Highly efficient derivation of functional human induced pluripotent stem cell-derived macrophages under serum-free conditions to study innate immune responses

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INTRODUCTION: Macrophages are essential components of innate immunity, serving as a frontline defense against pathogens and maintaining tissue homeostasis. Human induced pluripotent stem cell (iPSC)-derived macrophages (iMacs) provide a powerful platform for studying human innate immunity and macrophage biology. Here, we describe a robust, reproducible, efficient serum-free and feeder-free protocol for generating functional iMacs and characterizing their innate immune properties. METHODS: A 30-day monolayer culture system was utilized to continually generate hematopoietic progenitor cells (HPCs) from iPSCs starting on day 9, followed by macrophage differentiation over 21 days. Macrophage identity was assessed by flow cytometry, while functional assays evaluated phagocytosis and cytokine production, including interferons (IFNs). Transcriptomic profiling was performed by RNAseq across differentiation stages and following IFN stimulation. RESULTS: The optimized protocol consistently yielded iMacs with >99% purity, expressing canonical macrophage markers including CD14, CD16, CD163, HLA-DR, and CD11b. iMacs demonstrated robust phagocytic capacity and cytokine production in response to microbial stimuli. RNA sequencing revealed distinct gene signatures during differentiation, highlighting key transitions from pluripotency to progenitors, then to mature macrophages. iMac transcriptomes aligned with tissue-resident macrophage profiles, supporting their relevance for modelling tissue-specific immunity. iMacs displayed differential interferon responses, with a strong response to type I IFNs. CONCLUSION: This study establishes a highly efficient and robust protocol for generating functional human iPSC-derived macrophages, providing a versatile model for investigating innate immunity, host-pathogen interactions, and interferon signaling.

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