The changing landscape of gene editing in hematopoietic stem cells: a step towards Cas9 clinical translation

Abstract

Purpose of review 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 hematopotieic stem cells (HSC), which posses 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 hematopotieic stem cells (GE-HSC) from the discovery stage to the preclinical stage, with the imminent goal of clinical translational for the treatment of serious genetic diseases of the blood and immune system. Recent Findings 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 hematopotieic stem cells (HSC) has bloomed. We have observed that over the last two 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. Summary 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 two 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 hematopotieic diseases that are candidates for curative allogeneic bone marrow transplantation.

Genome Editing for Mucopolysaccharidoses

“…Advantages of the ex vivo approach include the control over which cells are targeted and the ability to fully characterize the editing outcomes, both intended (on-target) and unintended (off-target), in the targeted population. This approach has been extensively used in the hematopoietic system, where the isolation, culture, and transplantation of these cells is now routine [35,36]. However, not all organ functions can be replaced by transplantation of genome edited cells modified ex vivo.…”

Unleashing the cure: Overcoming persistent obstacles in the translation and expanded use of hematopoietic stem cell-based therapies

“…An alternative to lentiviral‐mediated gene integration is genome editing, where an engineered nuclease is used to create a site‐specific DNA double‐strand break (DSB), subsequently activating the cell's endogenous repair machinery to create insertions, deletions, or when a homologous template is provided, to introduce precise changes to the targeted locus. There are now multiple nuclease platforms demonstrated to edit HSPCs with high efficiency including zinc finger nucleases (ZFNs), TAL effector nucleases (TALENs), mega‐TALs, and the CRISPR/Cas9 system (clustered regularly interspaced short palindromic repeat/CRISPR‐associated protein), reviewed by Dever and Porteus . The most clinically advanced are the ZFNs, which have been shown to be safe and effective in inactivating the CCR5 locus in primary T‐cells from patients with HIV infection .…”

“…All stages, see Porteus. 29 The most clinically advanced are the ZFNs, which have been shown to be safe and effective in inactivating the CCR5 locus in primary T-cells from patients with HIV infection. 30 Several new clinical trials using ZFNs to inactivate genetic elements in HSPCs are ongoing, including CCR5 gene disruption as treatment for HIV infection, and disabling the erythroid specific enhancer in the BCL11A gene to derepress fetal globin expression as treatment for sickle cell disease and β-thalassemia.…”

Hope for hematological diseases

“…The ideal HSCT therapeutic paradigm (at least for nonmalignant hematological diseases) would be the transplantation of healthy autologous patient-derived HSCs without preconditioning. CRISPR/Cas9 genome editing technologies have opened the door for efficient autologous HSC gene correction for numerous hematological diseases (4). Unfortunately, however, the clinical success of these new HSCT strategies (as well as existing lentivirus-or retrovirus-based HSCT gene therapies) remains challenging because of the limited window for ex vivo perturbation (usually <72 hours) and the often inadequate numbers of HSCs collectable from patients.…”