Lentiviral-mediated genetic correction of hematopoietic and mesenchymal progenitor cells from Fanconi anemia patients

Abstract

Previous clinical trials based on the genetic correction of purified CD34(+) cells with gamma-retroviral vectors have demonstrated clinical efficacy in different monogenic diseases, including X-linked severe combined immunodeficiency, adenosine deaminase deficient severe combined immunodeficiency and chronic granulomatous disease. Similar protocols, however, failed to engraft Fanconi anemia (FA) patients with genetically corrected cells. In this study, we first aimed to correlate the hematological status of 27 FA patients with CD34(+) cell values determined in their bone marrow (BM). Strikingly, no correlation between these parameters was observed, although good correlations were obtained when numbers of colony-forming cells (CFCs) were considered. Based on these results, and because purified FA CD34(+) cells might have suboptimal repopulating properties, we investigated the possibility of genetically correcting unselected BM samples from FA patients. Our data show that the lentiviral transduction of unselected FA BM cells mediates an efficient phenotypic correction of hematopoietic progenitor cells and also of CD34(-) mesenchymal stromal cells (MSCs), with a reported role in hematopoietic engraftment. Our results suggest that gene therapy protocols appropriate for the treatment of different monogenic diseases may not be adequate for stem cell diseases like FA. We propose a new approach for the gene therapy of FA based on the rapid transduction of unselected hematopoietic grafts with lentiviral vectors (LVs).

Figures

Figure 1

Functional significance of BM CD34+ cells and CFCs in FA patients. (a) Correlation analysis between the percentage of CD34+ cells and the number of CFCs/105 cells in the BM of FA patients. Percentages of CD34+ cells and numbers of CFCs/105 cells in the bone marrow of healthy donors were 1.6 ± 0.2% and 191.3 ± 37.9, respectively. (b) Correlation between either the percentage of bone marrow CD34+ cells or the proportion of bone marrow CFCs with respect to relevant hematological parameters of these patients. BM, bone marrow; FA, Fanconi anemia; CFC, colony-forming cell.

Figure 2

Improved transduction of Fanconi anemia lymphoblast cell lines mediated by dynamic preloadings of GALV-TR packaged lentiviral vectors. (a) Similar transduction efficacies mediated by one or four static preloadings of infective LVs in human FA-A lymphoblasts. (b) Improved transduction efficacy mediated by the dynamic preloading of infective supernatants (data show transduction efficacies induced by a single preloading with the vectors). (c) Relative improvement in the infectivity of LVs when dynamic preloadings were conducted at 4, 20, and 32 °C. **P < 0.05. (d) Improved infectivity associated to repetitive transduction cycles, each consisting of a single dynamic preloading of 2 hours followed by a transduction of 4 hours. Data corresponding to six individual experiments are shown. In all instances samples were transduced with EGFP-LVs. Analyses of EGFP+ cells were made 5 days after transduction by flow cytometry. Each point represents transduction efficacies conferred by supernatants with a wide range of infectivity. EGFP, enhanced green fluorescent protein; FA-A, Fanconi anemia group A; GALV-TR, gibbon ape leukemia virus-terminal repeat, LV, lentiviral vector.

Figure 3

Improved transduction efficacy of cryopreserved BM progenitors from FA patients. (a) Samples were subjected to standard transductions consisting in a single transduction cycle (16 hours) after 2 hours of static preloading (white bars; 1 × S) or improved transduction consisting in three transduction cycles (2 hours + 2 hours + 12 hours) each mediated by a dynamic preloading (2 hours) of the lentiviral vectors (grey bars; 3 × D). (b) Analysis of the relevance of transducing FA BM samples (three cycles of transduction as in panel a) and culturing the hematopoietic progenitors (14 days of CFCs growth) in low (3%) or conventional (21%) oxygen concentration. White bars represent CFCs/105 cells and black bars the % of transduction. BM, bone marrow; CFC, colony-forming cell; FA, Fanconi anemia.

Figure 4

Generation of lentivirally transduced stromal stem cells from unselected Fanconi anemia bone marrow samples transduced under optimized conditions. (a) Characteristic phenotype of MSCs generated by unselected FA bone marrow samples transduced with LVs expressing the FANCA and EGFP transgenes, under conditions shown in Supplementary Figure S1b. (b) Phase-contrast microphotography of MSCs three passages after transduction with LVs and differentiation of MSCs into osteogenic (phosphatase alkaline positive cells) and adipogenic lineages (oil red positive cells), respectively. (c) Restored generation of FANCD2 foci in MSCs generated by BM previously transduced with FANCA/EGFP LVs. As a control, a sample transduced with a control LV (EGFP-LV) is shown. In all instances FANCD2 foci were determined in green fluorescent cells. Alk. phophatase, alkaline phosphatase; MSC, mesenchymal stromal cell; LV, lentiviral vector.