Background

Human pluripotent stem cells (hPSCs) have become indispensable tools for studying development, modeling disease, and evaluating new therapeutics. Many of these applications rely on stable expression of transgenes, such as fluorescent reporters and components used for genetic engineering. However, transgenes are frequently silenced as pluripotent stem cells differentiate into mature cell types, limiting long-term genetic studies and reducing the reliability of stem cell-based experimental models. Existing approaches can maintain transgene expression in undifferentiated stem cells but often fail to preserve expression as differentiation progresses.

Stem cell workflow

To overcome transgene silencing, Uenaka et al. developed the TK4 PiggyBac vector, an optimized genetic expression system designed to maintain stable transgene expression throughout stem cell differentiation. After identifying promoter and regulatory element combinations that resisted silencing, the researchers evaluated the system across multiple independent differentiation protocols. Among these validation studies, human pluripotent stem cells maintained on Biolaminin® 521 were differentiated into midbrain dopaminergic neurons, with stable transgene expression maintained as the cells progressed through differentiation. This provided one example of the TK4 system performing within a defined stem cell culture workflow for neuronal differentiation.

Results

The TK4 vector was further validated across seven independent laboratories using a range of neuronal and microglial differentiation protocols. Transgene expression remained stable across diverse stem cell models and independently performed experiments, supporting the broader applicability of the system beyond a single differentiation protocol. The researchers also identified three novel genomic safe harbor loci that supported sustained transgene expression from genomic regions outside annotated genes, expanding the available strategies for stable genetic modification of hPSCs.

Future outlook

Maintaining transgene expression as stem cells acquire specialized identities is important for the reliability of genetically engineered hPSC models. By addressing silencing across multiple cell types and independent differentiation protocols, the TK4 system provided a practical approach for studies that require sustained genetic expression over time. Its broad validation could support more robust use of engineered hPSCs in applications ranging from mechanistic research to complex disease models.

Cited study: Uenaka T, Napole A, Saha AD, et al. Prevention of transgene silencing during human pluripotent stem cell differentiation. Cell Stem Cell. 2026;33:517–530. https://doi.org/10.1016/j.stem.2026.01.007

Product used in this study:

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  Biolaminin 521 LN (LN521)

  Full-length human recombinant laminin-521

  Biolaminin 521 LN is a full-length laminin-521 substrate—the natural laminin for pluripotent stem cells, reliably facilitating ESC and iPSC self-r […]
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