Lentiviral vectors for the treatment of primary immunodeficiencies

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.

Primary Immunodeficiency in the NICU

Primary immunodeficiency disorders (PIDs) are genetic diseases that lead to increased susceptibility to infection. Hundreds of PIDs have now been described, but a select subset commonly presents in the neonatal period. Neonates, especially premature newborns, have relative immune immaturity that makes it challenging to differentiate PIDs from intrinsic immaturity. Nonetheless, early identification and appropriate management of PIDs are critical, and the neonatal clinician should be familiar with a range of PIDs and their presentations. The neonatal clinician should also be aware of the importance of consulting with an immunologist when a PID is suspected. The role of newborn screening for severe combined immunodeficiency, as well as the initial steps of laboratory evaluation for a PID should be familiar to those caring for neonates. Finally, it is important for providers to be familiar with the initial management steps that can be taken to reduce the risk of infection in affected patients.

Gene therapy for primary immunodeficiency

Gene therapy is now being trialled as a therapeutic option for an expanding number of conditions, based primarily on the successful treatment over the past two decades of patients with specific primary immunodeficiencies (PIDs) including severe combined immunodeficiency and Wiskott–Aldrich syndrome and metabolic conditions such as leukodystrophy. The field has evolved from the use of gammaretroviral vectors to more sophisticated lentiviral platforms that offer an improved biosafety profile alongside greater efficiency for hematopoietic stem cells gene transfer. Here we review more recent developments including licensing of gene therapies, use of gene corrected autologous T cells as an alternative strategy for some PIDs and the potential of targeted gene correction using various gene editing platforms. Given the promising results of recent clinical trials, it is likely that autologous gene therapies will become standard of care for a number of devastating diseases in the coming decade.

Integrating HDAd5/35++ Vectors as a New Platform for HSC Gene Therapy of Hemoglobinopathies

We generated an integrating, CD46-targeted, helper-dependent adenovirus HDAd5/35++ vector system for hematopoietic stem cell (HSC) gene therapy. The ∼12-kb transgene cassette included a β-globin locus control region (LCR)/promoter driven human γ-globin gene and an elongation factor alpha-1 (EF1α)-mgmtP140K expression cassette, which allows for drug-controlled increase of γ-globin-expressing erythrocytes. We transduced bone marrow lineage-depleted cells from human CD46-transgenic mice and transplanted them into lethally irradiated recipients. The percentage of γ-globin-positive cells in peripheral blood erythrocytes in primary and secondary transplant recipients was stable and greater than 90%. The γ-globin level was 10%-20% of adult mouse globin. Transgene integration, mediated by a hyperactive Sleeping Beauty SB100x transposase, was random, without a preference for genes. A second set of studies was performed with peripheral blood CD34+ cells from mobilized donors. 10 weeks after transplantation of transduced cells, human cells were harvested from the bone marrow and differentiated ex vivo into erythroid cells. Erythroid cells expressed γ-globin at a level of 20% of adult α-globin. Our studies suggest that HDAd35++ vectors allow for efficient transduction of long-term repopulating HSCs and high-level, almost pancellular γ-globin expression in erythrocytes. Furthermore, our HDAd5/35++ vectors have a larger insert capacity and a safer integration pattern than currently used lentivirus vectors.

NADPH Oxidase Deficiency: A Multisystem Approach

The immune system is a complex system able to recognize a wide variety of host agents, through different biological processes. For example, controlled changes in the redox state are able to start different pathways in immune cells and are involved in the killing of microbes. The generation and release of ROS in the form of an “oxidative burst” represent the pivotal mechanism by which phagocytic cells are able to destroy pathogens. On the other hand, impaired oxidative balance is also implicated in the pathogenesis of inflammatory complications, which may affect the function of many body systems. NADPH oxidase (NOX) plays a pivotal role in the production of ROS, and the defect of its different subunits leads to the development of chronic granulomatous disease (CGD). The defect of the different NOX subunits in CGD affects different organs. In this context, this review will be focused on the description of the effect of NOX2 deficiency in different body systems. Moreover, we will also focus our attention on the novel insight in the pathogenesis of immunodeficiency and inflammation-related manifestations and on the protective role of NOX2 deficiency against the development of atherosclerosis.

Novel GP64 envelope variants for improved delivery to human airway epithelial cells

Lentiviral vectors pseudotyped with the baculovirus envelope protein GP64 transduce primary cultures of human airway epithelia (HAE) at their apical surface. Our goal in this study was to harness a directed evolution approach to develop a novel envelope glycoprotein with increased transduction properties for HAE. Using error-prone PCR, a library of GP64 mutants was generated and used to prepare a diverse pool of lentiviral virions pseudotyped with GP64 variants. The library was serially passaged on HAE and three GP64 mutations were recovered. Single-, double- and the triple-combination mutant envelope glycoproteins were compared with wild-type GP64 for their ability to transduce HAE. Our results suggest that lentiviral vectors pseudotyped with evolved GP64 transduced HAE with greater efficiency than wild-type GP64. This effect was not observed in primary cultures of porcine airway epithelial cells, suggesting that the directed evolution protocol was species specific. In summary, our studies indicate that serial passage of a GP64 mutant library yielded specific variants with improved HAE cell tropism, yielding tools with the potential to improve the success of gene therapy for airway diseases.

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.

A Simple High Efficiency Intra-Islet Transduction Protocol Using Lentiviral Vectors

Successful normalization of blood glucose in patients transplanted with pancreatic islets isolated from cadaveric donors established the proof-of-concept that Type 1 Diabetes Mellitus is a curable disease. Nonetheless, major caveats to the widespread use of this cell therapy approach have been the shortage of islets combined with the low viability and functional rates subsequent to transplantation. Gene therapy targeted to enhance survival and performance prior to transplantation could offer a feasible approach to circumvent these issues and sustain a durable functional β-cell mass in vivo. However, efficient and safe delivery of nucleic acids to intact islet remains a challenging task. Here we describe a simple and easy-to-use lentiviral transduction protocol that allows the transduction of approximately 80 % of mouse and human islet cells while preserving islet architecture, metabolic function and glucose-dependent stimulation of insulin secretion. Our protocol will facilitate to fully determine the potential of gene expression modulation of therapeutically promising targets in entire pancreatic islets for xenotransplantation purposes.

Clinical applications of gene therapy for primary immunodeficiencies

Primary immunodeficiencies (PIDs) have represented a paradigmatic model for successes and pitfalls of hematopoietic stem cells gene therapy. First clinical trials performed with gamma retroviral vectors (γ-RV) for adenosine deaminase severe combined immunodeficiency (ADA-SCID), X-linked SCID (SCID-X1), and Wiskott-Aldrich syndrome (WAS) showed that gene therapy is a valid therapeutic option in patients lacking an HLA-identical donor. No insertional mutagenesis events have been observed in more than 40 ADA-SCID patients treated so far in the context of different clinical trials worldwide, suggesting a favorable risk-benefit ratio for this disease. On the other hand, the occurrence of insertional oncogenesis in SCID-X1, WAS, and chronic granulomatous disease (CGD) RV clinical trials prompted the development of safer vector construct based on self-inactivating (SIN) retroviral or lentiviral vectors (LVs). Here we present the recent results of LV-mediated gene therapy for WAS showing stable multilineage engraftment leading to hematological and immunological improvement, and discuss the differences with respect to the WAS RV trial. We also describe recent clinical results of SCID-X1 gene therapy with SIN γ-RV and the perspectives of targeted genome editing techniques, following early preclinical studies showing promising results in terms of specificity of gene correction. Finally, we provide an overview of the gene therapy approaches for other PIDs and discuss its prospects in relation to the evolving arena of allogeneic transplant.

Overview of Immunodeficiency Disorders

The spectrum of primary immunodeficiency disorders (PIDs) is expanding. It includes typical disorders that primarily present with defective immunity as well as disorders that predominantly involve other systems and show few features of impaired immunity. The rapidly growing list of new immunodeficiency disorders and treatment modalities makes it imperative for providers to stay abreast of the latest and best management strategies. This article presents a brief overview of recent clinical advances in PIDs.

Progress in gene therapy for primary immunodeficiencies using lentiviral vectors

PURPOSE OF REVIEW

This review gives an overview over the most recent progress in the field of lentiviral gene therapy for primary immunodeficiencies (PIDs). The history and state-of-the-art of lentiviral vector development are summarized and the recent advancements for a number of selected diseases are reviewed in detail. Past retroviral vector trials for these diseases, the most recent improvements of lentiviral vector platforms and their application in preclinical development as well as ongoing clinical trials are discussed.

RECENT FINDINGS

Main focus is on the preclinical studies and clinical trials for the treatment of Wiskott-Aldrich syndrome, chronic granulomatous disease, adenosine deaminase deficient severe combined immunodeficiency (ADA-SCID) and X-linked severe combined immunodeficiency with lentiviral gene therapy.

SUMMARY

Gene therapy for PIDs is an effective treatment, providing potential long-term clinical benefit for affected patients. Substantial progress has been made to make lentiviral gene therapy platforms available for a number of rare genetic diseases. Although many ongoing gene therapy trials are based on ex-vivo approaches with autologous hematopoietic stem cells, other approaches such as in-vivo gene therapy or gene-repair platforms might provide further advancement for certain PIDs.