Optimizing autologous cell grafts to improve stem cell gene therapy

MiR-182-5p Mediated by Exosomes Derived From Bone Marrow Mesenchymal Stem Cell Attenuates Inflammatory Responses by Targeting TLR4 in a Mouse Model of Myocardial Infraction

Exosomes derived from mesenchymal stem cells (MSCs) could protect against myocardial infarction (MI). TLR4 is reported to play an important role in MI, while microRNA-182-5p (miR-182-5p) negatively regulates TLR4 expression. Therefore, we hypothesize that MSCs-derived exosomes overexpressing miR-182-5p may have beneficial effects on MI. We generated bone marrow mesenchymal stem cells (BM-MSCs) and overexpressed miR-182-5p in these cells for exosome isolation. H₂O₂-stimulated neonatal mouse ventricle myocytes (NMVMs) and MI mouse model were employed, which were subjected to exosome treatment. The expression of inflammatory factors, heart function, and TLR4 signaling pathway activation were monitored. It was found that miR-182-5p decreased TLR4 expression in BM-MSCs and NMVMs. Administration of exosomes overexpressing miR-182-5p to H₂O₂-stimulated NMVMs enhanced cell viability and suppressed the expression of inflammatory cytokines. In addition, they promoted heart function, suppressed inflammatory responses, and de-activated TLR4/NF-κB signaling pathway in MI mice. In conclusion, miR-182-5p transferred by the exosomes derived from BM-MSCs protected against MI-induced impairments by targeting TLR4.

Ex vivo expansion and functional activity preservation of adult hematopoietic stem cells by a diarylheptanoid from Curcuma comosa

Hematopoietic stem cells (HSCs, CD34+ cells) have shown therapeutic efficacy for transplantation in various hematological disorders. However, a large quantity of HSCs is required for transplantation. Therefore, strategies to increase HSC numbers and preserve HSC functions through ex vivo culture are critically required. Here, we report that expansion medium supplemented with ASPP 049, a diarylheptanoid isolated from Curcuma comosa, and a cocktail of cytokines markedly increased numbers of adult CD34+ cells. Interestingly, phenotypically defined primitive HSCs (CD34+CD38-CD90+) were significantly increased under ASPP 049 treatment relative to control. ASPP 049 treatment also improved two functional properties of HSCs, as evidenced by an increased number of CD34+CD38- cells in secondary culture (self-renewal) and the growth of colony-forming units as assessed by colony formation assay (multilineage differentiation). Transplantation of cultured CD34+ cells into immunodeficient mice demonstrated the long-term reconstitution and differentiation ability of ASPP 049-expanded cells. RNA sequencing and KEGG analysis revealed that Hippo signaling was the most likely pathway involved in the effects of ASPP 049. These results suggest that ASPP 049 improved ex vivo expansion and functional preservation of expanded HSCs. Our findings provide a rationale for the use of ASPP 049 to grow HSCs prior to hematological disease treatment.

β-Hemoglobinopathies: The Test Bench for Genome Editing-Based Therapeutic Strategies

Hemoglobin is a tetrameric protein composed of two α and two β chains, each containing a heme group that reversibly binds oxygen. The composition of hemoglobin changes during development in order to fulfill the need of the growing organism, stably maintaining a balanced production of α-like and β-like chains in a 1:1 ratio. Adult hemoglobin (HbA) is composed of two α and two β subunits (α2β2 tetramer), whereas fetal hemoglobin (HbF) is composed of two γ and two α subunits (α2γ2 tetramer). Qualitative or quantitative defects in β-globin production cause two of the most common monogenic-inherited disorders: β-thalassemia and sickle cell disease. The high frequency of these diseases and the relative accessibility of hematopoietic stem cells make them an ideal candidate for therapeutic interventions based on genome editing. These strategies move in two directions: the correction of the disease-causing mutation and the reactivation of the expression of HbF in adult cells, in the attempt to recreate the effect of hereditary persistence of fetal hemoglobin (HPFH) natural mutations, which mitigate the severity of β-hemoglobinopathies. Both lines of research rely on the knowledge gained so far on the regulatory mechanisms controlling the differential expression of globin genes during development.

The Future of Gene Therapy for Transfusion-Dependent Beta-Thalassemia: The Power of the Lentiviral Vector for Genetically Modified Hematopoietic Stem Cells

β-thalassemia, a disease that results from defects in β-globin synthesis, leads to an imbalance of β- and α-globin chains and an excess of α chains. Defective erythroid maturation, ineffective erythropoiesis, and shortened red blood cell survival are commonly observed in most β-thalassemia patients. In severe cases, blood transfusion is considered as a mainstay therapy; however, regular blood transfusions result in chronic iron overload with life-threatening complications, e.g., endocrine dysfunction, cardiomyopathy, liver disease, and ultimately premature death. Therefore, transplantation of healthy hematopoietic stem cells (HSCs) is considered an alternative treatment. Patients with a compatible human leukocyte antigen (HLA) matched donor can be cured by allogeneic HSC transplantation. However, some recipients faced a high risk of morbidity/mortality due to graft versus host disease or graft failure, while a majority of patients do not have such HLA match-related donors. Currently, the infusion of autologous HSCs modified with a lentiviral vector expressing the β-globin gene into the erythroid progenitors of the patient is a promising approach to completely cure β-thalassemia. Here, we discuss a history of β-thalassemia treatments and limitations, in particular the development of β-globin lentiviral vectors, with emphasis on clinical applications and future perspectives in a new era of medicine.

Ex vivo expansion of hematopoietic stem cells: Finally transitioning from the lab to the clinic

Hematopoietic stem cells (HSCs) have been used for therapeutic purposes for decades in the form of autologous and allogeneic transplantation and are currently emerging as an attractive target for gene therapy. A low stem cell dose is a major barrier to the application of HSC therapy in several situations, primarily umbilical cord blood transplantation and gene modification. Strategies that promote ex vivo expansion of the numbers of functional HSCs could overcome this barrier, hence have been the subject of intense and prolonged research. Several ex vivo expansion strategies have advanced to evaluation clinical trials, which are showing favorable outcomes along with convincing safety signals. Preclinical studies have recently confirmed beneficial incorporation of ex vivo expansion into HSC gene modification protocols. Collectively, ex vivo HSC expansion holds promise for significantly broadening the availability of cord blood units for transplantation, and for optimizing gene therapy protocols to enable their clinical application.

CD74 is a regulator of hematopoietic stem cell maintenance

Hematopoietic stem and progenitor cells (HSPCs) are a small population of undifferentiated cells that have the capacity for self-renewal and differentiate into all blood cell lineages. These cells are the most useful cells for clinical transplantations and for regenerative medicine. So far, it has not been possible to expand adult hematopoietic stem cells (HSCs) without losing their self-renewal properties. CD74 is a cell surface receptor for the cytokine macrophage migration inhibitory factor (MIF), and its mRNA is known to be expressed in HSCs. Here, we demonstrate that mice lacking CD74 exhibit an accumulation of HSCs in the bone marrow (BM) due to their increased potential to repopulate and compete for BM niches. Our results suggest that CD74 regulates the maintenance of the HSCs and CD18 expression. Its absence leads to induced survival of these cells and accumulation of quiescent and proliferating cells. Furthermore, in in vitro experiments, blocking of CD74 elevated the numbers of HSPCs. Thus, we suggest that blocking CD74 could lead to improved clinical insight into BM transplant protocols, enabling improved engraftment.

Hematopoietic stem and progenitor cells (HSPCs) can self-renew and differentiate into all blood cell lineages, making them useful for clinical transplantations and regenerative medicine. This study shows that blocking the MIF receptor CD74 increases the accumulation of HSPCs and could improve the efficacy of bone marrow transplantation protocols.

Expansion and preservation of the functional activity of adult hematopoietic stem cells cultured ex vivo with a histone deacetylase inhibitor

Attempts to expand ex vivo the numbers of human hematopoietic stem cells (HSCs) without compromising their marrow repopulating capacity and their ability to establish multilineage hematopoiesis has been the subject of intense investigation. Although most such efforts have focused on cord blood HSCs, few have been applied to adult HSCs, a more clinically relevant HSC source for gene modification. To date, the strategies that have been used to expand adult HSCs have resulted in modest effects or HSCs with lineage bias and a limited ability to generate T cells in vivo. We previously reported that culturing umbilical cord blood CD34+ cells in serum‐free media supplemented with valproic acid (VPA), a histone deacetylase inhibitor, and a combination of cytokines led to the expansion of the numbers of fully functional HSCs. In the present study, we used this same approach to expand the numbers of adult human CD34+ cells isolated from mobilized peripheral blood and bone marrow. This approach resulted in a significant increase in the numbers of phenotypically defined HSCs (CD34+CD45RA‐CD90+D49f+). Cells incubated with VPA also exhibited increased aldehyde dehydrogenase activity and decreased mitochondrial membrane potential, each functional markers of HSCs. Grafts harvested from VPA‐treated cultures were able to engraft in immune‐deficient mice and, importantly, to generate cellular progeny belonging to each hematopoietic lineage in similar proportion to that observed with unmanipulated CD34+ cells. These data support the utility of VPA‐mediated ex vivo HSC expansion for gene modification of adult HSCs.

Gene Therapy For Beta-Thalassemia: Updated Perspectives

Allogeneic hematopoietic stem cell transplantation was until very recently, the only permanent curative option available for patients suffering from transfusion-dependent beta-thalassemia. Gene therapy, by autologous transplantation of genetically modified hematopoietic stem cells, currently represents a novel therapeutic promise, after many years of extensive preclinical research for the optimization of gene transfer protocols. Nowadays, clinical trials being held on a worldwide setting, have demonstrated that, by re-establishing effective hemoglobin production, patients may be rendered transfusion- and chelation-independent and evade the immunological complications that normally accompany allogeneic hematopoietic stem cell transplantation. The present review will offer a retrospective scope of the long way paved towards successful implementation of gene therapy for beta-thalassemia, and will pinpoint the latest strategies employed to increase globin expression that extend beyond the classic transgene addition perspective. A thorough search was performed using Pubmed in order to identify studies that provide a proof of principle on the aforementioned topic at a preclinical and clinical level. Inclusion criteria also regarded gene transfer technologies of the past two decades, as well as publications outlining the pitfalls that precluded earlier successful implementation of gene therapy for beta-thalassemia. Overall, after decades of research, that included both successes and pitfalls, the path towards a permanent, donor-irrespective cure for beta-thalassemia patients is steadily becoming a realistic approach.

Gene Therapy for Beta-Hemoglobinopathies: Milestones, New Therapies and Challenges

Inherited monogenic disorders such as beta-hemoglobinopathies (BH) are fitting candidates for treatment via gene therapy by gene transfer or gene editing. The reported safety and efficacy of lentiviral vectors in preclinical studies have led to the development of several clinical trials for the addition of a functional beta-globin gene. Across trials, dozens of transfusion-dependent patients with sickle cell disease (SCD) and transfusion-dependent beta-thalassemia (TDT) have been treated via gene therapy and have achieved reduced transfusion requirements. While overall results are encouraging, the outcomes appear to be strongly influenced by the level of lentiviral integration in transduced cells after engraftment, as well as the underlying genotype resulting in thalassemia. In addition, the method of procurement of hematopoietic stem cells can affect their quality and thus the outcome of gene therapy both in SCD and TDT. This suggests that new studies aimed at maximizing the number of corrected cells with long-term self-renewal potential are crucial to ensure successful treatment for every patient. Recent advancements in gene transfer and bone marrow transplantation have improved the success of this approach, and the results obtained by using these strategies demonstrated significant improvement of gene transfer outcome in patients. The advent of new gene-editing technologies has suggested additional therapeutic options. These are primarily focused on correcting the defective beta-globin gene or editing the expression of genes or genomic segments that regulate fetal hemoglobin synthesis. In this review, we aim to establish the potential benefits of gene therapy for BH, to summarize the status of the ongoing trials, and to discuss the possible improvement or direction for future treatments.

CRISPR/Cas9-modified hematopoietic stem cells-present and future perspectives for stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a standard therapeutic intervention for hematological malignancies and several monogenic diseases. However, this approach has limitations related to lack of a suitable donor, graft-versus-host disease and infectious complications due to immune suppression. On the contrary, autologous HSCT diminishes the negative effects of allogeneic HSCT. Despite the good efficacy, earlier gene therapy trials with autologous HSCs and viral vectors have raised serious safety concerns. However, the CRISPR/Cas9-edited autologous HSCs have been proposed to be an alternative option with a high safety profile. In this review, we summarized the possibility of CRISPR/Cas9-mediated autologous HSCT as a potential treatment option for various diseases supported by preclinical gene-editing studies. Furthermore, we discussed future clinical perspectives and possible clinical grade improvements of CRISPR/cas9-mediated autologous HSCT.

Single-Cell Transcriptome Analysis of CD34+ Stem Cell-Derived Myeloid Cells Infected With Human Cytomegalovirus

Myeloid cells are important sites of lytic and latent infection by human cytomegalovirus (CMV). We previously showed that only a small subset of myeloid cells differentiated from CD34⁺ hematopoietic stem cells is permissive to CMV replication, underscoring the heterogeneous nature of these populations. The exact identity of resistant and permissive cell types, and the cellular features characterizing the latter, however, could not be dissected using averaging transcriptional analysis tools such as microarrays and, hence, remained enigmatic. Here, we profile the transcriptomes of ∼7000 individual cells at day 1 post-infection using the 10× genomics platform. We show that viral transcripts are detectable in the majority of the cells, suggesting that virion entry is unlikely to be the main target of cellular restriction mechanisms. We further show that viral replication occurs in a small but specific sub-group of cells transcriptionally related to, and likely derived from, a cluster of cells expressing markers of Colony Forming Unit – Granulocyte, Erythrocyte, Monocyte, Megakaryocyte (CFU-GEMM) oligopotent progenitors. Compared to the remainder of the population, CFU-GEMM cells are enriched in transcripts with functions in mitochondrial energy production, cell proliferation, RNA processing and protein synthesis, and express similar or higher levels of interferon-related genes. While expression levels of the former are maintained in infected cells, the latter are strongly down-regulated. We thus propose that the preferential infection of CFU-GEMM cells may be due to the presence of a pre-established pro-viral environment, requiring minimal optimization efforts from viral effectors, rather than to the absence of specific restriction factors. Together, these findings identify a potentially new population of myeloid cells permissive to CMV replication, and provide a possible rationale for their preferential infection.

The Functional Effect of Repeated Cryopreservation on Transduced CD34+ Cells from Patients with Thalassemia

Stable gene marking and effective engraftment of gene-modified CD34⁺ hematopoietic stem cells is a prerequisite for gene therapy success but may be challenged by the inevitable cryopreservation of the final product prior to extensive quality assurance testing. We investigated the β-globin gene transfer potency in fresh and cryopreserved CD34⁺ cells from mobilized patients with β-thalassemia, as well as the qualitative impact of repeated freeze/thaw cycles on the functionality of cultured and unmanipulated CD34⁺ cells in terms of engrafting capacity in a xenotransplantation model, under partial myeloablation. Cells transduced fresh or after one freeze-thaw cycle yielded similar clonogenic and gene transfer frequencies. Repeated cryopreservation cycles did not affect the transduction rates whereas either one or two freeze-thaw cycles of cultured-but not of unmanipulated-cells significantly reduced their clonogenicity. No differences in the engrafting potential of gene-corrected cells subjected to either none or up to two cryopreservation cycles, were encountered post xenotransplantation. Overall, we assessed the gene transfer efficiency, clonogenicity and engrafting capacity of cryopreserved CD34⁺ cells and the impact of repeated freeze/thaw cycles in their performance. These observations may prove essential in the design of gene therapy trials, considerably facilitating their logistics.

Rapid prediction of stem cell mobilization using volume and conductivity data from automated hematology analyzers

BACKGROUND

Rapid analytics to predict circulating hematopoietic stem cells are valuable for optimal management of mobilization, particularly for the use of newer and costly mobilization agents such as plerixafor.

STUDY DESIGN AND METHODS

We used stepwise, linear multiple regression modeling applied to cell population data collected by routine hematology analyzers (Beckman Coulter DxH 800) on patients undergoing autologous stem cell collection (n = 131). Beta coefficients were used to derive a formula for a stem cell index (SCI). We then tested the correlation of SCI with stem cell counts and performance of the SCI as a predictor of poor mobilization with external validation in a separate cohort (n = 183).

RESULTS

The SCI correlated strongly with CD34 counts by flow cytometry (r = 0.8372 in the development cohort, r = 0.8332 in the external validation cohort) and compares favorably with other rapid stem cell enumerating technologies. In the external validation cohort, the SCI performed well as a predictor (receiver operating characteristic area under the curve, 0.9336) of poor mobilization (CD34 count < 10), with a sensitivity of 72% and a specificity of 93%. When prevalence of poor mobilization was 33%, this resulted in a positive predictive value of 83% and a negative predictive value of 87%. The SCI also showed promise in tracking responses to plerixafor administration.

CONCLUSION

The findings demonstrate the utility of the cell population data collected by hematology analyzers to provide rapid data beyond standard complete blood counts, particularly for stem cell count prediction, requiring no additional reagents, specimen, or instrumentation.

Curative approaches for sickle cell disease: A review of allogeneic and autologous strategies

Despite sickle cell disease (SCD) first being reported >100years ago and molecularly characterized >50years ago, patients continue to experience severe morbidity and early mortality. Although there have been substantial clinical advances with immunizations, penicillin prophylaxis, hydroxyurea treatment, and transfusion therapy, the only cure that can be offered is hematopoietic stem cell transplantation (HSCT). In this work, we summarize the various allogeneic curative approaches reported to date and discuss open and upcoming clinical research protocols. Then we consider gene therapy and gene editing strategies that may enable cure based on autologous HSCs.

Brief Report: A Differential Transcriptomic Profile of Ex Vivo Expanded Adult Human Hematopoietic Stem Cells Empowers Them for Engraftment Better than Their Surface Phenotype

Transplantation of small cord blood (CB) units, or of autologous ex vivo‐genetically modified adult hematopoietic stem cells (HSC), face the common challenge of suboptimal HSC doses for infusion and impaired engraftment of the transplanted cells. Ex vivo expansion of HSCs, using either cell‐based coculture approaches or especially small molecules have been successfully tested mainly in CB and in prolonged cultures. Here, we explored whether innovative combinations of small molecules can sufficiently, after short culture, expand adult HSCs while retaining their functionality in vivo. We found that 5‐day cultured cells, in the presence of the small molecule combinations tested, achieved higher engraftment levels in NSG mice than both their uncultured and their cytokine only‐cultured counterparts. Surprisingly, the engraftment levels were neither concordant to the numbers of phenotypically similar HSCs expanded under different small molecule combinations, nor explained by their distinct companion cells present. Transcriptomic comparative analysis of sorted, phenotypically similar, ex vivo generated HSCs transplanted in equal numbers, suggested that HSCs generated under expansion conditions that maintain low expression of the Rap1/Ras/PI3K‐AKT pathway exhibit a superior functional profile in vivo. Stem Cells Translational Medicine2017;6:1852–1858

Poor stem cell harvest may not always be related to poor mobilization: lessons gained from a mobilization study in patients with β-thalassemia major

BACKGROUND

Hematopoietic stem cell mobilization and leukapheresis in adult patients with β-thalassemia have recently been optimized in the context of clinical trials for obtaining hematopoietic stem cells for thalassemia gene therapy. In some patients, however, the yield of cluster of differentiation 34-positive (CD34+) cells was poor despite successful mobilization, and a modification of apheresis settings was mandatory for harvest rescue.

STUDY DESIGN AND METHODS

Data were analyzed from 20 adult patients with β-thalassemia who were enrolled in a clinical trial of optimizing mobilization strategies for stem cell gene therapy. The aim of this post-hoc analysis was to assess how certain hematological and/or clinical parameters may correlate with low collection efficiency in the presence of adequate numbers of circulating stem cells after pharmacological mobilization and standard leukapheresis procedures.

RESULTS

Among 19 patients who achieved optimal mobilization with Plerixafor, four who underwent splenectomy demonstrated disproportionately poor CD34+ cell harvests, as determined by their circulating CD34+ cell counts after mobilization. All four patients who underwent splenectomy presented at baseline and before first apheresis with lymphocytosis resulting in lymphocyte/neutrophil ratios well above 1 and marked reticulocytosis compared with patients who achieved optimal mobilization/CD34+ cell harvest. Such unexpected expansion of specific cell populations disrupted the normal cell layer separation and necessitated modification of the apheresis settings to rescue the harvests.

CONCLUSIONS

By close examination of certain hematological and/or clinical parameters before leukapheresis, patients who, despite adequate mobilization, are at risk for poor CD34+ cell harvests may be identified, and harvest failure can be prevented by adjusting the apheresis settings.

Mitochondrial Neurogastrointestinal Encephalomyopathy Caused by Thymidine Phosphorylase Enzyme Deficiency: From Pathogenesis to Emerging Therapeutic Options

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a progressive metabolic disorder caused by thymidine phosphorylase (TP) enzyme deficiency. The lack of TP results in systemic accumulation of deoxyribonucleosides thymidine (dThd) and deoxyuridine (dUrd). In these patients, clinical features include mental regression, ophthalmoplegia, and fatal gastrointestinal complications. The accumulation of nucleosides also causes imbalances in mitochondrial DNA (mtDNA) deoxyribonucleoside triphosphates (dNTPs), which may play a direct or indirect role in the mtDNA depletion/deletion abnormalities, although the exact underlying mechanism remains unknown. The available therapeutic approaches include dialysis and enzyme replacement therapy, both can only transiently reverse the biochemical imbalance. Allogeneic hematopoietic stem cell transplantation is shown to be able to restore normal enzyme activity and improve clinical manifestations in MNGIE patients. However, transplant related complications and disease progression result in a high mortality rate. New therapeutic approaches, such as adeno-associated viral vector and hematopoietic stem cell gene therapy have been tested in Tymp^-/-Upp1^-/- mice, a murine model for MNGIE. This review provides background information on disease manifestations of MNGIE with a focus on current management and treatment options. It also outlines the pre-clinical approaches toward future treatment of the disease.

Gene Therapy with Hematopoietic Stem Cells: The Diseased Bone Marrow's Point of View

When considering inherited diseases that can be treated by gene transfer into hematopoietic stem cells (HSCs), there are only two in which the HSC and progenitor cell distribution inside the bone marrow and its microenvironment are exactly the same as in a healthy subject: metachromatic leukodystrophy (MLD) and adrenoleukodystrophy (ALD). In all other settings [X-linked severe combined immunodeficiency (X-SCID), adenosine deaminase deficiency, Wiskott-Aldrich syndrome, and β-hemoglobinopathies], the bone marrow content of the different stem and precursor cells and the cells' relationship with the stroma have very specific characteristics. These peculiarities can influence the cells' harvesting and behavior in culture, and the postgraft uptake and further behavior of the gene-modified hematopoietic/precursor cells. In the present mini-review, we shall briefly summarize these characteristics and outline the possible consequences and challenges.