Ex vivo Generation of Genetically Modified Macrophages from Human Induced Pluripotent Stem Cells

Immunosenescence and macrophages: From basics to therapeutics

Ageing decreases the function of the immune system and increases susceptibility to some chronic, infectious, and autoimmune diseases. Senescence cells, which produce senescence-associated secretory phenotypes (SASPs), can activate the innate and adaptive immune responses. Macrophages are among the most abundant innate immune cell types in senescent microenvironments. Senescence-associated macrophages, recruited by SASPs, play a vital role in establishing the essential microenvironments for maintaining tissue homeostasis. However, it's important to note that these senescence-associated macrophages can also influence senescent processes, either by enhancing or impeding the functions of tissue-resident senescent cells. In this discussion, we describe the potential targets of immunosenescence and shed light on the probable mechanisms by which macrophages influence cellular senescence. Furthermore, we analyze their dual function in both clearing senescent cells and modulating age-related diseases. This multifaceted influence operates through processes including heightened inflammation, phagocytosis, efferocytosis, and autophagy. Given the potential off-target effects and immune evasion mechanisms associated with traditional anti-ageing strategies (senolytics and senomorphics), 'resetting' immune system tolerance or targeting senescence-related macrophage functions (i.e., phagocytotic capacity and immunosurveillance) will inform treatment of age-related diseases. Therefore, we review recent advances in the use of macrophage therapeutics to treat ageing and age-associated disorders, and outline the key gaps in this field.

A Model of iPSC-Derived Macrophages with TNFAIP3 Overexpression Reveals the Peculiarities of TNFAIP3 Protein Expression and Function in Human Macrophages

Macrophages play a crucial role in the development and control of inflammation. Understanding the mechanisms balancing macrophage inflammatory activity is important to develop new strategies for treating inflammation-related diseases. TNF-α-induced protein 3 (TNFAIP3, A20) is a negative regulator of intracellular inflammatory cascades; its deficiency induces hyper-inflammatory reactions. Whether A20 overexpression can dampen macrophage inflammatory response remains unclear. Here, we generated human-induced pluripotent stem cells with tetracycline-inducible A20 expression and differentiated them into macrophages (A20-iMacs). A20-iMacs displayed morphology, phenotype, and phagocytic activity typical of macrophages, and they displayed upregulated A20 expression in response to doxycycline. A20 overexpression dampened the A20-iMac response to TNF-α, as shown by a decreased expression of IL1B and IL6 mRNA. A dynamic analysis of A20 expression following the generation of A20-iMacs and control iMacs showed that the expression declined in iMacs and that iMacs expressed a lower molecular weight form of the A20 protein (~70 kDa) compared with less differentiated cells (~90 kDa). A low-level expression of A20 and the predominance of a low-molecular-weight A20 form were also characteristic of monocyte-derived macrophages. The study for the first time developed a model for generating macrophages with an inducible expression of a target gene and identified the peculiarities of A20 expression in macrophages that likely underlie macrophage preparedness for inflammatory reactivity. It also suggested the possibility of mitigating inflammatory macrophage responses via A20 overexpression.

Continuous human iPSC-macrophage mass production by suspension culture in stirred tank bioreactors

Macrophages derived from human induced pluripotent stem cells (iPSCs) have the potential to enable the development of cell-based therapies for numerous disease conditions. We here provide a detailed protocol for the mass production of iPSC-derived macrophages (iPSC-Mac) in scalable suspension culture on an orbital shaker or in stirred-tank bioreactors (STBRs). This strategy is straightforward, robust and characterized by the differentiation of primed iPSC aggregates into 'myeloid-cell-forming-complex' intermediates by means of a minimal cytokine cocktail. In contrast to the 'batch-like differentiation approaches' established for other iPSC-derived lineages, myeloid-cell-forming-complex-intermediates are stably maintained in suspension culture and continuously generate functional and highly pure iPSC-Mac. Employing a culture volume of 120 ml in the STBR platform, ~1-4 × 107 iPSC-Mac can be harvested at weekly intervals for several months. The STBR technology allows for real-time monitoring of crucial process parameters such as biomass, pH, dissolved oxygen, and nutrition levels; the system also promotes systematic process development, optimization and linear upscaling. The process duration, from the expansion of iPSC until the first iPSC-Mac harvest, is 28 d. Successful application of the protocol requires expertise in pluripotent stem cell culture, differentiation and analytical methods, such as flow cytometry. Fundamental know-how in biotechnology is also advantageous to run the process in the STBR platform. The continuous, scalable production of well-defined iPSC-Mac populations is highly relevant to various fields, ranging from developmental biology, immunology and cell therapies to industrial applications for drug safety and discovery.

Senescent cells and macrophages: key players for regeneration?

Over the last decade, our understanding of the physiological role of senescent cells has drastically evolved, from merely indicators of cellular stress and ageing to having a central role in regeneration and repair. Increasingly, studies have identified senescent cells and the senescence-associated secretory phenotype (SASP) as being critical in the regenerative process following injury; however, the timing and context at which the senescence programme is activated can lead to distinct outcomes. For example, a transient induction of senescent cells followed by rapid clearance at the early stages following injury promotes repair, while the long-term accumulation of senescent cells impairs tissue function and can lead to organ failure. A key role of the SASP is the recruitment of immune cells to the site of injury and the subsequent elimination of senescent cells. Among these cell types are macrophages, which have well-documented regulatory roles in all stages of regeneration and repair. However, while the role of senescent cells and macrophages in this process is starting to be explored, the specific interactions between these cell types and how these are important in the different stages of injury/reparative response still require further investigation. In this review, we consider the current literature regarding the interaction of these cell types, how their cooperation is important for regeneration and repair, and what questions remain to be answered to advance the field.

Macrophages Derived From Human Induced Pluripotent Stem Cells Are Low-Activated "Naïve-Like" Cells Capable of Restricting Mycobacteria Growth

In peripheral tissues, immune protection critically depends on the activity of tissue resident macrophages, which makes our understanding of the biology of these cells of great significance. Until recently, human macrophage studies were largely based on the analysis of monocyte-derived macrophages that differ from tissue resident macrophages by many characteristics. To model tissue resident macrophages, methods of generating macrophages from pluripotent stem cells have been developed. However, the immunological properties of macrophages derived from pluripotent stem cells remain under-investigated. In this study, we aimed to perform the multifarious immunological characteristics of macrophages generated from human induced pluripotent stem cells (iMϕs), including an analysis of their phenotype, secretory and antibacterial activities, as well as their comparison with macrophages derived from blood monocytes and infected lung tissue. We report that iMϕs displayed the morphology and the CD11b⁺CD45⁺CD14⁺ phenotype typical for mononuclear phagocytes. The cells co-expressed markers known to be associated with classically (CD80, CD86, CCR5) and alternatively (CD163 and CD206) activated macrophages, with a bias toward a higher expression of the latter. iMϕs secreted pro-inflammatory (IL-6, CXCL8, CCL2, CCL4, CXCL1, CXCL10) and anti-inflammatory (IL-10, IL-1RA, CCL22) cytokines with a high IL-10/IL-12p70 index (>20). iMϕs were phagocytic and restricted Mycobacterium tuberculosis growth in vitro by >75%. iMϕs differed from blood monocytes/macrophages by a lower expression level of HLA-DR and the CD14⁺CD16^int phenotype and shared several phenotypic characteristics with lung macrophages. In response to LPS, iMϕs up-regulated HLA-DR and produced TNF-α. IFN-γ increased iMϕ reactivity to LPS, but did not increase iMϕ mycobactericidal capacity. The results characterize iMϕs as differentiated but low-activated/low-polarized “naïve-like” macrophages that are capable of mounting inflammatory and antibacterial responses when exposed to inflammatory stimuli or pathogens. iMϕs represent a valuable model for studying antibacterial responses of tissue resident macrophages and for developing approaches to modulating macrophage activity.

Role of immune cells in the removal of deleterious senescent cells

Cellular senescence is an essentially irreversible arrest of cell proliferation coupled to a complex senescence-associated secretory phenotype (SASP). The senescence arrest prevents the development of cancer, and the SASP can promote tissue repair. Recent data suggest that the prolonged presence of senescent cells, and especially the SASP, could be deleterious, and their beneficial effects early in life can become maladaptive such that they drive aging phenotypes and pathologies late in life. It is therefore important to develop strategies to eliminate senescent cells. There are currently under development or approved several immune cell-based therapies for cancer, which could be redesigned to target senescent cells. This review focuses on this possible use of immune cells and discusses how current cell-based therapies could be used for senescent cell removal.

Generation of gene-corrected functional osteoclasts from osteopetrotic induced pluripotent stem cells

Background

Infantile malignant osteopetrosis (IMO) is an autosomal recessive disorder characterized by non-functional osteoclasts and a fatal outcome early in childhood. About 50% of patients have mutations in the TCIRG1 gene.

Methods

IMO iPSCs were generated from a patient carrying a homozygous c.11279G>A (IVS18+1) mutation in TCIRG1 and transduced with a lentiviral vector expressing human TCIRG1. Embryoid bodies were generated and differentiated into monocytes. Non-adherent cells were harvested and further differentiated into osteoclasts on bovine bone slices.

Results

Release of the bone resorption biomarker CTX-I into the media of gene-corrected osteoclasts was 5-fold higher than that of the uncorrected osteoclasts and 35% of that of control osteoclasts. Bone resorption potential was confirmed by the presence of pits on the bones cultured with gene-corrected osteoclasts, absent in the uncorrected IMO osteoclasts.

Conclusions

The disease phenotype was partially corrected in vitro, providing a valuable resource for therapy development for this form of severe osteopetrosis.

Methods for macrophage differentiation and in vitro generation of human tumor associated-like macrophages

Tumor-associated macrophages (TAMs) are becoming a promising target for cancer immunotherapy. Significant efforts have been made to study the detrimental role of TAMs both in vivo and in vitro. However, it remains challenging to isolate these macrophages to study their function in human cancers and there is the need to seek alternatives to address these limitations. In this review, we will focus on the three most relevant approaches to obtain in vitro fully differentiated macrophages i.e. peripheral blood, immortalized cell lines such as THP-1 or human induced pluripotent stem cells. We will also provide protocols for the polarization of human macrophages to a TAM-like cells in vitro.

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

Targeted Gene Editing in Human Pluripotent Stem Cells Using Site-Specific Nucleases

Introduction of induced pluripotent stem cell (iPSC) technology and site-directed nucleases brought a major breakthrough in the development of regenerative therapies and biomedical research. With the advancement of ZFNs, TALENs, and the CRISPR/Cas9 technology, straightforward and precise manipulation of the genome of human pluripotent stem cells (PSC) became possible, allowing relatively easy and fast generation of gene knockouts, integration of transgenes, or even introduction of single nucleotide changes for correction or introduction of disease-specific mutations. We review current applications of site-specific nucleases in human PSCs and focus on trends and challenges for efficient gene editing and improvement of targeting strategies. Graphical Abstract.

A human iPSC line capable of differentiating into functional macrophages expressing ZsGreen: a tool for the study and in vivo tracking of therapeutic cells

We describe the production of a human induced pluripotent stem cell (iPSC) line, SFCi55-ZsGr, that has been engineered to express the fluorescent reporter gene, ZsGreen, in a constitutive manner. The CAG-driven ZsGreen expression cassette was inserted into the AAVS1 locus and a high level of expression was observed in undifferentiated iPSCs and in cell lineages derived from all three germ layers including haematopoietic cells, hepatocytes and neurons. We demonstrate efficient production of terminally differentiated macrophages from the SFCi55-ZsGreen iPSC line and show that they are indistinguishable from those generated from their parental SFCi55 iPSC line in terms of gene expression, cell surface marker expression and phagocytic activity. The high level of ZsGreen expression had no effect on the ability of macrophages to be activated to an M(LPS + IFNγ), M(IL10) or M(IL4) phenotype nor on their plasticity, assessed by their ability to switch from one phenotype to another. Thus, targeting of the AAVS1 locus in iPSCs allows for the production of fully functional, fluorescently tagged human macrophages that can be used for in vivo tracking in disease models. The strategy also provides a platform for the introduction of factors that are predicted to modulate and/or stabilize macrophage function.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Human-induced pluripotent stem cell-derived macrophages and their immunological function in response to tuberculosis infection

BACKGROUND

Induced pluripotent stem cells (iPS) represent an innovative source for the standardized in vitro generation of macrophages (Mφ). Mφ show great promise in disease pathogenesis, particularly tuberculosis. However, there is no information about human iPS-derived (hiPS) macrophages (hiPS-Mφ) in response to tuberculosis infection.

METHODS

In the present study, macrophages derived from hiPS were established via embryoid body (EB) formation by using feeder-free culture conditions, and the human monocyte cell line THP-1 (THP-1-Mφ) was used as control. iPS-Mφ were characterized by using morphology, Giemsa staining, nonspecific esterase staining (α-NAE), phagocytosis, and surface phenotype. Additionally, after treatment with Bacillus Calmette-Guérin (BCG) for 24 h, cell apoptosis was detected by using an Annexin V-FITC Apoptosis Detection assay. The production of nitric oxide (NO), expression of tumor necrosis factor alpha (TNF-α), activity of apoptosis-related protein cysteine-3 (Caspase-3) and expression of B-cell lymphoma-2 (Bcl-2) were analyzed.

RESULTS

With respect to morphology, surface phenotype, and function, the iPS-Mφ closely resembled their counterparts generated in vitro from a human monocyte cell line. iPS-Mφ exhibited the typically morphological characteristics of macrophages, such as round, oval, fusiform and irregular characteristics. The cells were Giemsa-stained-positive, α-NAE-positive, and possessed phagocytic ability. iPS-Mφ express high levels of CD14, CD11b, CD40, CD68, and major histocompatibility complex II (MHC-II). Moreover, with regard to the apoptotic rate, the production of NO, expression of TNF-α, and activity of Caspase-3 and Bcl-2, iPS-Mφ closely resemble that of their counterparts generated in vitro from human monocyte cell line in response to BCG infection. The rate of apoptosis of BCG-treated iPS-Mφ was 37.77 ± 7.94% compared to that of the untreated group at 4.97 ± 1.60% (P < 0.01) by using Annexin V-FITC Apoptosis Detection. Additionally, the rate of apoptosis of BCG-treated THP-1-Mφ was 37.1 ± 2.84% compared to that of the untreated group at 6.19 ± 1.68% (P < 0.001). The expression of TNF-α and the production of NO were significantly increased (P < 0.001), and the activity of Caspase-3 was increased. However, the expression of Bcl-2 was inhibited (P < 0.001).

CONCLUSIONS

Our results demonstrate that Mφ derived from hiPS perform the immunological function in response to Bacillus Calmette-Guérin infection by undergoing apoptosis, increasing the production of NO and expression of TNF-α. Thus, our study may help to overcome the limitations of research into certain rare diseases due to the lack of adequate supply of disease-specific primary cells.

TALEN-mediated functional correction of human iPSC-derived macrophages in context of hereditary pulmonary alveolar proteinosis

Hereditary pulmonary alveolar proteinosis (herPAP) constitutes a rare, life threatening lung disease characterized by the inability of alveolar macrophages to clear the alveolar airspaces from surfactant phospholipids. On a molecular level, the disorder is defined by a defect in the CSF2RA gene coding for the GM-CSF receptor alpha-chain (CD116). As therapeutic options are limited, we currently pursue a cell and gene therapy approach aiming for the intrapulmonary transplantation of gene-corrected macrophages derived from herPAP-specific induced pluripotent stem cells (herPAP-iPSC) employing transcriptional activator-like effector nucleases (TALENs). Targeted insertion of a codon-optimized CSF2RA-cDNA driven by the hybrid cytomegalovirus (CMV) early enhancer/chicken beta actin (CAG) promoter into the AAVS1 locus resulted in robust expression of the CSF2RA gene in gene-edited herPAP-iPSCs as well as thereof derived macrophages. These macrophages displayed typical morphology, surface phenotype, phagocytic and secretory activity, as well as functional CSF2RA expression verified by STAT5 phosphorylation and GM-CSF uptake studies. Thus, our study provides a proof-of-concept, that TALEN-mediated integration of the CSF2RA gene into the AAVS1 safe harbor locus in patient-specific iPSCs represents an efficient strategy to generate functionally corrected monocytes/macrophages, which in the future may serve as a source for an autologous cell-based gene therapy for the treatment of herPAP.