Jacques Vargaftig

Leukemia-initiating cells from some acute myeloid leukemia patients with mutated nucleophosmin reside in the CD34− fraction

Leukemia-initiating cells (LICs) in acute myeloid leukemia (AML) are believed to be restricted to the CD34(+) fraction. However, one of the most frequently mutated genes in AML is nucleophosmin (NPM), and this is associated with low CD34 expression. We, therefore, investigated whether NPM-mutated AMLs have LICs restricted to the CD34(+) fraction. We transplanted sorted fractions of primary NPM-mutated AML into immunodeficient mice to establish which fractions initiate leukemia. Approximately one-half of cases had LICs exclusively within the CD34(-) fraction, whereas the CD34(+) fraction contained normal multilineage hematopoietic repopulating cells. Most of the remaining cases had LICs in both CD34(+) and CD34(-) fractions. When samples were sorted based on CD34 and CD38 expression, multiple fractions initiated leukemia in primary and secondary recipients. The data indicate that the phenotype of LICs is more heterogeneous than previously realized and can vary even within a single sample. This feature of LICs may make them particularly difficult to eradicate using therapies targeted against surface antigens.

Age-related changes in human hematopoietic stem/progenitor cells

Adult stem cells are critical for maintaining cellular homeostasis throughout life, yet the effects of age on their regenerative capacity are poorly understood. All lymphoid and myeloid blood cell lineages are continuously generated from hematopoietic stem cells present in human bone marrow. With age, significant changes in the function and composition of mature blood cells are observed. In this study, we report that age‐related changes also occur in the human hematopoietic stem cell compartment. We find that the proportion of multipotent CD34+CD38− cells increases in the bone marrow of elderly (>70 years) individuals. CD34+CD38+CD90−CD45RA+/−CD10− and CD34+CD33+ myeloid progenitors persist at the same level in the bone marrow, while the frequency of early CD34+CD38+CD90−CD45RA+CD10+ and committed CD34+CD19+ B‐lymphoid progenitors decreases with age. In contrast to mice models of aging, transplantation experiments with immunodeficient NOD/SCID/IL‐2Rγ null (NSG) mice showed that the frequency of NSG repopulating cells does not change significantly with age, and there is a decrease in myeloid lineage reconstitution. An age‐related decrease in the capacity of CD34+ cells to generate myeloid cells was also seen in colony‐forming assays in vitro. Thus, with increasing age, human hematopoietic stem/progenitor cells undergo quantitative changes as well as functional modifications.

Absence or low expression of fas-associated protein with death domain in acute myeloid leukemia cells predicts resistance to chemotherapy and poor outcome

In acute myeloid leukemia (AML), coexpression of death receptors and ligands of the tumor necrosis factor (TNF) receptor/TNF-α superfamily on leukemic cells after chemotherapy is not always accompanied by apoptosis, suggesting that the apoptotic death receptor signaling pathway is disrupted. Because Fas-associated protein with death domain (FADD) is the main adaptor for transmitting the Fas, TNF-related apoptosis-inducing ligand receptors, and TNF receptor 1 death signal, expression of FADD was analyzed by Western blot and immunocytochemistry in leukemic cells of 70 de novo AML patients treated with the European Organization of Research and Treatment of Cancer AML-10 randomized trial before initiation of induction chemotherapy. Thirty seven percent of patients (17 of 46) with FADD negative/low (FADD−/low) leukemic cells had a primary refractory disease compared with 12% of FADD+ patients (3 of 24; P = 0.05). FADD−/low expression was significantly associated with a worse event-free survival [EFS (P = 0.04)] and overall survival (P = 0.04). In multivariate analysis, FADD−/low protein expression was independently associated with a poor EFS and overall survival (P = 0.002 and P = 0.026, respectively). Importantly, FADD−/low protein expression predicted poor EFS even in patients with standard- or good-risk AML (P = 0.009). Thus, we identified low or absent expression of the FADD protein in leukemic cells at diagnosis as a poor independent prognostic factor that can predict worse clinical outcome even for patients with standard- or good-risk AML.

A Niche-Like Culture System Allowing the Maintenance of Primary Human Acute Myeloid Leukemia-Initiating Cells: A New Tool to Decipher Their Chemoresistance and Self-Renewal Mechanisms

Acute myeloid leukemia‐initiating cells (LICs) are responsible for the emergence of leukemia and relapse after chemotherapy. Despite their identification more than 15 years ago, our understanding of the mechanisms responsible for their self‐renewal activity and their chemoresistance remains poor. The slow progress in this area is partly due to the difficulty of studying these cells ex vivo. Indeed, current studies are reliant on xenotransplantation assays in immunodeficient mice. In this paper, we report that by modeling key elements of the bone marrow niche using different stromal feeder layers and hypoxic culture conditions, we can maintain LICs over at least 3 weeks and support their self‐renewal properties demonstrated through primary and secondary successful xenograft. We provide a proof of principle that this niche‐like culture system can be used to study LIC chemoresistance following in vitro cytarabine treatment similarly to the xenograft chemotherapy model. We found that although LICs are believed to be more chemoresistant than non‐LICs, functionally defined LICs are not enriched after cytarabine treatment, and heterogeneity in their resistance to treatment can be seen between patients and even within the same patient. We present a culture system that can be used as an in vitro surrogate for xenotransplantation and that has the potential to dramatically increase the throughput of the investigation of LICs. This would further provide the means by which to identify and target the functionality of the different signaling pathways involved in the maintenance and resistance of LICs to improve acute myeloid leukemia treatments.

Intensive chemotherapy with thiotepa, busulfan and cyclophosphamide and hematopoietic stem cell rescue in relapsed or refractory primary central nervous system lymphoma and intraocular lymphoma: a retrospective study of 79 cases

Background Relapsing primary central nervous system lymphoma carries a poor prognosis when treated with conventional chemotherapy with a one-year overall survival of 25-40%. Encouraging results have been shown with intensive chemotherapy followed by autologous hematopoietic stem cell rescue. We report the results of a large multicenter retrospective analysis of intensive chemotherapy followed by hematopoietic stem cell rescue in immunocompetent adult patients with primary central nervous system lymphoma or intraocular lymphoma after the failure of high-dose methotrexate-based treatment. Design and Methods Patients were included if they received intensive chemotherapy with a combination of thiotepa, busulfan and cyclophosphamide. Seventy-nine patients (median age 52.4 years, range 23-67 years) were identified. All of the patients except 5 received a salvage treatment after the failure of high-dose methotrexate. After salvage treatment and just before intensive chemotherapy followed by hematopoietic stem cell rescue, 32 patients were in complete response, 26 patients were in partial response, 2 patients had stable disease and 19 patients had progressive disease. Results With a median follow up of 56 months, the 5-year overall survival probability was 51% in the whole population and 62% among patients who were chemosensitive to the salvage treatment. The 5-year event-free survival probability was 37.8% in the whole population and 43.7% in the chemosensitive subpopulation. Neurocognitive assessments in a subset of patients suggest no evidence of intensive chemotherapy-induced neurocognitive decline. Conclusions Thiotepa, busulfan and cyclophosphamide-based intensive chemotherapy is an effective treatment for refractory and recurrent primary central nervous system lymphoma in chemosensitive patients up to 65 years of age. The role of intensive chemotherapy followed by hematopoietic stem cell rescue in chemorefractory patients needs to be more accurately defined.

Heterogeneous sensitivity of human acute myeloid leukemia to β-catenin down-modulation

Dysregulation of the Wnt/β-catenin pathway has been observed in various malignancies, including acute myeloid leukemia (AML), where the overexpression of β-catenin is an independent adverse prognostic factor. β-catenin was found upregulated in the vast majority of AML samples and more frequently localized in the nucleus of leukemic stem cells compared with normal bone marrow CD34+ cells. The knockdown of β-catenin, using a short hairpin RNA (shRNA) lentiviral approach, accelerates all-trans retinoic acid-induced differentiation and impairs the proliferation of HL60 leukemic cell line. Using in vivo quantitative tracking of these cells, we observed a reduced engraftment potential after xenotransplantation when β-catenin was silenced. However, when studying primary AML cells, despite effective downregulation of β-catenin we did not observe any impairment of their in vitro long-term maintenance on MS-5 stroma nor of their engraftment potential in vivo. Altogether, these results show that despite a frequent β-catenin upregulation in AML, leukemia-initiating cells might not be ‘addicted’ to this pathway and thus targeted therapy against β-catenin might not be successful in all patients.

Frequency and dynamics of leukemia-initiating cells during short-term ex vivo culture informs outcomes in acute myeloid leukemia patients

Acute myeloid leukemia (AML) is sustained by a subpopulation of rare leukemia-initiating cells (LIC) detected in the xenograft assay by their capacity to self-renew and to generate non-LICs in vivo The xenotransplantation model captures functional properties of LICs that have clinical prognostic value. However, the long duration of this in vivo assay has hampered its use as a prognostic tool. Here, we show, using an ex vivo coculture system, that intermediate and poor risk AML patient samples at diagnosis have a 5 to 7 times higher frequency of leukemic long-term culture-initiating cells (L-LTC-IC) compared with the good risk group. We defined a fluorescence dilution factor (FDF) parameter that monitors sample proliferation over 1 week and established a strong correlation of this parameter with the L-LTC-IC frequency. A higher FDF was found for poor prognostic AMLs or for samples capable of engrafting NSG mice compared with good risk AMLs or nonengrafters. Importantly, FDF could classify normal karyotype intermediate risk patients into two groups with a significant difference in their overall survival, thus making this nongenetic and non-in vivo approach a new clinically relevant tool for better diagnosis of AML patients. Cancer Res; 76(8); 2082-6. ©2016 AACR.

Efficacy and long‐term toxicity of the rituximab‐fludarabine‐cyclophosphamide combination therapy in Waldenstrom's macroglobulinemia

Waldenstroms macroglobulinemia is generally treated with alkylating agents, purine analogs and monoclonal antibodies, alone or in combination. We report the outcomes of 82 patients (median age 61 years) treated with the RFC combination. Twenty‐five patients were treatment‐naive. RFC was administered every 4 weeks, for a median of five cycles. At treatment discontinuation, the overall response rate was 85.4%. The responses improved after treatment discontinuation in 25 patients, with a median time to best response achievement of 10.8 months, raising the major response rate (PR, VGPR and CR) from 64.6% to 76.8%. With a median follow‐up of 47 months, the median progression‐free survival time had not been reached (67% PFS at 48 months) and was influenced by age and treatment status before RFC. Likewise, the median time to next therapy had not been reached. Two cases of myelodysplastic syndrome/AML and 3 cases of transformation to aggressive lymphoma occurred. Thirteen patients died. The 3‐year overall survival rate was 90%. Long‐lasting cytopenias occurred in 19 patients. The RFC combination thus gave a high response rate and durable responses, even in heavily treatment‐experienced patients. The high incidence of long‐lasting cytopenia might be reduced by giving fewer courses and thereby minimizing myelotoxicity. Am. J. Hematol. 91:782–786, 2016.

Acute myeloid leukemia xenograft success prediction: Saving time

HIGHLIGHTS • Extracellular phenotype, apoptosis, or cell cycle profile at thawing cannot predict acute myeloid leukemia (AML) xenograft potential.• Leukemic long-term culture-initiating cell content distinguishes fast and delayed engraftment potential.• Defined here is a 1-week carboxyfluorescein succinimidyl ester-based assay that predicts AML xenograft success.