Dr. Daniel Dever is a Research Instructor in the laboratory of Dr. Matthew Porteus at Stanford University, in the Department of Pediatrics, Division of Stem Cell Transplantation and Regenerative Medicine. He completed his PhD in molecular toxicology at the University of Rochester where he studied the mechanisms of the aryl hydrocarbon receptor in mediating cerebellar transcriptional programs. During his postdoctoral work in the Porteus group, he (with others) developed a CRISPR/Cas9-based beta-globin (HBB) gene editing by homologous recombination methodology (gene targeting) in CD34+ hematopoietic stem cells as a potential therapeutic strategy to treat severe sickle cell disease. Dr. Dever (along with collaborators) has now successfully used this methodology to efficiently target >15 genes in primary blood cells that are associated with hematopoiesis, hematopoietic genetic diseases, hematopoietic malignancies, or safe harbor sites. Dr. Dever's primary research interests are to continue to leverage CRISPR/Cas9-based genome editing technologies to study the molecular mechanisms of gene targeting in human hematopoietic stem cells with the ultimate goal of optimizing and further developing novel cell and gene therapies for disease of the blood and the immune system. Currently, he is leading IND-enabling preclinical efficacy, feasibility, safety and tumorigenicity studies for FDA approval of a first-in-human clinical trial at Stanford in 2018 for the treatment of severe sickle cell disease using CRISPR/Cas9-based HBB gene targeting in autologous hematopoietic stem cells.
Instructor, Pediatrics - Stem Cell Transplantation
Doctor of Philosophy, University of Rochester, Toxicology (2014)
Multiplexed genetic engineering of human hematopoietic stem and progenitor cells using CRISPR/Cas9 and AAV6.
Precise and efficient manipulation of genes is crucial for understanding the molecular mechanisms that govern human hematopoiesis and for developing novel therapies for diseases of the blood and immune system. Current methods do not enable precise engineering of complex genotypes that can be easily tracked in a mixed population of cells. We describe a method to multiplex homologous recombination (HR) in human hematopoietic stem and progenitor cells and primary human T cells by combining rAAV6 donor delivery and the CRISPR/Cas9 system delivered as ribonucleoproteins (RNPs). In addition, the use of reporter genes allows FACS-purification and tracking of cells that have had multiple alleles or loci modified by HR. We believe this method will enable broad applications not only to the study of human hematopoietic gene function and networks, but also to perform sophisticated synthetic biology to develop innovative engineered stem cell-based therapeutics.
View details for DOI 10.7554/eLife.27873
View details for PubMedID 28956530
CRISPR/Cas9 ß-globin gene targeting in human haematopoietic stem cells.
The β-haemoglobinopathies, such as sickle cell disease and β-thalassaemia, are caused by mutations in the β-globin (HBB) gene and affect millions of people worldwide. Ex vivo gene correction in patient-derived haematopoietic stem cells followed by autologous transplantation could be used to cure β-haemoglobinopathies. Here we present a CRISPR/Cas9 gene-editing system that combines Cas9 ribonucleoproteins and adeno-associated viral vector delivery of a homologous donor to achieve homologous recombination at the HBB gene in haematopoietic stem cells. Notably, we devise an enrichment model to purify a population of haematopoietic stem and progenitor cells with more than 90% targeted integration. We also show efficient correction of the Glu6Val mutation responsible for sickle cell disease by using patient-derived stem and progenitor cells that, after differentiation into erythrocytes, express adult β-globin (HbA) messenger RNA, which confirms intact transcriptional regulation of edited HBB alleles. Collectively, these preclinical studies outline a CRISPR-based methodology for targeting haematopoietic stem cells by homologous recombination at the HBB locus to advance the development of next-generation therapies for β-haemoglobinopathies.
View details for DOI 10.1038/nature20134
View details for PubMedID 27820943
The changing landscape of gene editing in hematopoietic stem cells: a step towards Cas9 clinical translation.
Current opinion in hematology
Since the discovery two decades ago that programmable endonucleases can be engineered to modify human cells at single nucleotide resolution, the concept of genome editing was born. Now these technologies are being applied to therapeutically relevant cell types, including hematopoietic stem cells (HSC), which possess the power to repopulate an entire blood and immune system. The purpose of this review is to discuss the changing landscape of genome editing in hematopoietic stem cells (GE-HSC) from the discovery stage to the preclinical stage, with the imminent goal of clinical translation for the treatment of serious genetic diseases of the blood and immune system.With the discovery that the RNA-programmable (sgRNA) clustered regularly interspace short palindromic repeats (CRISPR)-Cas9 nuclease (Cas9/sgRNA) systems can be easily used to precisely modify the human genome in 2012, a genome-editing revolution of hematopoietic stem cells (HSC) has bloomed. We have observed that over the last 2 years, academic institutions and small biotech companies are developing HSC-based Cas9/sgRNA genome-editing curative strategies to treat monogenic disorders, including β-hemoglobinopathies and primary immunodeficiencies. We will focus on recent publications (within the past 2 years) that employ different genome-editing strategies to 'hijack' the cell's endogenous double-strand repair pathways to confer a disease-specific therapeutic advantage.The number of genome-editing strategies in HSCs that could offer therapeutic potential for diseases of the blood and immune system have dramatically risen over the past 2 years. The HSC-based genome-editing field is primed to enter clinical trials in the subsequent years. We will summarize the major advancements for the development of novel autologous GE-HSC cell and gene therapy strategies for hematopoietic diseases that are candidates for curative allogeneic bone marrow transplantation.
View details for DOI 10.1097/MOH.0000000000000385
View details for PubMedID 28806273
Technical Considerations for the Use of CRISPR/Cas9 in Hematology Research.
The hematopoietic system is responsible for transporting oxygen and nutrients, fighting infections, and repairing tissue damage. Hematopoietic system dysfunction therefore causes a range of serious health consequences. Lifelong hematopoiesis is maintained by repopulating multipotent hematopoietic stem cells (HSCs) that replenish shorter-lived, mature blood cell types. A prokaryotic mechanism of immunity, the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 nuclease system, has recently been "repurposed" to efficiently mutate mammalian genomes in a sequence-specific manner. The application of this genome-editing technology to hematology has afforded new approaches for functional genomics and even the prospect of "correcting" dysfunctional HSCs in the treatment of serious genetic hematological diseases. In this Perspective, we provide an overview of three recent CRISPR/Cas9 methods in hematology: gene disruption, gene targeting, and saturating mutagenesis. We also summarize the technical considerations and advice provided during the May 2017 International Society of Experimental Hematology New Investigator Committee webinar on the same topic.
View details for DOI 10.1016/j.exphem.2017.07.006
View details for PubMedID 28757433
Aryl hydrocarbon receptor deletion in cerebellar granule neuron precursors impairs neurogenesis
2016; 76 (5): 533-550
The aryl hydrocarbon receptor (AhR) is a ligand-activated member of the basic-helix-loop-helix/PER-ARNT-SIM(PAS) transcription factor superfamily that also mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Increasing evidence suggests that AhR influences the development of many tissues, including the central nervous system. Our previous studies suggest that sustained AhR activation by TCDD and/or AhR deletion disrupts cerebellar granule neuron precursor (GNP) development. In the current study, to determine whether endogenous AhR controls GNP development in a cell-autonomous manner, we created a GNP-specific AhR deletion mouse, AhR(fx/fx) /Math1(CRE/+) (AhR CKO). Selective AhR deletion in GNPs produced abnormalities in proliferation and differentiation. Specifically, fewer GNPs were engaged in S-phase, as demonstrated by ∼25% reductions in thymidine (in vitro) and Bromodeoxyuridine (in vivo) incorporation. Furthermore, total granule neuron numbers in the internal granule layer at PND21 and PND60 were diminished in AhR conditional knockout (CKO) mice compared with controls. Conversely, differentiation was enhanced, including ∼40% increase in neurite outgrowth and 50% increase in GABARα6 receptor expression in deletion mutants. Our results suggest that AhR activity plays a role in regulating granule neuron number and differentiation, possibly by coordinating this GNP developmental transition. These studies provide novel insights for understanding the normal roles of AhR signaling during cerebellar granule cell neurogenesis and may have important implications for the effects of environmental factors in cerebellar dysgenesis.
View details for DOI 10.1002/dneu.22330
View details for Web of Science ID 000373930600005
View details for PubMedID 26243376
The Aryl Hydrocarbon Receptor Contributes to the Proliferation of Human Medulloblastoma Cells
2012; 81 (5): 669-678
The aryl hydrocarbon receptor (AhR), a ligand-activated member of the basic helix-loop-helix (bHLH)/PER-ARNT-SIM (PAS) transcription superfamily, is known to regulate the toxicity of polyaromatic halogenated hydrocarbon environmental chemicals, most notably dioxin. However, the AhR has also been implicated in multiple stages of tumorigenesis. Medulloblastoma (MB), a primary cerebellar brain tumor arising in infants and children, is thought to originate from abnormally proliferating cerebellar granule neuron precursors (GNPs). GNPs express high levels of the AhR in the external germinal layer of the developing cerebellum. Moreover, our laboratory has previously reported that either abnormal activation or deletion of the AhR leads to dysregulation of GNP cell cycle activity and maturation. These observations led to the hypothesis that the AhR promotes the growth of MB. Therefore, this study evaluated whether the AhR serves a pro-proliferative role in an immortalized MB tumor cell line (DAOY). We produced a stable AhR knockdown DAOY cell line [AhR short hairpin RNA (shRNA)], which exhibited a 70% reduction in AhR protein levels. Compared with wild-type DAOY cells, AhR shRNA DAOY cells displayed an impaired G(1)-to-S cell cycle transition, decreased DNA synthesis, and reduced proliferation. Furthermore, these cell cycle perturbations were correlated with decreased levels of the pro-proliferative gene Hes1 and increased levels of the cell cycle inhibitor p27(kip1). Supplementation experiments with human AhR restored the proliferative activity in AhR shRNA DAOY cells. Taken together, our data show that the AhR promotes proliferation of MB cells, suggesting that this pathway should be considered as a potential therapeutic target for MB treatment.
View details for DOI 10.1124/mol.111.077305
View details for Web of Science ID 000302934500005
View details for PubMedID 22311706
Subchronic Polychlorinated Biphenyl (Aroclor 1254) Exposure Produces Oxidative Damage and Neuronal Death of Ventral Midbrain Dopaminergic Systems
2012; 125 (2): 496-508
Recent epidemiologic studies have demonstrated a link between organochlorine and pesticide exposure to an enhanced risk for neurodegenerative disorders such as Parkinson's disease (PD). A common biological phenomenon underlying cell injury associated with both polychlorinated biphenyl (PCB) exposure and dopaminergic neurodegeneration during aging is oxidative stress (OS). In this study, we tested the hypothesis that oral PCB exposure, via food ingestion, impairs dopamine systems in the adult murine brain. We determined whether PCB exposure was associated with OS in dopaminergic neurons, a population of cells that selectively degenerate in PD. After 4 weeks of oral exposure to the PCB mixture Aroclor 1254, several congeners, mostly ortho substituted, accumulated throughout the brain. Significant increases in locomotor activity were observed within 2 weeks, which persisted after cessation of PCB exposure. Stereologic analyses revealed a significant loss of dopaminergic neurons within the substantia nigra and ventral tegmental area. However, striatal dopamine levels were elevated, suggesting that compensatory mechanisms exist to maintain dopamine homeostasis, which could contribute to the observed increases in locomotor activity following PCB exposure. Biochemical experiments revealed alterations in OS markers, including increases in SOD and HO-1 levels and the presence of oxidatively modified lipids and proteins. These findings were accompanied by elevated iron levels within the striatal and midbrain regions, perhaps due to the observed dysregulation of transferrin receptors and ferritin levels following PCB exposure. In this study, we suggest that both OS and the uncoupling of iron regulation contribute to dopamine neuron degeneration and hyperactivity following PCB exposure.
View details for DOI 10.1093/toxsci/kfr313
View details for Web of Science ID 000299346000017
View details for PubMedID 22094459
2,3,7,8-tetracholorodibenzo-p-dioxin exposure disrupts granule neuron precursor maturation in the developing mouse cerebellum
2008; 103 (1): 125-136
The widespread environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been linked to developmental neurotoxicity associated with abnormal cerebellar maturation in both humans and rodents. TCDD mediates toxicity via binding to the aryl hydrocarbon receptor (AhR), a transcription factor that regulates the expression of xenobiotic metabolizing enzymes and growth regulatory molecules. Our previous studies demonstrated that cerebellar granule neuron precursor cells (GNPs) express transcriptionally active AhR during critical developmental periods. TCDD exposure also impaired GNP proliferation and survival in vitro. Therefore, this study tested the hypothesis that TCDD exposure disrupts cerebellar development by interfering with GNP differentiation. In vivo experiments indicated that TCDD exposure on postnatal day (PND) 6 resulted in increased expression of a mitotic marker and increased thickness of the external granule layer (EGL) on PND10. Expression of the early differentiation marker TAG-1 was also more pronounced in postmitotic, premigratory granule neurons of the EGL, and increased apoptosis of GNPs was observed. On PND21, expression of the late GNP differentiation marker GABA(A alpha 6) receptor (GABAR(A alpha 6)) and total estimated cell numbers were both reduced following exposure on PND6. Studies in unexposed adult AhR(-/-) mice revealed lower GABAR(A alpha 6) levels and DNA content. In vitro studies showed elevated expression of the early differentiation marker p27/Kip1 and the GABAR(A alpha 6) in GNPs following TCDD exposure, and the expression patterns of proteins related to granule cell neurite outgrowth, beta III-tubulin and polysialic acid neural cell adhesion molecule, were consistent with enhanced neuroblast differentiation. Together, our data suggest that TCDD disrupts a normal physiological role of AhR, resulting in compromised GNP maturation and neuroblast survival, which impacts final cell number in the cerebellum.
View details for DOI 10.1093/toxsci/kfn017
View details for Web of Science ID 000254955500014
View details for PubMedID 18227101