Towards access for all: 1st Working Group Report for the Global Gene Therapy Initiative (GGTI).

The gene and cell therapy field saw its first approved treatments in Europe in 2012 and the United States in 2017 and is projected to be at least a $10B USD industry by 2025. Despite this success, a massive gap exists between the companies, clinics, and researchers developing these therapeutic approaches, and their availability to the patients who need them. The unacceptable reality is a geographic exclusion of low-and middle-income countries (LMIC) in gene therapy development and ultimately the provision of gene therapies to patients in LMIC. This is particularly relevant for gene therapies to treat human immunodeficiency virus infection and hemoglobinopathies, global health crises impacting tens of millions of people primarily located in LMIC. Bridging this divide will require research, clinical and regulatory infrastructural development, capacity-building, training, an approval pathway and community adoption for success and sustainable affordability. In 2020, the Global Gene Therapy Initiative was formed to tackle the barriers to LMIC inclusion in gene therapy development. This working group includes diverse stakeholders from all sectors and has set a goal of introducing two gene therapy Phase I clinical trials in two LMIC, Uganda and India, by 2024. Here we report on progress to date for this initiative.

Resveratrol trimer enhances gene delivery to hematopoietic stem cells by reducing antiviral restriction at endosomes.

Therapeutic gene delivery to hematopoietic stem cells (HSCs) holds great potential as a life-saving treatment of monogenic, oncologic, and infectious diseases. However, clinical gene therapy is severely limited by intrinsic HSC resistance to modification with lentiviral vectors (LVs), thus requiring high doses or repeat LV administration to achieve therapeutic gene correction. Here we show that temporary coapplication of the cyclic resveratrol trimer caraphenol A enhances LV gene delivery efficiency to human and nonhuman primate hematopoietic stem and progenitor cells with integrating and nonintegrating LVs. Although significant ex vivo, this effect was most dramatically observed in human lineages derived from HSCs transplanted into immunodeficient mice. We further show that caraphenol A relieves restriction of LV transduction by altering the levels of interferon-induced transmembrane (IFITM) proteins IFITM2 and IFITM3 and their association with late endosomes, thus augmenting LV core endosomal escape. Caraphenol A-mediated IFITM downregulation did not alter the LV integration pattern or bias lineage differentiation. Taken together, these findings compellingly demonstrate that the pharmacologic modification of intrinsic immune restriction factors is a promising and nontoxic approach for improving LV-mediated gene therapy.

Targeted homology-directed repair in blood stem and progenitor cells with CRISPR nanoformulations.

Ex vivo CRISPR gene editing in haematopoietic stem and progenitor cells has opened potential treatment modalities for numerous diseases. The current process uses electroporation, sometimes followed by virus transduction. While this complex manipulation has resulted in high levels of gene editing at some genetic loci, cellular toxicity was observed. We have developed a CRISPR nanoformulation based on colloidal gold nanoparticles with a unique loading design capable of cellular entry without the need for electroporation or viruses. This highly monodispersed nanoformulation avoids lysosomal entrapment and localizes to the nucleus in primary human blood progenitors without toxicity. Nanoformulation-mediated gene editing is efficient and sustained with different CRISPR nucleases at multiple loci of therapeutic interest. The engraftment kinetics of nanoformulation-treated primary cells in humanized mice are better relative to those of non-treated cells, with no differences in differentiation. Here we demonstrate non-toxic delivery of the entire CRISPR payload into primary human blood progenitors.

Minimal conditioning in Fanconi anemia promotes multi-lineage marrow engraftment at 10-fold lower cell doses.

BACKGROUND: Gene therapy approaches for the treatment of Fanconi anemia (FA) hold promise for patients without a suitably matched donor for an allogeneic bone marrow transplant. However, significant limitations include the collection of sufficient stem cell numbers from patients, the fragility of these cells during ex vivo manipulation, and clinically meaningful engraftment following transplantation. With these challenges in mind, we were interested in determining (i) whether gene-corrected cells at progressively lower numbers can successfully engraft in FA; (ii) whether low-dose conditioning facilitates this engraftment; and (iii) whether these cells can be selected for post-transplant. METHODS: Utilizing a well characterized mouse model of FA, we infused donor bone marrow from healthy heterozygote littermates that are unaffected carriers of the FANCA mutation to mimic a gene-corrected product, after administering low-dose conditioning. Once baseline engraftment was observed, we administered a second, very-low selective dose to determine whether gene-corrected cells could be selected for in vivo. RESULTS: We demonstrate that upfront low-dose conditioning greatly increases successful engraftment of hematopoietic corrected cells in a pre-clinical animal model of FA. Additionally, without conditioning, cells can still engraft and demonstrate a selective advantage in vivo over time following transplantation, and these corrected cells can be directly selected for in vivo after engraftment. CONCLUSIONS: Minimal conditioning prior to bone marrow transplant in Fanconi anemia promotes the multi-lineage engraftment of 10-fold fewer cells compared to nonconditioned controls. These data provide important insights into the potential of minimally toxic conditioning protocols for FA gene therapy applications.

Novel lineage depletion preserves autologous blood stem cells for gene therapy of Fanconi anemia complementation group A.

A hallmark of Fanconi anemia is accelerated decline in hematopoietic stem and progenitor cells (CD34 +) leading to bone marrow failure. Long-term treatment requires hematopoietic cell transplantation from an unaffected donor but is associated with potentially severe side-effects. Gene therapy to correct the genetic defect in the patient's own CD34+ cells has been limited by low CD34+ cell numbers and viability. Here we demonstrate an altered ratio of CD34Hi to CD34Lo cells in Fanconi patients relative to healthy donors, with exclusive in vitro repopulating ability in only CD34Hi cells, underscoring a need for novel strategies to preserve limited CD34+ cells. To address this need, we developed a clinical protocol to deplete lineage+(CD3+, CD14+, CD16+ and CD19+) cells from blood and marrow products. This process depletes >90% of lineage+cells while retaining ≥60% of the initial CD34+cell fraction, reduces total nucleated cells by 1-2 logs, and maintains transduction efficiency and cell viability following gene transfer. Importantly, transduced lineage- cell products engrafted equivalently to that of purified CD34+ cells from the same donor when xenotransplanted at matched CD34+ cell doses. This novel selection strategy has been approved by the regulatory agencies in a gene therapy study for Fanconi anemia patients (NCI Clinical Trial Reporting Program Registry ID NCI-2011-00202; clinicaltrials.gov identifier: 01331018).

Plerixafor+G-CSF-mobilized CD34+ cells represent an optimal graft source for thalassemia gene therapy.

Globin gene therapy requires abundant numbers of highly engraftable, autologous hematopoietic stem cells expressing curative levels of ß-globin on differentiation. In this study, CD34+ cells from 31 thalassemic patients mobilized with hydroxyurea+granulocyte colony-stimulating factor (G-CSF), G-CSF, Plerixafor, or Plerixafor+G-CSF were transduced with the TNS9.3.55 ß-globin lentivector and compared for transducibility and globin expression in vitro, as well as engraftment potential in a xenogeneic model after partial myeloablation. Transduction efficiency and vector copy number (VCN) averaged 48.4 ± 2.8% and 1.91 ± 0.04, respectively, whereas expression approximated the one-copy normal ß-globin output. Plerixafor+G-CSF cells produced the highest ß-globin expression/VCN. Long-term multilineage engraftment and persistent VCN and vector expression was encountered in all xenografted groups, with Plerixafor+G-CSF-mobilized cells achieving superior short-term engraftment rates, with similar numbers of CD34+ cells transplanted. Overall, Plerixafor+G-CSF not only allows high CD34+ cell yields but also provides increased ß-globin expression/VCN and enhanced early human chimerism under nonmyeloablative conditions, thus representing an optimal graft for thalassemia gene therapy.

Rapamycin relieves lentiviral vector transduction resistance in human and mouse hematopoietic stem cells.

Transplantation of genetically modified hematopoietic stem cells (HSCs) is a promising therapeutic strategy for genetic diseases, HIV, and cancer. However, a barrier for clinical HSC gene therapy is the limited efficiency of gene delivery via lentiviral vectors (LVs) into HSCs. We show here that rapamycin, an allosteric inhibitor of the mammalian target of rapamycin complexes, facilitates highly efficient lentiviral transduction of mouse and human HSCs and dramatically enhances marking frequency in long-term engrafting cells in mice. Mechanistically, rapamycin enhanced postbinding endocytic events, leading to increased levels of LV cytoplasmic entry, reverse transcription, and genomic integration. Despite increasing LV copy number, rapamycin did not significantly alter LV integration site profile or chromosomal distribution in mouse HSCs. Rapamycin also enhanced in situ transduction of mouse HSCs via direct intraosseous infusion. Collectively, rapamycin strongly augments LV transduction of HSCs in vitro and in vivo and may prove useful for therapeutic gene delivery.

Intravenous injection of a foamy virus vector to correct canine SCID-X1.

Current approaches to hematopoietic stem cell (HSC) gene therapy involve the collection and ex vivo manipulation of HSCs, a process associated with loss of stem cell multipotency and engraftment potential. An alternative approach for correcting blood-related diseases is the direct intravenous administration of viral vectors, so-called in vivo gene therapy. In this study, we evaluated the safety and efficacy of in vivo gene therapy using a foamy virus vector for the correction of canine X-linked severe combined immunodeficiency (SCID-X1). In newborn SCID-X1 dogs, injection of a foamy virus vector expressing the human IL2RG gene resulted in an expansion of lymphocytes expressing the common γ chain and the development of CD3(+) T lymphocytes. CD3(+) cells expressed CD4 and CD8 coreceptors, underwent antigen receptor gene rearrangement, and demonstrated functional maturity in response to T-cell mitogens. Retroviral integration site analysis in 4 animals revealed a polyclonal pattern of integration in all dogs with evidence for dominant clones. These results demonstrate that a foamy virus vector can be administered with therapeutic benefit in the SCID-X1 dog, a clinically relevant preclinical model for in vivo gene therapy.

VISA--Vector Integration Site Analysis server: a web-based server to rapidly identify retroviral integration sites from next-generation sequencing.

BACKGROUND: Analyzing the integration profile of retroviral vectors is a vital step in determining their potential genotoxic effects and developing safer vectors for therapeutic use. Identifying retroviral vector integration sites is also important for retroviral mutagenesis screens. RESULTS: We developed VISA, a vector integration site analysis server, to analyze next-generation sequencing data for retroviral vector integration sites. Sequence reads that contain a provirus are mapped to the human genome, sequence reads that cannot be localized to a unique location in the genome are filtered out, and then unique retroviral vector integration sites are determined based on the alignment scores of the remaining sequence reads. CONCLUSIONS: VISA offers a simple web interface to upload sequence files and results are returned in a concise tabular format to allow rapid analysis of retroviral vector integration sites.

Efficient generation, purification, and expansion of CD34(+) hematopoietic progenitor cells from nonhuman primate-induced pluripotent stem cells.

Induced pluripotent stem cell (iPSC) therapeutics are a promising treatment for genetic and infectious diseases. To assess engraftment, risk of neoplastic formation, and therapeutic benefit in an autologous setting, testing iPSC therapeutics in an appropriate model, such as the pigtail macaque (Macaca nemestrina; Mn), is crucial. Here, we developed a chemically defined, scalable, and reproducible specification protocol with bone morphogenetic protein 4, prostaglandin-E2 (PGE2), and StemRegenin 1 (SR1) for hematopoietic differentiation of Mn iPSCs. Sequential coculture with bone morphogenetic protein 4, PGE2, and SR1 led to robust Mn iPSC hematopoietic progenitor cell formation. The combination of PGE2 and SR1 increased CD34(+)CD38(-)Thy1(+)CD45RA(-)CD49f(+) cell yield by 6-fold. CD34(+)CD38(-)Thy1(+)CD45RA(-)CD49f(+) cells isolated on the basis of CD34 expression and cultured in SR1 expanded 3-fold and maintained this long-term repopulating HSC phenotype. Purified CD34(high) cells exhibited 4-fold greater hematopoietic colony-forming potential compared with unsorted hematopoietic progenitors and had bilineage differentiation potential. On the basis of these studies, we calculated the cell yields that must be achieved at each stage to meet a threshold CD34(+) cell dose that is required for engraftment in the pigtail macaque. Our protocol will support scale-up and testing of iPSC-derived CD34(high) cell therapies in a clinically relevant nonhuman primate model.

Cas9 RNP Physiochemical Analysis for Enhanced CRISPR-AuNP Assembly and Function.

CRISPR therapy for hematological disease has proven effective for transplant dependent beta thalassemia and sickle cell anemia, with additional disease targets in sight. The success of these therapies relies on high rates of CRISPR-induced double strand DNA breaks in hematopoietic stem and progenitor cells (HSPC). To achieve these levels, CRISPR complexes are typically delivered by electroporation ex vivo which is toxic to HSPCs. HSPCs are then cultured in stimulating conditions that promote error-prone DNA repair, requiring conditioning with chemotherapy to facilitate engraftment after reinfusion. In vivo delivery by nanocarriers of CRISPR gene editing tools has the potential to mitigate this complexity and toxicity and make this revolutionary therapy globally available. To achieve in vivo delivery, the inherent restriction factors against oligonucleotide delivery into HSPCs, that make ex vivo manipulation including electroporation and stimulation essential, must be overcome. To this end, our group developed a CRISPR carrying gold nanoparticle (CRISPR-AuNP) capable of delivering either Cas9 or Cas12a CRISPRs as ribonucleoprotein complexes (RNP) without compromising HSPC fitness. However, the most commonly used CRISPR, Cas9, demonstrated inconsistent activity in this delivery system, with lower activity relative to Cas12a. Investigation of Cas9 RNP biophysics relative to Cas12a revealed duplex RNA instability during the initial loading onto Au cores, resulting in undetectable Cas9 loading to the particle surface. Here we demonstrate preformation of RNP before loading, coupled with optimization of the loading chemistry and conditions, resulted in 39.6 ± 7.0 Cas9 RNP/AuNP without compromising RNP activity in both in vitro assays and primary human HSPC. The same alterations improved Cas12a RNP/AuNP loading 10-fold over previously reported levels. To achieve particle stability, the reported polyethyleneimine outer coating was altered to include PEGylation and the resulting 2nd generation CRISPR-AuNP demonstrates favorable nanoformulation characteristics for in vivo administration, with a hydrophilic, more neutral nanoparticle surface. Direct treatment of HSPC in vitro showed 72.5 ± 7.37% uptake of 2nd generation CRISPR-AuNP in primary human HSPC, but with endosomal accumulation and low rates of gene editing consistent with low levels of endosomal escape.

Nothing about us without us: Advocacy and engagement in genetic medicine.

The development of new genetic medicines to treat sickle cell disease highlights the need for greater collaboration between researchers and people with lived experiences. Drawing on the adage "Nothing about us, without us," we call for increased investments in community advocacy and engagement.

The translational gap for gene therapies in low- and middle-income countries.

Gene therapies are designed to address the root cause of disease. As scientific understanding of disease prevention, diagnosis, and treatment improves in tandem with technological innovation, gene therapies have the potential to become safe and effective treatment options for a wide range of genetic and nongenetic diseases. However, as the medical scope of gene therapies expands, consideration must be given to those who will benefit and what proactive steps must be taken to widen development and access potential, particularly in regions carrying a high disease burden.

CRISPR Gene Editing of Hematopoietic Stem and Progenitor Cells.

Genetic editing of hematopoietic stem and progenitor cells can be employed to understand gene-function relationships underlying hematopoietic cell biology, leading to new therapeutic approaches to treat disease. The ability to collect, purify, and manipulate primary cells outside the body permits testing of many different gene editing approaches. RNA-guided nucleases, such as CRISPR, have revolutionized gene editing based simply on Watson-Crick base-pairing, employed to direct activity to specific genomic loci. Given the ease and affordability of synthetic, custom RNA guides, testing of precision edits or large random pools in high-throughput screening studies is now widely available. With the ever-growing number of CRISPR nucleases being discovered or engineered, researchers now have a plethora of options for directed genomic change, including single base edits, nicks or double-stranded DNA cuts with blunt or staggered ends, as well as the ability to target CRISPR to other cellular oligonucleotides such as RNA or mitochondrial DNA. Except for single base editing strategies, precise rewriting of larger segments of the genetic code requires delivery of an additional component, templated DNA oligonucleotide(s) encoding the desired changes flanked by homologous sequences that permit recombination at or near the site of CRISPR activity. Altogether, the ever-growing CRISPR gene editing toolkit is an invaluable resource. This chapter outlines available technologies and the strategies for applying CRISPR-based editing in hematopoietic stem and progenitor cells.

Decentralized manufacturing of anti CD19 CAR-T cells using CliniMACS Prodigy®: real-world experience and cost analysis in India.

Chimeric Antigen Receptor (CAR) T cell therapy is an accepted standard of care for relapsed/refractory B cell malignancies. However, the high cost of existing industry-driven centralized production makes this therapy unaffordable in low and middle-income countries. Decentralized or point of care manufacturing has the potential to overcome some of these challenges. Here we demonstrate a decentralized manufacturing process for anti-CD19-CAR-T cells using a fully automated closed system (Miltenyi CliniMACS Prodigy®) is feasible in a developing country setting. Validation run data, as part of a pre-clinical trial safety evaluation, demonstrates the successful and robust manufacturing of anti-CD19 CAR-T cells with T cell expansion of 25 to 47-fold. The median transduction efficiency was 48.8%, with a median viability of 98% and fulfillment of all standard release criteria assays for clinical application. Evaluation of production costs in an academic, not for profit setting in India provide a benchmark for low and middle-income pricing which could greatly increase access to this therapy. Based on our analysis, the cost per product would be approximately $35,107 US dollars. Our data highlights the safety, efficacy, and reproducibility of the process for use in planned future clinical trials.

Safeguarding nonhuman primate iPS cells with suicide genes.

The development of technology to generate induced pluripotent stem (iPS) cells constitutes one of the most exciting scientific breakthroughs because of the enormous potential for regenerative medicine. However, the safety of iPS cell-related products is a major concern for clinical translation. Insertional mutagenesis, possible oncogenic transformation of iPS cells or their derivatives, or the contamination of differentiated iPS cells with undifferentiated cells, resulting in the formation of teratomas, have remained considerable obstacles. Here, we demonstrate the utility of suicide genes to safeguard iPS cells and their derivatives. We found suicide genes can control the cell fate of iPS cells in vitro and in vivo without interfering with their pluripotency and self-renewal capacity. This study will be useful to evaluate the safety of iPS cell technology in a clinically highly relevant, large animal model and further benefit the clinical use of human iPS cells.

Stem cell gene therapy for fanconi anemia: report from the 1st international Fanconi anemia gene therapy working group meeting.

Survival rates after allogeneic hematopoietic cell transplantation (HCT) for Fanconi anemia (FA) have increased dramatically since 2000. However, the use of autologous stem cell gene therapy, whereby the patient's own blood stem cells are modified to express the wild-type gene product, could potentially avoid the early and late complications of allogeneic HCT. Over the last decades, gene therapy has experienced a high degree of optimism interrupted by periods of diminished expectation. Optimism stems from recent examples of successful gene correction in several congenital immunodeficiencies, whereas diminished expectations come from the realization that gene therapy will not be free of side effects. The goal of the 1st International Fanconi Anemia Gene Therapy Working Group Meeting was to determine the optimal strategy for moving stem cell gene therapy into clinical trials for individuals with FA. To this end, key investigators examined vector design, transduction method, criteria for large-scale clinical-grade vector manufacture, hematopoietic cell preparation, and eligibility criteria for FA patients most likely to benefit. The report summarizes the roadmap for the development of gene therapy for FA.

Intraosseous delivery of platelet-targeted factor VIII lentiviral vector in humanized NBSGW mice.

We previously showed that intraosseous (IO) delivery of factor VIII (FVIII, gene F8) lentiviral vector (LV) driven by the megakaryocyte-specific promoter Gp1bα (G-F8-LV) partially corrected the bleeding phenotype in hemophilia A (HemA) mice for up to 5 months. In this study, we further characterized and confirmed the successful transduction of self-regenerating hematopoietic stem and progenitor cells (HSPCs) in treated mice. In addition, secondary transplant of HSPCs isolated from G-F8-LV-treated mice corrected the bleeding phenotype of the recipient HemA mice, indicating the potential of long-term transgene expression following IO-LV therapy. To facilitate the translation of this technology to human applications, we evaluated the safety and efficacy of this gene transfer therapy into human HSPCs. In vitro transduction of human HSPCs by the platelet-targeted G-F8-LV confirmed megakaryocyte-specific gene expression after preferential differentiation of HSPCs to megakaryocyte lineages. Lentiviral integration analysis detected a polyclonal integration pattern in G-F8-LV-transduced human cells, profiling the clinical safety of hemophilia treatment. Most importantly, IO delivery of G-F8-LV to humanized NBSGW mice produced persistent FVIII expression in human platelets after gene therapy, and the megakaryocytes differentiated from human CD34+ HSPCs isolated from LV-treated humanized mice showed up to 10.2% FVIII expression, indicating efficient transduction of self-regenerating human HSPCs. Collectively, these results indicate the long-term safety and efficacy of the IO-LV gene therapy strategy for HemA in a humanized model, adding further evidence to the feasibility of translating this method for clinical applications.