Gene replacement of α-globin with β-globin restores hemoglobin balance in β-thalassemia-derived hematopoietic stem and progenitor cells

Precise measurement of CRISPR genome editing outcomes through single-cell DNA sequencing

Gene therapy for clinical applications necessitates a comprehensive, accurate, and precise measurement of gene-edited drug products. State-of-the-art pipelines for evaluating editing outcomes rely primarily on bulk sequencing approaches, which are limited to population-level assessment. Here, we leveraged Tapestri, a single-cell sequencing technology for an in-depth analysis of editing outcomes. Using this platform, we characterized the genotype of triple-edited cells simultaneously at more than 100 loci, including editing zygosity, structural variations, and cell clonality. Our findings revealed a unique editing pattern in nearly every edited cell, highlighting the importance of single-cell resolution measurement to ensure the highest safety standards.

A differentiated β-globin gene replacement strategy uses heterologous introns to restore physiological expression

β-Hemoglobinopathies are common monogenic disorders. In sickle cell disease (SCD), a single mutation in the β-globin (HBB) gene results in dysfunctional hemoglobin protein, while in β-thalassemia, over 300 mutations distributed across the gene reduce β-globin levels and cause severe anemia. Genetic engineering replacing the whole HBB gene through homology-directed repair (HDR) is an ideal strategy to restore a benign genotype and rescue HBB expression for most genotypes. However, this is technically challenging because (1) the insert must not be homologous to the endogenous gene and (2) synonymous codon-optimized, intron-less sequences may not reconstitute adequate β-globin levels. Here, we developed an HBB gene replacement strategy using CRISPR-Cas9 that successfully addresses these challenges. We determined that a DNA donor containing a diverged HBB coding sequence and heterologous introns to avoid sequence homology provides proper physiological expression. We identified a DNA donor that uses truncated γ-globin introns, results in 34% HDR, and rescues β-globin expression in in vitro models of SCD and β-thalassemia in hematopoietic stem and progenitor cells (HSPCs). Furthermore, while HDR allele frequency dropped in vivo, it was maintained at ∼15%, demonstrating editing of long-term repopulating HSPCs. In summary, our HBB gene replacement strategy offers a differentiated approach by restoring naturally regulated adult hemoglobin expression.

Multilayered HIV-1 resistance in HSPCs through CCR5 Knockout and B cell secretion of HIV-inhibiting antibodies

Allogeneic transplantation of CCR5 null hematopoietic stem and progenitor cells (HSPCs) is the only known cure for HIV-1 infection. However, this treatment is limited because of the rarity of CCR5-null matched donors, the morbidities associated with allogeneic transplantation, and the prevalence of HIV-1 strains resistant to CCR5 knockout (KO) alone. Here, we propose a one-time therapy through autologous transplantation of HSPCs genetically engineered ex vivo to produce both CCR5 KO cells and long-term secretion of potent HIV-1 inhibiting antibodies from B cell progeny. CRISPR-Cas9-engineered HSPCs engraft and reconstitute multiple hematopoietic lineages in vivo and can be engineered to express multiple antibodies simultaneously (in pre-clinical models). Human B cells engineered to express each antibody secrete neutralizing concentrations capable of inhibiting HIV-1 pseudovirus infection in vitro. This work lays the foundation for a potential one-time functional cure for HIV-1 through combining the long-term delivery of therapeutic antibodies against HIV-1 and the known efficacy of CCR5 KO HSPC transplantation.

Gene therapy for β-thalassemia: current and future options

Beta-thalassemia is a severe, hereditary blood disorder characterized by anemia, transfusion dependence, reduced life expectancy, and poor quality of life. Allogeneic transplantation of hematopoietic stem cells (HSCs) is the only curative treatment for transfusion-dependent β-thalassemia, but a lack of compatible donors prevents the use of this approach for most patients. Over the past 20 years, the rise of gene therapy and the development of lentiviral vectors and genome-editing tools has extended curative options to a broader range of patients. Here, we review breakthroughs in gene addition- and genome-editing-based therapies for β-thalassemia, the clinical outcomes enabling approval by regulatory agencies, and perspectives for further development.

MetaQ: fast, scalable and accurate metacell inference via single-cell quantization

To overcome the computational barriers of analyzing large-scale single-cell sequencing data, we introduce MetaQ, a metacell algorithm that scales to arbitrarily large datasets with linear runtime and constant memory usage. Inspired by cellular development, MetaQ conceptualizes each metacell as a collective ancestor of biologically similar cells. By quantizing cells into a discrete codebook, where each entry represents a metacell capable of reconstructing the original cells it quantizes, MetaQ identifies homogeneous cell subsets for efficient and accurate metacell inference. This approach reduces computational complexity from exponential to linear while maintaining or surpassing the performance of existing metacell algorithms. Extensive experiments demonstrate that MetaQ excels in downstream tasks such as cell type annotation, developmental trajectory inference, batch integration, and differential expression analysis. Thanks to its superior efficiency and effectiveness, MetaQ makes analyzing datasets with millions of cells practical, offering a powerful solution for single-cell studies in the era of high-throughput profiling.

Engineering synthetic signaling receptors to enable erythropoietin-free erythropoiesis

Blood transfusion plays a vital role in modern medicine, but frequent shortages occur. Ex vivo manufacturing of red blood cells (RBCs) from universal donor cells offers a potential solution, yet the high cost of recombinant cytokines remains a barrier. Erythropoietin (EPO) signaling is crucial for RBC development, and EPO is among the most expensive media components. To address this challenge, we develop highly optimized small molecule-inducible synthetic EPO receptors (synEPORs) using design-build-test cycles and genome editing. By integrating synEPOR at the endogenous EPOR locus in O-negative induced pluripotent stem cells, we achieve equivalent erythroid differentiation, transcriptomic changes, and hemoglobin production using small molecules compared to EPO-supplemented cultures. This approach dramatically reduces culture media costs. Our strategy not only addresses RBC production challenges but also demonstrates how protein and genome engineering can introduce precisely regulated cellular behaviors, potentially improving scalable manufacturing of a wide range of clinically relevant cell types.

Dual α-globin-truncated erythropoietin receptor knockin restores hemoglobin production in α-thalassemia-derived erythroid cells

The most severe form of α-thalassemia results from loss of all four copies of α-globin. Postnatally, patients face challenges similar to β-thalassemia, including severe anemia and erythrotoxicity due to the imbalance of β-globin and α-globin chains. Despite progress in genome editing treatments for β-thalassemia, there is no analogous curative option for α-thalassemia. To address this, we designed a Cas9/AAV6-mediated genome editing strategy that integrates a functional α-globin gene into the β-globin locus in α-thalassemia patient-derived hematopoietic stem and progenitor cells (HSPCs). Incorporation of a truncated erythropoietin receptor transgene into the α-globin integration cassette significantly increased erythropoietic output from edited HSPCs and led to the most robust production of α-globin, and consequently hemoglobin tetramers. By directing edited HSPCs toward increased production of clinically relevant erythroid cells, this approach has the potential to mitigate the limitations of current treatments for the hemoglobinopathies, including low genome editing and low engraftment rates.

Enhancement of erythropoietic output by Cas9-mediated insertion of a natural variant in haematopoietic stem and progenitor cells

Some gene polymorphisms can lead to monogenic diseases, whereas other polymorphisms may confer beneficial traits. A well-characterized example is congenital erythrocytosis-the non-pathogenic hyper-production of red blood cells-that is caused by a truncated erythropoietin receptor. Here we show that Cas9-mediated genome editing in CD34+ human haematopoietic stem and progenitor cells (HSPCs) can recreate the truncated form of the erythropoietin receptor, leading to substantial increases in erythropoietic output. We also show that combining the expression of the cDNA of a truncated erythropoietin receptor with a previously reported genome-editing strategy to fully replace the HBA1 gene with an HBB transgene in HSPCs (to restore normal haemoglobin production in cells with a β-thalassaemia phenotype) gives the edited HSPCs and the healthy red blood cell phenotype a proliferative advantage. Combining knowledge of human genetics with precise genome editing to insert natural human variants into therapeutic cells may facilitate safer and more effective genome-editing therapies for patients with genetic diseases.

Gene therapy for polygenic or complex diseases

Gene therapy utilizes nucleic acid drugs to treat diseases, encompassing gene supplementation, gene replacement, gene silencing, and gene editing. It represents a distinct therapeutic approach from traditional medications and introduces novel strategies for genetic disorders. Over the past two decades, significant advancements have been made in the field of gene therapy, leading to the approval of various gene therapy drugs. Gene therapy was initially employed for treating genetic diseases and cancers, particularly monogenic conditions classified as orphan diseases due to their low prevalence rates; however, polygenic or complex diseases exhibit higher incidence rates within populations. Extensive research on the etiology of polygenic diseases has unveiled new therapeutic targets that offer fresh opportunities for their treatment. Building upon the progress achieved in gene therapy for monogenic diseases and cancers, extending its application to polygenic or complex diseases would enable targeting a broader range of patient populations. This review aims to discuss the strategies of gene therapy, methods of gene editing (mainly CRISPR-CAS9), and carriers utilized in gene therapy, and highlight the applications of gene therapy in polygenic or complex diseases focused on applications that have either entered clinical stages or are currently undergoing clinical trials.

Adeno-Associated Virus Vectors-a Target of Cellular and Humoral Immunity-are Expanding Their Reach Toward Hematopoietic Stem Cell Modification and Immunotherapies

All current market-approved gene therapy medical products for in vivo gene therapy of monogenic diseases rely on adeno-associated virus (AAV) vectors. Advances in gene editing technologies and vector engineering have expanded the spectrum of target cells and, thus, diseases that can be addressed. Consequently, AAV vectors are now being explored to modify cells of the hematopoietic system, including hematopoietic stem and progenitor cells (HSPCs), to develop novel strategies to treat monogenic diseases, but also to generate cell- and vaccine-based immunotherapies. However, the cell types that represent important new targets for the AAV vector system are centrally involved in immune responses against the vector and its transgene product as discussed briefly in the first part of this review. In the second part, studies exploring AAV vectors for genetic engineering of HSPCs, T and B lymphocytes, and beyond are presented.

Exploring non-viral methods for the delivery of CRISPR-Cas ribonucleoprotein to hematopoietic stem cells

Gene manipulation of hematopoietic stem cells (HSCs) using the CRISPR/Cas system as a potent genome editing tool holds immense promise for addressing hematologic disorders. An essential hurdle in advancing this treatment lies in effectively delivering CRISPR/Cas to HSCs. While various delivery formats exist, Ribonucleoprotein complex (RNP) emerges as a particularly efficient option. RNP complexes offer enhanced gene editing capabilities, devoid of viral vectors, with rapid activity and minimized off-target effects. Nevertheless, novel delivery methods such as microfluidic-based techniques, filtroporation, nanoparticles, and cell-penetrating peptides are continually evolving. This study aims to provide a comprehensive review of these methods and the recent research on delivery approaches of RNP complexes to HSCs.

Therapeutic Relevance of Inducing Autophagy in β-Thalassemia

The β-thalassemias are inherited genetic disorders affecting the hematopoietic system. In β-thalassemias, more than 350 mutations of the adult β-globin gene cause the low or absent production of adult hemoglobin (HbA). A clinical parameter affecting the physiology of erythroid cells is the excess of free α-globin. Possible experimental strategies for a reduction in excess free α-globin chains in β-thalassemia are CRISPR-Cas9-based genome editing of the β-globin gene, forcing "de novo" HbA production and fetal hemoglobin (HbF) induction. In addition, a reduction in excess free α-globin chains in β-thalassemia can be achieved by induction of the autophagic process. This process is regulated by the Unc-51-like kinase 1 (Ulk1) gene. The interplay with the PI3K/Akt/TOR pathway, with the activity of the α-globin stabilizing protein (AHSP) and the involvement of microRNAs in autophagy and Ulk1 gene expression, is presented and discussed in the context of identifying novel biomarkers and potential therapeutic targets for β-thalassemia.

CRISPR-Based Gene Therapies: From Preclinical to Clinical Treatments

In recent years, clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) protein have emerged as a revolutionary gene editing tool to treat inherited disorders affecting different organ systems, such as blood and muscles. Both hematological and neuromuscular genetic disorders benefit from genome editing approaches but face different challenges in their clinical translation. The ability of CRISPR/Cas9 technologies to modify hematopoietic stem cells ex vivo has greatly accelerated the development of genetic therapies for blood disorders. In the last decade, many clinical trials were initiated and are now delivering encouraging results. The recent FDA approval of Casgevy, the first CRISPR/Cas9-based drug for severe sickle cell disease and transfusion-dependent β-thalassemia, represents a significant milestone in the field and highlights the great potential of this technology. Similar preclinical efforts are currently expanding CRISPR therapies to other hematologic disorders such as primary immunodeficiencies. In the neuromuscular field, the versatility of CRISPR/Cas9 has been instrumental for the generation of new cellular and animal models of Duchenne muscular dystrophy (DMD), offering innovative platforms to speed up preclinical development of therapeutic solutions. Several corrective interventions have been proposed to genetically restore dystrophin production using the CRISPR toolbox and have demonstrated promising results in different DMD animal models. Although these advances represent a significant step forward to the clinical translation of CRISPR/Cas9 therapies to DMD, there are still many hurdles to overcome, such as in vivo delivery methods associated with high viral vector doses, together with safety and immunological concerns. Collectively, the results obtained in the hematological and neuromuscular fields emphasize the transformative impact of CRISPR/Cas9 for patients affected by these debilitating conditions. As each field suffers from different and specific challenges, the clinical translation of CRISPR therapies may progress differentially depending on the genetic disorder. Ongoing investigations and clinical trials will address risks and limitations of these therapies, including long-term efficacy, potential genotoxicity, and adverse immune reactions. This review provides insights into the diverse applications of CRISPR-based technologies in both preclinical and clinical settings for monogenic blood disorders and muscular dystrophy and compare advances in both fields while highlighting current trends, difficulties, and challenges to overcome.

Dual α-globin and truncated EPO receptor knockin restores hemoglobin production in α-thalassemia-derived red blood cells

Alpha-thalassemia is an autosomal recessive disease with increasing worldwide prevalence. The molecular basis is due to mutation or deletion of one or more duplicated α-globin genes, and disease severity is directly related to the number of allelic copies compromised. The most severe form, α-thalassemia major (αTM), results from loss of all four copies of α-globin and has historically resulted in fatality in utero. However, in utero transfusions now enable survival to birth. Postnatally, patients face challenges similar to β-thalassemia, including severe anemia and erythrotoxicity due to imbalance of β-globin and α-globin chains. While curative, hematopoietic stem cell transplantation (HSCT) is limited by donor availability and potential transplant-related complications. Despite progress in genome editing treatments for β-thalassemia, there is no analogous curative option for patients suffering from α-thalassemia. To address this, we designed a novel Cas9/AAV6-mediated genome editing strategy that integrates a functional α-globin gene into the β-globin locus in αTM patient-derived hematopoietic stem and progenitor cells (HSPCs). Incorporation of a truncated erythropoietin receptor transgene into the α-globin integration cassette dramatically increased erythropoietic output from edited HSPCs and led to the most robust production of α-globin, and consequently normal hemoglobin. By directing edited HSPCs toward increased production of clinically relevant RBCs instead of other divergent cell types, this approach has the potential to mitigate the limitations of traditional HSCT for the hemoglobinopathies, including low genome editing and low engraftment rates. These findings support development of a definitive ex vivo autologous genome editing strategy that may be curative for α-thalassemia.

Lineage-tracing hematopoietic stem cell origins in vivo to efficiently make human HLF+ HOXA+ hematopoietic progenitors from pluripotent stem cells

The developmental origin of blood-forming hematopoietic stem cells (HSCs) is a longstanding question. Here, our non-invasive genetic lineage tracing in mouse embryos pinpoints that artery endothelial cells generate HSCs. Arteries are transiently competent to generate HSCs for 2.5 days (∼E8.5-E11) but subsequently cease, delimiting a narrow time frame for HSC formation in vivo. Guided by the arterial origins of blood, we efficiently and rapidly differentiate human pluripotent stem cells (hPSCs) into posterior primitive streak, lateral mesoderm, artery endothelium, hemogenic endothelium, and >90% pure hematopoietic progenitors within 10 days. hPSC-derived hematopoietic progenitors generate T, B, NK, erythroid, and myeloid cells in vitro and, critically, express hallmark HSC transcription factors HLF and HOXA5-HOXA10, which were previously challenging to upregulate. We differentiated hPSCs into highly enriched HLF+ HOXA+ hematopoietic progenitors with near-stoichiometric efficiency by blocking formation of unwanted lineages at each differentiation step. hPSC-derived HLF+ HOXA+ hematopoietic progenitors could avail both basic research and cellular therapies.

High-efficiency transgene integration by homology-directed repair in human primary cells using DNA-PKcs inhibition

Therapeutic applications of nuclease-based genome editing would benefit from improved methods for transgene integration via homology-directed repair (HDR). To improve HDR efficiency, we screened six small-molecule inhibitors of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key protein in the alternative repair pathway of non-homologous end joining (NHEJ), which generates genomic insertions/deletions (INDELs). From this screen, we identified AZD7648 as the most potent compound. The use of AZD7648 significantly increased HDR (up to 50-fold) and concomitantly decreased INDELs across different genomic loci in various therapeutically relevant primary human cell types. In all cases, the ratio of HDR to INDELs markedly increased, and, in certain situations, INDEL-free high-frequency (>50%) targeted integration was achieved. This approach has the potential to improve the therapeutic efficacy of cell-based therapies and broaden the use of targeted integration as a research tool.

Interplay between α-thalassemia and β-hemoglobinopathies: Translating genotype-phenotype relationships into therapies

α-Thalassemia represents one of the most important genetic modulators of β-hemoglobinopathies. During this last decade, the ongoing interest in characterizing genotype-phenotype relationships has yielded incredible insights into α-globin gene regulation and its impact on β-hemoglobinopathies. In this review, we provide a holistic update on α-globin gene expression stemming from DNA to RNA to protein, as well as epigenetic mechanisms that can impact gene expression and potentially influence phenotypic outcomes. Here, we highlight defined α-globin targeted strategies and rationalize the use of distinct molecular targets based on the restoration of balanced α/β-like globin chain synthesis. Considering the therapies that either increase β-globin synthesis or reactivate γ-globin gene expression, the modulation of α-globin chains as a disease modifier for β-hemoglobinopathies still remains largely uncharted in clinical studies.

Genetically corrected RAG2-SCID human hematopoietic stem cells restore V(D)J-recombinase and rescue lymphoid deficiency

ABSTRACT

Recombination-activating genes (RAG1 and RAG2) are critical for lymphoid cell development and function by initiating the variable (V), diversity (D), and joining (J) (V(D)J)-recombination process to generate polyclonal lymphocytes with broad antigen specificity. The clinical manifestations of defective RAG1/2 genes range from immune dysregulation to severe combined immunodeficiencies (SCIDs), causing life-threatening infections and death early in life without hematopoietic cell transplantation (HCT). Despite improvements, haploidentical HCT without myeloablative conditioning carries a high risk of graft failure and incomplete immune reconstitution. The RAG complex is only expressed during the G0-G1 phase of the cell cycle in the early stages of T- and B-cell development, underscoring that a direct gene correction might capture the precise temporal expression of the endogenous gene. Here, we report a feasibility study using the CRISPR/Cas9-based "universal gene-correction" approach for the RAG2 locus in human hematopoietic stem/progenitor cells (HSPCs) from healthy donors and RAG2-SCID patient. V(D)J-recombinase activity was restored after gene correction of RAG2-SCID-derived HSPCs, resulting in the development of T-cell receptor (TCR) αβ and γδ CD3+ cells and single-positive CD4+ and CD8+ lymphocytes. TCR repertoire analysis indicated a normal distribution of CDR3 length and preserved usage of the distal TRAV genes. We confirmed the in vivo rescue of B-cell development with normal immunoglobulin M surface expression and a significant decrease in CD56bright natural killer cells. Together, we provide specificity, toxicity, and efficacy data supporting the development of a gene-correction therapy to benefit RAG2-deficient patients.

Impact of CRISPR/HDR editing versus lentiviral transduction on long-term engraftment and clonal dynamics of HSPCs in rhesus macaques

For precise genome editing via CRISPR/homology-directed repair (HDR), effective and safe editing of long-term engrafting hematopoietic stem cells (LT-HSCs) is required. The impact of HDR on true LT-HSC clonal dynamics in a relevant large animal model has not been studied. To track the output and clonality of HDR-edited cells and to provide a comparison to lentivirally transduced HSCs in vivo, we developed a competitive rhesus macaque (RM) autologous transplantation model, co-infusing HSCs transduced with a barcoded GFP-expressing lentiviral vector (LV) and HDR edited at the CD33 locus. CRISPR/HDR-edited cells showed a two-log decrease by 2 months following transplantation, with little improvement via p53 inhibition, in comparison to minimal loss of LV-transduced cells long term. HDR long-term clonality was oligoclonal in contrast to highly polyclonal LV-transduced HSCs. These results suggest marked clinically relevant differences in the impact of current genetic modification approaches on HSCs.

A simultaneous knockout knockin genome editing strategy in HSPCs potently inhibits CCR5- and CXCR4-tropic HIV-1 infection

Allogeneic hematopoietic stem and progenitor cell transplant (HSCT) of CCR5 null (CCR5Δ32) cells can be curative for HIV-1-infected patients. However, because allogeneic HSCT poses significant risk, CCR5Δ32 matched bone marrow donors are rare, and CCR5Δ32 transplant does not confer resistance to the CXCR4-tropic virus, it is not a viable option for most patients. We describe a targeted Cas9/AAV6-based genome editing strategy for autologous HSCT resulting in both CCR5- and CXCR4-tropic HIV-1 resistance. Edited human hematopoietic stem and progenitor cells (HSPCs) maintain multi-lineage repopulation capacity in vivo, and edited primary human T cells potently inhibit infection by both CCR5-tropic and CXCR4-tropic HIV-1. Modification rates facilitated complete loss of CCR5-tropic replication and up to a 2,000-fold decrease in CXCR4-tropic replication without CXCR4 locus disruption. This multi-factor editing strategy in HSPCs could provide a broad approach for autologous HSCT as a functional cure for both CCR5-tropic and CXCR4-tropic HIV-1 infections.

Functional screening in human HSPCs identifies optimized protein-based enhancers of Homology Directed Repair

Homology Directed Repair (HDR) enables precise genome editing, but the implementation of HDR-based therapies is hindered by limited efficiency in comparison to methods that exploit alternative DNA repair routes, such as Non-Homologous End Joining (NHEJ). In this study, we develop a functional, pooled screening platform to identify protein-based reagents that improve HDR in human hematopoietic stem and progenitor cells (HSPCs). We leverage this screening platform to explore sequence diversity at the binding interface of the NHEJ inhibitor i53 and its target, 53BP1, identifying optimized variants that enable new intermolecular bonds and robustly increase HDR. We show that these variants specifically reduce insertion-deletion outcomes without increasing off-target editing, synergize with a DNAPK inhibitor molecule, and can be applied at manufacturing scale to increase the fraction of cells bearing repaired alleles. This screening platform can enable the discovery of future gene editing reagents that improve HDR outcomes.

Impact of α-Globin Gene Expression and α-Globin Modifiers on the Phenotype of β-Thalassemia and Other Hemoglobinopathies: Implications for Patient Management

In this short review, we presented and discussed studies on the expression of globin genes in β-thalassemia, focusing on the impact of α-globin gene expression and α-globin modifiers on the phenotype and clinical severity of β-thalassemia. We first discussed the impact of the excess of free α-globin on the phenotype of β-thalassemia. We then reviewed studies focusing on the expression of α-globin-stabilizing protein (AHSP), as a potential strategy of counteracting the effects of the excess of free α-globin on erythroid cells. Alternative processes controlling α-globin excess were also considered, including the activation of autophagy by β-thalassemia erythroid cells. Altogether, the studies reviewed herein are expected to have a potential impact on the management of patients with β-thalassemia and other hemoglobinopathies for which reduction in α-globin excess is clinically beneficial.

Combining Cell-Intrinsic and -Extrinsic Resistance to HIV-1 By Engineering Hematopoietic Stem Cells for CCR5 Knockout and B Cell Secretion of Therapeutic Antibodies

Autologous transplantation of CCR5 null hematopoietic stem and progenitor cells (HSPCs) is the only known cure for HIV-1 infection. However, this treatment is limited because of the rarity of CCR5 -null matched donors, the morbidities associated with allogeneic transplantation, and the prevalence of HIV-1 strains resistant to CCR5 knockout (KO) alone. Here, we propose a one-time therapy through autologous transplantation of HSPCs genetically engineered ex vivo to produce both CCR5 KO cells and long-term secretion of potent HIV-1 inhibiting antibodies from B cell progeny. CRISPR-Cas9-engineered HSPCs maintain engraftment capacity and multi-lineage potential in vivo and can be engineered to express multiple antibodies simultaneously. Human B cells engineered to express each antibody secrete neutralizing concentrations capable of inhibiting HIV-1 pseudovirus infection in vitro . This work lays the groundwork for a potential one-time functional cure for HIV-1 through combining the long-term delivery of therapeutic antibodies against HIV-1 and the known efficacy of CCR5 KO HSPC transplantation.

Gene regulation in inborn errors of immunity: Implications for gene therapy design and efficacy

Inborn errors of immunity (IEI) present a unique paradigm in the realm of gene therapy, emphasizing the need for precision in therapeutic design. As gene therapy transitions from broad-spectrum gene addition to careful modification of specific genes, the enduring safety and effectiveness of these therapies in clinical settings have become crucial. This review discusses the significance of IEIs as foundational models for pioneering and refining precision medicine. We explore the capabilities of gene addition and gene correction platforms in modifying the DNA sequence of primary cells tailored for IEIs. The review uses four specific IEIs to highlight key issues in gene therapy strategies: X-linked agammaglobulinemia (XLA), X-linked chronic granulomatous disease (X-CGD), X-linked hyper IgM syndrome (XHIGM), and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX). We detail the regulatory intricacies and therapeutic innovations for each disorder, incorporating insights from relevant clinical trials. For most IEIs, regulated expression is a vital aspect of the underlying biology, and we discuss the importance of endogenous regulation in developing gene therapy strategies.

Transient inhibition of 53BP1 increases the frequency of targeted integration in human hematopoietic stem and progenitor cells

Genome editing by homology directed repair (HDR) is leveraged to precisely modify the genome of therapeutically relevant hematopoietic stem and progenitor cells (HSPCs). Here, we present a new approach to increasing the frequency of HDR in human HSPCs by the delivery of an inhibitor of 53BP1 (named "i53") as a recombinant peptide. We show that the use of i53 peptide effectively increases the frequency of HDR-mediated genome editing at a variety of therapeutically relevant loci in HSPCs as well as other primary human cell types. We show that incorporating the use of i53 recombinant protein allows high frequencies of HDR while lowering the amounts of AAV6 needed by 8-fold. HDR edited HSPCs were capable of long-term and bi-lineage hematopoietic reconstitution in NSG mice, suggesting that i53 recombinant protein might be safely integrated into the standard CRISPR/AAV6-mediated genome editing protocol to gain greater numbers of edited cells for transplantation of clinically meaningful cell populations.

HBB as a Novel Biomarker for the Diagnosis and Monitoring of Lung Cancer Regulates Cell Proliferation via ERK1/2 Pathway

Objective: Recent studies have revealed that hemoglobin beta (HBB) plays an important role not only in blood disorders but also in malignancies. The aim of this study is to investigate the clinical significance, diagnostic value, and biological function of HBB in lung cancer. Methods: HBB expression was examined in lung cancer tissues and plasma samples using quantitative real-time polymerase chain reaction, and its relationship with clinical pathological characteristics was analyzed. Receiver operating characteristic (ROC) curves were constructed to evaluate the diagnostic value of HBB in lung cancer. The proliferation of A549 and SPCA1 cells was analyzed using a cell counting kit-8 assay and protein expressions were detected by western blot. Results: The expressions of HBB were found to be down-regulated in both lung cancer tissues and plasma samples. Notably, plasma HBB levels were significantly elevated in postoperative samples when compared to their preoperative counterparts. Across 66 cases of lung cancer tissues, a correlation was observed between HBB levels and both gender and tumor, node, metastasis staging. ROC curve analysis further confirmed the high diagnostic potential of HBB expression in lung cancer. Moreover, the combination of HBB and carcinoembryonic antigen (CEA) had greater significance than HBB or CEA alone in the diagnosis of lung cancer. Knocking out or overexpressing HBB could affect lung cancer cell proliferation through the ERK1/2 signaling pathway. Conclusion: HBB can serve as a novel biomarker for the diagnosis and monitoring of lung cancer, regulating cell proliferation via the ERK1/2 pathway and playing a pivotal role in the oncogenesis and progression of the disease.

Impact of CRISPR/HDR-editing versus lentiviral transduction on long-term engraftment and clonal dynamics of HSPCs in rhesus macaques

For precise genome editing via CRISPR/homology-directed repair (HDR), effective and safe editing of long-term engrafting hematopoietic stem cells (LT-HSCs) requires both sufficient HDR efficiency and protection of LT-HSC function and number. The impact of HDR on true LT-HSCs clonal dynamics in a relevant large animal model has not previously been studied. To track the HDR-edited cells, autologous rhesus macaque (RM) CD34 + cells were electroporated with the gRNA/Cas9 ribonucleoprotein (RNP) and HDR cassette barcode library structure and reinfused into RMs following myeloablation. For competitive model animals, fractionated CD34 + cells were transduced with a barcoded GFP-expressing lentiviral vector (LV) and electroporated via HDR machinery, respectively. CD33 knockout (KO) neutrophils were prevalent early following engraftment and then rapidly decreased, resulting in less than 1% total editing efficiency. Interestingly, in competitive animals, a higher concentration of i53 mRNA result in a less steep reduction in CD33 KO cells, presented a modest decrease in HDR rate (0.1-0.2%) and total indels (1.5-6.5%). In contrast, the drop off of LV-transduced GFP + cells stabilized at 20% after 2 months. We next retrieved embedded barcodes and revealed that various clones contributed to early hematopoietic reconstitution, then after dominant clones appeared at steady state throughout the animals. In conclusion, CRISPR/HDR edited cells disappeared rapidly after the autologous transplantation in RM despite substantial gene editing outcome, whereas LV-transduced cells were relatively well maintained. Clonality of HDR-edited cells drastically shrank at early stage and then relied on several dominant clones, which can be mildly mitigated by the introduction of i53 mRNA.

Base editing of the HBG promoter induces potent fetal hemoglobin expression with no detectable off-target mutations in human HSCs

Reactivating silenced γ-globin expression through the disruption of repressive regulatory domains offers a therapeutic strategy for treating β-hemoglobinopathies. Here, we used transformer base editor (tBE), a recently developed cytosine base editor with no detectable off-target mutations, to disrupt transcription-factor-binding motifs in hematopoietic stem cells. By performing functional screening of six motifs with tBE, we found that directly disrupting the BCL11A-binding motif in HBG1/2 promoters triggered the highest γ-globin expression. Via a side-by-side comparison with other clinical and preclinical strategies using Cas9 nuclease or conventional BEs (ABE8e and hA3A-BE3), we found that tBE-mediated disruption of the BCL11A-binding motif at the HBG1/2 promoters triggered the highest fetal hemoglobin in healthy and β-thalassemia patient hematopoietic stem/progenitor cells while exhibiting no detectable DNA or RNA off-target mutations. Durable therapeutic editing by tBE persisted in repopulating hematopoietic stem cells, demonstrating that tBE-mediated editing in HBG1/2 promoters is a safe and effective strategy for treating β-hemoglobinopathies.

CRISPR-Cas9 engineering of the RAG2 locus via complete coding sequence replacement for therapeutic applications

RAG2-SCID is a primary immunodeficiency caused by mutations in Recombination-activating gene 2 (RAG2), a gene intimately involved in the process of lymphocyte maturation and function. ex-vivo manipulation of a patient's own hematopoietic stem and progenitor cells (HSPCs) using CRISPR-Cas9/rAAV6 gene editing could provide a therapeutic alternative to the only current treatment, allogeneic hematopoietic stem cell transplantation (HSCT). Here we show an innovative RAG2 correction strategy that replaces the entire endogenous coding sequence (CDS) for the purpose of preserving the critical endogenous spatiotemporal gene regulation and locus architecture. Expression of the corrective transgene leads to successful development into CD3+TCRαβ+ and CD3+TCRγδ+ T cells and promotes the establishment of highly diverse TRB and TRG repertoires in an in-vitro T-cell differentiation platform. Thus, our proof-of-concept study holds promise for safer gene therapy techniques of tightly regulated genes.

The p53 challenge of hematopoietic stem cell gene editing

Ex vivo gene editing in hematopoietic stem and progenitor cells (HSPCs) represents a promising curative treatment strategy for monogenic blood disorders. Gene editing using the homology-directed repair (HDR) pathway enables precise genetic modifications ranging from single base pair correction to replacement or insertion of large DNA segments. Hence, HDR-based gene editing could facilitate broad application of gene editing across monogenic disorders, but the technology still faces challenges for clinical translation. Among these, recent studies demonstrate induction of a DNA damage response (DDR) and p53 activation caused by DNA double-strand breaks and exposure to recombinant adeno-associated virus vector repair templates, resulting in reduced proliferation, engraftment, and clonogenic capacity of edited HSPCs. While different mitigation strategies can reduce this DDR, more research is needed on this phenomenon to ensure safe and efficient implementation of HDR-based gene editing in the clinic.

The recombinase activating genes: architects of immune diversity during lymphocyte development

The mature lymphocyte population of a healthy individual has the remarkable ability to recognise an immense variety of antigens. Instead of encoding a unique gene for each potential antigen receptor, evolution has used gene rearrangements, also known as variable, diversity, and joining gene segment (V(D)J) recombination. This process is critical for lymphocyte development and relies on recombination-activating genes-1 (RAG1) and RAG2, here collectively referred to as RAG. RAG serves as powerful genome editing tools for lymphocytes and is strictly regulated to prevent dysregulation. However, in the case of dysregulation, RAG has been implicated in cases of cancer, autoimmunity and severe combined immunodeficiency (SCID). This review examines functional protein domains and motifs of RAG, describes advances in our understanding of the function and (dys)regulation of RAG, discuss new therapeutic options, such as gene therapy, for RAG deficiencies, and explore in vitro and in vivo methods for determining RAG activity and target specificity.

Homology-Directed-Repair-Based Genome Editing in HSPCs for the Treatment of Inborn Errors of Immunity and Blood Disorders

Genome engineering via targeted nucleases, specifically CRISPR-Cas9, has revolutionized the field of gene therapy research, providing a potential treatment for diseases of the blood and immune system. While numerous genome editing techniques have been used, CRISPR-Cas9 homology-directed repair (HDR)-mediated editing represents a promising method for the site-specific insertion of large transgenes for gene knock-in or gene correction. Alternative methods, such as lentiviral/gammaretroviral gene addition, gene knock-out via non-homologous end joining (NHEJ)-mediated editing, and base or prime editing, have shown great promise for clinical applications, yet all possess significant drawbacks when applied in the treatment of patients suffering from inborn errors of immunity or blood system disorders. This review aims to highlight the transformational benefits of HDR-mediated gene therapy and possible solutions for the existing problems holding the methodology back. Together, we aim to help bring HDR-based gene therapy in CD34+ hematopoietic stem progenitor cells (HSPCs) from the lab bench to the bedside.

Comparative analysis of CRISPR off-target discovery tools following ex vivo editing of CD34+ hematopoietic stem and progenitor cells

While a number of methods exist to investigate CRISPR off-target (OT) editing, few have been compared head-to-head in primary cells after clinically relevant editing processes. Therefore, we compared in silico tools (COSMID, CCTop, and Cas-OFFinder) and empirical methods (CHANGE-Seq, CIRCLE-Seq, DISCOVER-Seq, GUIDE-Seq, and SITE-Seq) after ex vivo hematopoietic stem and progenitor cell (HSPC) editing. We performed editing using 11 different gRNAs complexed with Cas9 protein (high-fidelity [HiFi] or wild-type versions), then performed targeted next-generation sequencing of nominated OT sites identified by in silico and empirical methods. We identified an average of less than one OT site per guide RNA (gRNA) and all OT sites generated using HiFi Cas9 and a 20-nt gRNA were identified by all OT detection methods with the exception of SITE-seq. This resulted in high sensitivity for the majority of OT nomination tools and COSMID, DISCOVER-Seq, and GUIDE-Seq attained the highest positive predictive value (PPV). We found that empirical methods did not identify OT sites that were not also identified by bioinformatic methods. This study supports that refined bioinformatic algorithms could be developed that maintain both high sensitivity and PPV, thereby enabling more efficient identification of potential OT sites without compromising a thorough examination for any given gRNA.

Gene Therapy and Gene Editing for β-Thalassemia

After many years of intensive research, emerging data from clinical trials indicate that gene therapy for transfusion-dependent β-thalassemia is now possible. Strategies for therapeutic manipulation of patient hematopoietic stem cells include lentiviral transduction of a functional erythroid-expressed β-globin gene and genome editing to activate fetal hemoglobin production in patient red blood cells. Gene therapy for β-thalassemia and other blood disorders will invariably improve as experience accumulates over time. The best overall approaches are not known and perhaps not yet established. Gene therapy comes at a high cost, and collaboration between multiple stakeholders is required to ensure that these new medicines are administered equitably.

Molecular Basis and Genetic Modifiers of Thalassemia

Thalassemia syndromes are common monogenic disorders and represent a significant health issue worldwide. In this review, the authors elaborate on fundamental genetic knowledge about thalassemias, including the structure and location of globin genes, the production of hemoglobin during development, the molecular lesions causing α-, β-, and other thalassemia syndromes, the genotype-phenotype correlation, and the genetic modifiers of these conditions. In addition, they briefly discuss the molecular techniques applied for diagnosis and innovative cell and gene therapy strategies to cure these conditions.

Prime editing in hematopoietic stem cells—From ex vivo to in vivo CRISPR-based treatment of blood disorders

Prime editing of human hematopoietic stem cells has the potential to become a safe and efficient way of treating diseases of the blood directly in patients. By allowing site-targeted gene intervention without homology-directed repair donor templates and DNA double-stranded breaks, the invention of prime editing fuels the exploration of alternatives to conventional recombination-based ex vivo genome editing of hematopoietic stem cells. Prime editing is as close as we get today to a true genome editing drug that does not require a separate DNA donor. However, to adapt the technology to perform in vivo gene correction, key challenges remain to be solved, such as identifying effective prime editing guide RNAs for clinical targets as well as developing efficient vehicles to deliver prime editors to stem cells in vivo. In this review, we summarize the current progress in delivery of prime editors both in vitro and in vivo and discuss future challenges that need to be adressed to allow in vivo prime editing as a cure for blood disorders.

Editing human hematopoietic stem cells: advances and challenges

Genome editing of hematopoietic stem and progenitor cells is being developed for the treatment of several inherited disorders of the hematopoietic system. The adaptation of CRISPR-Cas9-based technologies to make precise changes to the genome, and developments in altering the specificity and efficiency, and improving the delivery of nucleases to target cells have led to several breakthroughs. Many clinical trials are ongoing, and several pre-clinical models have been reported that would allow these genetic therapies to one day offer a potential cure to patients with diseases where limited options currently exist. However, there remain several challenges with respect to establishing safety, expanding accessibility and improving the manufacturing processes of these therapeutic products. This review focuses on some of the recent advances in the field of genome editing of hematopoietic stem and progenitor cells and illustrates the ongoing challenges.

Production and Characterization of K562 Cellular Clones Hyper-Expressing the Gene Encoding α-Globin: Preliminary Analysis of Biomarkers Associated with Autophagy

One of the most relevant pathophysiological hallmarks of β-thalassemia is the accumulation of toxic α-globin chains inside erythroid cells, which is responsible for their premature death (hemolysis). In this context, the availability of an experimental model system mimicking the excess in α-globin chain production is still lacking. The objective of the present study was to produce and characterize K562 cellular clones forced to produce high amounts of α-globin, in order to develop an experimental model system suitable for studies aimed at the reduction of the accumulation of toxic α-globin aggregates. In the present study, we produced and characterized K562 cellular clones that, unlike the original K562 cell line, stably produced high levels of α-globin protein. As expected, the obtained clones had a tendency to undergo apoptosis that was proportional to the accumulation of α-globin, confirming the pivotal role of α-globin accumulation in damaging erythroid cells. Interestingly, the obtained clones seemed to trigger autophagy spontaneously, probably to overcome the accumulation/toxicity of the α-globin. We propose this new model system for the screening of pharmacological agents able to activate the full program of autophagy to reduce α-globin accumulation, but the model may be also suitable for new therapeutical approaches targeted at the reduction of the expression of the α-globin gene.

Rare immune diseases paving the road for genome editing-based precision medicine

Clustered regularly interspaced short palindromic repeats (CRISPR) genome editing platform heralds a new era of gene therapy. Innovative treatments for life-threatening monogenic diseases of the blood and immune system are transitioning from semi-random gene addition to precise modification of defective genes. As these therapies enter first-in-human clinical trials, their long-term safety and efficacy will inform the future generation of genome editing-based medicine. Here we discuss the significance of Inborn Errors of Immunity as disease prototypes for establishing and advancing precision medicine. We will review the feasibility of clustered regularly interspaced short palindromic repeats-based genome editing platforms to modify the DNA sequence of primary cells and describe two emerging genome editing approaches to treat RAG2 deficiency, a primary immunodeficiency, and FOXP3 deficiency, a primary immune regulatory disorder.

Identification of RPGR ORF15 mutation for X-linked retinitis pigmentosa in a large Chinese family and in vitro correction with prime editor

X-linked retinitis pigmentosa (XLRP) is the most severe form of Retinitis Pigmentosa (RP) and one of the leading causes of blindness in the world. Currently, there is no effective treatment for RP. In the present study, we recruited a XLRP family and identified a 4 bp deletion mutation (c. 2234_2237del) in RPGR ORF15 with Sanger sequencing, which was located in the exact same region as the missing XES (X chromosome exome sequencing) coverage. Then, we generated cell lines harboring the identified mutation and corrected it via enhanced prime editing system (ePE). Collectively, Sanger sequencing identified a pathogenic mutation in RPGR ORF15 for XLRP which was corrected with ePE. This study provides a valuable insight for genetic counseling of the afflicted family members and prenatal diagnosis, also paves a way for applying prime editing based gene therapy in those patients.

Hematopoietic stem and progenitors cells gene editing: Beyond blood disorders

Lessons learned from decades-long practice in the transplantation of hematopoietic stem and progenitor cells (HSPCs) to treat severe inherited disorders or cancer, have set the stage for the current ex vivo gene therapies using autologous gene-modified hematopoietic stem and progenitor cells that have treated so far, hundreds of patients with monogenic disorders. With increased knowledge of hematopoietic stem and progenitor cell biology, improved modalities for patient conditioning and with the emergence of new gene editing technologies, a new era of hematopoietic stem and progenitor cell-based gene therapies is poised to emerge. Gene editing has the potential to restore physiological expression of a mutated gene, or to insert a functional gene in a precise locus with reduced off-target activity and toxicity. Advances in patient conditioning has reduced treatment toxicities and may improve the engraftment of gene-modified cells and specific progeny. Thanks to these improvements, new potential treatments of various blood- or immune disorders as well as other inherited diseases will continue to emerge. In the present review, the most recent advances in hematopoietic stem and progenitor cell gene editing will be reported, with a focus on how this approach could be a promising solution to treat non-blood-related inherited disorders and the mechanisms behind the therapeutic actions discussed.

GATA2 deficiency and MDS/AML: Experimental strategies for disease modelling and future therapeutic prospects

The importance of predisposition to leukaemia in clinical practice is being increasingly recognized. This is emphasized by the establishment of a novel WHO disease category in 2016 called "myeloid neoplasms with germline predisposition". A major syndrome within this group is GATA2 deficiency, a heterogeneous immunodeficiency syndrome with a very high lifetime risk to develop myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML). GATA2 deficiency has been identified as the most common hereditary cause of MDS in adolescents with monosomy 7. Allogenic haematopoietic stem cell transplantation is the only curative option; however, chances of survival decrease with progression of immunodeficiency and MDS evolution. Penetrance and expressivity within families carrying GATA2 mutations is often variable, suggesting that co-operating extrinsic events are required to trigger the disease. Predictive tools are lacking, and intrafamilial heterogeneity is poorly understood; hence there is a clear unmet medical need. On behalf of the ERAPerMed GATA2 HuMo consortium, in this review we describe the genetic, clinical, and biological aspects of familial GATA2-related MDS, highlighting the importance of developing robust disease preclinical models to improve early detection and clinical decision-making of GATA2 carriers.

Ultra-deep sequencing validates safety of CRISPR/Cas9 genome editing in human hematopoietic stem and progenitor cells

As CRISPR-based therapies enter the clinic, evaluation of safety remains a critical and active area of study. Here, we employ a clinical next generation sequencing (NGS) workflow to achieve high sequencing depth and detect ultra-low frequency variants across exons of genes associated with cancer, all exons, and genome wide. In three separate primary human hematopoietic stem and progenitor cell (HSPC) donors assessed in technical triplicates, we electroporated high-fidelity Cas9 protein targeted to three loci (AAVS1, HBB, and ZFPM2) and harvested genomic DNA at days 4 and 10. Our results demonstrate that clinically relevant delivery of high-fidelity Cas9 to primary HSPCs and ex vivo culture up to 10 days does not introduce or enrich for tumorigenic variants and that even a single SNP in a gRNA spacer sequence is sufficient to eliminate Cas9 off-target activity in primary, repair-competent human HSPCs.

Improved engraftment and therapeutic efficacy by human genome-edited hematopoietic stem cells with Busulfan-based myeloablation

Autologous hematopoietic stem cell transplantation using genome-edited cells can become a definitive therapy for hematological and non-hematological disorders with neurological involvement. Proof-of-concept studies using human genome-edited hematopoietic stem cells have been hindered by the low efficiency of engraftment of the edited cells in the bone marrow and their modest efficacy in the CNS. To address these challenges, we tested a myeloablative conditioning regimen based on Busulfan in an immunocompromised model of mucopolysaccharidosis type 1. Compared with sub-lethal irradiation, Busulfan conditioning enhanced the engraftment of edited CD34+ cells in the bone marrow, as well the long-term homing and survival of bone-marrow-derived cells in viscera, and in the CNS, resulting in higher transgene expression and biochemical correction in these organs. Edited cell selection using a clinically compatible marker resulted in a population with low engraftment potential. We conclude that conditioning can impact the engraftment of edited hematopoietic stem cells. Furthermore, Busulfan-conditioned recipients have a higher expression of therapeutic proteins in target organs, particularly in the CNS, constituting a better conditioning approach for non-hematological diseases with neurological involvement.

CRISPR/Cas-Based Gene Editing Strategies for DOCK8 Immunodeficiency Syndrome

Defects in the DOCK8 gene causes combined immunodeficiency termed DOCK8 immunodeficiency syndrome (DIDS). DIDS previously belonged to the disease category of autosomal recessive hyper IgE syndrome (AR-HIES) but is now classified as a combined immunodeficiency (CID). This genetic disorder induces early onset of susceptibility to severe recurrent viral and bacterial infections, atopic diseases and malignancy resulting in high morbidity and mortality. This pathological state arises from impairment of actin polymerization and cytoskeletal rearrangement, which induces improper immune cell migration-, survival-, and effector functions. Owing to the severity of the disease, early allogenic hematopoietic stem cell transplantation is recommended even though it is associated with risk of unintended adverse effects, the need for compatible donors, and high expenses. So far, no alternative therapies have been developed, but the monogenic recessive nature of the disease suggests that gene therapy may be applied. The advent of the CRISPR/Cas gene editing system heralds a new era of possibilities in precision gene therapy, and positive results from clinical trials have already suggested that the tool may provide definitive cures for several genetic disorders. Here, we discuss the potential application of different CRISPR/Cas-mediated genetic therapies to correct the DOCK8 gene. Our findings encourage the pursuit of CRISPR/Cas-based gene editing approaches, which may constitute more precise, affordable, and low-risk definitive treatment options for DOCK8 deficiency.

CRISPR/Cas9 ribonucleoprotein-mediated genome and epigenome editing in mammalian cells

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein (Cas) system has revolutionized the ability to edit the mammalian genome, providing a platform for the correction of pathogenic mutations and further investigation into gene function. CRISPR reagents can be delivered into the cell as DNA, RNA, or pre-formed ribonucleoproteins (RNPs). RNPs offer numerous advantages over other delivery approaches due to their ability to rapidly target genomic sites and quickly degrade thereafter. Here, we review the production steps and delivery methods for Cas9 RNPs. Additionally, we discuss how RNPs enhance genome and epigenome editing efficiencies, reduce off-target editing activity, and minimize cellular toxicity in clinically relevant mammalian cell types. We include details on a broad range of editing approaches, including novel base and prime editing techniques. Finally, we summarize key challenges for the use of RNPs, and propose future perspectives on the field.

Hematopoietic stem cell gene editing and expansion: State-of-the-art technologies and recent applications

Hematopoietic stem cell transplantation (HSCT) is a curative therapy for a range of hematological diseases, from leukemias to immunodeficiencies and anemias. The aim in using HSCT is to replace a patient's dysfunctional blood system with a functional one by transplanting healthy hematopoietic stem cells (HSCs). HSCs may be collected from a healthy donor (for allogeneic HSCT) or from the patient for genetic correction (for autologous HSCT gene therapies). Despite the curative potential of HSCT, several hurdles to its wider and safer use remain, including how to efficiently genetically correct HSCs and how to increase donor HSC numbers to improve the donor pool. In recent years, the development of state-of-the-art technologies, such as Cas9-AAV6 technologies and identification of the small molecule HSC agonist UM171, have accelerated progress in HSC gene editing and expansion. These translational research efforts were the focus of the Spring 2021 International Society for Experimental Hematology (ISEH) webinar. Here we present a summary and discussion of the implications of these new approaches to improve HSC-based therapy.