Gene therapy for adenosine deaminase–deficient severe combined immune deficiency: clinical comparison of retroviral vectors and treatment plans

Abstract

We conducted a gene therapy trial in 10 patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency using 2 slightly different retroviral vectors for the transduction of patients' bone marrow CD34 ؉ cells. Four subjects were treated without pretransplantation cytoreduction and remained on ADA enzyme-replacement therapy (ERT) throughout the procedure. Only transient (months), low-level (< 0.01%) gene marking was observed in PBMCs of 2 older subjects (15 and 20 years of age), whereas some gene marking of PBMC has persisted for the past 9 years in 2 younger subjects (4 and 6 years). Six additional subjects were treated using the same gene transfer protocol, but after withdrawal of ERT and administration of low-dose busulfan (65-90 mg/m 2 ). Three of these remain well, off ERT (5, 4, and 3 years postprocedure), with gene marking in PBMC of 1%-10%, and ADA enzyme expression in PBMC near or in the normal range. Two subjects were restarted on ERT because of poor gene marking and immune recovery, and one had a subsequent allogeneic hematopoietic stem cell transplantation. These studies directly demonstrate the importance of providing nonmyeloablative pretransplantation conditioning to achieve therapeutic benefits with gene therapy for ADA-deficient severe combined immunodeficiency. (Blood. 2012;120(18):3635-3646)

Cytoreductive conditioning intensity predicts clonal diversity in ADA-SCID retroviral gene therapy patients

“…[2][3][4][5][6][7][8] In contrast to the patients in the trial reported herein and despite the similarity between the retroviral vector backbones used, the majority of patients in a clinical trial for Wiskott-Aldrich syndrome (WAS) developed leukemias after treatment. 9,10 Other retroviral trials for SCID-X1 and chronic granulomatous disease (CGD) using vectors based on murine leukemia virus or spleen focus forming virus have also observed vector-related leukemias and dysplastic events.…”

“…An adaptation of nonrestrictive linear amplification-mediated PCR (nrLAM-PCR) was used to produce integration site sequencing libraries for Illumina sequencing. 5,[15][16][17][18][19][20][21] …”

“…Five of these patients have been reported on previously (the "300 series": 301, 303, 304, 305, and 306), and they were treated with 2 vectors to compare the efficacy of the differing viral long terminal repeats. 5 The remaining 10 patients were treated on a new trial using only the MND-ADA vector (the "400 series": 401-410), which has performed better in the laboratory and in patients than vectors more closely related to murine leukemia virus. 5,8,35 Molecular methods were designed to detect both vectors with equal efficiency, and except where noted, integrations of the 2 vectors are reported together.…”

“…5 The remaining 10 patients were treated on a new trial using only the MND-ADA vector (the "400 series": 401-410), which has performed better in the laboratory and in patients than vectors more closely related to murine leukemia virus. 5,8,35 Molecular methods were designed to detect both vectors with equal efficiency, and except where noted, integrations of the 2 vectors are reported together. Cumulatively across all patients and samples, we sequenced 91 680 integration sites with 49 612 692 sequence reads.…”

“…5 Briefly, bone marrow was harvested from the iliac crest, and a backup was cryopreserved. Mononuclear cells were obtained by density centrifugation with FicollHypaque, and CD34 1 cells were enriched for the 300 series with an Isolex 300i instrument (Baxter Therapeutics) and for the 400 series with a CliniMacs (Miltenyi Biotec Inc., Auburn, CA).…”