Optimizing the Method for Differentiation of Macrophages from Human Induced Pluripotent Stem Cells

c-Myc alone is enough to reprogram fibroblasts into functional macrophages

BACKGROUND

Macrophage-based cell therapy is promising in solid tumors, but the efficient acquisition of macrophages remains a challenge. Induced pluripotent stem cell (iPSC)-induced macrophages are a valuable source, but time-consuming and costly. The application of reprogramming technologies allows for the generation of macrophages from somatic cells, thereby facilitating the advancement of cell-based therapies for numerous malignant diseases.

METHODS

The composition of CD45+ myeloid-like cell complex (MCC) and induced macrophage (iMac) were analyzed by flow cytometry and single-cell RNA sequencing. The engraftment capacity of CD45+ MCC was evaluated by two transplantation assays. Regulation of c-Myc on MafB was evaluated by ChIP-qPCR and promoter reporter and dual luciferase assays. The phenotype and phagocytosis of iMac were explored by flow cytometry and immunofluorescence. Leukemia, breast cancer, and patient-derived tumor xenograft models were used to explore the anti-tumor function of iMac.

RESULTS

Here we report on the establishment of a novel methodology allowing for reprogramming fibroblasts into functional macrophages with phagocytic activity by c-Myc overexpression. Fibroblasts with ectopic expression of c-Myc in iPSC medium rapidly generated CD45+ MCC intermediates with engraftment capacity as well as the repopulation of distinct hematopoietic compartments. MCC intermediates were stably maintained in iPSC medium and continuously generated functional and highly pure iMac just by M-CSF cytokine stimulation. Single-cell transcriptomic analysis of MCC intermediates revealed that c-Myc up-regulated the expression of MafB, a major regulator of macrophage differentiation, to promote macrophage differentiation. Characterization of the iMac activity showed NF-κB signaling activation and a pro-inflammatory phenotype. iMac cells displayed significantly increased in vivo persistence and inhibition of tumor progression in leukemia, breast cancer, and patient-derived tumor xenograft models.

CONCLUSIONS

Our findings demonstrate that c-Myc alone is enough to reprogram fibroblasts into functional macrophages, supporting that c-Myc reprogramming strategy of fibroblasts can help circumvent long-standing obstacles to gaining "off-the-shelf" macrophages for anti-cancer immunotherapy.

Building a human lung from pluripotent stem cells to model respiratory viral infections

To protect against the constant threat of inhaled pathogens, the lung is equipped with cellular defenders. In coordination with resident and recruited immune cells, this defence is initiated by the airway and alveolar epithelium following their infection with respiratory viruses. Further support for viral clearance and infection resolution is provided by adjacent endothelial and stromal cells. However, even with these defence mechanisms, respiratory viral infections are a significant global health concern, causing substantial morbidity, socioeconomic losses, and mortality, underlining the need to develop effective vaccines and antiviral medications. In turn, the identification of new treatment options for respiratory infections is critically dependent on the availability of tractable in vitro experimental models that faithfully recapitulate key aspects of lung physiology. For such models to be informative, it is important these models incorporate human-derived, physiologically relevant versions of all cell types that normally form part of the lungs anti-viral response. This review proposes a guideline using human induced pluripotent stem cells (iPSCs) to create all the disease-relevant cell types. iPSCs can be differentiated into lung epithelium, innate immune cells, endothelial cells, and fibroblasts at a large scale, recapitulating in vivo functions and providing genetic tractability. We advocate for building comprehensive iPSC-derived in vitro models of both proximal and distal lung regions to better understand and model respiratory infections, including interactions with chronic lung diseases.

The cross-talk between macrophages and tumor cells as a target for cancer treatment

Macrophages represent an important component of the innate immune system. Under physiological conditions, macrophages, which are essential phagocytes, maintain a proinflammatory response and repair damaged tissue. However, these processes are often impaired upon tumorigenesis, in which tumor-associated macrophages (TAMs) protect and support the growth, proliferation, and invasion of tumor cells and promote suppression of antitumor immunity. TAM abundance is closely associated with poor outcome of cancer, with impediment of chemotherapy effectiveness and ultimately a dismal therapy response and inferior overall survival. Thus, cross-talk between cancer cells and TAMs is an important target for immune checkpoint therapies and metabolic interventions, spurring interest in it as a therapeutic vulnerability for both hematological cancers and solid tumors. Furthermore, targeting of this cross-talk has emerged as a promising strategy for cancer treatment with the antibody against CD47 protein, a critical macrophage checkpoint recognized as the "don't eat me" signal, as well as other metabolism-focused strategies. Therapies targeting CD47 constitute an important milestone in the advancement of anticancer research and have had promising effects on not only phagocytosis activation but also innate and adaptive immune system activation, effectively counteracting tumor cells' evasion of therapy as shown in the context of myeloid cancers. Targeting of CD47 signaling is only one of several possibilities to reverse the immunosuppressive and tumor-protective tumor environment with the aim of enhancing the antitumor response. Several preclinical studies identified signaling pathways that regulate the recruitment, polarization, or metabolism of TAMs. In this review, we summarize the current understanding of the role of macrophages in cancer progression and the mechanisms by which they communicate with tumor cells. Additionally, we dissect various therapeutic strategies developed to target macrophage-tumor cell cross-talk, including modulation of macrophage polarization, blockade of signaling pathways, and disruption of physical interactions between leukemia cells and macrophages. Finally, we highlight the challenges associated with tumor hypoxia and acidosis as barriers to effective cancer therapy and discuss opportunities for future research in this field.

Germline Neurofibromin 1 mutation enhances the anti-tumour immune response and decreases juvenile myelomonocytic leukaemia tumourigenicity

Juvenile myelomonocytic leukaemia (JMML) is an aggressive paediatric leukaemia characterized by mutations in five canonical RAS pathway genes, including the NF1 gene. JMML is driven by germline NF1 gene mutations, with additional somatic aberrations resulting in the NF1 biallelic inactivation, leading to disease progression. Germline mutations in the NF1 gene alone primarily cause benign neurofibromatosis type 1 (NF1) tumours rather than malignant JMML, yet the underlying mechanism remains unclear. Here, we demonstrate that with reduced NF1 gene dose, immune cells are promoted in anti-tumour immune response. Comparing the biological properties of JMML and NF1 patients, we found that not only JMML but also NF1 patients driven by NF1 mutations could increase monocytes generation. But monocytes cannot further malignant development in NF1 patients. Utilizing haematopoietic and macrophage differentiation from iPSCs, we revealed that NF1 mutations or knockout (KO) recapitulated the classical haematopoietic pathological features of JMML with reduced NF1 gene dose. NF1 mutations or KO promoted the proliferation and immune function of NK cells and iMacs derived from iPSCs. Moreover, NF1-mutated iNKs had a high capacity to kill NF1-KO iMacs. NF1-mutated or KO iNKs administration delayed leukaemia progression in a xenograft animal model. Our findings demonstrate that germline NF1 mutations alone cannot directly drive JMML development and suggest a potential cell immunotherapy for JMML patients.

Application of human iPSC-derived macrophages in a miniaturized high-content-imaging-based efferocytosis assay

Macrophages play a pivotal role in drug discovery due to their key regulatory functions in health and disease. Overcoming the limited availability and donor variability of human monocyte-derived macrophages (MDMs), human induced pluripotent stem cell (iPSC)-derived macrophages (IDMs) could provide a promising tool for both disease modeling and drug discovery. To access large numbers of model cells for medium- to high-throughput application purposes, an upscaled protocol was established for differentiation of iPSCs into progenitor cells and subsequent maturation into functional macrophages. These IDM cells resembled MDMs both with respect to surface marker expression and phago- as well as efferocytotic function. A statistically robust high-content-imaging assay was developed to quantify the efferocytosis rate of IDMs and MDMs allowing for measurements both in the 384- and 1536-well microplate format. Validating the applicability of the assay, inhibitors of spleen tyrosine kinase (Syk) were shown to modulate efferocytosis in IDMs and MDMs with comparable pharmacology. The miniaturized cellular assay with the upscaled provision of macrophages opens new routes to pharmaceutical drug discovery in the context of efferocytosis-modulating substances.

Macrophage immunotherapy: overcoming impediments to realize promise

As an essential component of immunity, macrophages have key roles in mammalian host defense, tissue homeostasis, and repair, as well as in disease pathogenesis and pathophysiology. A source of fascination and extensive research, in this Opinion we challenge the utility of the M1-M2 paradigm, and discuss the importance of accurate characterization of human macrophages. We comment on the application of single cell analytics to define macrophage subpopulations and how this could advance therapeutic options. We argue that human macrophage cell therapy can be used to alleviate many diseases, and offer a viewpoint on the knowledge gaps that must be filled to render such a therapeutic approach a reality and, ideally, a common future practice in precision medicine.