Preclinical safety and efficacy of human CD34(+) cells transduced with lentiviral vector for the treatment of Wiskott-Aldrich syndrome

Abstract

Gene therapy with ex vivo-transduced hematopoietic stem/progenitor cells may represent a valid therapeutic option for monogenic immunohematological disorders such as Wiskott-Aldrich syndrome (WAS), a primary immunodeficiency associated with thrombocytopenia. We evaluated the preclinical safety and efficacy of human CD34(+) cells transduced with lentiviral vectors (LV) encoding WAS protein (WASp). We first set up and validated a transduction protocol for CD34(+) cells derived from bone marrow (BM) or mobilized peripheral blood (MPB) using a clinical grade, highly purified LV. Robust transduction of progenitor cells was obtained in normal donors and WAS patients' cells, without evidence of toxicity. To study biodistribution of human cells and exclude vector release in vivo, LV-transduced CD34(+) cells were transplanted in immunodeficient mice, showing a normal engraftment and differentiation ability towards transduced lymphoid and myeloid cells in hematopoietic tissues. Vector mobilization to host cells and transmission to germline cells of the LV were excluded by different molecular assays. Analysis of vector integrations showed polyclonal integration patterns in vitro and in human engrafted cells in vivo. In summary, this work establishes the preclinical safety and efficacy of human CD34(+) cells gene therapy for the treatment of WAS.

Figure 1

Optimization of transduction protocol using pre-GMP vectors. (a) VCN on CD34⁺ cells transduced with 1 or 2 hits of infection with two different MOI (n = 10 for 1 hit and n = 12 for 2 hits). Statistical analysis for significance was performed by Wilcoxon-matched paired test. In gray are indicated VCN of transduced CD34⁺ cells from WAS patients' BM or MPB. Lines indicate mean values. (b) CD34⁺ cells derived from healthy donors BM or (c) MPB were transduced with 1 or 2 hits after a prestimulation of 24 hours (BM, n = 11; MPB, n = 10) and 48 hours (BM, n = 6; MPB, n = 5) for 1 hit, and 24 hours (BM, n = 15; MPB, n = 9) for 2 hits. VCN/cell was calculated on cultured cells. (d) Total number of colonies derived from LTC-IC are reported for 1 (n = 5) and 2 hits (n = 5) of transduction at MOI 100, after 24 hours of prestimulation in the presence of cytokines. Results are reported as mean ± SD. *P value < 0.05, **P value < 0.01. BM, bone marrow; LTC-IC, long-term culture-initiating cell; MOI, multiplicity of infection; MPB, mobilized peripheral blood; UT, untransduced; VCN, vector copy number; WAS, Wiskott-Aldrich syndrome.

Figure 2

Efficient transduction of CD34⁺ cells by clinical LV vectors. BM or MPB from healthy donors (squares/white columns) or WAS patients (triangles/black columns) were transduced with 1 or 2 hits using GMP-grade lots of LV vector encoding WAS. (a) VCN/cell were calculated by qPCR on cultured CD34⁺ cells and (b) single transduced colonies. n for 1 hit trasduction protocol = 14 (6 MPB and 8 BM) and 8 (1 MPB and 7 BM) for HDs and WAS patients respectively, and n for 2 hits protocol = 17 (7 MPB and 10 BM) for HDs and 11 (2 MPB and 9 BM) for WAS patients. Lines indicate median values. *P value < 0.05, **P value < 0.01, ***P value < 0.001. BM, bone marrow; CFC, colony-forming cell; GMP, good manufacturing practice; HD, healthy donors; LV, lentiviral vectors; MPB, mobilized peripheral blood; qPCR, quantitative PCR; VCN, vector copy number; WAS, Wiskott-Aldrich syndrome.

Figure 3

Restoration of WASp expression in transduced cells. (a) The expression of WASp was evaluated after transduction of untransformed T cells (FACS analyses), (b) EBV-transformed B cell lines (western blot), and (c) CD34⁺ cells differentiated into myeloid cells (western blot) from normal donors and WAS patient(s). In a, in gray are indicated control cells, black lines indicated stained cells. Numbers represent the percentage of WASp positive cells. BM, bone marrow; EBV, Epstein–Barr virus; FACS, fluorescence-activated cell sorting; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HD, healthy donors; Pt, patient; UT, untransduced; WASp, WAS protein.

Figure 4

Engraftment of transduced human HSC in Rag2^−/−/γc^−/− mouse model. Rag2^−/−/γc^−/− mice were injected after sublethal irradiation with human UCB CD34⁺ cells either UM, UT or LV transduced. (a) Engraftment of human cells was calculated in terms of CD45⁺ cell in different organs. The percentage of most representative subpopulations in (b) BM, (c) spleen, and (d) thymus were evaluated by FACS on human CD45⁺ cells. (e) The percentage of engrafted BM-derived transduced CD34⁺ cells and (f) subpopulation distribution were evaluated on specified organs. (g) qPCR analysis was performed on cells from different organs or BM. BM, bone marrow; FACS, fluorescence-activated cell sorting; HSC, hematopoietic stem cells; LV, lentiviral vectors; qPCR, quantitative PCR; UCB, umbilical cord blood; UM, unmanipulated; UT, untransduced; VCN, vector copy number.

Figure 5

Analysis of w1.6 LV integration profile in human transduced CD34⁺ cells. LV integration analysis was performed by LAM-PCR on (a) BM-transduced CD34⁺ cells from healthy donors (left panel, n = 3) and patients (right panel, n = 2), (b) as well as transduced human UCB in vitro and in vivo upon engraftment in Rag2^−/−/γc^−/− mice. LAM-PCR products are shown on Spreadex gels are shown. (c) Shared identical integrations in BM and thymus of two individual mice (11 and 13) (upper circles) and in BM, thymus (Thy), and spleen (Spl) from a pool of three mice (lower circles). BM, bone marrow; gDNA, genomic DNA; IC, internal control; LAM-PCR, linear amplication-mediated PCR; LV, lentiviral vectors; Pt, patient; UCB, umbilical cord blood.