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.

Macrophage-based delivery of anti-fibrotic proteins alleviates bleomycin-induced pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by chronic, progressive, and fibrotic lung injury. Although remarkable progress has been made toward understanding the pathogenesis of PF, finding more effective treatments for this fatal disease remains a challenge. In this study, we describe an innovative macrophage-based approach to deliver anti-fibrotic protein to the lung and inhibit PF in a mouse model of bleomycin (BLM)-induced lung injury. We engineered macrophages to continuously secrete three types of proteins: interleukin-10, which prevents inflammation; TGFRcFc, a soluble truncated TGF-βR2 that blocks TGF-β; and CD147, which induces matrix metalloproteinases (MMPs) and causes collagen degradation. Infusing these engineered macrophages into the lungs of BLM-induced PF mouse models in an optimal pattern significantly ameliorated PF in mice. Specifically, the most effective therapeutic outcome was achieved by infusing IL-10-secreting macrophages on day 1, followed by TGFRcFc-secreting macrophages on day 7 and CD147-secreting macrophages on day 14 into the same mice after BLM treatment. Our data suggest that macrophage-based delivery of anti-fibrotic proteins to the lungs is a promising therapy for fibrotic lung disorders.

Aerosol pulmonary immune engineering

Aerosolization of immunotherapies poses incredible potential for manipulating the local mucosal-specific microenvironment, engaging specialized pulmonary cellular defenders, and accessing mucosal associated lymphoid tissue to redirect systemic adaptive and memory responses. In this review, we breakdown key inhalable immunoengineering strategies for chronic, genetic, and infection-based inflammatory pulmonary disorders, encompassing the historic use of immunomodulatory agents, the transition to biological inspired or derived treatments, and novel approaches of complexing these materials into drug delivery vehicles for enhanced release outcomes. Alongside a brief description of key immune targets, fundamentals of aerosol drug delivery, and preclinical pulmonary models for immune response, we survey recent advances of inhaled immunotherapy platforms, ranging from small molecules and biologics to particulates and cell therapies, as well as prophylactic vaccines. In each section, we address the formulation design constraints for aerosol delivery as well as advantages for each platform in driving desirable immune modifications. Finally, prospects of clinical translation and outlook for inhaled immune engineering are discussed.

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.

Gene therapy of Csf2ra deficiency in mouse fetal monocyte precursors restores alveolar macrophage development and function

Tissue-resident macrophage-based immune therapies have been proposed for various diseases. However, generation of sufficient numbers that possess tissue-specific functions remains a major handicap. Here, we showed that fetal liver monocytes cultured with GM-CSF (CSF2-cFLiMo) rapidly differentiated into a long-lived, homogeneous alveolar macrophage–like population in vitro. CSF2-cFLiMo retained the capacity to develop into bona fide alveolar macrophages upon transfer into Csf2ra^–/– neonates and prevented development of alveolar proteinosis and accumulation of apoptotic cells for at least 1 year in vivo. CSF2-cFLiMo more efficiently engrafted empty alveolar macrophage niches in the lung and protected mice from severe pathology induced by respiratory viral infection compared with transplantation of macrophages derived from BM cells cultured with M-CSF (CSF1-cBMM) in the presence or absence of GM-CSF. Harnessing the potential of this approach for gene therapy, we restored a disrupted Csf2ra gene in fetal liver monocytes and demonstrated their capacity to develop into alveolar macrophages in vivo. Altogether, we provide a platform for generation of immature alveolar macrophage–like precursors amenable for genetic manipulation, which will be useful to dissect alveolar macrophage development and function and for pulmonary transplantation therapy.

Long-term culture-expanded alveolar macrophages restore their full epigenetic identity after transfer in vivo

Alveolar macrophages (AMs) are lung tissue-resident macrophages that can be expanded in culture, but it is unknown to what extent culture affects their in vivo identity. Here we show that mouse long-term ex vivo expanded AMs (exAMs) maintained a core AM gene expression program, but showed culture adaptations related to adhesion, metabolism and proliferation. Upon transplantation into the lung, exAMs reacquired full transcriptional and epigenetic AM identity, even after several months in culture and could self-maintain long-term in the alveolar niche. Changes in open chromatin regions observed in culture were fully reversible in transplanted exAMs and resulted in a gene expression profile indistinguishable from resident AMs. Our results indicate that long-term proliferation of AMs in culture did not compromise cellular identity in vivo. The robustness of exAM identity provides new opportunities for mechanistic analysis and highlights the therapeutic potential of exAMs.

Single-Cell RNA Sequencing of Human Pluripotent Stem Cell-Derived Macrophages for Quality Control of The Cell Therapy Product

Macrophages exhibit high plasticity to achieve their roles in maintaining tissue homeostasis, innate immunity, tissue repair and regeneration. Therefore, macrophages are being evaluated for cell-based therapeutics against inflammatory disorders and cancer. To overcome the limitation related to expansion of primary macrophages and cell numbers, human pluripotent stem cell (hPSC)-derived macrophages are considered as an alternative source of primary macrophages for clinical application. However, the quality of hPSC-derived macrophages with respect to the biological homogeneity remains still unclear. We previously reported a technique to produce hPSC-derived macrophages referred to as iMACs, which is amenable for scale-up. In this study, we have evaluated the biological homogeneity of the iMACs using a transcriptome dataset of 6,230 iMACs obtained by single-cell RNA sequencing. The dataset provides a valuable genomic profile for understanding the molecular characteristics of hPSC-derived macrophage cells and provide a measurement of transcriptomic homogeneity. Our study highlights the usefulness of single cell RNA-seq data in quality control of the cell-based therapy products.

IL-6-elafin genetically modified macrophages as a lung immunotherapeutic strategy against Pseudomonas aeruginosa infections

Pseudomonas aeruginosa (P.a) infections are a major public health issue in ventilator-associated pneumoniae, cystic fibrosis, and chronic obstructive pulmonary disease exacerbations. P.a is multidrug resistant, and there is an urgent need to develop new therapeutic approaches. Here, we evaluated the effect of direct pulmonary transplantation of gene-modified (elafin and interleukin [IL]-6) syngeneic macrophages in a mouse model of acute P.a infection. Wild-type (WT) or Elafin-transgenic (eTg) alveolar macrophages (AMs) or bone marrow-derived macrophages (BMDMs) were recovered from bronchoalveolar lavage or generated from WT or eTg mouse bone marrow. Cells were modified with adenovirus IL-6 (Ad-IL-6), characterized in vitro, and transferred by oropharyngeal instillation in the lungs of naive mice. The protective effect was assessed during P.a acute infection (survival studies, mechanistic studies of the inflammatory response). We show that a single bolus of genetically modified syngeneic AMs or BMDMs provided protection in our P.a-induced model. Mechanistically, Elafin-modified AMs had an IL-6-IL-10-IL-4R-IL-22-antimicrobial molecular signature that, in synergy with IL-6, enhanced epithelial cell proliferation and tissue repair in the alveolar unit. We believe that this innovative cell therapy strategy could be of value in acute bacterial infections in the lung.

Autocrine, Paracrine, and Endocrine Signals That Can Alter Alveolar Macrophages Function

Alveolar macrophages (AMs) are extremely versatile cells with complex functions involved in health or diseases such as pneumonia, asthma, and pulmonary alveolar proteinosis. In recent years, it has been widely identified that the different functions and states of macrophages are the results from the complex interplay between microenvironmental signals and macrophage lineage. Diverse and complicated signals to which AMs respond are mentioned when they are described individually or in a particular state of AMs. In this review, the microenvironmental signals are divided into autocrine, paracrine, and endocrine signals based on their secreting characteristics. This new perspective on classification provides a more comprehensive and systematic introduction to the complex signals around AMs and is helpful for understanding the roles of AMs affected by physiological environment. The existing possible treatments of AMs are also mentioned in it. The thorough understanding of AMs signals modulation may be contributed to the development of more effective therapies for AMs-related lung diseases.

Advanced In Vitro Lung Models for Drug and Toxicity Screening: The Promising Role of Induced Pluripotent Stem Cells

The substantial socioeconomic burden of lung diseases, recently highlighted by the disastrous impact of the coronavirus disease 2019 (COVID-19) pandemic, accentuates the need for interventive treatments capable of decelerating disease progression, limiting organ damage, and contributing to a functional tissue recovery. However, this is hampered by the lack of accurate human lung research models, which currently fail to reproduce the human pulmonary architecture and biochemical environment. Induced pluripotent stem cells (iPSCs) and organ-on-chip (OOC) technologies possess suitable characteristics for the generation of physiologically relevant in vitro lung models, allowing for developmental studies, disease modeling, and toxicological screening. Importantly, these platforms represent potential alternatives for animal testing, according to the 3Rs (replace, reduce, refine) principle, and hold promise for the identification and approval of new chemicals under the European REACH (registration, evaluation, authorization and restriction of chemicals) framework. As such, this review aims to summarize recent progress made in human iPSC- and OOC-based in vitro lung models. A general overview of the present applications of in vitro lung models is presented, followed by a summary of currently used protocols to generate different lung cell types from iPSCs. Lastly, recently developed iPSC-based lung models are discussed.

Pulmonary macrophages and their different roles in health and disease

Macrophages are a heterogeneous population of myeloid cells with phenotype and function modulated according to the microenvironment in which they are found. The lung resident macrophages known as Alveolar Macrophages (AM) and Interstitial Macrophages (IM) are localized in two different compartments. During lung homeostasis, macrophages can remove inhaled particulates, cellular debris and contribute to some metabolic processes. Macrophages may assume a pro-inflammatory phenotype after being classically activated (M1) or anti-inflammatory when being alternatively activated (M2). M1 and M2 have different transcription profiles and act by eliminating bacteria, viruses and fungi from the host or repairing the damage triggered by inflammation, respectively. Nevertheless, macrophages also may contribute to lung damage during persistent inflammation or continuous exposure to antigens. In this review, we discuss the origin and function of pulmonary macrophages in the context of homeostasis, infectious and non-infectious lung diseases.

Impact of injection buffer volume to perform bronchoalveolar lavage fluid collection for isolating alveolar macrophages to investigate fine particle-induced IL-1α secretion

The importance of alveolar macrophages has been reported in many toxicology/immunology studies. Alveolar macrophages release interleukin (IL)-1α as a damage-associated molecular pattern (DAMP) when stimulated by fine particles. However, it is unclear whether cell isolation procedures affect ex vivo particle-induced responses in primary mouse alveolar macrophages (mAM). In this study, effects of injection buffer volume used to perform bronchoalveolar lavage fluid (BALF) collection to isolate mAM for use in ex vivo particle-induced responses were assessed. Among the mAM obtained from BALF collected using a 0.55 or 0.75 ml, but not a 1.0 ml buffer injection volume, decreased cell viability and IL-1α release were observed when cells were stimulated ex vivo with silica crystal or aluminum salt. Injected buffer composition did not affect the IL-1α release. On the other hand, IL-6 secretion induced by lipopolysaccharide (LPS) did not differ among mAM obtained from BALF collected using the different volumes. Expression levels of cell surface markers like CD11c, SiglecF, and CD64 did not differ among mAM obtained from BALF collected using the different injection buffer volumes. IL-1α release (and also necroptosis) induced by ex vivoparticle stimulation was suppressed by RIPK3 inhibitor or cytochalasin D co-treatment. Decreases in RIPK3 phosphorylation were noted in mAM obtained in BALF collected using the 1.0 ml injection volume compared with mAM obtained in BALF using 0.55 or 0.75 ml buffer. These observations illustrate that larger volumes of buffer used to collect BALF from mice can affect sensitivity of the isolated mAM to ex vivo particle-induced responses by inhibiting their functions.

Targeting monocytes/macrophages in fibrosis and cancer diseases: Therapeutic approaches

Over almost 140 years since their identification, the knowledge about macrophages has unbelievably evolved. The 'big eaters' from being thought of as simple phagocytic cells have been recognized as master regulators in immunity, homeostasis, healing/repair and organ development. Long considered to originate exclusively from bone marrow-derived circulating monocytes, macrophages have been also demonstrated to be the first immune cells colonizing tissues in the developing embryo and persisting in adult life by self-renewal, as long-lived tissue resident macrophages. Therefore, heterogeneous populations of macrophages with different ontogeny and functions co-exist in tissues. Macrophages act as sentinels of homeostasis and are intrinsically programmed to lead the wound healing and repair processes that occur after injury. However, in certain pathological circumstances macrophages get dysfunctional, and impaired or aberrant macrophage activities become key features of diseases. For instance, in both fibrosis and cancer, that have been defined 'wounds that do not heal', dysfunctional monocyte-derived macrophages overall play a key detrimental role. On the other hand, due to their plasticity these cells can be 're-educated' and exert anti-fibrotic and anti-cancer functions. Therefore macrophages represent an important therapeutic target in both fibrosis and cancer diseases. The current review will illustrate new insights into the role of monocytes/macrophages in these devastating diseases and summarize new therapeutic strategies and applications of macrophage-targeted drug development in their clinical setting.

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.

ReMeDy: a platform for integrating and sharing published stem cell research data with a focus on iPSC trials

ABSTRACT

Recent regenerative medicine studies have emphasized the need for increased standardization, harmonization and sharing of information related to stem cell product characterization, to help drive these innovative interventions toward public availability and to increase collaboration in the scientific community. Although numerous attempts and numerous databases have been made to manage these data, a platform that incorporates all the heterogeneous data collected from stem cell projects into a harmonized project-based framework is still lacking. The aim of the database, which is described in this study, is to provide an intelligent informatics solution that integrates comprehensive characterization of diverse stem cell product characteristics with research subject and project outcome information. In the resulting platform, heterogeneous data are validated using predefined ontologies and stored in a relational database, to ensure data quality and ease of access. Testing was performed using 51 published, publically available induced pluripotent stem cell projects conducted in clinical, preclinical and in-vitro evaluations. Future aims of this project include further increasing the database size to include all published stem cell trials and develop additional data visualization tools to improve usability. Our testing demonstrated the robustness of the proposed platform, by seamlessly harmonizing diverse common data elements, and the potential of this platform for driving knowledge generation from the aggregation and harmonization of these diverse data.

DATABASE URL

https://remedy.mssm.edu/.

Selection Criteria for Lung Transplantation: Controversies and New Developments

Lung transplantation is an accepted therapeutic option for end-stage lung diseases. The imbalance between limited availability and vast need of donor organs necessitates careful selection of recipient candidates, ensuring the best possible utilization of the scarce resource of organs. Nonetheless, possible lung transplant candidates who could experience a meaningful improvement in survival and quality of life should not be excluded solely based on the complexity of their case. In this review, controversial issues or difficult limitations for lung transplantation, and new developments in recipient selection criteria, are discussed, which may help broaden recipient eligibility for lung transplantation without compromising long-term outcomes.

Beyond "Big Eaters": The Versatile Role of Alveolar Macrophages in Health and Disease

Macrophages act as immune scavengers and are important cell types in the homeostasis of various tissues. Given the multiple roles of macrophages, these cells can also be found as tissue resident macrophages tightly integrated into a variety of tissues in which they fulfill crucial and organ-specific functions. The lung harbors at least two macrophage populations: interstitial and alveolar macrophages, which occupy different niches and functions. In this review, we provide the latest insights into the multiple roles of alveolar macrophages while unraveling the distinct factors which can influence the ontogeny and function of these cells. Furthermore, we will highlight pulmonary diseases, which are associated with dysfunctional macrophages, concentrating on congenital diseases as well as pulmonary infections and impairment of immunological pathways. Moreover, we will provide an overview about different treatment approaches targeting macrophage dysfunction. Improved knowledge of the role of macrophages in the onset of pulmonary diseases may provide the basis for new pharmacological and/or cell-based immunotherapies and will extend our understanding to other macrophage-related disorders.

Restored Macrophage Function Ameliorates Disease Pathophysiology in a Mouse Model for IL10 Receptor-deficient Very Early Onset Inflammatory Bowel Disease

BACKGROUND AND AIMS

Mutations in IL10 or the IL10 receptor lead to very early onset [VEO] inflammatory bowel disease [IBD], a life-threatening disease which is often unresponsive to conventional medication. Recent studies have demonstrated that defective IL-10 receptor signalling in innate immune cells is a key driver of severe intestinal inflammation in VEO-IBD. Specifically, IL10 unresponsiveness of macrophages, which govern the tight balance between pro- and anti-inflammatory responses in the intestinal system, plays a central role in the events leading to excessive inflammatory responses and the development of IBD.

METHODS AND RESULTS

We here evaluated haematopoietic stem cell gene therapy in a VEO-IBD mouse model and demonstrated that the therapeutic response closely correlates with gene correction of the IL10 signalling pathway in intestinal macrophages. This finding prompted us to evaluate the therapeutic efficacy of macrophage transplantation in the Il10rb-/- VEO-IBD mouse model. A 6-week regimen employing a combination of depletion of endogenous hyperinflammatory macrophages followed by intraperitoneal administration of wild-type [WT] macrophages significantly reduced colitis symptoms.

CONCLUSIONS

In summary, we show that the correction of the IL10 receptor defect in macrophages, either by genetic therapy or transfer of WT macrophages to the peritoneum, can ameliorate disease-related symptoms and potentially represent novel treatment approaches for VEO-IBD patients.

The lung microenvironment shapes a dysfunctional response of alveolar macrophages in aging

Alveolar macrophages orchestrate the response to viral infections. Age-related changes in these cells may underlie the differential severity of pneumonia in older patients. We performed an integrated analysis of single-cell RNA-Seq data that revealed homogenous age-related changes in the alveolar macrophage transcriptome in humans and mice. Using genetic lineage tracing with sequential injury, heterochronic adoptive transfer, and parabiosis, we found that the lung microenvironment drove an age-related resistance of alveolar macrophages to proliferation that persisted during influenza A viral infection. Ligand-receptor pair analysis localized these changes to the extracellular matrix, where hyaluronan was increased in aged animals and altered the proliferative response of bone marrow-derived macrophages to granulocyte macrophage colony-stimulating factor (GM-CSF). Our findings suggest that strategies targeting the aging lung microenvironment will be necessary to restore alveolar macrophage function in aging.

In-Depth Immune-Oncology Studies of the Tumor Microenvironment in a Humanized Melanoma Mouse Model

The presence and interaction of immune cells in the tumor microenvironment is of significant importance and has a great impact on disease progression and response to therapy. Hence, their identification is of high interest for prognosis and treatment decisions. Besides detailed phenotypic analyses of immune, as well as tumor cells, spatial analyses is an important parameter in the complex interplay of neoplastic and immune cells—especially when moving into focus efforts to develop and validate new therapeutic strategies. Ex vivo analysis of tumor samples by immunohistochemistry staining methods conserves spatial information is restricted to single markers, while flow cytometry (disrupting tissue into single cell suspensions) provides access to markers in larger numbers. Nevertheless, this comes at the cost of scarifying morphological information regarding tissue localization and cell–cell contacts. Further detrimental effects incurred by, for example, tissue digestion include staining artifacts. Consequently, ongoing efforts are directed towards methods that preserve, completely or in part, spatial information, while increasing the number of markers that can potentially be interrogated to the level of conventional flow cytometric methods. Progression in multiplex immunohistochemistry in the last ten years overcame the limitation to 1–2 markers in classical staining methods using DAB with counter stains or even pure chemical staining methods. In this study, we compared the multiplex method Chipcytometry to flow cytometry and classical IHC-P using DAB and hematoxylin. Chipcytometry uses frozen or paraffin-embedded tissue sections stained with readily available commercial fluorophore-labeled antibodies in repetitive cycles of staining and bleaching. The iterative staining approach enables sequential analysis of a virtually unlimited number of markers on the same sample, thereby identifying immune cell subpopulations in the tumor microenvironment in the present study in a humanized mouse melanoma model.

The Immune-Modulatory Properties of iPSC-Derived Antigen-Presenting Cells

Antigen-presenting cells (APCs), such as dendritic cells (DCs) and macrophages, are important regulators of the immune system, as they connect the innate and adaptive immunity by critically regulating T-cell responses. Thus, APCs are involved in both tissue homeostasis and tolerance, but also coordinate immune responses in case of infection and inflammation. Primary APCs are commonly generated from peripheral blood-derived monocytes and have been used as cell therapeutics in several (pre-)clinical settings, e.g., immune oncology, however, with varying efficiency. One promising alternative to study antigen presentation in vitro and to develop novel cell-based therapies are induced pluripotent stem cells (iPSCs). IPSCs can nowadays be generated from a variety of different cell types using several refined reprogramming techniques. Given their unlimited proliferation and differentiation potential, they hold great promise for regenerative medicine, and recently, first iPSC derivatives have found their way into first clinical studies for cell-based therapies. In this review article, we will give a brief overview of current methods for the generation and applications of primary APCs, but also specifically focus on different strategies for the generation of defined subsets of DCs and macrophages from human PSCs. Moreover, we will highlight the potential but also hurdles for the clinical translation of iPSC-derived APCs.

The Truncated Splice Variant of the Granulocyte-Macrophage-Colony-Stimulating Factor Receptor β- Chain in Peripheral Blood Serves as Severity Biomarker of Respiratory Failure in Newborns

BACKGROUND

The granulocyte-macrophage-colony-stimulating factor (GM-CSF) plays an important role in surfactant homeostasis. βC is a subunit of the GM-CSF receptor (GM-CSF-R), and its activation mediates surfactant catabolism in the lung. βIT is a physiological, truncated isoform of βC and is known to act as physiological inhibitor of βC.

OBJECTIVE

The aim of this study was to determine the ratio of βIT and βC in the peripheral blood of newborns and its association with the degree of respiratory failure at birth.

METHODS

We conducted a prospective cohort study in newborns with various degrees of respiratory impairment at birth. Respiratory status was assessed by a score ranging from no respiratory impairment (0) to invasive respiratory support (3). βIT and βC expression were determined in peripheral blood cells by real-time PCR. βIT expression, defined as the ratio of βIT and βC, was correlated with the respiratory score.

RESULTS

βIT expression was found in all 59 recruited newborns with a trend toward higher βIT in respiratory ill (score 2, 3) newborns than respiratory healthy newborns ([score 0, 1]; p = 0.066). Seriously ill newborns (score 3) had significantly higher βIT than healthy newborns ([score 0], p = 0.010). Healthy preterm infants had significantly higher βIT expression than healthy term infants (p = 0.019).

CONCLUSIONS

βIT is expressed in newborns with higher expression in respiratory ill than respiratory healthy newborns. We hypothesize that βIT may have a protective effect in postnatal pulmonary adaptation acting as a physiological inhibitor of βC and, therefore, maintaining surfactant in respiratory ill newborns.

Translating Basic Research into Safe and Effective Cell-based Treatments for Respiratory Diseases

Respiratory diseases, such as chronic obstructive pulmonary disease and pulmonary fibrosis, result in severely impaired quality of life and impose significant burdens on healthcare systems worldwide. Current disease management involves pharmacologic interventions, oxygen administration, reduction of infections, and lung transplantation in advanced disease stages. An increasing understanding of mechanisms of respiratory epithelial and pulmonary vascular endothelial maintenance and repair and the underlying stem/progenitor cell populations, including but not limited to airway basal cells and type II alveolar epithelial cells, has opened the possibility of cell replacement-based regenerative approaches for treatment of lung diseases. Further potential for personalized therapies, including in vitro drug screening, has been underscored by the recent derivation of various lung epithelial, endothelial, and immune cell types from human induced pluripotent stem cells. In parallel, immunomodulatory treatments using allogeneic or autologous mesenchymal stromal cells have shown a good safety profile in clinical investigations for acute inflammatory conditions, such as acute respiratory distress syndrome and septic shock. However, as yet, no cell-based therapy has been shown to be both safe and effective for any lung disease. Despite the investigational status of cell-based interventions for lung diseases, businesses that market unproven, unlicensed and potentially harmful cell-based interventions for respiratory diseases have proliferated in the United States and worldwide. The current status of various cell-based regenerative approaches for lung disease as well as the effect of the regulatory environment on clinical translation of such approaches are presented and critically discussed in this review.

Pulmonary alveolarproteinosis in children

Pulmonary alveolar proteinosis (PAP) is an umbrella term for a wide spectrum of conditions that have a very characteristic appearance on computed tomography. There is outlining of the secondary pulmonary lobules on the background of ground-glass shadowing and pathologically, filling of the alveolar spaces with normal or abnormal surfactant. PAP is rare and the common causes in children are very different from those seen in adults; autoimmune PAP is rare and macrophage blockade not described in children. There are many genetic causes of PAP, the best known of which are mutations in the genes encoding surfactant protein (SP)-B, SP-C, thyroid transcription factor 1, ATP-binding cassette protein 3, and the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor α- and β- chains. PAP may also be a manifestation of rheumatological and metabolic disease, congenital immunodeficiency, and haematological malignancy. Precise diagnosis of the underlying cause is essential in planning treatment, as well as for genetic counselling. The evidence base for treatment is poor. Some forms of PAP respond well to whole-lung lavage, and autoimmune PAP, which is much commoner in adults, responds to inhaled or subcutaneous GM-CSF. Emerging therapies based on studies in murine models of PAP include stem-cell transplantation for GM-CSF receptor mutations.

EDUCATIONAL AIMS

To understand when to suspect that a child has pulmonary alveolar proteinosis (PAP) and how to confirm that this is the cause of the presentation.To show that PAP is an umbrella term for conditions characterised by alveolar filling by normal or abnormal surfactant, and that this term is the start, not the end, of the diagnostic journey.To review the developmental differences in the spectrum of conditions that may cause PAP, and specifically to understand the differences between causes in adults and children.To discuss when to treat PAP with whole-lung lavage and/or granulocyte-macrophage colony-stimulating factor, and review potential promising new therapies.

AKT3 deficiency in M2 macrophages impairs cutaneous wound healing by disrupting tissue remodeling

AKT signaling and M2 macrophage-guided tissue repair are key factors in cutaneous wound healing. A delay in this process threatens human health worldwide. However, the role of AKT3 in delayed cutaneous wound healing is largely unknown. In this study, histological staining and transcriptomics demonstrated that prolonged tissue remodeling delayed wound healing. This delay was accompanied by defects in AKT3, collagen alpha-1(I) chain (COL1A1), and collagen alpha-1(XI) chain (COL11A1) expression and AKT signaling. The defect in AKT3 expression was M2 macrophage-specific, and decreased AKT3 protein levels were observed in CD68/CD206-positive macrophages from delayed wound tissue. Downregulation of AKT3 in M2 macrophages did not influence cell polarization but impaired collagen organization by inhibiting COL1A1 and COL11A1 expression in human skin fibroblasts (HSFs). Moreover, a co-culture model revealed that the downregulation of AKT3 in the human monocytic cell line (THP-1)-derived M2 macrophages impaired HSF proliferation and migration. Finally, cutaneous wound healing in AKT3^-/- mice was much slower than that of AKT3^+/+ mice, and F4/80 macrophages from the AKT3^-/- mice had an impaired ability to promote wound healing. Thus, the downregulation of AKT3 in M2 macrophages prolonged tissue remodeling and delayed cutaneous wound healing.

Targeted Integration of Inducible Caspase-9 in Human iPSCs Allows Efficient in vitro Clearance of iPSCs and iPSC-Macrophages

Induced pluripotent stem cells (iPSCs) offer great promise for the field of regenerative medicine, and iPSC-derived cells have already been applied in clinical practice. However, potential contamination of effector cells with residual pluripotent cells (e.g., teratoma-initiating cells) or effector cell-associated side effects may limit this approach. This also holds true for iPSC-derived hematopoietic cells. Given the therapeutic benefit of macrophages in different disease entities and the feasibility to derive macrophages from human iPSCs, we established human iPSCs harboring the inducible Caspase-9 (iCasp9) suicide safety switch utilizing transcription activator-like effector nuclease (TALEN)-based designer nuclease technology. Mono- or bi-allelic integration of the iCasp9 gene cassette into the AAVS1 locus showed no effect on the pluripotency of human iPSCs and did not interfere with their differentiation towards macrophages. In both, iCasp9-mono and iCasp9-bi-allelic clones, concentrations of 0.1 nM AP20187 were sufficient to induce apoptosis in more than 98% of iPSCs and their progeny-macrophages. Thus, here we provide evidence that the introduction of the iCasp9 suicide gene into the AAVS1 locus enables the effective clearance of human iPSCs and thereof derived macrophages.

IL-17 regulates DC migration to the peribronchial LNs and allergen presentation in experimental allergic asthma

IL-17 is associated with different phenotypes of asthma, however, it is not fully elucidated how it influences induction and maintenance of asthma and allergy. In order to determine the role of IL-17 in development of allergic asthma, we used IL-17A/F double KO (IL-17A/F KO) and WT mice with or without neutralization of IL-17 in an experimental allergic asthma model and analyzed airway hyperresponsiveness, lung inflammation, T helper cell polarization, and DCs influx and activation. We report that the absence of IL-17 reduced influx of DCs into lungs and lung draining LNs. Compared to WT mice, IL-17A/F KO mice or WT mice after neutralization of IL-17A showed reduced airway hyperresponsiveness, eosinophilia, mucus hypersecretion, and IgE levels. DCs from draining LNs of allergen-challenged IL-17A/F KO mice showed a reduction in expression of migratory and costimulatory molecules CCR7, CCR2, MHC-II, and CD40 compared to WT DCs. Moreover, in vivo stimulation of adoptively transferred antigen-specific cells was attenuated in lung-draining LNs in the absence of IL-17. Thus, we report that IL-17 enhances airway DC activation, migration, and function. Consequently, lack of IL-17 leads to reduced antigen-specific T cell priming and impaired development of experimental allergic asthma.

Macrophage Transplantation Fails to Improve Repair of Critical-Sized Calvarial Defects

INTRODUCTION

Over 500,000 bone grafting procedures are performed every year in the United States for neoplastic and traumatic lesions of the craniofacial skeleton, costing $585 million in medical care. Current bone grafting procedures are limited, and full-thickness critical-sized defects (CSDs) of the adult human skull thus pose a substantial reconstructive challenge for the craniofacial surgeon. Cell-based strategies have been shown to safely and efficaciously accelerate the rate of bone formation in CSDs in animals. The authors recently demonstrated that supraphysiological transplantation of macrophages seeded in pullalan-collagen composite hydrogels significantly accelerated wound healing in wild type and diabetic mice, an effect mediated in part by enhancing angiogenesis. In this study, the authors investigated the bone healing effects of macrophage transplantation into CSDs of mice.

METHODS

CD1 athymic nude mice (60 days of age) were anesthetized, and unilateral full-thickness critical-sized (4 mm in diameter) cranial defects were created in the right parietal bone, avoiding cranial sutures. Macrophages were isolated from FVB-L2G mice and seeded onto hydroxyapatite-poly (lactic-co-glycolic acid) (HA-PLGA) scaffolds (1.0 × 10 cells per CSD). Scaffolds were incubated for 24 hours before they were placed into the CSDs. Macrophage survival was assessed using three-dimensional in vivo imaging system (3D IVIS)/micro-CT. Micro-CT at 0, 2, 4, 6, and 8 weeks was performed to evaluate gross bone formation, which was quantified using Adobe Photoshop. Microscopic evidence of bone regeneration was assessed at 8 weeks by histology. Bone formation and macrophage survival were compared at each time point using independent samples t tests.

RESULTS

Transplantation of macrophages at supraphysiological concentration had no effect on the formation of bones in CSDs as assessed by either micro-CT data at any time point analyzed (all P > 0.05). These results were corroborated by histology. 3D IVIS/micro-CT demonstrated survival of macrophages through 8 weeks.

CONCLUSION

Supraphysiologic delivery of macrophages to CSDs of mice had no effect on bone formation despite survival of transplanted macrophages through to 8 weeks posttransplantation. Further research into the physiological effects of macrophages on bone regeneration is needed to assess whether recapitulation of these conditions in macrophage-based therapy can promote the healing of large cranial defects.

Von Hippel-Lindau Protein Is Required for Optimal Alveolar Macrophage Terminal Differentiation, Self-Renewal, and Function

The rapid transit from hypoxia to normoxia in the lung that follows the first breath in newborn mice coincides with alveolar macrophage (AM) differentiation. However, whether sensing of oxygen affects AM maturation and function has not been previously explored. We have generated mice whose AMs show a deficient ability to sense oxygen after birth by deleting Vhl, a negative regulator of HIF transcription factors, in the CD11c compartment (CD11cΔVhl mice). VHL-deficient AMs show an immature-like phenotype and an impaired self-renewal capacity in vivo that persists upon culture ex vivo. VHL-deficient phenotype is intrinsic in AMs derived from monocyte precursors in mixed bone marrow chimeras. Moreover, unlike control Vhl^fl/fl, AMs from CD11cΔVhl mice do not reverse pulmonary alveolar proteinosis when transplanted into Csf2rb^−/− mice, demonstrating that VHL contributes to AM-mediated surfactant clearance. Thus, our results suggest that optimal AM terminal differentiation, self-renewal, and homeostatic function requires their intact oxygen-sensing capacity.

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Hypoxia and glycolysis signatures are downregulated during alveolar macrophage maturation

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VHL-deficient alveolar macrophages induce HIF-target genes and are more glycolytic

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VHL-deficient alveolar macrophages show an intrinsic immature-like phenotype

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VHL promotes alveolar macrophage self-renewal and surfactant clearance capacity

Human macrophages and innate lymphoid cells: Tissue-resident innate immunity in humanized mice

Macrophages and innate lymphoid cells (ILCs) are tissue-resident cells that play important roles in organ homeostasis and tissue immunity. Their intricate relationship with the organs they reside in allows them to quickly respond to perturbations of organ homeostasis and environmental challenges, such as infection and tissue injury. Macrophages and ILCs have been extensively studied in mice, yet important species-specific differences exist regarding innate immunity between humans and mice. Complementary to ex-vivo studies with human cells, humanized mice (i.e. mice with a human immune system) offer the opportunity to study human macrophages and ILCs in vivo within their surrounding tissue microenvironments. In this review, we will discuss how humanized mice have helped gain new knowledge about the basic biology of these cells, as well as their function in infectious and malignant conditions. Furthermore, we will highlight active areas of investigation related to human macrophages and ILCs, such as their cellular heterogeneity, ontogeny, tissue residency, and plasticity. In the near future, we expect more fundamental discoveries in these areas through the combined use of improved humanized mouse models together with state-of-the-art technologies, such as single-cell RNA-sequencing and CRISPR/Cas9 genome editing.

The annexin A1/FPR2 signaling axis expands alveolar macrophages, limits viral replication, and attenuates pathogenesis in the murine influenza A virus infection model

Pattern recognition receptors (PRRs) are key elements in the innate immune response. Formyl peptide receptor (FPR) 2 is a PRR that, in addition to proinflammatory, pathogen-derived compounds, also recognizes the anti-inflammatory endogenous ligand annexin A1 (AnxA1). Because the contribution of this signaling axis in viral infections is undefined, we investigated AnxA1-mediated FPR2 activation on influenza A virus (IAV) infection in the murine model. AnxA1-treated mice displayed significantly attenuated pathology upon a subsequent IAV infection with significantly improved survival, impaired viral replication in the respiratory tract, and less severe lung damage. The AnxA1-mediated protection against IAV infection was not caused by priming of the type I IFN response but was associated with an increase in the number of alveolar macrophages (AMs) and enhanced pulmonary expression of the AM-regulating cytokine granulocyte-M-CSF (GM-CSF). Both AnxA1-mediated increase in AM levels and GM-CSF production were abrogated when mouse (m)FPR2 signaling was antagonized but remained up-regulated in mice genetically deleted for mFPR1, an mFPR2 isoform also serving as AnxA1 receptor. Our results indicate a novel protective function of the AnxA1-FPR2 signaling axis in IAV pathology via GM-CSF–associated maintenance of AMs, expanding knowledge on the potential use of proresolving mediators in host defense against pathogens.—Schloer, S., Hübel, N., Masemann, D., Pajonczyk, D., Brunotte, L., Ehrhardt, C., Brandenburg, L.-O., Ludwig, S., Gerke, V., Rescher, U. The annexin A1/FPR2 signaling axis expands alveolar macrophages, limits viral replication, and attenuates pathogenesis in the murine influenza A virus infection model.

Chimeric antigen receptor macrophage therapy for breast tumours mediated by targeting the tumour extracellular matrix

Background

The extracellular matrix (ECM) is essential for malignant tumour progression, as it is a physical barrier to various kinds of anticancer therapies. Matrix metalloproteinase (MMPs) can degrade almost all ECM components, and macrophages are an important source of MMPs. Studies using macrophages to treat tumours have shown that macrophages can enter tumour tissue to play a regulatory role.

Methods

We modified macrophages with a designed chimeric antigen receptor (CAR), which could be activated after recognition of the tumour antigen HER2 to trigger the internal signalling of CD147 and increase the expression of MMPs.

Results

Although CAR-147 macrophage treatment did not affect tumour cell growth in vitro compared with control treatment. However, we found that the infusion of CAR-147 macrophages significantly inhibited HER2-4T1 tumour growth in BALB/c mice. Further investigation showed that CAR-147 macrophages could reduce tumour collagen deposition and promote T-cell infiltration into tumours, which were consistent with expectations. Interestingly, the levels of the inflammatory cytokines TNF-α and IL-6, which are key factors in cytokine release syndrome, were significantly decreased in the peripheral blood in CAR-147 macrophage-transfused mice.

Conclusion

Our data suggest that targeting the ECM by engineered macrophages would be an effective treatment strategy for solid tumours.

Pulmonary Transplantation of Human Induced Pluripotent Stem Cell-derived Macrophages Ameliorates Pulmonary Alveolar Proteinosis

RATIONALE

Although the transplantation of induced pluripotent stem cell (iPSC)-derived cells harbors enormous potential for the treatment of pulmonary diseases, in vivo data demonstrating clear therapeutic benefits of human iPSC-derived cells in lung disease models are missing.

OBJECTIVES

We have tested the therapeutic potential of iPSC-derived macrophages in a humanized disease model of hereditary pulmonary alveolar proteinosis (PAP). Hereditary PAP is caused by a genetic defect of the GM-CSF (granulocyte-macrophage colony-stimulating factor) receptor, which leads to disturbed macrophage differentiation and protein/surfactant degradation in the lungs, subsequently resulting in severe respiratory insufficiency.

METHODS

Macrophages derived from human iPSCs underwent intrapulmonary transplantation into humanized PAP mice, and engraftment, in vivo differentiation, and therapeutic efficacy of the transplanted cells were analyzed.

MEASUREMENTS AND MAIN RESULTS

On intratracheal application, iPSC-derived macrophages engrafted in the lungs of humanized PAP mice. After 2 months, transplanted cells displayed the typical morphology, surface markers, functionality, and transcription profile of primary human alveolar macrophages. Alveolar proteinosis was significantly reduced as demonstrated by diminished protein content and surfactant protein D levels, decreased turbidity of the BAL fluid, and reduced surfactant deposition in the lungs of transplanted mice.

CONCLUSIONS

We here demonstrate for the first time that pulmonary transplantation of human iPSC-derived macrophages leads to pulmonary engraftment, their in situ differentiation to an alveolar macrophage phenotype, and a reduction of alveolar proteinosis in a humanized PAP model. To our knowledge, this finding presents the first proof-of-concept for the therapeutic potential of human iPSC-derived cells in a pulmonary disease and may have profound implications beyond the rare disease of PAP.

Monopoiesis in humans and mice

Monocytes are a widely conserved cell population in vertebrates with important roles in both inflammation and homeostasis. Under both settings, monocytes continuously arise from hematopoietic progenitors in the bone marrow and, on demand, migrate into tissues through the bloodstream. Monocytes are classified into three subsets-classical, intermediate and non-classical-based on their cell surface expression of CD14 and CD16 in humans and Ly6C, CX3CR1 and CCR2 in mice. In tissues, monocytes differentiate further into monocyte-derived macrophages and dendritic cells to mediate innate and adaptive immune responses and maintain tissue homeostasis. Recently, the progenitors that strictly give rise to monocytes were identified in both humans and mice, thereby revealing the monocyte differentiation pathways.

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.

The role of macrophages in the resolution of inflammation

Macrophages are tissue-resident or infiltrated immune cells critical for innate immunity, normal tissue development, homeostasis, and repair of damaged tissue. Macrophage function is a sum of their ontogeny, the local environment in which they reside, and the type of injuries or pathogen to which they are exposed. In this Review, we discuss the role of macrophages in the restoration of tissue function after injury, highlighting important questions about how they respond to and modify the local microenvironment to restore homeostasis.

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.

Isolation and Long-term Cultivation of Mouse Alveolar Macrophages

Alveolar macrophages (AM) are tissue-resident macrophages that colonize the lung around birth and can self-maintain long-term in an adult organism without contribution of monocytes. AM are located in the pulmonary alveoli and can be harvested by washing the lungs using the method of bronchoalveolar lavage (BAL). Here, we compared different conditions of BAL to obtain high yields of murine AM for in vitro culture and expansion of AM. In addition, we describe specific culture conditions, under which AM proliferate long-term in liquid culture in the presence of granulocyte-macrophage colony-stimulating factor. This method can be used to obtain large numbers of AM for in vivo transplantation or for in vitro experiments with primary mouse macrophages.

Concise Review: Towards the Clinical Translation of Induced Pluripotent Stem Cell-Derived Blood Cells-Ready for Take-Off

Since their discovery in 2006, induced pluripotent stem cells (iPSCs) have opened up a world of possibilities for regenerative medicine and novel cell‐based therapeutics. Now, over a decade later, robust reprogramming and expansion and differentiation protocols have been developed, and iPSC‐derived cells have been used in a wide variety of small and large animal models to treat many different diseases. Furthermore, the first iPSC derivatives are on their way into clinical trials. In this line, (i) GMP‐compliant generation, cultivation, and differentiation, (ii) preclinical efficacy and safety, as well as (iii) ethical and regulatory compliance of stem cell research represent important aspects that need to be evaluated for proper clinical translation of iPSCs and their derivatives. In this review article, we provide an overview of the current advances and challenges of the clinical translation of iPSC‐derived blood cells and highlight the most pressing problems that have to be overcome in the next years. stem cells translational medicine2019;8:332–339

Protective Effect of Colla corii asini against Lung Injuries Induced by Intratracheal Instillation of Artificial Fine Particles in Rats

Environmental issues pose huge threats to public health, particularly the damage caused by fine particulate matter (PM_2.5). However, the mechanisms of injury require further investigation and medical materials that can protect the lungs from PM_2.5 are needed. We have found that Colla corii asini, a traditional Chinese medicine that has long been used to treat various ailments, is a good candidate to serve this purpose. To understand the mechanisms of PM_2.5-induced lung toxicity and the protective effects of Colla corii asini, we established a rat model of lung injury via intratracheal instillation of artificial PM_2.5 (aPM_2.5). Our results demonstrated that Colla corii asini significantly protected against lung function decline and pathologic changes. Inflammation was ameliorated by suppression of Arg-1 to adjust the disturbed metabolic pathways induced by aPM_2.5, such as arginine and nitrogen metabolism and aminoacyl-tRNA biosynthesis, for 11 weeks. Our work found that metabolomics was a useful tool that contributed to further understanding of PM_2.5-induced respiratory system damage and provided useful information for further pharmacological research on Colla corii asini, which may be valuable for therapeutic intervention.

Bioreactor-based mass production of human iPSC-derived macrophages enables immunotherapies against bacterial airway infections

The increasing number of severe infections with multi-drug-resistant pathogens worldwide highlights the need for alternative treatment options. Given the pivotal role of phagocytes and especially alveolar macrophages in pulmonary immunity, we introduce a new, cell-based treatment strategy to target bacterial airway infections. Here we show that the mass production of therapeutic phagocytes from induced pluripotent stem cells (iPSC) in industry-compatible, stirred-tank bioreactors is feasible. Bioreactor-derived iPSC-macrophages (iPSC-Mac) represent a highly pure population of CD45⁺CD11b⁺CD14⁺CD163⁺ cells, and share important phenotypic, functional and transcriptional hallmarks with professional phagocytes, however with a distinct transcriptome signature similar to primitive macrophages. Most importantly, bioreactor-derived iPSC-Mac rescue mice from Pseudomonas aeruginosa-mediated acute infections of the lower respiratory tract within 4-8 h post intra-pulmonary transplantation and reduce bacterial load. Generation of specific immune-cells from iPSC-sources in scalable stirred-tank bioreactors can extend the field of immunotherapy towards bacterial infections, and may allow for further innovative cell-based treatment strategies.

Pulmonary infections constitute a substantial health problem worldwide. Here the authors show that phagocytes similar to primitive macrophages can be generated from human induced pluripotent stem cells, by the use of industry-compatible, stirred-tank bioreactors, and applied as a cell-based therapy to treat acute bacterial infections in mice.

An immune cell spray (ICS) formulation allows for the delivery of functional monocyte/macrophages

Macrophages are key cells of the innate immune system and act as tissue resident macrophages (TRMs) in the homeostasis of various tissues. Given their unique functions and therapeutic use as well as the feasibility to derive macrophages in vitro from hematopoietic stem cell (HSC) sources, we propose an “easy-to-use” immune cell spray (ICS) formulation to effectively deliver HSC-derived macrophages. To achieve this aim, we used classical pump spray devices to spray either the human myeloid cell line U937 or primary murine HSC-derived macrophages. For both cell types used, one puff could deliver cells with maintained morphology and functionality. Of note, cells tolerated the spraying process very well with a recovery of more than 90%. In addition, we used osmotic preconditioning to reduce the overall cell size of macrophages. While a 800 mosm hyperosmolar sucrose solution was able to reduce the cell size by 27%, we identified 600 mosm to be effective to reduce the cell size by 15% while maintaining macrophage morphology and functionality. Using an isolated perfused rat lung preparation, the combinatorial use of the ICS with preconditioned and genetically labeled U937 cells allowed the intra-pulmonary delivery of cells, thus paving the way for a new cell delivery platform.

Absence of Regulatory T Cells Causes Phenotypic and Functional Switch in Murine Peritoneal Macrophages

Tissue macrophages are important components of tissue homeostasis and inflammatory pathologies. In the peritoneal cavity, resident macrophages interact with a variety of immune cells and can exhibit broad range of phenotypes and functions. Forkhead-box-P3 (FOXP3)⁺ regulatory T cells (Tregs) play an indispensable role in maintaining immunological tolerance, yet whether, and how the pathological condition that results from the lack of functional Tregs affects peritoneal macrophages (PM) is largely unknown. We used FOXP3-deficient scurfy (Sf) mice to investigate PM behavior in terms of the missing crosstalk with Tregs. Here, we report that Treg deficiency induced a marked increase in PM numbers, which was reversed after adoptive transfer of CD4⁺ T cells or neutralization of macrophage colony-stimulating factor. Ex vivo assays demonstrated a pro-inflammatory state of PM from Sf mice and signs of excessive activation and exhaustion. In-depth immunophenotyping of Sf PM using single-cell chipcytometry and transcriptome analysis revealed upregulation of molecules involved in the initiation of innate and adaptive immune responses. Moreover, upon transfer to non-inflammatory environment or after injection of CD4⁺ T cells, PM from Sf mice reprogramed their functional phenotype, indicating remarkable plasticity. Interestingly, frequencies, and immune polarization of large and small PM subsets were dramatically changed in the FOXP3-deficient mice, suggesting distinct origin and specialized function of these subsets in inflammatory conditions. Our findings demonstrate the significant impact of Tregs in shaping PM identity and dynamics. A better understanding of PM function in the Sf mouse model may have clinical implication for the treatment of immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, and other forms of immune-mediated enteropathies.

iPSC-Derived Macrophages Effectively Treat Pulmonary Alveolar Proteinosis in Csf2rb-Deficient Mice

Induced pluripotent stem cell (iPSC)-derived hematopoietic cells represent a highly attractive source for cell and gene therapy. Given the longevity, plasticity, and self-renewal potential of distinct macrophage subpopulations, iPSC-derived macrophages (iPSC-Mφ) appear of particular interest in this context. We here evaluated the airway residence, plasticity, and therapeutic efficacy of iPSC-Mφ in a murine model of hereditary pulmonary alveolar proteinosis (herPAP). We demonstrate that single pulmonary macrophage transplantation (PMT) of 2.5–4 × 10⁶ iPSC-Mφ yields efficient airway residence with conversion of iPSC-Mφ to an alveolar macrophage (AMφ) phenotype characterized by a distinct surface marker and gene expression profile within 2 months. Moreover, PMT significantly improves alveolar protein deposition and other critical herPAP disease parameters. Thus, our data indicate iPSC-Mφ as a source of functional macrophages displaying substantial plasticity and therapeutic potential that upon pulmonary transplantation will integrate into the lung microenvironment, adopt an AMφ phenotype and gene expression pattern, and profoundly ameliorate pulmonary disease phenotypes.

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iPSCs as a source of functional macrophages with substantial plasticity

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iPSC-derived macrophages have therapeutic potential in hereditary PAP

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Pulmonary-transplanted iPSC-Mφ integrate into the lung microenvironment

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iPSC-Mφ can adopt an AMφ phenotype and gene expression pattern