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Synthetic biology is the discipline of engineering application-driven biological functionalities that were not evolved by nature. Early breakthroughs of cell engineering, which were based on ectopic (over)expression of single sets of transgenes, have already had a revolutionary impact on the biotechnology industry, regenerative medicine and blood transfusion therapies. Now, we require larger-scale, rationally assembled genetic circuits engineered to programme and control various human cell functions with high spatiotemporal precision in order to solve more complex problems in applied life sciences, biomedicine and environmental sciences. This will open new possibilities for employing synthetic biology to advance personalized medicine by converting cells into living therapeutics to combat hitherto intractable diseases.

Extracellular vesicles (EVs) are biocompatible, nano‐sized secreted vesicles containing many types of biomolecules, including proteins, RNAs, DNAs, lipids, and metabolites. Their low immunogenicity and ability to functionally modify recipient cells by transferring diverse bioactive constituents make them an excellent candidate for a next‐generation drug delivery system. Here, the recent advances in EV biology and emerging strategies of EV bioengineering are summarized, and the prospects for clinical translation of bioengineered EVs and the challenges to be overcome are discussed. Extracellular vesicles (EVs) managing diverse intercellular communication networks are attracting increasing interest in developing next‐generation drug delivery systems. This review provides a comprehensive state‐of‐the‐art coverage of EV biogenesis, transport, release, and uptake as well as cargo sorting and discusses the progress and challenges of engineering EVs for therapeutic applications.

Key Points A decade after the report of the first devices, synthetic biology has developed into an engineering science that provides novel opportunities to understand, diagnose, prevent and treat diseases. Chemical synthesis and reconstruction of extinct or difficult-to-propagate viral genomes improves our understanding of virulence factors. The de novo synthesis of deoptimized viral genomes enables the production of safe life vaccines. Engineering environmentally responsive dominant-lethal genetic circuits into disease-transmitting insects provides a highly specific approach for controlling disease propagation. The reconstruction of bacterial resistance circuits in mammalian cells enables the integrated discovery of agents to overcome resistance. Engineered bacteria and synthetic genetic circuits that specifically detect and destroy neoplastic cells will provide momentum to future cancer therapies. Molecular prostheses that detect disease states and autonomously trigger a therapeutic response in a closed-loop control configuration provide novel opportunities in the treatment of genetic and acquired diseases. Synthetic gene circuits will provide novel opportunities for future gene and cell-based therapies. Synthetic biological devices can be engineered to achieve high levels of precision and specificity, which makes them ideally suited for use in clinical settings. Devices are being developed to meet a range of biomedical needs, including specific cancer therapies and metabolic control. Synthetic biology aims to create functional devices, systems and organisms with novel and useful functions on the basis of catalogued and standardized biological building blocks. Although they were initially constructed to elucidate the dynamics of simple processes, designed devices now contribute to the understanding of disease mechanisms, provide novel diagnostic tools, enable economic production of therapeutics and allow the design of novel strategies for the treatment of cancer, immune diseases and metabolic disorders, such as diabetes and gout, as well as a range of infectious diseases. In this Review, we cover the impact and potential of synthetic biology for biomedical applications.

Designer cells executing rationally assembled genetic programs that can process input signals with programmable logic are combined in a 3D cell culture that performs three-input, two-output full-adder computations.Synthetic biologists have advanced the design of trigger-inducible gene switches and their assembly into input-programmable circuits that enable engineered human cells to perform arithmetic calculations reminiscent of electronic circuits. By designing a versatile plug-and-play molecular-computation platform, we have engineered nine different cell populations with genetic programs, each of which encodes a defined computational instruction. When assembled into 3D cultures, these engineered cell consortia execute programmable multicellular full-adder logics in response to three trigger compounds.

Controlling gene expression with sophisticated logic gates has been and remains one of the central aims of synthetic biology. However, conventional implementations of biocomputers use central processing units (CPUs) assembled from multiple protein-based gene switches, limiting the programming flexibility and complexity that can be achieved within single cells. Here, we introduce a CRISPR/Cas9-based core processor that enables different sets of user-defined guide RNA inputs to program a single transcriptional regulator (dCas9-KRAB) to perform a wide range of bitwise computations, from simple Boolean logic gates to arithmetic operations such as the half adder. Furthermore, we built a dual-core CPU combining two orthogonal core processors in a single cell. In principle, human cells integrating multiple orthogonal CRISPR/Cas9-based core processors could offer enormous computational capacity.

Cell therapy approaches that employ engineered mammalian cells for on-demand production of therapeutic agents in the patient’s body are moving beyond proof-of-concept in translational medicine. The therapeutic cells can be customized to sense user-defined signals, process them, and respond in a programmable and predictable way. In this paper, we introduce the available tools and strategies employed to design therapeutic cells. Then, various approaches to control cell behaviors, including open-loop and closed-loop systems, are discussed. We also highlight therapeutic applications of engineered cells for early diagnosis and treatment of various diseases in the clinic and in experimental disease models. Finally, we consider emerging technologies such as digital devices and their potential for incorporation into future cell-based therapies.

Existing devices for generating electrical power from water vapor in ambient air require high levels of relative humidity (RH), cannot operate for prolonged periods, and provide insufficient output for most practical applications. Here a heterogeneous moisture‐driven electrical power generator (MODEG) is developed in the form of a free‐standing bilayer of polyelectrolyte films, one consisting of a hygroscopic matrix of graphene oxide(GO)/polyaniline(PANI) [(GO)PANI] and the other consisting of poly(diallyldimethylammonium chloride)(PDDA)‐modified fluorinated Nafion (F‐Nafion (PDDA)). One MODEG unit (1 cm2) can deliver a stable open‐circuit output of 0.9 V at 8 µA for more than 10 h with a matching external load. The device works over a wide range of temperature (−20 to +50 °C) and relative humidity (30% to 95% RH). It is shown that series and parallel combinations of MODEG units can directly supply sufficient power to drive commercial electronic devices such as light bulbs, supercapacitors, circuit boards, and screen displays. The (GO)PANI:F‐Nafion (PDDA) hybrid film is embedded in a mask to harvest the energy from exhaled water vapor in human breath under real‐life conditions. The device could consistently generate 450–600 mV during usual breathing, and provides sufficient power to drive medical devices, wearables, and emergency communication. A heterogeneous hybrid film based on graphene oxide/polyaniline:poly(diallyldimethylammonium chloride)‐modified fluorinated Nafion is designed and a moisture‐driven electrical power generator (MODEG) is assembled. MODEGs can deliver a stable open‐circuit output of 0.9 V at 8 µA for more than 10 h with a matching external load.

Exosomes are cell-derived nanovesicles (50–150 nm), which mediate intercellular communication, and are candidate therapeutic agents. However, inefficiency of exosomal message transfer, such as mRNA, and lack of methods to create designer exosomes have hampered their development into therapeutic interventions. Here, we report a set of EXOsomal transfer into cells (EXOtic) devices that enable efficient, customizable production of designer exosomes in engineered mammalian cells. These genetically encoded devices in exosome producer cells enhance exosome production, specific mRNA packaging, and delivery of the mRNA into the cytosol of target cells, enabling efficient cell-to-cell communication without the need to concentrate exosomes. Further, engineered producer cells implanted in living mice could consistently deliver cargo mRNA to the brain. Therapeutic catalase mRNA delivery by designer exosomes attenuated neurotoxicity and neuroinflammation in in vitro and in vivo models of Parkinson’s disease, indicating the potential usefulness of the EXOtic devices for RNA delivery-based therapeutic applications. Exosomes function as intercellular information transmitters and are candidates for delivery of therapeutic agents. Here the authors present EXOtic, a synthetic biology device for in-situ production of designer exosomes and demonstrate in vivo application in models of Parkinson's disease.

Synthetic receptors targeted to the secretory pathway often fail to exhibit the expected activity due to post-translational modifications (PTMs) and/or improper folding. Here, we engineered synthetic receptors that reside in the cytoplasm, inside the endoplasmic reticulum (ER), or on the plasma membrane through orientation adjustment of the receptor parts and by elimination of dysfunctional PTMs sites. The cytoplasmic receptors consist of split-TEVp domains that reconstitute an active protease through chemically-induced dimerization (CID) that is triggered by rapamycin, abscisic acid, or gibberellin. Inside the ER, however, some of these receptors were non-functional, but their activity was restored by mutagenesis of cysteine and asparagine, residues that are typically associated with PTMs. Finally, we engineered o rthogonal c hemically a ctivated cell-surface r eceptors (OCARs) consisting of the Notch1 transmembrane domain fused to cytoplasmic tTA and extracellular CID domains. Mutagenesis of cysteine residues in CID domains afforded functional OCARs which enabled fine-tuning of orthogonal signalling in mammalian cells. Artificial receptors targeted to the secretory pathway often fail to exhibit the expected activity due to post-translational modifications and/or improper folding. Here, the authors engineer diverse synthetic receptors that reside in the cytoplasm, inside the endoplasmic reticulum, or on the plasma membrane through orientation adjustment of the receptor parts and by elimination of dysfunctional PTMs sites.

Arming human cells with synthetic gene circuits enables to expand their capacity to execute superior sensing and response actions, offering tremendous potential for innovative cellular therapeutics. This can be achieved by assembling components from an ever‐expanding molecular toolkit, incorporating switches based on transcriptional, translational, or post‐translational control mechanisms. This review provides examples from the three classes of switches, and discusses their advantages and limitations to regulate the activity of therapeutic cells in vivo. Genetic switches designed to recognize internal disease‐associated signals often encode intricate actuation programs that orchestrate a reduction in the sensed signal, establishing a closed‐loop architecture. Conversely, switches engineered to detect external molecular or physical cues operate in an open‐loop fashion, switching on or off upon signal exposure. The integration of such synthetic gene circuits into the next generation of chimeric antigen receptor T‐cells is already enabling precise calibration of immune responses in terms of magnitude and timing, thereby improving the potency and safety of therapeutic cells. Furthermore, pre‐clinical engineered cells targeting other chronic diseases are gathering increasing attention, and this review discusses the path forward for achieving clinical success. With synthetic biology at the forefront, cellular therapeutics holds great promise for groundbreaking treatments. This review details examples of synthetic gene circuits based on transcriptional, translational, and post‐translational control mechanisms and discusses how they can be used for conditional regulation of protein expression and/or activity in response to specific internal or external stimuli, thereby enhancing the therapeutic efficacy and safety of engineered cell therapies.