Reinfusion of leukemic cells with the autologous marrow graft: preclinical studies on lodging and regrowth of leukemia

Cellular Reprogramming Allows Generation of Autologous Hematopoietic Progenitors From AML Patients That Are Devoid of Patient-Specific Genomic Aberrations

Current treatments that use hematopoietic progenitor cell (HPC) transplantation in acute myeloid leukemia (AML) patients substantially reduce the risk of relapse, but are limited by the availability of immune compatible healthy HPCs. Although cellular reprogramming has the potential to provide a novel autologous source of HPCs for transplantation, the applicability of this technology toward the derivation of healthy autologous hematopoietic cells devoid of patient-specific leukemic aberrations from AML patients must first be evaluated. Here, we report the generation of human AML patient-specific hematopoietic progenitors that are capable of normal in vitro differentiation to myeloid lineages and are devoid of leukemia-associated aberration found in matched patient bone marrow. Skin fibroblasts were obtained from AML patients whose leukemic cells possessed a distinct, leukemia-associated aberration, and used to create AML patient-specific induced pluripotent stem cells (iPSCs). Through hematopoietic differentiation of AML patient iPSCs, coupled with cytogenetic interrogation, we reveal that AML patient-specific HPCs possess normal progenitor capacity and are devoid of leukemia-associated mutations. Importantly, in rare patient skin samples that give rise to mosaic fibroblast cultures that continue to carry leukemia-associated mutations; healthy hematopoietic progenitors can also be generated via reprogramming selection. Our findings provide the proof of principle that cellular reprogramming can be applied on a personalized basis to generate healthy HPCs from AML patients, and should further motivate advances toward creating transplantable hematopoietic stem cells for autologous AML therapy. Stem Cells2013;33:1839–1849

Animal models of acute myelogenous leukaemia - development, application and future perspectives

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

Differences in heat sensitivity between normal and acute myeloid leukemic stem cells: feasibility of hyperthermic purging of leukemic cells from autologous stem cell grafts

OBJECTIVES

In autologous stem cell transplantation contamination of the graft with malignant cells is frequently noticed and necessitates the use of in vivo or in vitro purging modalities. The hematopoietic recovery after transplantation depends on the number of stem and progenitor cells in the transplant. Therefore, in the present study the effects of hyperthermic treatment on the human normal and acute myeloid leukemic (AML) stem cell compartment were investigated.

METHODS

Normal bone marrow and AML blasts were heat treated up to 120 minutes at 43 degrees C. The surviving fractions of the different stem cell subsets were determined using in vitro methylcellulose and cobblestone area-forming cell (CAFC) clonogenic assays, as well as the in vivo NOD/SCID repopulating assay. The leukemic nature of the colonies from AML cells was confirmed by RT-PCR analysis. In order to increase the therapeutic index of the hyperthermic purging modality, the heat treatment was preceded by a 3-hour incubation at 37 degrees C with the ether lipid ET-18-OCH(3) (25 microg/mL).

RESULTS

It could be demonstrated that normal progenitor cells are far more resistant to hyperthermia than leukemic progenitor cells (56%+/-7% vs 9.9%+/-2.6% survival after 60 minutes at 43 degrees C, respectively). Furthermore, normal hematopoietic stem cells appear to be extremely resistant to the heat treatment (94%+/-9% survival after 60 minutes at 43 degrees C). In contrast, in the leukemic stem cell compartment no significant differences in heat sensitivity between the stem cells and progenitor subsets could be observed (12.3%+/-2.9% vs 9.9%+/-2.6% survival after 60 minutes at 43 degrees C, respectively). The combined treatment resulted in a survival for normal progenitor and stem cells of 32%+/-6% and 85%+/-15% after 60 minutes at 43 degrees C, respectively. Under these conditions the number of leukemic stem cells was reduced to 1%+/-0.3%. After 120 minutes at 43 degrees C, no AML-colonies could be detected anymore.

CONCLUSIONS

Our data demonstrate that leukemic stem cells have an increased hyperthermic sensitivity compared to their normal counterparts and that this difference can be further increased in combination with ET-18-OCH(3). These striking differences in heat sensitivity warrant the use of hyperthermia as a clinically applicable purging modality in autologous stem cell transplantation.

Little evidence for clonal evolution of malignant haematopoietic cells following relapse after autologous bone marrow transplantation

By screening for immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements in bone marrow samples aspirated at different time points during the course of disease from 43 patients with acute leukaemia we have analysed the extent of clonal evolution after autologous bone marrow transplantation (ABMT) and addressed the issue of whether the Southern Blot method has the power to reveal clonal proliferations representing minimal residual disease (MRD) in the autologous bone marrow grafts. Our results show that no clonal proliferations were detectable in any of the 43 bone marrow grafts analysed, even after we analysed DNA preparations in 5 cases from cells highly enriched for cells of the original malignant immunophenotype. Moreover, as judged by the Ig- and TCR gene configurations in 11 patients, relapse arose from the original clone even though minor clonal variations did occur in about half of the relapsing patients. We conclude that while the Southern Blot method can detect gene receptor rearrangements in the majority of patients with acute leukaemias and high-grade non-Hodgkins lymphomas, it is not useful for predicting relapse after ABMT. On the other hand, it is possible-by employing it-to evaluate whether or not relapse after ABMT arises from the original malignant clone and to what extent clonal evolution has taken place.

In vitro purging of clonogenic leukemic cells from human bone marrow by heat: simulation experiments for autologous bone marrow transplantation

In order to apply a simple purging method by heat to autologous bone marrow transplantation (ABMT), we have revaluated the ability to purge clonogenic leukemic cells from the simulated marrow mixture of normal marrow cells and leukemic cell lines (HL-60, Molt-3 and HEL) in vitro by heat, using two different clonogenic assays for normal granulocyte-macrophage progenitors (CFU-GM) and leukemic cell lines. It appeared that in vitro hyperthermia (42 degrees C for 120 min) is able to selectively remove clonogenic leukemic cells from simulated tumor cell-normal marrow mixtures even when leukemic cell concentrations are increased up to 3 x 10(6) cells/ml in vitro, and results in a 4-6 log destruction of clonogenic leukemic cells/ml according to a limiting dilution assay, while leaving half of normal CFU-GM surviving. The hyperthermic purging of clonogenic leukemic cells was not affected in the presence of normal marrow cells in vitro. This high level of clonogenic leukemic cell depletion by heat correlated with that of immunologic and pharmacologic studies. These results suggest that in vitro hyperthermia could be applied effectively and safely for the elimination of residual clonogenic leukemic cells in autologous marrow grafts before ABMT.

A simple elimination of clonogenic tumor cells from human bone marrow in vitro by heat: its application to autologous bone marrow transplantation for B-cell lymphoma

The application of hyperthermia to the treatment of neoplastic disease has focused on solid tumors. Since the hyperthermic sensitivity of human B-cell lymphoma cells is not known, we have examined the effect of hyperthermia on the growth of B-cell lymphoma cell lines (Raji and Daudi) in vitro to evaluate the ability to purge tumor cells from normal bone marrow by heat, utilizing a limiting-dilution assay to measure log depletion of tumor cells in a 20-fold excess of normal bone marrow. When exposed at 42 degrees C and 43 degrees C for 120 min, both clonogenic Raji and Daudi cells were dramatically decreased (a 4- to 6-log reduction) with exposure time, while leaving over half of the normal granulocyte-macrophage progenitor cells surviving at 42 degrees C and 10% at 43 degrees C. This high level of lymphoma-cell depletion by heat correlated with that obtained in immunologic and pharmacologic studies. These results suggest that in vitro hyperthermia might be applied effectively for the elimination of residual lymphoma cells in autologous marrow grafts before autologous bone marrow transplantation in B-cell non-Hodgkin's lymphoma.

Minimal residual disease in acute leukaemia: preclinical studies in a relevant rat model (BNML)

The AML model in the BN rat has contributed considerably to improved understanding of the various aspects of leukaemia growth, responses to chemotherapy, application of BMT as treatment modality and the possibilities and limitations for the detection of residual disease during the remission phase. Obviously, there are restrictions with regard to the extrapolation of the rat data to the human situation. Leukaemia growth in inbred rats is highly reproducible, while in humans it presents a high degree of individual variation. However, several characteristics are shared and the aim should be to identify the similarities as well as the dissimilarities between human and rat leukaemia. In that way progress may be envisaged with respect to reaching the final goal of curing human leukaemia.

Minimal residual disease in leukemia: studies in an animal model for acute myelocytic leukemia (BNML)

The possibilities for studying minimal residual disease (MRD) in human acute myelocytic leukemia (AML) are limited. Animal models are, therefore, indispensable for gaining insight into the characteristics of leukemia growth during the MRD phase. Studies were done to compare AML to acute myelocytic leukemia in the Brown Norway rat (BNML). The BNML model exhibited a high degree of similarity to human AML with regard to its general growth characteristics, its cell kinetic parameters, its biophysical parameters and its response to chemotherapy. This implied that studies of the BNML model have predictive value for clinical application. In the BNML model a number of independent methods are available to quantify the number of leukemic cells, i.e., indirectly by means of various bioassays or directly by using monoclonal antibody labeling and flow cytometry. Studies of the BNML model in relation to the understanding of various aspects of MRD in leukemia are discussed in this concise review. Insight has been obtained with regard to the kinetics of MRD; the efficacy of certain treatment modalities, e.g., cytostatic drug treatment with or without total body irradiation to eradicate MRD; the efficacy of various methods for eliminating residual leukemic cells from autologous marrow grafts; the emergence of drug resistance during MRD; and the progression of residual disease during the remission phase ultimately leading to a relapse and the implications of these observations for staging leukemia patients during the phase of MRD.

Autologous bone marrow transplantation in acute myeloid leukemia in first remission: first Dutch prospective study

We have prospectively compared the values of autologous BMT (auto-BMT) and allogeneic marrow transplantation (allo-BMT) in patients (age 15-60 years) with acute myeloid leukemia (AML) who attained complete remission (CR) following remission-induction therapy. In 90/117 cases CR was reached. In 32 of those complete responders auto-BMT was undertaken and in 21 eligible cases HLA-matched allo-BMT. AML relapse was the predominant cause of failure after auto-BMT (17/32). The incidence of relapse after allo-BMT was 6/21. Patients treated with auto-BMT and allo-BMT have an overall survival of 37% and 66% at 3 years posttransplant (P = 0.05). Survival of the nongrafted complete responders is less than 10%. Allo-BMT in adult patients with AML in first complete remission provides a superior outcome when directly compared with the results of auto-BMT.