Function and Safety of Lentivirus-Mediated Gene Transfer for CSF2RA-Deficiency

A toxicology study of Csf2ra complementation and pulmonary macrophage transplantation therapy of hereditary PAP in mice

Pulmonary macrophage transplantation (PMT) is a gene and cell transplantation approach in development as therapy for hereditary pulmonary alveolar proteinosis (hPAP), a surfactant accumulation disorder caused by mutations in CSF2RA/B (and murine homologs). We conducted a toxicology study of PMT of Csf2ra gene-corrected macrophages (mGM-Rα+Mϕs) or saline-control intervention in Csf2raKO or wild-type (WT) mice including single ascending dose and repeat ascending dose studies evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics. Lentiviral-mediated Csf2ra cDNA transfer restored GM-CSF signaling in mGM-Rα+Mϕs. Following PMT, mGM-Rα+Mϕs engrafted, remained within the lungs, and did not undergo uncontrolled proliferation or result in bronchospasm, pulmonary function abnormalities, pulmonary or systemic inflammation, anti-transgene product antibodies, or pulmonary fibrosis. Aggressive male fighting caused a similarly low rate of serious adverse events in saline- and PMT-treated mice. Transient, minor pulmonary neutrophilia and exacerbation of pre-existing hPAP-related lymphocytosis were observed 14 days after PMT of the safety margin dose but not the target dose (5,000,000 or 500,000 mGM-Rα+Mϕs, respectively) and only in Csf2raKO mice but not in WT mice. PMT reduced lung disease severity in Csf2raKO mice. Results indicate PMT of mGM-Rα+Mϕs was safe, well tolerated, and therapeutically efficacious in Csf2raKO mice, and established a no adverse effect level and 10-fold safety margin.

Modulation of plasmacytoid dendritic cell and CD4+ T cell differentiation accompanied by upregulation of the cholinergic anti-inflammatory pathway induced by enterovirus 71

Enterovirus 71 (EV71) is a neurotropic enterovirus associated with hand, foot, and mouth disease (HFMD) fatalities. In this study, we investigated the impact of EV71 on plasmacytoid dendritic cells (pDCs) and CD4+ T cells. The results showed that pDCs were promptly activated, secreting interferon (IFN)-α and inducing CD4+ T cell proliferation and differentiation during early EV71 infection. This initiated adaptive immune responses and promoted proinflammatory cytokine production by CD4+ T cells. Over time, viral nucleic acids and proteins were synthesized in pDCs and CD4+ T cells. Concurrently, the cholinergic anti-inflammatory pathway (CAP) was activated, exhibiting an anti-inflammatory role. With constant viral stimulation, pDCs and CD4+ T cells showed reduced differentiation and cytokine secretion. Defects in pDCs were identified as a key factor in CD4+ T cell tolerance. CAP had a more significant regulatory effect on CD4+ T cells than on pDCs and was capable of inhibiting inflammation in these cells.

Pulmonary Alveolar Proteinosis and new therapeutic concepts

Pulmonary alveolar proteinosis (PAP) is an umbrella term used to refer to a pulmonary syndrome which is characterized by excessive accumulation of surfactant in the lungs of affected individuals. In general, PAP is a rare lung disease affecting children and adults, although its prevalence and incidence is variable among different countries. Even though PAP is a rare disease, it is a prime example on how modern medicine can lead to new therapeutic concepts, changing ways and techniques of (genetic) diagnosis which ultimately led into personalized treatments, all dedicated to improve the function of the impaired lung and thus life expectancy and quality of life in PAP patients. In fact, new technologies, such as new sequencing technologies, gene therapy approaches, new kind and sources of stem cells and completely new insights into the ontogeny of immune cells such as macrophages have increased our understanding in the onset and progression of PAP, which have paved the way for novel therapeutic concepts for PAP and beyond. As of today, classical monocyte-derived macrophages are known as important immune mediator and immune sentinels within the innate immunity. Furthermore, macrophages (known as tissue resident macrophages (TRMs)) can also be found in various tissues, introducing e. g. alveolar macrophages in the broncho-alveolar space as crucial cellular determinants in the onset of PAP and other lung disorders. Given recent insights into the onset of alveolar macrophages and knowledge about factors which impede their function, has led to the development of new therapies, which are applied in the context of PAP, with promising implications also for other diseases in which macrophages play an important role. Thus, we here summarize the latest insights into the various forms of PAP and introduce new pre-clinical work which is currently conducted in the framework of PAP, introducing new therapies for children and adults who still suffer from this severe, potentially life-threatening disease.

Emerging Treatments for Childhood Interstitial Lung Disease

Childhood interstitial lung disease (chILD) is a large and heterogeneous group of disorders characterized by diffuse lung parenchymal markings on chest imaging and clinical signs such as dyspnea and hypoxemia from functional impairment. While some children already present in the neonatal period with interstitial lung disease (ILD), others develop ILD during their childhood and adolescence. A timely and accurate diagnosis is essential to gauge treatment and improve prognosis. Supportive care can reduce symptoms and positively influence patients' quality of life; however, there is no cure for many of the chILDs. Current therapeutic options include anti-inflammatory or immunosuppressive drugs. Due to the rarity of the conditions and paucity of research in this field, most treatments are empirical and based on case series, and less than a handful of small, randomized trials have been conducted thus far. A trial on hydroxychloroquine yielded good safety but a much smaller effect size than anticipated. A trial in fibrotic disease with the multitargeted tyrosine kinase inhibitor nintedanib showed similar pharmacokinetics and safety as in adults. The unmet need for the treatment of chILDs remains high. This article summarizes current treatments and explores potential therapeutic options for patients suffering from chILD.

Alveolar macrophages in pulmonary alveolar proteinosis: origin, function, and therapeutic strategies

Pulmonary alveolar proteinosis (PAP) is a rare pulmonary disorder that is characterized by the abnormal accumulation of surfactant within the alveoli. Alveolar macrophages (AMs) have been identified as playing a pivotal role in the pathogenesis of PAP. In most of PAP cases, the disease is triggered by impaired cholesterol clearance in AMs that depend on granulocyte-macrophage colony-stimulating factor (GM-CSF), resulting in defective alveolar surfactant clearance and disruption of pulmonary homeostasis. Currently, novel pathogenesis-based therapies are being developed that target the GM-CSF signaling, cholesterol homeostasis, and immune modulation of AMs. In this review, we summarize the origin and functional role of AMs in PAP, as well as the latest therapeutic strategies aimed at addressing this disease. Our goal is to provide new perspectives and insights into the pathogenesis of PAP, and thereby identify promising new treatments for this disease.

Improving the Safety of Mesenchymal Stem Cell-Based Ex Vivo Therapy Using Herpes Simplex Virus Thymidine Kinase

Human mesenchymal stem cells (MSCs) are multipotent stem cells that have been intensively studied as therapeutic tools for a variety of disorders. To enhance the efficacy of MSCs, therapeutic genes are introduced using retroviral and lentiviral vectors. However, serious adverse events (SAEs) such as tumorigenesis can be induced by insertional mutagenesis. We generated lentiviral vectors encoding the wild-type herpes simplex virus thymidine kinase (HSV-TK) gene and a gene containing a point mutation that results in an alanine to histidine substitution at residue 168 (TK(A168H)) and transduced expression in MSCs (MSC-TK and MSC-TK(A168H)). Transduction of lentiviral vectors encoding the TK(A168H) mutant did not alter the proliferation capacity, mesodermal differentiation potential, or surface antigenicity of MSCs. The MSC-TK(A168H) cells were genetically stable, as shown by karyotyping. MSC-TK(A168H) responded to ganciclovir (GCV) with an half maximal inhibitory concentration (IC50) value 10-fold less than that of MSC-TK. Because MSC-TK(A168H) cells were found to be non-tumorigenic, a U87-TK(A168H) subcutaneous tumor was used as a SAE-like condition and we evaluated the effect of valganciclovir (vGCV), an oral prodrug for GCV. U87-TK(A168H) tumors were more efficiently ablated by 200 mg/kg vGCV than U87-TK tumors. These results indicate that MSC-TK(A168H) cells appear to be pre-clinically safe for therapeutic use. We propose that genetic modification with HSV-TK(A168H) makes allogeneic MSC-based ex vivo therapy safer by eliminating transplanted cells during SAEs such as uncontrolled cell proliferation.

Ex Vivo Generation of CAR Macrophages from Hematopoietic Stem and Progenitor Cells for Use in Cancer Therapy

Chimeric antigen receptor (CAR) T-cell therapies have shown impressive results in patients with hematological malignancies; however, little success has been achieved in the treatment of solid tumors. Recently, macrophages (MΦs) were identified as an additional candidate for the CAR approach, and initial proof of concept studies using peripheral blood-derived monocytes showed antigen-redirected activation of CAR MΦs. However, some patients may not be suitable for monocyte-apheresis, and prior cancer treatment regimens may negatively affect immune cell number and functionality. To address this problem, we here introduce primary human hematopoietic stem and progenitor cells (HSPCs) as a cell source to generate functional CAR MΦs ex vivo. Our data showed successful CAR expression in cord blood (CB)-derived HSPCs, with considerable cell expansion during differentiation to CAR MΦs. HSPC-derived MΦs showed typical MΦ morphology, phenotype, and basic anti-bacterial functionality. CAR MΦs targeting the carcinoembryonic antigen (CEA) and containing either a DAP12- or a CD3ζ-derived signaling domain showed antigen redirected activation as they secreted pro-inflammatory cytokines specifically upon contact with CEA⁺ target cells. In addition, CD3ζ-expressing CAR MΦs exhibited significantly enhanced phagocytosis of CEA⁺ HT1080 cells. Our data establish human HSPCs as a suitable cell source to generate functional CAR MΦs and further support the use of CAR MΦs in the context of solid tumor therapy.

New approaches to moderate CRISPR-Cas9 activity: Addressing issues of cellular uptake and endosomal escape

CRISPR-Cas9 is rapidly entering molecular biology and biomedicine as a promising gene-editing tool. A unique feature of CRISPR-Cas9 is a single-guide RNA directing a Cas9 nuclease toward its genomic target. Herein, we highlight new approaches for improving cellular uptake and endosomal escape of CRISPR-Cas9. As opposed to other recently published works, this review is focused on non-viral carriers as a means to facilitate the cellular uptake of CRISPR-Cas9 through endocytosis. The majority of non-viral carriers, such as gold nanoparticles, polymer nanoparticles, lipid nanoparticles, and nanoscale zeolitic imidazole frameworks, is developed with a focus toward optimizing the endosomal escape of CRISPR-Cas9 by taking advantage of the acidic environment in the late endosomes. Among the most broadly used methods for in vitro and ex vivo ribonucleotide protein transfection are electroporation and microinjection. Thus, other delivery formats are warranted for in vivo delivery of CRISPR-Cas9. Herein, we specifically revise the use of peptide and nanoparticle-based systems as platforms for CRISPR-Cas9 delivery in vivo. Finally, we highlight future perspectives of the CRISPR-Cas9 gene-editing tool and the prospects of using non-viral vectors to improve its bioavailability and therapeutic potential.

Pulmonary transplantation of alpha-1 antitrypsin (AAT)-transgenic macrophages provides a source of functional human AAT in vivo

Inherited deficiency of the antiprotease alpha-1 antitrypsin (AAT) is associated with liver failure and early-onset emphysema. In mice, in vivo lentiviral transduction of alveolar macrophages (AMs) has been described to yield protective pulmonary AAT levels and ameliorate emphysema development. We here investigated the pulmonary transplantation of macrophages (PMT) transgenic for AAT as a potential therapy for AAT deficiency-associated lung pathology. Employing third-generation SIN-lentiviral vectors expressing the human AAT cDNA from the CAG or Cbx-EF1α promoter, we obtained high-level AAT secretion in a murine AM cell line as well as murine bone marrow-derived macrophages differentiated in vitro (AAT MΦ). Secreted AAT demonstrated a physiologic glycosylation pattern as well as elastase-inhibitory and anti-apoptotic properties. AAT MΦ preserved normal morphology, surface phenotype, and functionality. Furthermore, in vitro generated murine AAT MΦ successfully engrafted in AM-deficient Csf2rb^-/- mice and converted into a CD11c⁺/Siglec-F⁺ AM phenotype as detected in bronchoalveolar lavage fluid and homogenized lung tissue 2 months after PMT. Moreover, human AAT was detected in the lung epithelial lining fluid of transplanted animals. Efficient AAT expression and secretion were also demonstrated for human AAT MΦ, confirming the applicability of our vectors in human cells.

Children's Interstitial and Diffuse Lung Diseases (ChILD) in 2020

The term children interstitial lung diseases (chILD) refers to a heterogeneous group of rare diseases that diffusely affect the lung. ChILD specific to children younger than 2 years of age include diffuse developmental disorders, growth abnormalities, specific conditions of undefined etiology (neuroendocrine cell hyperplasia of infancy and pulmonary interstitial glycogenosis) and surfactant protein disorders. Clinical manifestations are highly variable, ranging from the absence of relevant symptoms to a severe onset. Most commonly, chILD presents with nonspecific respiratory signs and symptoms, such as dyspnea, polypnea, dry cough, wheezing, recurrent respiratory infections and exercise intolerance. In the diagnostic approach to a child with suspected ILD, chest high resolution computed tomography and genetic tests play a central role. Then, if the diagnosis remains uncertain, laryngotracheal-bronchoscopy and lung biopsy are needed. Pharmacological treatment is mostly empiric and based on anti-inflammatory and immunomodulatory drugs including corticosteroids, hydroxychloroquine and azithromycin. Despite chILD overall rarity, pediatric pulmonologists must be familiar with these diseases in order to carry out a timely diagnosis and patient treatment.

Effective hematopoietic stem cell-based gene therapy in a murine model of hereditary pulmonary alveolar proteinosis

Hereditary pulmonary alveolar proteinosis due to GM-CSF receptor deficiency (herPAP) constitutes a life-threatening lung disease characterized by alveolar deposition of surfactant protein secondary to defective alveolar macrophage function. As current therapeutic options are primarily symptomatic, we have explored the potential of hematopoietic stem cell-based gene therapy. Using Csf2rb^-/- mice, a model closely reflecting the human herPAP disease phenotype, we here demonstrate robust pulmonary engraftment of an alveolar macrophage population following intravenous transplantation of lentivirally corrected hematopoietic stem and progenitor cells. Engraftment was associated with marked improvement of critical herPAP disease parameters, including bronchoalveolar fluid protein, cholesterol and cytokine levels, pulmonary density on computed tomography scans, pulmonary deposition of Periodic Acid-Schiff⁺ material as well as respiratory mechanics. These effects were stable for at least nine months. With respect to engraftment and alveolar macrophage differentiation kinetics, we demonstrate the rapid development of CD11c⁺/SiglecF⁺ cells in the lungs from a CD11c^-/SiglecF⁺ progenitor population within four weeks after transplantation. Based on these data, we suggest hematopoietic stem cell-based gene therapy as an effective and cause-directed treatment approach for herPAP.

Long-Term Safety and Efficacy of Gene-Pulmonary Macrophage Transplantation Therapy of PAP in Csf2ra-/- Mice

Hereditary pulmonary alveolar proteinosis (PAP) is a genetic lung disease characterized by surfactant accumulation and respiratory failure arising from disruption of GM-CSF signaling. While mutations in either CSF2RA or CSF2RB (encoding GM-CSF receptor α or β chains, respectively) can cause PAP, α chain mutations are responsible in most patients. Pulmonary macrophage transplantation (PMT) is a promising new cell therapy in development; however, no studies have evaluated this approach for hereditary PAP (hPAP) caused by Csf2ra mutations. Here, we report on the preclinical safety, tolerability, and efficacy of lentiviral-vector (LV)-mediated Csf2ra expression in macrophages and PMT of gene-corrected macrophages (gene-PMT therapy) in Csf2ra gene-ablated (Csf2ra^-/-) mice. Gene-PMT therapy resulted in a stable transgene integration and correction of GM-CSF signaling and functions in Csf2ra^-/- macrophages in vitro and in vivo and resulted in engraftment and long-term persistence of gene-corrected macrophages in alveoli; restoration of pulmonary surfactant homeostasis; correction of PAP-specific cytologic, histologic, and biomarker abnormalities; and reduced inflammation associated with disease progression in untreated mice. No adverse consequences of gene-PMT therapy in Csf2ra^-/- mice were observed. Results demonstrate that gene-PMT therapy of hPAP in Csf2ra^-/- mice was highly efficacious, durable, safe, and well tolerated.

The influence of genetics on therapeutic developments in pulmonary alveolar proteinosis

PURPOSE OF REVIEW

Pulmonary alveolar proteinosis (PAP) is characterized by the massive accumulation of lipoproteinaceous material within alveoli, which results in progressive respiratory failure. The abnormalities in surfactant clearance are caused by defective pulmonary macrophages, whose terminal differentiation is GM-CSF-dependent. In hereditary PAP, the rupture of GM-CSF signaling is because of mutations in the GM-CSF receptor genes. This review focus on the innovative technologies of gene-correction proposed for the development of new therapeutic strategies, for hereditary PAP patients.

RECENT FINDINGS

Hematopoietic stem cell gene therapy has been successfully experimented in murine models to restore the expression of the GM-CSF receptor, however, a therapeutic approach based on bone marrow transplantation requires a preconditioning, which could be hazardous in PAP patients, who are highly susceptible to pulmonary infections. Gene-corrected pulmonary macrophages, administered directly to the lung, could represent an improved approach. Finally, patient-derived induced pluripotent stem cells seem to be promising to overcome the limited availability of primary patient cells and to generate gene-corrected macrophages, able to recover pulmonary surfactant clearance.

SUMMARY

WLL is the gold standard therapy for PAP. However, its use in hereditary PAP is limited by the difficulty of performing this technique in paediatric patients and by its purely symptomatic efficacy. The recent advances in genome engineering could provide efficacious strategies for clinical application.

Pulmonary alveolar proteinosis in adults: pathophysiology and clinical approach

Pulmonary alveolar proteinosis (PAP) is a diffuse lung disease that results from the accumulation of lipoproteinaceous material in the alveoli and alveolar macrophages due to abnormal surfactant homoeostasis. Identification of the granulocyte-macrophage colony-stimulating factor (GM-CSF) as an indispensable mediator of macrophage maturation and surfactant catabolism was the key discovery leading to the current understanding of the pathogenesis of most forms of PAP. Impaired GM-CSF bioavailability due to anti-GM-CSF autoimmunity is the cause of approximately 90% of adult PAP cases. Abnormal macrophage function due to endogenous or exogenous triggers, GM-CSF receptor defects, and other genetic abnormalities of surfactant production account for the remainder of causes. The usual physiological consequence of PAP is impairment of gas exchange, which can lead to dyspnoea, hypoxaemia, or even respiratory failure and death. Pulmonary fibrosis occurs occasionally in patients with PAP. For patients with moderate to severe disease, whole lung lavage is still the first-line treatment of choice. Supplemental GM-CSF is also useful, but details about indications, choice of agent, and dosing remain unclear. Other therapies, including rituximab, plasmapheresis, and lung transplantation have been described but should be reserved for refractory cases.