Lentiviral Vector-Mediated Correction of a Mouse Model of Leukocyte Adhesion Deficiency Type I

Gene therapy for inborn error of immunity - current status and future perspectives

PURPOSE OF REVIEW

Development of hematopoietic stem cell (HSC) gene therapy (GT) for inborn errors of immunity (IEIs) continues to progress rapidly. Although more patients are being treated with HSC GT based on viral vector mediated gene addition, gene editing techniques provide a promising new approach, in which transgene expression remains under the control of endogenous regulatory elements.

RECENT FINDINGS

Many gene therapy clinical trials are being conducted and evidence showing that HSC GT through viral vector mediated gene addition is a successful and safe curative treatment option for various IEIs is accumulating. Gene editing techniques for gene correction are, on the other hand, not in clinical use yet, despite rapid developments during the past decade. Current studies are focussing on improving rates of targeted integration, while preserving the primitive HSC population, which is essential for future clinical translation.

SUMMARY

As HSC GT is becoming available for more diseases, novel developments should focus on improving availability while reducing costs of the treatment. Continued follow up of treated patients is essential for providing information about long-term safety and efficacy. Editing techniques have great potential but need to be improved further before the translation to clinical studies can happen.

Preclinical safety and efficacy of lentiviral-mediated gene therapy for leukocyte adhesion deficiency type I

Leukocyte adhesion deficiency type I (LAD-I) is a primary immunodeficiency caused by mutations in the ITGB2 gene, which encodes for the CD18 subunit of β₂-integrins. Deficient expression of β₂-integrins results in impaired neutrophil migration in response to bacterial and fungal infections. Using a lentiviral vector (LV) that mediates a preferential myeloid expression of human CD18 (Chim.hCD18-LV), we first demonstrated that gene therapy efficiently corrected the phenotype of mice with severe LAD-I. Next, we investigated if the ectopic hCD18 expression modified the phenotypic characteristics of human healthy donor hematopoietic stem cells and their progeny. Significantly, transduction of healthy CD34⁺ cells with the Chim.hCD18-LV did not modify the membrane expression of CD18 nor the adhesion of physiological ligands to transduced cells. Additionally, we observed that the repopulating properties of healthy CD34⁺ cells were preserved following transduction with the Chim.hCD18-LV, and that a safe polyclonal repopulation pattern was observed in transplanted immunodeficient NOD scid gamma (NSG) mice. In a final set of experiments, we demonstrated that transduction of CD34⁺ cells from a severe LAD-I patient with the Chim.hCD18-LV restores the expression of β₂-integrins in these cells. These results offer additional preclinical safety and efficacy evidence supporting the gene therapy of patients with severe LAD-I.

CIBERER: Spanish National Network for Research on Rare Diseases: a highly productive collaborative initiative

CIBER (Center for Biomedical Network Research; Centro de Investigación Biomédica En Red) is a public national consortium created in 2006 under the umbrella of the Spanish National Institute of Health Carlos III (ISCIII). This innovative research structure comprises 11 different specific areas dedicated to the main public health priorities in the National Health System. CIBERER, the thematic area of CIBER focused on rare diseases (RDs) currently consists of 75 research groups belonging to universities, research centers, and hospitals of the entire country. CIBERER's mission is to be a center prioritizing and favoring collaboration and cooperation between biomedical and clinical research groups, with special emphasis on the aspects of genetic, molecular, biochemical, and cellular research of RDs. This research is the basis for providing new tools for the diagnosis and therapy of low‐prevalence diseases, in line with the International Rare Diseases Research Consortium (IRDiRC) objectives, thus favoring translational research between the scientific environment of the laboratory and the clinical setting of health centers. In this article, we intend to review CIBERER's 15‐year journey and summarize the main results obtained in terms of internationalization, scientific production, contributions toward the discovery of new therapies and novel genes associated to diseases, cooperation with patients' associations and many other topics related to RD research.

Preclinical Optimization and Safety Studies of a New Lentiviral Gene Therapy for p47phox-Deficient Chronic Granulomatous Disease

Chronic granulomatous disease (CGD) is an inherited blood disorder of phagocytic cells that renders patients susceptible to infections and inflammation. A recent clinical trial of lentiviral gene therapy for the most frequent form of CGD, X-linked, has demonstrated stable correction over time, with no adverse events related to the gene therapy procedure. We have recently developed a parallel lentiviral vector for p47^phox-deficient CGD (p47^phoxCGD), the second most common form of this disease. Using this vector, we have observed biochemical correction of CGD in a mouse model of the disease. In preparation for clinical trial approval, we have performed standardized preclinical studies following Good Laboratory Practice (GLP) principles, to assess the safety of the gene therapy procedure. We report no evidence of adverse events, including mutagenesis and tumorigenesis, in human hematopoietic stem cells transduced with the lentiviral vector. Biodistribution studies of transduced human CD34⁺ cells indicate that the homing properties or engraftment ability of the stem cells is not negatively affected. CD34⁺ cells derived from a p47^phoxCGD patient were subjected to an optimized transduction protocol and transplanted into immunocompromised mice. After the procedure, patient-derived neutrophils resumed their function, suggesting that gene correction was successful. These studies pave the way to a first-in-man clinical trial of lentiviral gene therapy for the treatment of p47^phoxCGD.

Gene Therapy for Primary Immunodeficiency

Over the past 3 decades, there has been significant progress in refining gene therapy technologies and procedures. Transduction of hematopoietic stem cells ex vivo using lentiviral vectors can now create a highly effective therapeutic product, capable of reconstituting many different immune system dysfunctions when reinfused into patients. Here, we review the key developments in the gene therapy landscape for primary immune deficiency, from an experimental therapy where clinical efficacy was marred by adverse events, to a commercialized product with enhanced safety and efficacy. We also discuss progress being made in preclinical studies for challenging disease targets and emerging gene editing technologies that are showing promising results, particularly for conditions where gene regulation is important for efficacy.

Gene therapy for primary immunodeficiencies

Primary immunodeficiencies (PIDs) are a group of rare inherited disorders of the immune system. Many PIDs are devastating and require a definitive therapy to prevent progressive morbidity and premature mortality. Allogeneic haematopoietic stem cell transplantation (alloHSCT) is curative for many PIDs, and while advances have resulted in improved outcomes, the procedure still carries a risk of mortality and morbidity from graft failure or graft-versus-host disease (GvHD). Autologous haematopoietic stem cell gene therapy (HSC GT) has the potential to correct genetic defects across haematopoietic lineages without the complications of an allogeneic approach. HSC GT for PID has been in development for the last two decades and the first licensed HSC-GT product for adenosine deaminase-deficient severe combined immunodeficiency (ADA-SCID) is now available. New gene editing technologies have the potential to circumvent some of the problems associated with viral gene-addition. HSC GT for PID shows great promise, but requires a unique approach for each disease and carries risks, notably insertional mutagenesis from gamma-retroviral gene addition approaches and possible off-target toxicities from gene-editing techniques. In this review, we discuss the development of HSC GT for PID and outline the current state of clinical development before discussing future developments in the field.

Gene therapy for primary immunodeficiencies: up-to-date

INTRODUCTION

Primary immunodeficiencies (PIDs) are monogenic disorders of the immune system associated with increased susceptibility to life-threatening infection. Curative treatment has been limited to hematopoietic stem cell transplant (HSCT), however toxic immunosuppression, graft failure, and graft versus host disease greatly reduce overall survival rates. Gene therapy is a targeted curative therapy that reduces these risks by utilizing autologous hematopoietic stem cells. The treatment has found significant success and is anticipated to become the standard of care in a number of PIDs.

AREAS COVERED

This review is a summary of the developments in gene therapy, gene editing, and current gene therapy approaches in specific PIDs.

EXPERT OPINION

The field of gene therapy has rapidly developed over the last three decades, with the first licensed pharmaceutical gene therapy product now available. After initial clinical trials discovered serious adverse events in the form of insertional oncogenesis, significant improvements in vector design have made the treatment a viable curative therapy. Cryopreservation has expanded the scope of gene therapy by increasing accessibility of the product to wider geographic locations. Targeted gene editing using engineered nucleases, while still in early stages of development, will further add to the repertoire of potential treatments available for PIDs.

Lentiviral gene therapy rescues p47phox chronic granulomatous disease and the ability to fight Salmonella infection in mice

Chronic granulomatous disease (CGD) is an inherited primary immunodeficiency disorder characterised by recurrent and often life-threatening infections and hyperinflammation. It is caused by defects of the phagocytic NADPH oxidase, a multicomponent enzyme system responsible for effective pathogen killing. A phase I/II clinical trial of lentiviral gene therapy is underway for the most common form of CGD, X-linked, caused by mutations in the gp91^phox subunit of the NADPH oxidase. We propose to use a similar strategy to tackle p47^phox-deficient CGD, caused by mutations in NCF1, which encodes the p47^phox cytosolic component of the enzymatic complex. We generated a pCCLCHIM-p47^phox lentiviral vector, containing the chimeric Cathepsin G/FES myeloid promoter and a codon-optimised version of the human NCF1 cDNA. Here we show that transduction with the pCCLCHIM-p47^phox vector efficiently restores p47^phox expression and biochemical NADPH oxidase function in p47^phox-deficient human and murine cells. We also tested the ability of our gene therapy approach to control infection by challenging p47^phox-null mice with Salmonella Typhimurium, a leading cause of sepsis in CGD patients, and found that mice reconstituted with lentivirus-transduced hematopoietic stem cells had a reduced bacterial load compared with untreated mice. Overall, our results potentially support the clinical development of a gene therapy approach using the pCCLCHIM-p47^phox vector.

β2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease

β2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant β (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding β2 integrin, but all β2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of β2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of β2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, β2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, β2 integrin activity on leukocytes has been implicated in tumor development.

Leukocyte adhesion defect: Where do we stand circa 2019?

Migration of polymorphonuclear leukocytes from bloodstream to the site of inflammation is an important event required for surveillance of foreign antigens. This trafficking of leukocytes from bloodstream to the tissue occurs in several distinct steps and involves several adhesion molecules. Defect in adhesion of leukocytes to vascular endothelium affecting their subsequent migration to extravascular space gives rise to a group of rare primary immunodeficiency diseases (PIDs) known as Leukocyte Adhesion Defects (LAD). Till date, four classes of LAD are discovered with LAD I being the most common form. LAD I is caused by loss of function of common chain, cluster of differentiation (CD)18 of β2 integrin family. These patients suffer from life-threatening bacterial infections and in its severe form death usually occurs in childhood without bone marrow transplantation. LAD II results from a general defect in fucose metabolism. These patients suffer from less severe bacterial infections and have growth and mental retardation. Bombay blood group phenotype is also observed in these patients. LAD III is caused by abnormal integrin activation. LAD III patients suffer from severe bacterial and fungal infections. Patients frequently show delayed detachment of umbilical cord, impaired wound healing and increased tendency to bleed. LAD IV is the most recently described class. It is caused by defects in β2 and α4β1 integrins which impairs lymphocyte adhesion. LAD IV patients have monogenic defect in cystic-fibrosis-transmembrane-conductance-regulator (CFTR) gene, resulting in cystic fibrosis. Pathophysiology and genetic etiology of all LAD syndromes are discussed in detail in this paper.

A novel mutation of the ITGB2 gene in a Chinese Zhuang minority patient with leukocyte adhesion deficiency type 1 and glucose-6-phosphate dehydrogenase deficiency

OBJECTIVES

To explore the clinical and molecular characteristics of a Chinese Zhuang minority patient with leukocyte adhesion deficiency type-1 (LAD-1) and glucose-6-phosphate dehydrogenase deficiency (G6PDD).

METHODS

Routine clinical and physical examinations were performed, and patient data was collected and analyzed. Protein expression levels of Itgb2 and glucose-6-phosphate dehydrogenase (G6pd) proteins were assessed by flow cytometry and the glucose-6-phosphate (G6P) substrate method, respectively. Whole exome sequencing was performed to investigate genetic variations of the patient and his parents.

RESULTS

The patient had fester disease and delayed separation of the umbilical cord at birth. Staphylococcus was detected in the fluid secretion of the auditory meatus of the patient. He exhibited a recurrent cheek scab, swollen hand, and swollen gum. Hematological examination indicated dramatic elevation of leukocytes including lymphocytes, monocytes, neutrophils and eosinophils. A novel homozygous mutation was detected in the ITGB2 gene of the patient, which was determined to be a two nucleotide deletion at the site of c.1537-1538 (c.1537-1538delGT), causing a frameshift of 24 amino acids from p.513 and inducing a stop codon (p.V513Lfs*24). A base substitution mutation was identified at c.1466 (c.1466G>T) of G6PD on chromosome X of the patient, which resulted in an amino acid change from arginine to leucine at p.489 (p.R489L). The patient also showed deficient lymphocyte expression of CD18 (2.99%) and significant downregulation of the G6pd protein.

CONCLUSIONS

The patient was diagnosed with G6PDD and moderate LAD-1. The combination of LAD-1 and G6PDD in this case may have been due to the high incidence of genetic disease in this minority ethnic population. Analyzing existing LAD-1 and G6PDD cases from different populations can facilitate disease diagnosis and treatment. Particularly, reporting pathogenic mutations of LAD-1 and G6PDD will be crucial for genetic testing and prenatal diagnosis in an effort to decrease the incidence of these diseases.

Advances in the gene therapy of monogenic blood cell diseases

Hematopoietic gene therapy has markedly progressed during the last 15 years both in terms of safety and efficacy. While a number of serious adverse events (SAE) were initially generated as a consequence of genotoxic insertions of gamma-retroviral vectors in the cell genome, no SAEs and excellent outcomes have been reported in patients infused with autologous hematopoietic stem cells (HSCs) transduced with self-inactivated lentiviral and gammaretroviral vectors. Advances in the field of HSC gene therapy have extended the number of monogenic diseases that can be treated with these approaches. Nowadays, evidence of clinical efficacy has been shown not only in primary immunodeficiencies, but also in other hematopoietic diseases, including beta-thalassemia and sickle cell anemia. In addition to the rapid progression of non-targeted gene therapies in the clinic, new approaches based on gene editing have been developed thanks to the discovery of designed nucleases and improved non-integrative vectors, which have markedly increased the efficacy and specificity of gene targeting to levels compatible with its clinical application. Based on advances achieved in the field of gene therapy, it can be envisaged that these therapies will soon be part of the therapeutic approaches used to treat life-threatening diseases of the hematopoietic system.

Gene Therapy Approaches to Immunodeficiency

Transfer of gene-corrected autologous hematopoietic stem cells in patients with primary immunodeficiencies has emerged as a new therapeutic approach. Patients with various conditions lacking a suitable donor have been treated with retroviral vectors and a gene-addition strategy. Initial promising results were shadowed by the occurrence of malignancies in some of these patients. Current trials, developed in the last decade, use safer viral vectors to overcome the risk of genotoxicity and have led to improved clinical outcomes. This review reflects the progresses made in specific disorders, including adenosine deaminase deficiency, X-linked severe combined immunodeficiency, chronic granulomatous disease, and Wiskott-Aldrich syndrome.

Evolving Gene Therapy in Primary Immunodeficiency

Prior to the first successful bone marrow transplant in 1968, patients born with severe combined immunodeficiency (SCID) invariably died. Today, with a widening availability of newborn screening, major improvements in the application of allogeneic procedures, and the emergence of successful hematopoietic stem and progenitor cell (HSC/P) gene therapy, the majority of these children can be identified and cured. Here, we trace key steps in the development of clinical gene therapy for SCID and other primary immunodeficiencies (PIDs), and review the prospects for adoption of new targets and technologies.

Lentiviral Vector Gene Therapy Protects XCGD Mice From Acute Staphylococcus aureus Pneumonia and Inflammatory Response

Chronic granulomatous disease (CGD) is a primary immunodeficiency due to a deficiency in one of the subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. CGD patients are characterized by an increased susceptibility to bacterial and fungal infections, and to granuloma formation due to the excessive inflammatory responses. Several gene therapy approaches with lentiviral vectors have been proposed but there is a lack of in vivo data on the ability to control infections and inflammation. We set up a mouse model of acute infection that closely mimic the airway infection in CGD patients. It involved an intratracheal injection of a methicillin-sensitive reference strain of S. aureus. Gene therapy, with hematopoietic stem cells transduced with regulated lentiviral vectors, restored the functional activity of NADPH oxidase complex (with 20-98% of dihydrorhodamine positive granulocytes and monocytes) and saved mice from death caused by S. aureus, significantly reducing the bacterial load and lung damage, similarly to WT mice even at low vector copy number. When challenged, gene therapy-treated XCGD mice showed correction of proinflammatory cytokines and chemokine imbalance at levels that were comparable to WT. Examined together, our results support the clinical development of gene therapy protocols using lentiviral vectors for the protection against infections and inflammation.