Fertility-preserving myeloablative conditioning using single-dose CD117 antibody-drug conjugate in a rhesus gene therapy model

Gene therapy in transfusion-dependent non-β0/β0 genotype β-thalassemia: first real-world experience of beti-cel

ABSTRACT

Gene addition and editing strategies for transfusion-dependent β-thalassemia have gained momentum as potentially curative treatment options, with studies showcasing their efficacy and safety. We report, to our knowledge, the first real-world application of betibeglogene autotemcel (beti-cel; Zynteglo) during its period of active license in Europe from January 2020 to March 2022 for patients aged ≥12 years without a β0/β0 genotype and without a HLA-matched sibling donor, before beti-cel marketing authorization was withdrawn by its holder because of nonsafety reasons. Among 15 screened patients, 4 opted out for fertility and safety concerns, 2 were excluded because of marked hepatic siderosis, and 1 had apheresis collection failure. Eight patients received beti-cel after busulfan myeloablative conditioning, all achieving transfusion independence within 8 to 59 days, with posttreatment hemoglobin levels ranging from 11.3 to 19.3 g/dL. No deaths occurred, but acute toxicity mirrored busulfan's known effects. Posttreatment platelet management faced challenges because of HLA-antibodies in 3 patients. Monitoring up to month 24 revealed pituitary-gonadal endocrine dysfunction in all 3 female and in 2 of 5 male patients. Additionally, we observed unexpected posttreatment sequelae: 1 patient developed polycythemia that could not be explained by known genetic or acquired mechanisms, 1 patient developed posttreatment depression and anxiety prohibiting her from returning to work, and 1 patient developed fatigue severely compromising both quality of life and work capacity. This real-world experience corroborates beti-cel's efficacy and safety and provides information on adverse events observed during real-world use of the therapy.

Gene therapy for sickle cell disease: recent advances, clinical trials and future directions

Sickle cell disease (SCD) is the most common inherited blood disorder worldwide, impacting millions and imposing severe healthcare challenges, particularly in resource-limited regions. Current treatments have variable efficacy and require lifelong adherence. Allogeneic Hematopoietic Stem Cell Transplantation can be curative but comes with significant side effects and limited donor availability limits its widespread applicability. Gene therapy, by addressing the root genetic causes, offers a revolutionary alternative. This article discusses the molecular mechanisms of SCD and β-thalassemia and highlights advancements in gene therapy, such as gene addition via lentiviral vectors and gene editing with CRISPR/Cas9 technology. Clinical trials have brought about significant progress but challenges remain, including leukemogenesis, delivery efficiency and cost. Future efforts must focus on enhancing efficiency, reducing costs, developing nongenotoxic conditioning regimens and methods for in vivo application.

BCL11A +58/+55 enhancer-editing facilitates HSPC engraftment and HbF induction in rhesus macaques conditioned with a CD45 antibody-drug conjugate

Editing the +58 region of the BCL11A erythroid enhancer has shown promise in treating β-globin disorders. To address variations in fetal hemoglobin (HbF) response, we investigated editing both +58 and +55 enhancers. Rhesus macaques transplanted with edited hematopoietic stem/progenitor cells (HSPCs) following busulfan conditioning exhibited durable, high-level (∼90%) editing frequencies post transplantation with sustained HbF reactivation over 4 years, without hematological perturbations. HbF levels were further boosted by stress erythropoiesis or hydroxyurea. Bone marrow analysis revealed that gene edits were predominantly programmed deletions, programmed inversions, and short indels, each disrupting the enhancer core TGN7-9WGATAR half E-box/GATA binding motifs. Nonprogrammed long deletions were disfavored in engrafting cells. CD45 antibody-drug conjugate (ADC) conditioning achieved comparable engraftment and HbF reactivation, whereas lentiviral vector tracking showed polyclonal reconstitution with dynamics similar to animals conditioned with total body irradiation (TBI) or busulfan. Joining CD45-ADC conditioning with combined enhancer editing presents an effective strategy for β-hemoglobinopathies, enabling durable HbF reactivation without chemotherapy.

A single-chain variable fragment-based bispecific T-cell activating antibody against CD117 enables T-cell mediated lysis of acute myeloid leukemia and hematopoietic stem and progenitor cells

Acute myeloid leukemia (AML) derives from hematopoietic stem and progenitor cells (HSPCs). To date, no AML-exclusive, non-HSPC-expressed cell-surface target molecules for AML selective immunotherapy have been identified. Therefore, to still apply surface-directed immunotherapy in this disease setting, time-limited combined immune-targeting of AML cells and healthy HSPCs, followed by hematopoietic stem cell transplantation (HSCT), might be a viable therapeutic approach. To explore this, we generated a recombinant single-chain variable fragment-based bispecific T-cell engaging and activating antibody directed against CD3 on T-cells and CD117, the surface receptor for stem cell factor, expressed by both AML cells and healthy HSPCs. Bispecific CD117xCD3 targeting induced lysis of CD117-positive healthy human HSPCs, AML cell lines and patient-derived AML blasts in the presence of T-cells at subnanomolar concentrations in vitro. Furthermore, in immunocompromised mice, engrafted with human CD117-expressing leukemia cells and human T-cells, the bispecific molecule efficiently prevented leukemia growth in vivo. Additionally, in immunodeficient mice transplanted with healthy human HSPCs, the molecule decreased the number of CD117-positive cells in vivo. Therefore, bispecific CD117xCD3 targeting might be developed clinically in order to reduce CD117-expressing leukemia cells and HSPCs prior to HSCT.

Advances in Pompe Disease Treatment: From Enzyme Replacement to Gene Therapy

Pompe disease is a neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA), hydrolyzing glycogen to glucose. Pathological glycogen storage, the hallmark of the disease, disrupts the metabolism and function of various cell types, especially muscle cells, leading to cardiac, motor, and respiratory dysfunctions. The spectrum of Pompe disease manifestations spans two main forms: classical infantile-onset (IOPD) and late-onset (LOPD). IOPD, caused by almost complete GAA deficiency, presents at birth and leads to premature death by the age of 2 years without treatment. LOPD, less severe due to partial GAA activity, appears in childhood, adolescence, or adulthood with muscle weakness and respiratory problems. Since 2006, enzyme replacement therapy (ERT) has been approved for Pompe disease, offering clinical benefits but not a cure. However, advances in early diagnosis through newborn screening, recognizing disease manifestations, and developing improved treatments are set to enhance Pompe disease care. This article reviews recent progress in ERT and ongoing translational research, including the approval of second-generation ERTs, a clinical trial of in utero ERT, and preclinical development of gene and substrate reduction therapies. Notably, gene therapy using intravenous delivery of adeno-associated virus (AAV) vectors is in phase I/II clinical trials for both LOPD and IOPD. Promising data from LOPD trials indicate that most participants met the criteria to discontinue ERT several months after gene therapy. The advantages and challenges of this approach are discussed. Overall, significant progress is being made towards curative therapies for Pompe disease. While several challenges remain, emerging data are promising and suggest the potential for a once-in-a-lifetime treatment.

Targeted hematopoietic stem cell depletion through SCF-blockade

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a curative treatment for many diverse blood and immune diseases. However, HSCT regimens currently commonly utilize genotoxic chemotherapy and/or total body irradiation (TBI) conditioning which causes significant morbidity and mortality through inducing broad tissue damage triggering infections, graft vs. host disease, infertility, and secondary cancers. We previously demonstrated that targeted monoclonal antibody (mAb)-based HSC depletion with anti(α)-CD117 mAbs could be an effective alternative conditioning approach for HSCT without toxicity in severe combined immunodeficiency (SCID) mouse models, which has prompted parallel clinical αCD117 mAbs to be developed and tested as conditioning agents in clinical trials starting with treatment of patients with SCID. Subsequent efforts have built upon this work to develop various combination approaches, though none are optimal and how any of these mAbs fully function is unknown.

METHODS

To improve efficacy of mAb-based conditioning as a stand-alone conditioning approach for all HSCT settings, it is critical to understand the mechanistic action of αCD117 mAbs on HSCs. Here, we compare the antagonistic properties of αCD117 mAb clones including ACK2, 2B8, and 3C11 as well as ACK2 fragments in vitro and in vivo in both SCID and wildtype (WT) mouse models. Further, to augment efficacy, combination regimens were also explored.

RESULTS

We confirm that only ACK2 inhibits SCF binding fully and prevents HSC proliferation in vitro. Further, we verify that this corresponds to HSC depletion in vivo and donor engraftment post HSCT in SCID mice. We also show that SCF-blocking αCD117 mAb fragment derivatives retain similar HSC depletion capacity with enhanced engraftment post HSCT in SCID settings, but only full αCD117 mAb ACK2 in combination with αCD47 mAb enables enhanced donor HSC engraftment in WT settings, highlighting that the Fc region is not required for single-agent efficacy in SCID settings but is required in immunocompetent settings. This combination was the only non-genotoxic conditioning approach that enabled robust donor engraftment post HSCT in WT mice.

CONCLUSION

These findings shed new insights into the mechanism of αCD117 mAb-mediated HSC depletion. Further, they highlight multiple approaches for efficacy in SCID settings and optimal combinations for WT settings. This work is likely to aid in the development of clinical non-genotoxic HSCT conditioning approaches that could benefit millions of people world-wide.

CCR2 cooperativity promotes hematopoietic stem cell homing to the bone marrow

Cross-talk between hematopoietic stem and progenitor cells (HSPCs) and bone marrow (BM) cells is critical for homing and sustained engraftment after transplantation. In particular, molecular and physical adaptation of sinusoidal endothelial cells (ECs) promote HSPC BM occupancy; however, signals that govern these events are not well understood. Extracellular vesicles (EVs) are mediators of cell-cell communication crucial in shaping tissue microenvironments. Here, we demonstrate that integrin α4β7 on murine HSPC EVs targets uptake into ECs. In BM ECs, HSPC EVs induce up-regulation of C-C motif chemokine receptor 2 (CCR2) ligands that synergize with CXCL12-CXCR4 signaling to promote BM homing. In nonirradiated murine models, marrow preconditioning with HSPC EVs or recombinant CCR2 ligands improves homing and early graft occupancy after transplantation. These findings identify a role for HSPC EVs in remodeling ECs, newly define CCR2-dependent graft homing, and inform novel translational conditioning strategies to improve HSPC transplantation.

Gene therapies on the horizon for sickle cell disease: a clinician's perspective

INTRODUCTION

Sickle cell disease (SCD) is a monogenic disorder that exerts several detrimental health effects on those affected, ultimately resulting in significant morbidity and early mortality. There are millions of individuals globally impacted by this disease. Research in gene therapy has been growing significantly over the past decade, now with two FDA approved products, aiming to find another cure for this complex disease.

AREAS COVERED

This perspective article aims to provide a clinician's insight into the current landscape of gene therapies, exploring the novel approaches, clinical advances, and potential impact on the management and prognosis of SCD. A comprehensive literature search encompassing databases such as PubMed, Web of Science and Google Scholar was employed. The search covered literature published from 1980 to 2024, focusing on SCD and curative therapy.

EXPERT OPINION

After careful evaluation of the risks and benefits associated with the use of gene therapy for affected patients, the need for a cure outweighs the risks associated with treatment in most cases of SCD. With advances in current technologies, gene therapies can increase access to cures for patients with SCD.

Sickle cell disease and infertility risks: implications for counseling and care of affected girls and women

INTRODUCTION

Sickle cell disease (SCD), its treatments and cures present infertility risks. Fertility counseling is broadly indicated for affected girls and women and fertility preservation may appeal to some. Several streams of evidence suggest that the reproductive lifespan of women with SCD is reduced. Pregnancy is associated with high miscarriage rates. There are enduring questions about the effects of highly effective hydroxyurea treatment on female fertility. Current conditioning regimens for gene therapy or hematopoietic stem cell transplant are gonadotoxic. Fertility preservation methods exist as non-experimental standards of care for girls and women. Clinicians are challenged to overcome multifactorial barriers to incorporate fertility counseling and fertility preservation care into routine SCD care.

AREAS COVERED

Here we provide a narrative review of existing evidence regarding fertility and infertility risks in girls and women with SCD and consider counseling implications of existing evidence.

EXPERT OPINION

Addressing fertility for girls and women with SCD requires engaging concerns that emerge across the lifespan, acknowledging uncertainty and identifying barriers to care, some of which may be insurmountable without public policy changes. The contemporary SCD care paradigm can offer transformative SCD treatments alongside comprehensive counselling that addresses fertility risks and fertility preservation opportunities.

Efficacy and safety of antibody-drug conjugates in the treatment of urothelial cell carcinoma: a systematic review and meta-analysis of prospective clinical trials

Introduction: Urothelial carcinoma (UC) is a refractory disease for which achieving satisfactory outcomes remains challenging with current surgical interventions. Antibody-drug conjugates (ADCs) are a novel class of targeted therapeutics that have demonstrated encouraging results for UC. Although there is a limited number of high-quality randomized control trials (RCTs) examining the use of ADCs in patients with UC, some prospective non-randomized studies of interventions (NRSIs) provide valuable insights and pertinent information. We aim to assess the efficacy and safety of ADCs in patients with UC, particularly those with locally advanced and metastatic diseases. Methods: A systematic search was conducted across PubMed, Embase, the Cochrane Library, and Web of Science databases to identify pertinent studies. Outcomes, such as the overall response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), adverse events (AEs), and treatment-related adverse events (TRAEs), were extracted for further analyses. Results: Twelve studies involving 1,311 patients were included in this meta-analysis. In terms of tumor responses, the pooled ORR and DCR were 40% and 74%, respectively. Regarding survival analysis, the pooled median PFS and OS were 5.66 months and 12.63 months, respectively. The pooled 6-month PFS and OS were 47% and 80%, while the pooled 1-year PFS and OS were 22% and 55%, respectively. The most common TRAEs of the ADCs were alopecia (all grades: 45%, grades ≥ III: 0%), decreased appetite (all grades: 34%, grades ≥ III: 3%), dysgeusia (all grades: 40%, grades ≥ III: 0%), fatigue (all grades: 39%, grades ≥ III: 5%), nausea (all grades: 45%, grades ≥ III: 2%), peripheral sensory neuropathy (all grades: 37%, grades ≥ III: 2%), and pruritus (all grades: 32%, grades ≥ III: 1%). Conclusion: The meta-analysis in this study demonstrates that ADCs have promising efficacies and safety for patients with advanced or metastatic UC. Systematic review registration: https://www.crd.york.ac.uk/prospero/, identifier: CRD42023460232.

CRISPR technologies for genome, epigenome and transcriptome editing

Our ability to edit genomes lags behind our capacity to sequence them, but the growing understanding of CRISPR biology and its application to genome, epigenome and transcriptome engineering is narrowing this gap. In this Review, we discuss recent developments of various CRISPR-based systems that can transiently or permanently modify the genome and the transcriptome. The discovery of further CRISPR enzymes and systems through functional metagenomics has meaningfully broadened the applicability of CRISPR-based editing. Engineered Cas variants offer diverse capabilities such as base editing, prime editing, gene insertion and gene regulation, thereby providing a panoply of tools for the scientific community. We highlight the strengths and weaknesses of current CRISPR tools, considering their efficiency, precision, specificity, reliance on cellular DNA repair mechanisms and their applications in both fundamental biology and therapeutics. Finally, we discuss ongoing clinical trials that illustrate the potential impact of CRISPR systems on human health.

A Review of Gene Therapies for Hemoglobinopathies

Due to the significant morbidity and mortality of hemoglobinopathies, curative options have long been pursued. The overall goal of gene therapy is to modify a patient's own hematopoietic stem cells to overcome the deleterious effects of the underlying genetic defect by gene addition, gene editing, or gene silencing. Gene addition incorporates genes with superior function than the abnormal gene; gene editing takes advantage of molecular tools such as zinc finger proteins, Transcription Activator-Like Effector Nucleases and Clustered Regularly Interspaced Short Palindromic Repeats coupled with Cas9 proteins (CRISPR-Cas9) which allow for sequence-specific breaks in DNA that disrupt gene function; and gene silencing suppresses gene expression by interference with mRNA transcription/protein translation or epigenetic modification. The majority of gene therapy strategies for hemoglobinopathies have targeted erythroid-specific BCL11A, a major regulator of fetal hemoglobin repression at the gamma-globin locus, in the normal fetal-to-adult hemoglobin switch that occurs shortly after birth. Other goals have involved the incorporation of anti-sickling globins, such as βT87Q or βAS3. Landmark clinical trials of gene therapy in transfusion-dependent thalassemia and sickle cell disease have shown remarkable efficacy and acceptable safety and culminated in recent regulatory approvals of gene therapy for both diseases in Europe and the United States.

cMPL-Based Purification and Depletion of Human Hematopoietic Stem Cells: Implications for Pre-Transplant Conditioning

The transplantation of gene-modified autologous hematopoietic stem and progenitor cells (HSPCs) offers a promising therapeutic approach for hematological and immunological disorders. However, this strategy is often limited by the toxicities associated with traditional conditioning regimens. Antibody-based conditioning strategies targeting cKIT and CD45 antigens have shown potential in mitigating these toxicities, but their long-term safety and efficacy in clinical settings require further validation. In this study, we investigate the thrombopoietin (TPO) receptor, cMPL, as a novel target for conditioning protocols. We demonstrate that high surface expression of cMPL is a hallmark feature of long-term repopulating hematopoietic stem cells (LT-HSCs) within the adult human CD34+ HSPC subset. Targeting the cMPL receptor facilitates the separation of human LT-HSCs from mature progenitors, a delineation not achievable with cKIT. Leveraging this finding, we developed a cMPL-targeting immunotoxin, demonstrating its ability to selectively deplete host cMPLhigh LT-HSCs with a favorable safety profile and rapid clearance within 24 hours post-infusion in rhesus macaques. These findings present significant potential to advance our understanding of human hematopoiesis and enhance the therapeutic outcomes of ex vivo autologous HSPC gene therapies.

Streptavidin-drug conjugates streamline optimization of antibody-based conditioning for hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) conditioning using antibody-drug conjugates (ADC) is a promising alternative to conventional chemotherapy- and irradiation-based conditioning regimens. The drug payload bound to an ADC is a key contributor to its efficacy and potential toxicities; however, a comparison of HSCT conditioning ADCs produced with different toxic payloads has not been performed. Indeed, ADC optimization studies in general are hampered by the inability to produce and screen multiple combinations of antibody and drug payload in a rapid, cost-effective manner. Herein, we used Click chemistry to covalently conjugate four different small molecule payloads to streptavidin; these streptavidin-drug conjugates can then be joined to any biotinylated antibody to produce stable, indirectly conjugated ADCs. Evaluating CD45-targeted ADCs produced with this system, we found the pyrrolobenzodiazepine (PBD) dimer SGD-1882 was the most effective payload for targeting mouse and human hematopoietic stem cells (HSCs) and acute myeloid leukemia cells. In murine syngeneic HSCT studies, a single dose of CD45-PBD enabled near-complete conversion to donor hematopoiesis. Finally, human CD45-PBD provided significant antitumor benefit in a patient-derived xenograft model of acute myeloid leukemia. As our streptavidin-drug conjugates were generated in-house with readily accessible equipment, reagents, and routine molecular biology techniques, we anticipate this flexible platform will facilitate the evaluation and optimization of ADCs for myriad targeting applications.