BACKGROUND Hemophilia B, an X-linked disorder, is ideally suited for gene therapy. We investigated the use of a new gene therapy in patients with the disorder. METHODS We infused a single dose of a serotype-8–pseudotyped, self-complementary adenovirus-associated virus (AAV) vector expressing a codon-optimized human factor IX (FIX) transgene (scAAV2/8-LP1-hFIXco) in a peripheral vein in six patients with severe hemophilia B (FIX activity, <1% of normal values). Study participants were enrolled sequentially in one of three cohorts (given a high, intermediate, or low dose of vector), with two participants in each group. Vector was administered without immunosuppressive therapy, and participants were followed for 6 to 16 months. RESULTS AAV-mediated expression of FIX at 2 to 11% of normal levels was observed in all participants. Four of the six discontinued FIX prophylaxis and remained free of spontaneous hemorrhage; in the other two, the interval between prophylactic injections was increased. Of the two participants who received the high dose of vector, one had a transient, asymptomatic elevation of serum aminotransferase levels, which was associated with the detection of AAV8-capsid–specific T cells in the peripheral blood; the other had a slight increase in liver-enzyme levels, the cause of which was less clear. Each of these two participants received a short course of glucocorticoid therapy, which rapidly normalized aminotransferase levels and maintained FIX levels in the range of 3 to 11% of normal values. CONCLUSIONS Peripheral-vein infusion of scAAV2/8-LP1-hFIXco resulted in FIX transgene expression at levels sufficient to improve the bleeding phenotype, with few side effects. Although immune-mediated clearance of AAV-transduced hepatocytes remains a concern, this process may be controlled with a short course of glucocorticoids without loss of transgene expression. (Funded by the Medical Research Council and others; ClinicalTrials.gov number, NCT00979238.)

BACKGROUND In patients with severe hemophilia B, gene therapy that is mediated by a novel self-complementary adeno-associated virus serotype 8 (AAV8) vector has been shown to raise factor IX levels for periods of up to 16 months. We wanted to determine the durability of transgene expression, the vector dose–response relationship, and the level of persistent or late toxicity. METHODS We evaluated the stability of transgene expression and long-term safety in 10 patients with severe hemophilia B: 6 patients who had been enrolled in an initial phase 1 dose-escalation trial, with 2 patients each receiving a low, intermediate, or high dose, and 4 additional patients who received the high dose (2×1012 vector genomes per kilogram of body weight). The patients subsequently underwent extensive clinical and laboratory monitoring. RESULTS A single intravenous infusion of vector in all 10 patients with severe hemophilia B resulted in a dose-dependent increase in circulating factor IX to a level that was 1 to 6% of the normal value over a median period of 3.2 years, with observation ongoing. In the high-dose group, a consistent increase in the factor IX level to a mean (±SD) of 5.1±1.7% was observed in all 6 patients, which resulted in a reduction of more than 90% in both bleeding episodes and the use of prophylactic factor IX concentrate. A transient increase in the mean alanine aminotransferase level to 86 IU per liter (range, 36 to 202) occurred between week 7 and week 10 in 4 of the 6 patients in the high-dose group but resolved over a median of 5 days (range, 2 to 35) after prednisolone treatment. CONCLUSIONS In 10 patients with severe hemophilia B, the infusion of a single dose of AAV8 vector resulted in long-term therapeutic factor IX expression associated with clinical improvement. With a follow-up period of up to 3 years, no late toxic effects from the therapy were reported. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00979238.)

Adeno-associated virus vectors (AAV) show promise for liver-targeted gene therapy. In this study, we examined the long-term consequences of a single intravenous administration of a self-complementary AAV vector (scAAV2/ 8-LP1-hFIXco) encoding a codon optimized human factor IX (hFIX) gene in 24 nonhuman primates (NHPs). A dose-response relationship between vector titer and transgene expression was observed. Peak hFIX expression following the highest dose of vector (2 × 10(12) pcr-vector genomes (vg)/kg) was 21 ± 3 µg/ml (~420% of normal). Fluorescent in-situ hybridization demonstrated scAAV provirus in almost 100% of hepatocytes at that dose. No perturbations of clinical or laboratory parameters were noted and vector genomes were cleared from bodily fluids by 10 days. Macaques transduced with 2 × 10(11) pcr-vg/kg were followed for the longest period (~5 years), during which time expression of hFIX remained >10% of normal level, despite a gradual decline in transgene copy number and the proportion of transduced hepatocytes. All macaques developed serotype-specific antibodies but no capsid-specific cytotoxic T lymphocytes were detected. The liver was preferentially transduced with 300-fold more proviral copies than extrahepatic tissues. Long-term biochemical, ultrasound imaging, and histologic follow-up of this large cohort of NHP revealed no toxicity. These data support further evaluation of this vector in hemophilia B patients.

Purpose The addition of immunotherapy, including a combination of anti-GD2 monoclonal antibody (mAb), ch14.18, and cytokines, improves outcome for patients with high-risk neuroblastoma. However, this therapy is limited by ch14.18-related toxicities that may be partially mediated by complement activation. We report the results of a phase I trial to determine the maximum-tolerated dose (MTD), safety profile, and pharmacokinetics of hu14.18K322A, a humanized anti-GD2 mAb with a single point mutation (K322A) that reduces complement-dependent lysis. Patients and Methods Eligible patients with refractory or recurrent neuroblastoma received escalating doses of hu14.18K322A ranging from 2 to 70 mg/m2 per day for 4 consecutive days every 28 days (one course). Results Thirty-eight patients (23 males; median age, 7.2 years) received a median of two courses (range, one to 15). Dose-limiting grade 3 or 4 toxicities occurred in four of 36 evaluable patients and were characterized by cough, asthenia, sensory neuropathy, anorexia, serum sickness, and hypertensive encephalopathy. The most common non–dose-limiting grade 3 or 4 toxicities during course one were pain (68%) and fever (21%). Six of 31 patients evaluable for response by iodine-123 metaiodobenzylguanidine score had objective responses (four complete responses; two partial responses). The first-course pharmacokinetics of hu14.18K322A were best described by a two-compartment linear model. Median hu14.18K322A α (initial phase) and β (terminal phase) half-lives were 1.74 and 21.1 days, respectively. Conclusion The MTD, and recommended phase II dose, of hu14.18K322A is 60 mg/m2 per day for 4 days. Adverse effects, predominately pain, were manageable and improved with subsequent courses.

To generate sufficient clinical-grade vector to support a phase I/II clinical trial of adeno-associated virus serotype 8 (AAV8)-mediated factor IX (FIX) gene transfer for hemophilia B, we have developed a large-scale, good manufacturing practice (GMP)-compatible method for vector production and purification. We used a 293T-based two-plasmid transient transfection system coupled with a three-column chromatography purification process to produce high-quality self-complementary AAV2/8 FIX clinical-grade vector. Two consecutive production campaigns using a total of 432 independent 10-stack culture chambers produced a total of *2Â10 15 vector genomes (VG) by dot-blot hybridization. Benzonase-treated microfluidized lysates generated from pellets of transfected cells were purified by group separation on Sepharose beads followed by anion-exchange chromatography. The virus-containing fractions were further processed by gel filtration and ultrafiltration, using a 100-kDa membrane. The vector was formulated in phosphate-buffered saline plus 0.25% human serum albumin. Spectrophotometric analysis suggested *20% full particles, with only low quantities of nonviral proteins were visible on silver-stained sodium dodecyl sulfate-polyacrylamide gels. A sensitive assay for the detection of replication-competent AAV was developed, which did reveal trace quantities of such contaminants in the final product. Additional studies have confirmed the long-term stability of the vector at À808C for at least 24 months and for at least 24 hr formulated in the clinical diluent and stored at room temperature within intravenous bags. This material has been approved for use in clinical trials in the United States and the United Kingdom.

One of the main impediments to effective gene therapy of blood disorders is the resistance of human hematopoietic stem cells to stable genetic modification. We show here that a small minority of retrovirally transduced stem cells can be selectively enriched in vivo, which might be a way to circumvent this obstacle. We constructed two retroviral vectors containing an antifolate-resistant dihydrofolate reductase cDNA transcriptionally linked to a reporter gene. Mice were transplanted with transduced bone marrow cells and then treated with an antifolate-based regimen that kills unmodified stem cells. Drug treatment significantly increased the percentage of vector-expressing peripheral blood erythrocytes, platelets, granulocytes, and T and B lymphocytes. Secondary transplant experiments demonstrated that selection occurred at the level of hematopoietic stem cells. This system for in vivo stem-cell selection provides a means to increase the number of genetically modified cells after transplant, and may circumvent an substantial obstacle to successful gene therapy for human blood diseases.

Human marrow-derived mesenchymal progenitor cells (hMPCs), which have the capacity for osteogenic and marrow stromal differentiation, were transduced with the myeloproliferative sarcoma virus (MPSV)-based retrovirus, vM5LacZ, that contains the LacZ and neo genes. Stable transduction and gene expression occurred in 18% of cells. After culture expansion and selection in G418, approximately 70% of neo(r) hMPCs co-expressed LacZ. G418-selected hMPC retain their osteogenic potential and form bone in vivo when seeded into porous calcium phosphate ceramic cubes implanted subcutaneously into SCID mice. LacZ expression was evident within osteoblasts and osteocytes in bone developing within the ceramics 6 and 9 weeks after implantation. Likewise, hMPCs transduced with human interleukin-3 (hIL-3) cDNA, adhered to ceramic cubes and implanted into SCID mice, formed bone and secreted detectable levels of hIL-3 into the systemic circulation for at least 12 weeks. These data indicate that genetically transduced, culture-expanded bone marrow-derived hMPCs retain a precursor phenotype and maintain similar levels of transgene expression during osteogenic lineage commitment and differentiation in vivo. Because MPCs have been shown to differentiate into bone, cartilage, and tendon, these cells may be a useful target for gene therapy.

Bone marrow stromal cells (MSCs) are unique mesenchymal cells that have been utilized as vehicles for the delivery of therapeutic proteins in gene therapy protocols. However, there are several unresolved issues regarding their potential therapeutic applications. These include low transduction efficiency, attenuation of transgene expression, and the technical problems associated with drug-based selection markers. To address these issues, we have developed a transduction protocol that yields high-level gene transfer into human MSCs, employing a murine stem cell virus-based bicistronic vector containing the green fluorescent protein (GFP) gene as a selectable marker. Transduction of MSCs plated at low density for 6 hr per day for 3 days with high-titer viral supernatant resulted in a gene transfer efficiency of 80+/-6% (n = 10) as measured by GFP fluorescence. Neither centrifugation nor phosphate depletion increased transduction efficiency. Assessment of amphotropic receptor (Pit-2) expression by RT-PCR demonstrated that all MSCs expressing the receptor were successfully transduced. Cell cycle distribution profiles measured by propidium iodide staining showed no correlation with the susceptibility of MSCs to transduction by the retroviral vector. Human MSCs sequentially transduced with an adenoviral vector encoding the ecotropic receptor and ecotropic retroviral vector encoding GFP demonstrated that all MSCs are susceptible to retroviral transduction. We further showed that both genes of bicistronic vector are expressed for at least 6 months in vitro and that transgene expression did not affect the growth or osteogenic differentiation potential of MSCs. Future studies will be directed toward the development of gene therapy protocols employing this strategy.