Dr.Med., University of Ulm, Medicine, 1988.
M.D., University of Ulm, Medicine, 1987.
Conducting Preclinical and Clinical Studies of Gene Therapy
Hematopoietic stem cells (HSCs) are attractive targets for gene therapy because of their ability to permanently reconstitute the hematopoietic and immune systems after transplant. Many different congenital and acquired diseases could be treated by introducing new genes into stem cells. In fact, in certain diseases with a selective advantage of genetically modified cells such as severe combined immunodeficiency (SCID), stem cell gene therapy has already been successfully applied to affected patients. These studies, however, have also demonstrated potential side effects of stem cell gene therapy when some patients developed leukemia in part due to retroviral insertional mutagenesis. These findings have led to a shift in emphasis in the gene therapy field from efficacy to safety. Thus, significant efforts have been devoted to improve not only stem cell gene transfer efficiency but also safety. Unfortunately, mouse studies have not been predictive of stem cell gene transfer in large animals. We have recently shown in a direct comparison that distinct repopulating cells engraft in the NOD/SCID versus the nonhuman primate model, suggesting NOD/SCID repopulating cells are more differentiated than nonhuman primate repopulating cells. Thus, we have focused on stem cell gene transfer studies in clinically relevant large animals and have identified factors resulting in increased gene transfer, including lentiviral vectors (Horn et al, Blood 2004). The relatively high gene transfer levels, >20% in peripheral blood and marrow cells, obtained with these conditions suggest the potential for therapeutic efficacy in diseases affecting the hematopoietic system, especially in diseases with selective advantages for corrected cells. Future clinical gene therapy efforts are aimed at patients with Fanconi anemia. A major clinical problem in these patients is marrow failure, and phenotypically corrected cells should have a selective advantage over uncorrected cells.
For most genetic diseases, gene-corrected cells do not have selective advantages, and in vivo selection strategies will be required. To that end, we have used drug resistance genes for in vivo selection and chemo-protection. Using the methylguanine methyltransferase (MGMT) gene, which confers resistance to alkylating agents such as BCNU and temozolomide, we demonstrated efficient in vivo selection and, more importantly, chemo-protection of hematopoietic stem cells (Neff et al, JCI 2003). Based on these data, we are preparing a clinical study in patients with brain tumors. Patients will receive temozolomide and BCNU, and since a major and dose-limiting side effect of this treatment is myelosuppression, we propose to genetically protect stem cells with MGMT, which should allow for more intensive and effective chemotherapy. We also showed protection of allogeneic stem cells from chemotherapy-induced myelosuppression, suggesting this technology could be applied to facilitate nonmyeloablative allogeneic HCT.
We have also made progress in expanding repopulating cells using the transcription factor HOXB4, which expanded CD34+ cells ex vivo and significantly improved engraftment after myeloablative conditioning compared to control cells (Zhang et al, PlosMedicine 2006). We have also initiated studies with ES cells from nonhuman primates and are testing whether we can direct the differentiation to hematopoietic stem/progenitor cells. More recently, we have discovered that dogs given HOXB4-transduced cells developed leukemia about 500 days after HCT and are studying the events that led to leukemia (Zhang et al, JCI 2008). We anticipate using dogs to study novel mechanisms of leukemogenesis and novel treatment approaches for leukemia.
We are also performing studies to use RNAi technology to inhibit HIV infection of stem cells and are currently exploring these strategies in a nonhuman primate model of AIDS.
(Reading, Writing, Speaking)
German: (Fluent, Fluent, Fluent)
Modeling promising nonmyeloablative conditioning regimens in nonhuman primates.. Human gene therapy.. 2014.
Charting a Clear Path: The ASGCT Standardized Pathways Conference.. Molecular therapy : the journal of the American Society of Gene Therapy. 22(7):1235-8.. 2014.
Ectopic expression of HOXC6 blocks myeloid differentiation and predisposes to malignant transformation.. Experimental hematology. 42(2):114-125.e4.. 2014.
HIV eradication-from Berlin to Boston.. Nature biotechnology. 32(4):315-6.. 2014.
High-throughput genomic mapping of vector integration sites in gene therapy studies.. Methods in molecular biology (Clifton, N.J.). 1185:321-44.. 2014.
Transmission of Chagas Disease via Blood Transfusions in 2 Immunosuppressed Pigtailed Macaques (Macaca nemestrina).. Comparative medicine. 64(1):63-7.. 2014.
Establishment of a Pigtailed Macaque Model to Test the Effects of Chemoradiation and Ccr5 Gene Therapy on the Shiv Latent Viral Reservoir. Journal of medical primatology. 42:267-267.. 2013.
Robust suppression of env-SHIV viremia in Macaca nemestrina by 3-drug ART is independent of timing of initiation during chronic infection.. Journal of medical primatology. 42(5):237-46.. 2013.
Genetically Modified Hematopoietic Stem Cell Transplantation for HIV-1-infected Patients: Can We Achieve a Cure? Molecular therapy : the journal of the American Society of Gene Therapy.. 2013.
In vivo protection of activated Tyr22-DHFR gene-modified canine T lymphocytes from methotrexate.. The journal of gene medicine.. 2013.
Targeted gene disruption to cure HIV.. Current opinion in HIV and AIDS. 8(3):217-23.. 2013.
CD34(+) Expansion With Delta-1 and HOXB4 Promotes Rapid Engraftment and Transfusion Independence in a Macaca nemestrina Cord Blood Transplant Model.. Molecular therapy : the journal of the American Society of Gene Therapy. 21(6):1270-8.. 2013.
Genetic modification of hematopoietic stem cells as a therapy for HIV/AIDS.. Viruses. 5(12):2946-62.. 2013.
Cyclophosphamide-based in vivo T-cell depletion for HLA-haploidentical transplantation in Fanconi anemia.. Pediatric hematology and oncology. 29(6):568-78.. 2012.
Coupling endonucleases with DNA end-processing enzymes to drive gene disruption.. Nature methods. 9(10):973-5.. 2012.
Cyclophosphamide promotes engraftment of gene-modified cells in a mouse model of Fanconi anemia without causing cytogenetic abnormalities.. Journal of molecular medicine (Berlin, Germany). 90(11):1283-1294.. 2012.