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)
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.
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.
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.
Extended Survival of Glioblastoma Patients After Chemoprotective HSC Gene Therapy.. Science translational medicine. 4(133):133ra57.. 2012.
Hematopoietic stem cell expansion facilitates multilineage engraftment in a nonhuman primate cord blood transplantation model.. Experimental hematology. 40(3):187-196.. 2012.
Challenges in vector and trial design using retroviral vectors for long-term gene correction in hematopoietic stem cell gene therapy.. Molecular therapy : the journal of the American Society of Gene Therapy. 20(6):1084-94.. 2012.
Outside the box--novel therapeutic strategies for glioblastoma.. Cancer journal (Sudbury, Mass.). 18(1):51-8.. 2012.
Novel reporter systems for facile evaluation of I-SceI-mediated genome editing.. Nucleic acids research. 40(2). 2012.
Hematopoietic-stem-cell-based gene therapy for HIV disease.. Cell stem cell. 10(2):137-47.. 2012.
Gene Therapy for Fanconi Anemia: One Step Closer to the Clinic.. Human gene therapy. 23(2):141-144.. 2012.
Large animal models for foamy virus vector gene therapy.. Viruses. 4(12):3572-88.. 2012.
Current translational and clinical practices in hematopoietic cell and gene therapy.. Cytotherapy. 14(7):775-90.. 2012.
In vivo selection of autologous MGMT gene-modified cells following reduced-intensity conditioning with BCNU and temozolomide in the dog model.. Cancer gene therapy. 119(8):523-529.. 2012.
Abrogated cryptic activation of lentiviral transfer vectors.. Scientific reports. 2:438.. 2012.
Stem cell selection in vivo using foamy vectors cures canine pyruvate kinase deficiency.. PloS one. 7(9):e45173.. 2012.
Myelodysplasia in 2 Pig-Tailed Macaques (Macaca nemestrina) Associated With Retroviral Vector-Mediated Insertional Mutagenesis and Overexpression of HOXB4.. Veterinary pathology. 48(5):999-1001.. 2011.
Safeguarding nonhuman primate iPS cells with suicide genes.. Molecular therapy : the journal of the American Society of Gene Therapy. 19(9):1667-75.. 2011.