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Abstract Despite the array of mammalian transgene switches available for regulating therapeutic protein expression in response to small molecules or physical stimuli, issues remain, including cytotoxicity of chemical inducers and limited biocompatibility of physical cues. This study introduces gene switches driven by short peptides comprising eight or fewer amino acid residues. Utilizing a competence regulator (ComR) and sigma factor X‐inducing peptide (XIP) from Streptococcus vestibularis as the receptor and inducer, respectively, this study develops two strategies for a peptide‐activated transgene control system. The first strategy involves fusing ComR with a transactivation domain and utilizes ComR‐dependent synthetic promoters to drive expression of the gene‐of‐interest, activated by XIP, thereby confirming its membrane penetrability and intracellular functionality. The second strategy features an orthogonal synthetic receptor exposing ComR extracellularly (ComREXTRA), greatly increasing sensitivity with exceptional responsiveness to short peptides. In a proof‐of‐concept study, peptides are administered to type‐1 diabetic mice with microencapsulated engineered human cells expressing ComREXTRA for control of insulin expression, restoring normoglycemia. It is envisioned that this system will encourage the development of short peptide drugs and promote the introduction of non‐toxic, orthogonal, and highly biocompatible personalized biopharmaceuticals for gene‐ and cell‐based therapies.

Abstract Synthetic biology aims to engineer transgene switches for precise therapeutic protein control in cell‐based gene therapies. However, off‐the‐shelf trigger‐inducible gene circuits are usually switched on by single or structurally similar molecules. This study presents a mammalian gene‐switch platform that controls therapeutic gene expression by a wide range of molecules generating low, non‐toxic levels of reactive oxygen species (ROS). In this system, KEAP1 (Kelch‐like ECH‐associated protein 1) serves as ROS sensor, regulating the translocation of NRF2 (nuclear factor erythroid 2‐related factor 2) to the nucleus, where NRF2 binds to antioxidant response elements (ARE) to activate the expression of a gene of interest. It is found that a promoter containing eight‐tandem ARE repeats is highly sensitive to the low ROS levels generated by the soluble and volatile molecules, which include food preservatives, food additives, pharmaceuticals, and signal transduction inducers. In a proof‐of‐concept study, it is shown that many of these compounds can independently trigger microencapsulated engineered cells to produce sufficient insulin to restore normoglycemia in experimental type‐1 diabetic mice. It is believed that this system greatly extends the variety of small‐molecule inducers available to drive therapeutic gene switches.

Abstract Next‐generation gene and engineered‐cell therapies benefit from incorporating synthetic gene networks that can precisely regulate the therapeutic output in response to externally administered signal inputs that are safe, readily bioavailable and pleasant to take. To enable such therapeutic control, a mammalian gene switch is designed to be responsive to the natural sweetener xylose and its functionality is assessed in mouse studies. The gene switch consists of the bacterial transcription regulator XylR fused to a mammalian transactivator, which binds to an optimized promoter in the presence of xylose, thereby allowing dose‐dependent transgene expression. The sensitivity of SWEET (sweetener‐inducible expression of transgene) is improved by coexpressing a xylose transporter. Mice implanted with encapsulated SWEET‐engineered cells show increased blood levels of cargo protein when taking xylose‐sweetened water or coffee, or highly concentrated apple extract, while they do not respond to intake of a usual amount of carrots, which contain xylose. In a proof‐of‐concept therapeutic application study, type‐1 diabetic mice engineered with insulin‐expressing SWEET show lowered glycemia and increased insulin levels when administered this fairly diabetic‐compliant sweetener, compared to untreated mice. A SWEET‐based therapy appears to have the potential to integrate seamlessly into patients’ life‐style and food habits in the move toward personalized medicine.

Abstract Rapid insulin release plays an essential role in maintaining blood‐glucose homeostasis in mammalians. Patients diagnosed with type‐I diabetes mellitus experience chronic and remarkably high blood‐sugar levels, and require lifelong insulin injection therapy, so there is a need for more convenient and less invasive insulin delivery systems to increase patients’ compliance and also to enhance their quality of life. Here, an endoplasmic‐reticulum‐localized split sec‐tobacco etch virus protease (TEVp)‐based rapamycin‐actuated protein‐induction device (RAPID) is engineered, which is composed of the rapamycin‐inducible dimerization domains FK506 binding protein (FKBP) and FKBP‐rapamycin binding protein fused with modified split sec‐TEVp components. Insulin accumulation inside the endoplasmic reticulum (ER) is achieved through tagging its C‐terminus with KDEL, an ER‐retention signal, spaced by a TEVp cleavage site. In the presence of rapamycin, the split sec‐TEVp‐based RAPID components dimerize, regain their proteolytic activity, and remove the KDEL retention signal from insulin. This leads to rapid secretion of accumulated insulin from cells within few minutes. Using liver hydrodynamic transfection methodology, it is shown that RAPID quickly restores glucose homeostasis in type‐1‐diabetic (T1DM) mice treated with an oral dose of clinically licensed rapamycin. This rapid‐release technology may become the foundation for other cell‐based therapies requiring instantaneous biopharmaceutical availability.

Abstract Body temperature is maintained at around 37 °C in humans, but may rise to 40 °C or more during high‐grade fever, which occurs in most adults who are seriously ill. However, endogenous temperature sensors, such as ion channels and heat‐shock promoters, are fully activated only at noxious temperatures above this range, making them unsuitable for medical applications. Here, a genetically encoded protein thermometer (human enhanced gene activation thermometer; HEAT) is designed that can trigger transgene expression in the range of 37–40 °C by linking a mutant coiled‐coil temperature‐responsive protein sensor to a synthetic transcription factor. To validate the construct, a HEAT‐transgenic monoclonal human cell line, FeverSense, is generated and it is confirmed that it works as a fever sensor that can temperature‐ and exposure‐time‐dependently trigger reporter gene expression in vitro and in vivo. For translational proof of concept, microencapsulated designer cells stably expressing a HEAT‐controlled insulin production cassette in a mouse model of type‐1 diabetes are subcutaneously implanted and topical heating patches are used to apply heat corresponding to a warm sensation in humans. Insulin release is induced, restoring normoglycemia. Thus, HEAT appears to be suitable for practical electrothermal control of cell‐based therapy, and may also have potential for next‐generation treatment of fever‐associated medical conditions.