to peripheral cytopenias. Different processes are involved in its pathogenesis, such as (epi)genetic alterations and immunological dysfunctions. The nature of immune dysregulation is markedly different between various MDS risk groups. In low-risk MDS, the immune system is in a proinflammatory state, whereas in high-risk disease, immunosuppressive features facilitate expansion of the dysplastic clone and can eventually lead to disease progression to acute myeloid leukemia. Various cell types contribute to dysregulation of immune responses in MDS. Dendritic cells (DCs) are important regulators of immunity. However, the role of DCs in MDS has yet to be elucidated. It has been suggested that impaired DC function can hamper adequate immune responses. This review focuses on the involvement of DCs in immune dysregulation in low- and high-risk MDS and the implications for DC-targeted therapies.

Various ‘dendritic cell antigens’ are already expressed on uncultured blasts in acute myeloid leukemia and myelodysplastic syndromes

Aim and methods: Leukemia-derived dendritic cells (DCleu) potentially present the whole leukemic antigen repertoire. We studied antigen-expression profiles of blasts/dendritic cells (DCs) generated from 137 acute myeloid leukemia (AML)/49 myelodysplastic syndromes (MDS) patients with six different DC-generating media by flow-cytometry combining expression of blast/maturation and DC antigens (DCA:CD1a,b,c, CD25, CD40, CD80, CD83, CD86, CD137-L and CD206). Results: First, DCA are regularly and variably expressed on uncultured blasts/mononuclear cells (MNCs). Individual patients’ DCA profiles must be evaluated before DC-culture to find suitable DCA to estimate quality/quantity of DC after culture. Second, after culture in every patient, at least one marker fulfilled these criteria. Third, different DC-generating methods showed varying efficiency to generate DC: not every method was always successful. Fourth, individual FACS-DCA profiles showed a successful DC/DCleu generation with at least one of three previously tested methods in every given AML/MDS case. Fifth, pooling results of all selected best methods in every given case, 28/30% DC were generated from AML/MDS samples: >60% viable DC, on average 49/56% mature DC and on average 36% of blasts were convertible to DCleu resulting in on average 49% DCleu of AML-DC. Conclusions: Individual DCA-expression profiles should be evaluated before culture to evaluate DC counts/subtypes (mature/viableDC, DCleu) in individual patients.

Clinical evaluation of cellular immunotherapy in acute myeloid leukaemia

Immunotherapy is currently under active investigation as an adjuvant therapy to improve the overall survival of patients with acute myeloid leukaemia (AML) by eliminating residual leukaemic cells following standard therapy. The graft-versus-leukaemia effect observed following allogeneic haematopoietic stem cell transplantation has already demonstrated the significant role of immune cells in controlling AML, paving the way to further exploitation of this effect in optimized immunotherapy protocols. In this review, we discuss the current state of cellular immunotherapy as adjuvant therapy for AML, with a particular focus on new strategies and recently published results of preclinical and clinical studies. Therapeutic vaccines that are being tested in AML include whole tumour cells as an autologous source of multiple leukaemia-associated antigens (LAA) and autologous dendritic cells loaded with LAA as effective antigen-presenting cells. Furthermore, adoptive transfer of cytotoxic T cells or natural killer cells is under active investigation. Results from phase I and II trials are promising and support further investigation into the potential of cellular immunotherapeutic strategies to prevent or fight relapse in AML patients.

Recent advances in antigen-loaded dendritic cell-based strategies for treatment of minimal residual disease in acute myeloid leukemia

Therapeutic vaccination with dendritic cells (DCs) is recognized as an important experimental therapy for the treatment of minimal residual disease in acute myeloid leukemia. Many sources of leukemia-associated antigens and different methods for antigen loading of DCs have been used in an attempt to optimize anti-tumor responses. For instance, monocyte-derived DCs have been loaded with apoptotic whole-cell suspensions, necrotic cell lysates, tumor-associated peptides, eluted peptides and cellular DNA or RNA. Furthermore, monocyte-derived DCs can be chemically or electrically fused with leukemic blasts, and DCs have been cultured out of leukemic blasts. However, it remains a challenge in cancer immunotherapy to identify which of these methods is the most optimal for antigen loading and activation of DCs. This review discusses recent advances in DC research and the application of this knowledge towards new strategies for antigen loading of DCs in the treatment of minimal residual disease in acute myeloid leukemia.

Indoleamine 2,3-dioxygenase-expressing leukemic dendritic cells impair a leukemia-specific immune response by inducing potent T regulatory cells

BACKGROUND

The immunoregulatory enzyme indoleamine 2,3-dioxygenase, which catalyzes the conversion of tryptophan into kynurenine, is expressed in a significant subset of patients with acute myeloid leukemia, resulting in the inhibition of T-cell proliferation and the induction of regulatory T cells. Acute myeloid leukemia cells can be differentiated into dendritic cells, which have increased immunogenicity and have been proposed as vaccines against leukemia.

DESIGN AND METHODS

Leukemic dendritic cells were generated from acute myeloid leukemia cells and used as stimulators in functional assays, including the induction of regulatory T cells. Indoleamine 2,3-dioxygenase expression in leukemic dendritic cells was evaluated at molecular, protein and enzymatic levels.

RESULTS

We demonstrate that, after differentiation into dendritic cells, both indoleamine 2,3-dioxygenase-negative and indoleamine 2,3-dioxygenase-positive acute myeloid leukemia samples show induction and up-regulation of indoleamine 2,3-dioxygenase gene and protein, respectively. Indoleamine 2,3-dioxygenase-positive acute myeloid leukemia dendritic cells catabolize tryptophan into kynurenine metabolite and inhibit T-cell proliferation through an indoleamine 2,3-dioxygenase-dependent mechanism. Moreover, indoleamine 2,3-dioxygenase-positive leukemic dendritic cells increase the number of allogeneic and autologous CD4(+)CD25(+) Foxp3(+) T cells and this effect is completely abrogated by the indoleamine 2,3-dioxygenase-inhibitor, 1-methyl tryptophan. Purified CD4(+)CD25(+) T cells obtained from co-culture with indoleamine 2,3-dioxygenase-positive leukemic dendritic cells act as regulatory T cells as they inhibit naive T-cell proliferation and impair the complete maturation of normal dendritic cells. Importantly, leukemic dendritic cell-induced regulatory T cells are capable of in vitro suppression of a leukemia-specific T cell-mediated immune response, directed against the leukemia-associated antigen, Wilms' tumor protein.

CONCLUSIONS

These data identify indoleamine 2,3-dioxygenase-mediated catabolism as a tolerogenic mechanism exerted by leukemic dendritic cells and have clinical implications for the use of these cells for active immunotherapy of leukemia.

Clinical-grade manufacturing of autologous mature mRNA-electroporated dendritic cells and safety testing in acute myeloid leukemia patients in a phase I dose-escalation clinical trial

BACKGROUND AIMS

RNA-electroporated dendritic cell (DC)-based vaccines are rapidly gaining interest as therapeutic cancer vaccines. We report on a phase I dose-escalation trial using clinical-grade manufactured mature RNA-electroporated DC in acute myeloid leukemia (AML) patients.

METHODS

CD14(+) cells were isolated from leukapheresis products by immunomagnetic CliniMACS separation and differentiated into mature DC (mDC). mDC were electroporated with clinical-grade mRNA encoding the Wilm's tumor (WT1) antigen, and tested for viability, phenotype, sterility and recovery. To test product safety, increasing doses of DC were administered intradermally four times at 2-week intervals in 10 AML patients.

RESULTS

In a pre-clinical phase, immunomagnetic monocyte isolation proved superior over plastic adherence in terms of DC purity and lymphocyte contamination. We also validated a simplified DC maturation protocol yielding a consistent phenotype, migration and allogeneic T-cell stimulatory capacity in AML patients in remission. In the clinical trial, highly purified CD14(+) cells (94.5+/-3.4%) were obtained from all patients. A monocyte-to-mDC conversion factor of 25+/-10% was reached. All DC preparations exhibited high expression of mDC markers. Despite a decreased cell recovery of mDC after a combination of mRNA electroporation and cryopreservation, successful vaccine preparations were obtained in all AML patients. DC injections were well tolerated by all patients.

CONCLUSIONS

Our method yields a standardized, simplified and reproducible preparation of multiple doses of clinical-grade mRNA-transfected DC vaccines from a single apheresis with consistent mature phenotype, recovery, sterility and viability. Intradermal injection of such DC vaccines in AML patients is safe.

Dendritic cell-based immunotherapy in myeloid leukaemia: translating fundamental mechanisms into clinical applications

Immunotherapy for leukaemia patients, aiming at the generation of anti-leukaemic T cell responses, could provide a new therapeutic approach to eliminate minimal residual disease (MRD) cells in acute myeloid leukaemia (AML). Leukaemic blasts harbour several ways to escape the immune system including deficient MHC class II expression, low levels of co-stimulatory molecules and suppressive cytokines. Therapeutic vaccination with dendritic cells (DC) is now recognized as an important investigational therapy. Due to their unique antigen presenting capacity, immunosuppressive features of the leukaemic blasts can be circumvented. DC can be successfully cultured from leukaemic blasts in 60-70% of patients and show functional potential in vivo. Alternatively, monocyte derived DC obtained at time of complete remission loaded with leukaemia-specific antigens can be used as vaccine. Several sources of leukaemia-associated antigen and different methods of loading antigen onto DC have been used in an attempt to optimize antitumour responses including apoptotic cells, necrotic cell lysates and tumour-associated pep-tides. Currently, the AML-derived cell line MUTZ-3, an immortalized equivalent of CD34(+) DC precursor cells, is under investigation for vaccination purposes. For effective DC vaccination the intrinsic tolerant state of the patient must be overcome. Therefore, the development of efficient and safe adjuvants in antigen specific immunotherapeutic programs should be encouraged.

In vitro induction of a dendritic cell phenotype in primary human acute myelogenous leukemia (AML) blasts alters the chemokine release profile and increases the levels of T cell chemotactic CCL17 and CCL22

Immunotherapy is now considered in acute myelogenous leukemia (AML). A dendritic cell (DC) phenotype can be induced in primary human AML cells by in vitro culture in the presence of various cytokine combinations. The aim was to investigate whether this phenotypic alteration is associated with altered chemokine release. AML cells were cultured according to four protocols that have been characterized in detail for AML-DC induction: (1) granulocyte-macrophage colony-stimulating factor (GM-CSF) + interleukin-4 (IL-4) days 1-14 and tumor necrosis factor-alpha (TNF-alpha) for days 6-14, (2) GM-CSF + IL-4 + TNF-alpha + FMS-like tyrosine kinase 3-ligand (Fl3-L) for 8 days, (3) GM-CSF + IL-4 + TNF-alpha + Flt3-L + stem cell factor (SCF) + transforming growth factor-beta1 (TGF-beta1) for 8 days, and (4) 25 Gy gamma-irradiation combined with culture in the presence of GM-CSF + SCF + IL-3 for 4 days. Significantly increased AML-DC release of CCL17 and CCL22 was observed for protocols 1, 2, and 3, whereas effects on CCL2-5, CXCL8, and CXCL10 differed in all protocols. Neutralization studies using a transwell migration assay demonstrated the increased level of CCL17 and CCL22 release was important for AML-DC chemotaxis of normal T cells. Induction of a dendritic AML cell phenotype is associated with an altered chemokine release profile. Detailed characterization of chemokine release should be included in future studies of AML-DC vaccination.

Dendritic cell vaccines in acute leukaemia

There is a need for novel treatment for acute leukaemia as relapse rates remain unacceptably high. Immunotherapy aims to stimulate the patient's immune responses to recognize and destroy leukaemia cells whilst activating immune memory. The qualities of the most potent professional antigen-presenting cell, the dendritic cell (DC), can be used to stimulate leukaemia-specific cytotoxic T cells. DCs can be loaded with leukaemia antigens, or leukaemia blasts can be modified to express DC-like properties for use in vaccine therapy. This chapter will review the rationale for DC vaccine therapy, the preclinical and clinical trials to date, the barriers to successful DC vaccine therapies and the role of immune adjuncts to improve outcomes.

Dendritic cell-based immunotherapy in acute and chronic myeloid leukaemia

Persistence of residual leukaemia cells in acute and chronic myeloid leukaemia will eventually lead to a relapse of the disease. Dendritic cell-based vaccines might constitute a therapeutic option for leukaemia patients to control or eradicate minimal residual disease. Dendritic cells have the unique property to stimulate naïve T cells. In a majority of the myeloid leukaemia patients these cells can be generated directly from leukaemia cells, although several factors hamper the feasibility of this approach. Other options are being explored to make active specific DC-based immunotherapy in leukaemia more broadly applicable. This review summarises data on active specific DC-based immunotherapy in acute and chronic myeloid leukaemia and discusses current optimisation strategies.

Principles of dendritic cell-based immunotherapy in myeloid leukemia

Persistent presence of minimal residual disease in myeloid leukemia carries the risk of a relapse of the disease. In the setting of allogeneic transplants, leukemic cells have been proven to be susceptible to the action of immunocompetent T cells. Thus, an immunotherapeutic approach might hold promise in the attempt to eradicate or control residual leukemia cells. Dendritic cells (DCs) are very potent stimulators of immune responses and these cells have been widely used to target other types of malignancies. This review discusses the function and the applicability of leukemia-derived DCs for active specific immunotherapy in myeloid leukemia including possible pitfalls, and describes options to optimize DC-based vaccines.