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.
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Dose-adapted post-transplant cyclophosphamide for HLA-haploidentical transplantation in Fanconi anemia.. Bone marrow transplantation.. 2017.
Semi-automated closed system manufacturing of lentivirus gene-modified haematopoietic stem cells for gene therapy.. Nature communications. 7:13173.. 2016.
Endothelial Cells Promote Expansion of Long-Term Engrafting Marrow Hematopoietic Stem and Progenitor Cells in Primates.. Stem cells translational medicine.. 2016.
Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Children and Adolescents with Fanconi Anemia.. Biology of blood and marrow transplantation : journal of the American Society for Blood and Marrow Transplantation.. 2016.
Devouring the Hematopoietic Stem Cell: Setting the Table for Marrow Cell Transplantation.. Molecular therapy : the journal of the American Society of Gene Therapy. 24(11):1892-1894.. 2016.
The frequency of multipotent CD133(+)CD45RA(-)CD34(+) hematopoietic stem cells is not increased in fetal liver compared to adult stem cell sources.. Experimental hematology. 44(6):502-507.. 2016.
Safety and Efficacy of Combination Antiretroviral Therapy in Human Immunodeficiency Virus-Infected Adults Undergoing Autologous or Allogeneic Hematopoietic Cell Transplantation for Hematologic Malignancies. Biology of blood and marrow transplantation : journal of the American Society for Blood and Marrow Transplantation. 22(1):149-156.. 2016.
Cell-Delivered Entry Inhibitors for HIV-1: CCR5 Downregulation and Blocking Virus/Membrane Fusion in Defending the Host Cell Population.. AIDS patient care and STDs. 30(12):545-550.. 2016.
Efficient Modification of the CCR5 Locus in Primary Human T Cells With megaTAL Nuclease Establishes HIV-1 Resistance.. Molecular therapy. Nucleic acids. 5(8):e352.. 2016.
Rethinking the Regulatory Infrastructure for Human Gene Transfer Clinical Trials.. Molecular therapy : the journal of the American Society of Gene Therapy. 24(7):1173-7.. 2016.
Development of 3(rd) Generation Cocal Envelope Producer Cell Lines for Robust Lentiviral Gene Transfer into Hematopoietic Stem Cells and T Cells.. Molecular therapy : the journal of the American Society of Gene Therapy.. 2016.
A curative regimen would decrease HIV prevalence but not HIV incidence unless targeted to an ART-naïve population.. Scientific reports. 6:22183.. 2016.
Multilineage polyclonal engraftment of Cal-1 gene-modified cells and in vivo selection after SHIV infection in a nonhuman primate model of AIDS.. Molecular therapy. Methods & clinical development. 3:16007.. 2016.
Lentivirus-mediated Gene Transfer in Hematopoietic Stem Cells Is Impaired in SHIV-infected, ART-treated Nonhuman Primates.. Molecular therapy : the journal of the American Society of Gene Therapy. 23(5):943-51.. 2015.
Vascular niche promotes hematopoietic multipotent progenitor formation from pluripotent stem cells.. The Journal of clinical investigation. 125(3):1243-54.. 2015.
Gene therapy studies in a canine model of X-linked severe combined immunodeficiency.. Human gene therapy. Clinical development. 26(1):50-6.. 2015.
Combinatorial hematopoietic stem cell transplantation and vaccination reduces viral pathogenesis following SHIV89.6P-challenge.. Gene therapy. 22(12):1007-1012.. 2015.
Lack of viral control and development of combination antiretroviral therapy escape mutations in macaques after bone marrow transplantation.. AIDS (London, England). 29(13):1597-606.. 2015.
C peptides as entry inhibitors for gene therapy.. Advances in experimental medicine and biology. 848:191-209.. 2015.