Successful engraftment of gene-corrected hematopoietic stem cells in non-conditioned patients with Fanconi anemia.

Fanconi anemia (FA) is a DNA repair syndrome generated by mutations in any of the 22 FA genes discovered to date1,2. Mutations in FANCA account for more than 60% of FA cases worldwide3,4. Clinically, FA is associated with congenital abnormalities and cancer predisposition. However, bone marrow failure is the primary pathological feature of FA that becomes evident in 70-80% of patients with FA during the first decade of life5,6. In this clinical study (ClinicalTrials.gov, NCT03157804 ; European Clinical Trials Database, 2011-006100-12), we demonstrate that lentiviral-mediated hematopoietic gene therapy reproducibly confers engraftment and proliferation advantages of gene-corrected hematopoietic stem cells (HSCs) in non-conditioned patients with FA subtype A. Insertion-site analyses revealed the multipotent nature of corrected HSCs and showed that the repopulation advantage of these cells was not due to genotoxic integrations of the therapeutic provirus. Phenotypic correction of blood and bone marrow cells was shown by the acquired resistance of hematopoietic progenitors and T lymphocytes to DNA cross-linking agents. Additionally, an arrest of bone marrow failure progression was observed in patients with the highest levels of gene marking. The progressive engraftment of corrected HSCs in non-conditioned patients with FA supports that gene therapy should constitute an innovative low-toxicity therapeutic option for this life-threatening disorder.

Development of an in vitro model for the simultaneous study of the efficacy and hematotoxicity of antileukemic compounds.

Hematopoietic system displays a wide spectrum of cell populations hierarchically organized in the bone marrow. Homeostasis in this system requires equilibrium between the self-renewal of the stem cells and their capacity of differentiation. Any failure on this equilibrium could lead to fatal consequences, such as the development of leukemia. Due to its rapid rate of renewal, hematopoietic tissue is a major target for antitumoral compounds and often becomes a dose limiting factor in the development of antineoplastics. Our aim was to develop an in vitro model for predicting the efficacy of antitumoral compounds on leukemic cells and their toxic effects on the healthy hematopoietic cells. The mouse myelomonocytic leukemia WEHI-3b was transduced with a lentiviral vector for expressing the green fluorescence protein. Mixed semisolid clonogenic cultures of transduced WEHI-3b and murine bone marrow cells were exposed to five pharmaceuticals: daunorubicin (positive control), atropine sulphate (negative control) and three in different stages of clinical development (trabectedin, Zalypsis(®) and PM01183). Colonies of leukemic cells were distinguishable from healthy CFU-GM under fluorescence microscope. The sensitivity of leukemic cells to daunorubicin, trabectedin, Zalypsis(®) and PM01183 was higher compared to healthy cells. The effect of a non-antitumoral compound, atropine sulphate, was the same on both populations. Our results show that this in vitro model is a valuable tool for studying the effect of antitumoral compounds in both tumoral and normal hematopoietic cells under the same toxic microenvironment and could safe time and facilitate the reduction of the number of animals used in preclinical development of pharmaceuticals.

Prevalidation of the rat CFU-GM assay for in vitro toxicology applications.

In vitro haematotoxicity assays are thought to have the potential to significantly reduce and refine the use of animals for haematotoxicity testing. These assays are used successfully in all types of studies - however, their use is not so common in human toxicology studies in the preclinical setting, as they are not required for regulatory testing in this case. Furthermore, these assays could play a key role in bridging the gap between preclinical toxicology studies in animal models and clinical investigations. In previous studies, the Colony Forming Unit-Granulocyte Macrophage (CFU-GM) assay has been validated for testing drug haematotoxicity (with both mouse bone-marrow and human cord blood) and for predicting the in vivo human maximal tolerated dose (MTD) by adjusting in vivo data on mouse toxicity. Recently, a Colony Forming Unit-Megakaryocyte (CFU-MK) assay has also been prevalidated for testing drug toxicity toward megakaryocytes. The rat CFU-GM assay has been used by many researchers for its ability to evaluate in vitro haematotoxicity. Although it is not yet available, a standardised procedure for data comparison could be very important, since the rat is the most widely-used species for the in vivo testing of toxicants. This report presents the results of the prevalidation study developed to analyse the intra-laboratory and inter-laboratory variability of a standardised operating procedure for this assay and its performance for the in vitro determination of the inhibitory concentration (IC) values of drugs on rat myeloid progenitors (CFU-GM). The results demonstrate that the CFU-GM assay can be performed with cryopreserved rat bone-marrow cells (rBMC). The assay represents a useful tool for evaluating the toxicity of a compound, in terms of both relative toxicity (when different molecules are compared) and the prediction of the degree of in vivo toxicity. The use of this assay could greatly reduce the number of rats used in experimental procedures, and could also contribute to the accumulation of more toxicity data on compounds to be registered according to the criteria established by the European Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) programme.

In vitro sensitivity of granulo-monocytic progenitors as a new toxicological cell system and endpoint in the ACuteTox Project.

The ACuteTox Project (part of the EU 6th Framework Programme) was started up in January 2005. The aim of this project is to develop a simple and robust in vitro strategy for prediction of human acute systemic toxicity, which could replace animal tests used for regulatory purposes. Our group is responsible for the characterization of the effect of the reference chemicals on the hematopoietic tissue. CFU-GM assay based on the culture of human mononuclear cord blood cells has been used to characterize the effects of the selected compounds on the myeloid progenitors. Previous results have shown the relevance of the CFU-GM assay for the prediction of human acute neutropenia after treatment of antitumoral compounds, and this assay has been recently approved by the ECVAM's Scientific Advisory Committee. Among the compounds included in the study there were pharmaceuticals, environmental pollutants and industrial chemicals. Eleven out of 55 chemicals did not show any cytotoxic effect at the maximum concentration tested. The correlation coefficients of CFU-GM IC50, IC70 and IC90 values with human LC50 values (50% lethal concentration calculated from time-related sublethal and lethal human blood concentrations) were 0.4965, 0.5106 and 0.5142 respectively. Although this correlation is not improve respect to classical in vitro basal cytotoxicity tests such as 3T3 Neutral Red Uptake, chemicals which deviate substantially in the correlation with these assays (colchicine, digoxin, 5-Fluorouracil and thallium sulfate) fitted very well in the linear regression analysis of the CFU-GM progenitors. The results shown in the present study indicate that the sensitivity of CFU-GM progenitors correlates better than the sensitivity of HL-60 cells with human LC50 values and could help to refine the predictability for human acute systemic toxicity when a given chemical may affect to the hematopoietic myeloid system.