Production and Characterization of Human Macrophages from Pluripotent Stem Cells

Macrophages are present in most vertebrate tissues and comprise widely dispersed and heterogeneous cell populations with different functions. They are key ...

University of Edinburgh

Engineered nucleases have been used to generate knockout or reporter cell lines and a range of animal models for human disease. These new technologies also hold great promise for therapeutic genome editing. Current methods to evaluate the activity of these nucleases are time consuming, require extensive optimization and are hampered by readouts with low signals and high background. We have developed a simple and easy to perform method (SplitAx) that largely addresses these issues and provides a readout of nuclease activity. The assay involves splitting the N-terminal (amino acid 1-158) coding region of GFP and an out-of-frame of C-terminal region with a nuclease binding site sequence. Following exposure to the test nuclease, cutting and repair by error prone non-homologous end joining (NHEJ) restores the reading frame resulting in the production of a full length fluorescent GFP protein. Fluorescence can also be restored by complementation between the N-terminal and C-terminal coding sequences in trans. We demonstrate successful use of the SplitAx assay to assess the function of zinc finger nucleases, CRISPR hCAS9 and TALENS. We also test the activity of multiple gRNAs in CRISPR/hCas9/D10A systems. The zinc finger nucleases and guide RNAs that showed functional activity in the SplitAx assay were then used successfully to target the endogenous AAVS1, SOX6 and Cfms loci. This simple method can be applied to other unrelated proteins such as ZsGreen1 and provides a test system that does not require complex optimization.

SplitAx: A novel method to assess the function of engineered nucleases.

We have generated a drug-free, all-in-one dCAS9-SAM vector that can activate endogenous gene expression with the potential to modify cell fate. We demonstrate that this strategy can be used in a number of cell lines and avoids exceptionally high levels of gene expression that are observed in standard transgenic approaches. Compared to the multi-plasmid system, this all-in-one vector activates gene expression to a comparable level but the reduced overall DNA content results in significantly higher viability of transfected cells. This allowed us to use the RUNX1C-GFP human embryonic stem cell reporter cell line to monitor gene activation in individual cells and to show that activation could occur at all stages of the cell cycle.

An all-in-one UniSam vector system for efficient gene activation.

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  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  locus in iPSCs allows for the production of fully functional, fluorescently tagged human macrophages that can be used for  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'.

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

Red blood cells mature within the erythroblastic island (EI) niche that consists of specialized macrophages surrounded by differentiating erythroblasts. Here we establish an in vitro system to model the human EI niche using macrophages that are derived from human induced pluripotent stem cells (iPSCs), and are also genetically programmed to an EI-like phenotype by inducible activation of the transcription factor, KLF1. These EI-like macrophages increase the production of mature, enucleated erythroid cells from umbilical cord blood derived CD34 haematopoietic progenitor cells and iPSCs; this enhanced production is partially retained even when the contact between progenitor cells and macrophages is inhibited, suggesting that KLF1-induced secreted proteins may be involved in this enhancement. Lastly, we find that the addition of three secreted factors, ANGPTL7, IL-33 and SERPINB2, significantly enhances the production of mature enucleated red blood cells. Our study thus contributes to the ultimate goal of replacing blood transfusion with a manufactured product.

Genetic programming of macrophages generates an in vitro model for the human erythroid island niche.

The roles of tumor-associated macrophages (TAMs) and circulating monocytes in human cancer are poorly understood. Here, we show that monocyte subpopulation distribution and transcriptomes are significantly altered by the presence of endometrial and breast cancer. Furthermore, TAMs from endometrial and breast cancers are transcriptionally distinct from monocytes and their respective tissue-resident macrophages. We identified a breast TAM signature that is highly enriched in aggressive breast cancer subtypes and associated with shorter disease-specific survival. We also identified an auto-regulatory loop between TAMs and cancer cells driven by tumor necrosis factor alpha involving SIGLEC1 and CCL8, which is self-reinforcing through the production of CSF1. Together these data provide direct evidence that monocyte and macrophage transcriptional landscapes are perturbed by cancer, reflecting patient outcomes.

Human Tumor-Associated Macrophage and Monocyte Transcriptional Landscapes Reveal Cancer-Specific Reprogramming, Biomarkers, and Therapeutic Targets.

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.

Martha Lopez-Yrigoyen

Centre for Regenerative Medicine,
Scottish Centre for Regenerative Medicine,
Centre for Reproductive Health,
The Queen's Medical Research Institute,
Centre for Regenerative Medicine, Scottish Centre for Regenerative Medicine,
Centre for Reproductive Health, The Queen's Medical Research Institute

University of Edinburgh

Production and Characterization of Human Macrophages from Pluripotent Stem Cells