Table 2

Ongoing gene therapy studies for blood disorders

DisorderVector, dose range, and number and ages of patientsTransgene and promoterRoute of administration and cell targetScientific and clinical outcomesReference
Hemophilia B AAV8; 2 × 1011, 6 × 1011, or 2 × 1012 vg/kg body weight; 6 patients (27-64 y old) FIX gene, regulated by the human apolipoprotein hepatic control region and human α-1-antitrypsin promoter IV delivery targeting hepatocytes Durable circulating FIX at 2% to 11% normal levels; decreased frequency (2 of 6 patients) or cessation (8 of 10) of spontaneous hemorrhage 8 
X-SCID γ-Retrovirus; 10 patients (4-36 mo old); CD34+ cells were infused (without conditioning) at doses of 60 × 106 to 207 × 106 cells per patient IL-2 receptor common γ-chain, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Functional polyclonal T-cell response restored in all patients; 1 patient developed acute T-cell lymphoblastic leukemia 39 
γ-Retrovirus; 9 patients (1-11 mo old); CD34+ cells were infused (without conditioning) at doses of 1 × 106 to 22 × 106 cells per kg IL-2 receptor common γ-chain, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Functional T-cell numbers reached normal ranges. Transduced T cells were detected for up to 10.7 y after gene therapy. Four patients developed acute T-cell lymphoblastic leukemia, and 1 died. 38 
Adenosine deaminase deficiency resulting in severe combined immunodeficiency (ADA-SCID) γ-Retrovirus; 6 patients (6-39 mo old); CD34+ cells were infused (after nonmyeloablative conditioning with melphalan [Alkeran], 140 mg/m2 body surface area, or busulfan [Myleran], 4 mg/kg) at doses of <0.5 × 106 to 5.8 × 106 cells per kg ADA gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Restoration of immune function in 4 of 6 patients; 3 of 6 taken off enzyme-replacement therapy; 4 of 6 remain free of infection 40 
γ-Retrovirus; 10 patients (1-5 mo old); CD34+ cells were infused (after nonmyeloablative conditioning with busulfan, 4 mg/kg) at doses of 3.1 × 106 to 13.6 × 106 cells per kg ADA gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine of 10 patients had immune reconstitution with increases in T-cell counts (median count at 3 y, 1.07 × 109/L) and normalization of T-cell function. Eight of 10 patients do not require enzyme-replacement therapy. 42 
CGD A range of studies, using γ-retrovirus vectors pseudotyped either with gibbon ape leukemia virus envelope or with an amphotrophic envelope; various nonmyeloablative conditioning strategies Gp91phox, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Twelve of 12 patients showed short-term functional correction of neutrophils with resolution of life-threatening infections. Three patients developed myeloproliferative disease. 57 
Wiskott-Aldrich syndrome (WAS) γ-Retrovirus; 10 patients; CD34+ cells were infused (after nonmyeloablative conditioning with busulfan, 4 mg/kg) WAS gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine of 10 patients showed improvement of immunologic function and platelet count. Four patients developed acute T-cell lymphoblastic leukemia. 7, 23 
β-Thalassemia Self-inactivating HIV-1–derived lentivirus; 1 patient (18 y old) received fully myeloablative conditioning with busulfan; 3.9 × 106 CD34+ cells per kg Mutated adult β-globin (βA(T87Q)) with antisickling properties, LCR control Ex vivo, CD34+ hematopoietic stem and progenitor cells Patient has been transfusion independent for 7 y. Blood hemoglobin is maintained between 9 and 10 g/dL, of which one-third contains vector-encoded β-globin. 35 
Adrenoleukodystrophy (ALD) Self-inactivating HIV-1–derived lentivirus; 2 patients (7 and 7.5 y old) received myeloablative conditioning with cyclophosphamide (Cytoxan) and busulfan; transduced CD34+ cells, 4.6 × 106 and 7.2 × 106 cells per kg, respectively. Two younger patients also treated with short-term follow-up. Wild-type ABCD1 complementary DNA under the control of the MND viral promoter Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine percent to 14% of granulocytes, monocytes, and T and B lymphocytes expressing the ALD protein; beginning 14-16 mo after infusion of the genetically corrected cells, progressive cerebral demyelination in the 2 patients attenuated. 61-63 
Gene therapy for cancer      
 B-cell leukemia and lymphoma Self-inactivating lentivirus expressing a chimeric T-cell receptor; a single patient was conditioned with pentostatin (Nipent; 4 mg/m2) and cyclophosphamide (600 mg/m2) before receiving 1.5 × 105 transduced T cells per kg (total 3 × 108 T cells, of which 5% were transduced) Anti-CD19 scFv derived from FMC63 murine monoclonal antibody, human CD8α hinge and trans-membrane domain, and human 4-1BB and CD3ζ signaling domains Ex vivo, autologous T cells, IV infusion, split over 3 d Transduced T cells expanded more than 1000 times in vivo, with delayed development of the tumor lysis syndrome and complete remission, ongoing 10 mo after treatment. Engineered cells persisted at high levels for 6 mo in the blood and bone marrow. 80 
Murine stem cell virus–based splice-gag (retroviral) vector expressing CD19 CAR; 8 patients (47-63 y old) with progressive B-cell malignancies received cyclophosphamide and fludarabine (Fludara) before CAR-transduced autologous T cells and IL-2. Patients received 0.3 × 107 to 3.0 × 107 CAR+ T cells per kg, of which an average of 55% were transduced. Anti-CD19 scFv derived from the FMC63 mouse hybridoma, a portion of the human CD28 molecule and the intracellular component of the human TCR-ζ molecule Ex vivo, autologous T cells, single IV infusion, followed (3 h) by a course of IL-2 Varied levels of anti-CD19-CAR–transduced T cells could be detected in the blood of all patients. One patient died on trial, with influenza A pneumonia, nonbacterial thrombotic endocarditis, and cerebral infarction. Four patients had prominent elevations in serum levels of interferon γ and tumor necrosis factor, correlating with severity of acute toxicities. Six of the 8 patients treated obtained objective remissions. 81 
 Acute leukemia SFG retrovirus expressing an inducible suicide system for improved safety of stem cell transplantation to prevent GVHD; transduced haploidentical T cells (1 × 106 to 1 × 107 T cells per kg); 5 patients (3-17 y old) FK506-binding protein linked to modified human caspase 9 with truncated CD19 as a selectable marker; in the presence of the drug, the iCasp9 promolecule dimerizes and activates apoptosis; retroviral LTR Ex vivo, allodepleted haploidentical T cells, infused IV into recipients of allogeneic bone marrow transplants The genetically modified T cells were detected in peripheral blood from all 5 patients and increased in number over time. A single dose of dimerizing drug, given to 4 patients in whom GVHD developed, eliminated >90% of the modified T cells within 30 min after administration and ended the GVHD without recurrence. 69 
DisorderVector, dose range, and number and ages of patientsTransgene and promoterRoute of administration and cell targetScientific and clinical outcomesReference
Hemophilia B AAV8; 2 × 1011, 6 × 1011, or 2 × 1012 vg/kg body weight; 6 patients (27-64 y old) FIX gene, regulated by the human apolipoprotein hepatic control region and human α-1-antitrypsin promoter IV delivery targeting hepatocytes Durable circulating FIX at 2% to 11% normal levels; decreased frequency (2 of 6 patients) or cessation (8 of 10) of spontaneous hemorrhage 8 
X-SCID γ-Retrovirus; 10 patients (4-36 mo old); CD34+ cells were infused (without conditioning) at doses of 60 × 106 to 207 × 106 cells per patient IL-2 receptor common γ-chain, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Functional polyclonal T-cell response restored in all patients; 1 patient developed acute T-cell lymphoblastic leukemia 39 
γ-Retrovirus; 9 patients (1-11 mo old); CD34+ cells were infused (without conditioning) at doses of 1 × 106 to 22 × 106 cells per kg IL-2 receptor common γ-chain, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Functional T-cell numbers reached normal ranges. Transduced T cells were detected for up to 10.7 y after gene therapy. Four patients developed acute T-cell lymphoblastic leukemia, and 1 died. 38 
Adenosine deaminase deficiency resulting in severe combined immunodeficiency (ADA-SCID) γ-Retrovirus; 6 patients (6-39 mo old); CD34+ cells were infused (after nonmyeloablative conditioning with melphalan [Alkeran], 140 mg/m2 body surface area, or busulfan [Myleran], 4 mg/kg) at doses of <0.5 × 106 to 5.8 × 106 cells per kg ADA gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Restoration of immune function in 4 of 6 patients; 3 of 6 taken off enzyme-replacement therapy; 4 of 6 remain free of infection 40 
γ-Retrovirus; 10 patients (1-5 mo old); CD34+ cells were infused (after nonmyeloablative conditioning with busulfan, 4 mg/kg) at doses of 3.1 × 106 to 13.6 × 106 cells per kg ADA gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine of 10 patients had immune reconstitution with increases in T-cell counts (median count at 3 y, 1.07 × 109/L) and normalization of T-cell function. Eight of 10 patients do not require enzyme-replacement therapy. 42 
CGD A range of studies, using γ-retrovirus vectors pseudotyped either with gibbon ape leukemia virus envelope or with an amphotrophic envelope; various nonmyeloablative conditioning strategies Gp91phox, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Twelve of 12 patients showed short-term functional correction of neutrophils with resolution of life-threatening infections. Three patients developed myeloproliferative disease. 57 
Wiskott-Aldrich syndrome (WAS) γ-Retrovirus; 10 patients; CD34+ cells were infused (after nonmyeloablative conditioning with busulfan, 4 mg/kg) WAS gene, retroviral LTR Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine of 10 patients showed improvement of immunologic function and platelet count. Four patients developed acute T-cell lymphoblastic leukemia. 7, 23 
β-Thalassemia Self-inactivating HIV-1–derived lentivirus; 1 patient (18 y old) received fully myeloablative conditioning with busulfan; 3.9 × 106 CD34+ cells per kg Mutated adult β-globin (βA(T87Q)) with antisickling properties, LCR control Ex vivo, CD34+ hematopoietic stem and progenitor cells Patient has been transfusion independent for 7 y. Blood hemoglobin is maintained between 9 and 10 g/dL, of which one-third contains vector-encoded β-globin. 35 
Adrenoleukodystrophy (ALD) Self-inactivating HIV-1–derived lentivirus; 2 patients (7 and 7.5 y old) received myeloablative conditioning with cyclophosphamide (Cytoxan) and busulfan; transduced CD34+ cells, 4.6 × 106 and 7.2 × 106 cells per kg, respectively. Two younger patients also treated with short-term follow-up. Wild-type ABCD1 complementary DNA under the control of the MND viral promoter Ex vivo, CD34+ hematopoietic stem and progenitor cells Nine percent to 14% of granulocytes, monocytes, and T and B lymphocytes expressing the ALD protein; beginning 14-16 mo after infusion of the genetically corrected cells, progressive cerebral demyelination in the 2 patients attenuated. 61-63 
Gene therapy for cancer      
 B-cell leukemia and lymphoma Self-inactivating lentivirus expressing a chimeric T-cell receptor; a single patient was conditioned with pentostatin (Nipent; 4 mg/m2) and cyclophosphamide (600 mg/m2) before receiving 1.5 × 105 transduced T cells per kg (total 3 × 108 T cells, of which 5% were transduced) Anti-CD19 scFv derived from FMC63 murine monoclonal antibody, human CD8α hinge and trans-membrane domain, and human 4-1BB and CD3ζ signaling domains Ex vivo, autologous T cells, IV infusion, split over 3 d Transduced T cells expanded more than 1000 times in vivo, with delayed development of the tumor lysis syndrome and complete remission, ongoing 10 mo after treatment. Engineered cells persisted at high levels for 6 mo in the blood and bone marrow. 80 
Murine stem cell virus–based splice-gag (retroviral) vector expressing CD19 CAR; 8 patients (47-63 y old) with progressive B-cell malignancies received cyclophosphamide and fludarabine (Fludara) before CAR-transduced autologous T cells and IL-2. Patients received 0.3 × 107 to 3.0 × 107 CAR+ T cells per kg, of which an average of 55% were transduced. Anti-CD19 scFv derived from the FMC63 mouse hybridoma, a portion of the human CD28 molecule and the intracellular component of the human TCR-ζ molecule Ex vivo, autologous T cells, single IV infusion, followed (3 h) by a course of IL-2 Varied levels of anti-CD19-CAR–transduced T cells could be detected in the blood of all patients. One patient died on trial, with influenza A pneumonia, nonbacterial thrombotic endocarditis, and cerebral infarction. Four patients had prominent elevations in serum levels of interferon γ and tumor necrosis factor, correlating with severity of acute toxicities. Six of the 8 patients treated obtained objective remissions. 81 
 Acute leukemia SFG retrovirus expressing an inducible suicide system for improved safety of stem cell transplantation to prevent GVHD; transduced haploidentical T cells (1 × 106 to 1 × 107 T cells per kg); 5 patients (3-17 y old) FK506-binding protein linked to modified human caspase 9 with truncated CD19 as a selectable marker; in the presence of the drug, the iCasp9 promolecule dimerizes and activates apoptosis; retroviral LTR Ex vivo, allodepleted haploidentical T cells, infused IV into recipients of allogeneic bone marrow transplants The genetically modified T cells were detected in peripheral blood from all 5 patients and increased in number over time. A single dose of dimerizing drug, given to 4 patients in whom GVHD developed, eliminated >90% of the modified T cells within 30 min after administration and ended the GVHD without recurrence. 69 

Adapted from Seymour and Thrasher.2 

CAR, chimeric antigen receptor; GVHD, graft-vs-host disease; IV, intravenous/intravenously; LCR, locus control region.

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