Controlled Detachment of Chemically Glued Cells

An Enzyme-Responsive Self-Immolative Recognition Marker for Manipulating Cell-Cell Interactions

The development of innovative strategies for cell membranes engineering is of prime interest to explore and manipulate cell-cell interactions. Herein, an enzyme-sensitive recognition marker that can be introduced on cell surface via bioorthogonal chemistry is designed. Once functionalized in this fashion, the cells gain the ability to assemble with cell partners coated with the complementary marker through non-covalent click chemistry. The artificial cell adhesion induces natural biological processes associated with cell proximity such as inhibiting cancer cell proliferation and migration. On the other hand, the enzymatic activation of the stimuli-responsive marker triggers the disassembly of cells, thereby restoring the tumor cell proliferation and migration rates. Thus, the study shows that the ready-to-use complementary markers are valuable tools for controlling the formation and the breaking of bonds between cells, offering an easy way to investigate biological processes associated to cell proximity.

Integrating Metabolic Oligosaccharide Engineering and SPAAC Click Chemistry for Constructing Fibrinolytic Cell Surfaces

To effectively solve the problem of significant loss of transplanted cells caused by thrombosis during cell transplantation, this study simulates the human fibrinolytic system and combines metabolic oligosaccharide engineering with strain-promoted azide-alkyne cycloaddition (SPAAC) click chemistry to construct a cell surface with fibrinolytic activity. First, a copolymer (POL) of oligoethylene glycol methacrylate (OEGMA) and 6-amino-2-(2-methylamido)hexanoic acid (Lys) was synthesized by reversible addition-fragmentation chain transfer (RAFT) copolymerization, and the dibenzocyclooctyne (DBCO) functional group was introduced into the side chain of the copolymer through an active ester reaction, resulting in a functionalized copolymer DBCO-PEG4-POL with ε-lysine ligands. Then, azide functional groups were introduced onto the surface of HeLa model cells through metabolic oligosaccharide engineering, and DBCO-PEG4-POL was further specifically modified onto the surface of HeLa cells via the SPAAC "click" reaction. In vitro investigations revealed that compared with unmodified HeLa cells, modified cells not only resist the adsorption of nonspecific proteins such as fibrinogen and human serum albumin but also selectively bind to plasminogen in plasma while maintaining good cell viability and proliferative activity. More importantly, upon the activation of adsorbed plasminogen into plasmin, the modified cells exhibited remarkable fibrinolytic activity and were capable of promptly dissolving the primary thrombus formed on their surfaces. This research not only provides a novel approach for constructing transplantable cells with fibrinolytic activity but also offers a new perspective for effectively addressing the significant loss of transplanted cells caused by thrombosis.

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Metabolic Glycoengineering: A Promising Strategy to Remodel Microenvironments for Regenerative Therapy

Cell-based regenerative therapy utilizes the differentiation potential of stem cells to rejuvenate tissues. But the dynamic fate of stem cells is calling for precise control to optimize their therapeutic efficiency. Stem cell fate is regulated by specific conditions called "microenvironments." Among the various factors in the microenvironment, the cell-surface glycan acts as a mediator of cell-matrix and cell-cell interactions and manipulates the behavior of cells. Herein, metabolic glycoengineering (MGE) is an easy but powerful technology for remodeling the structure of glycan. By presenting unnatural glycans on the surface, MGE provides us an opportunity to reshape the microenvironment and evoke desired cellular responses. In this review, we firstly focused on the determining role of glycans on cellular activity; then, we introduced how MGE influences glycosylation and subsequently affects cell fate; at last, we outlined the application of MGE in regenerative therapy, especially in the musculoskeletal system, and the future direction of MGE is discussed.

Cell-Membrane-Anchored Upconversion Nanoprobe for Near-Infrared Light Triggered Cell-Cell Interactions

Manipulating cell-cell interactions is of great significance in cell communication and cell-based therapies. Although efforts have been made to construct cell-cell assembly by stimuli-responsive host-guest interactions, controllable cell-cell interactions by near-infrared (NIR) light triggered reversible assembly remain a challenge. Herein, we develop a NIR-controlled system based on β-cyclodextrin (β-CD) modified upconversion nanoparticles (UCNPs) for reversible and noninvasive manipulation of cell assembly and disassembly, which is realized by host-guest interactions between E/Z-photoisomerization of arylazopyrazole (AAP) and β-CD under the NIR irradiation. UCNPs can convert NIR to ultraviolet light, which leads to the transformation of AAP from the E-isomer to the Z-isomer. And it can be reverted back to the E-isomer under visible light irradiation. This reversible photoisomerization can modulate the host-guest interaction between β-CD and AAP, thus leading to reversible cell assembly and disassembly. Furthermore, by precise regulating cell-cell interactions by NIR light, cell-cell communication and molecular transportation can be realized. Given the diversity of host and guest molecules and the advantages of NIR light in biological applications, reversible cell-cell assembly has great potential for the regulation of cell behaviors and cell-based therapies.

The Applications of Metabolic Glycoengineering

Mammalian cell membranes are decorated by the glycocalyx, which offer versatile means of generating biochemical signals. By manipulating the set of glycans displayed on cell surface, it is vital for gaining insight into the cellular behavior modulation and medical and biotechnological adhibition. Although genetic engineering is proven to be an effective approach for cell surface modification, the technique is only suitable for natural and genetically encoded molecules. To circumvent these limitations, non-genetic approaches are developed for modifying cell surfaces with unnatural but functional groups. Here, we review latest development of metabolic glycoengineering (MGE), which enriches the chemical functions of the cell surface and is becoming an intriguing new tool for regenerative medicine and tissue engineering. Particular emphasis of this review is placed on discussing current applications and perspectives of MGE.

Manipulation of Multiple Cell-Cell Interactions by Tunable DNA Scaffold Networks

Manipulation of cell-cell interactions via cell surface engineering has potential biomedical applications in tissue engineering and cell therapy. However, manipulation of the comprehensive and multiple intercellular interactions remains a challenge and missing elements. Herein, utilizing a DNA triangular prism (TP) and a branched polymer (BP) as functional modules, we fabricate tunable DNA scaffold networks on the cell surface. The responsiveness of cell-cell recognition, aggregation and dissociation could be modulated by aptamer-functionalized DNA scaffold networks with high accuracy and specificity. By regulating the DNA scaffold networks coated on the cell surface, controlled intercellular molecular transportation is achieved. Our tunable network provides a simple and extendible strategy which addresses a current need in cell surface engineering to precisely manipulate cell-cell interactions and shows promise as a general tool for controllable cell behavior.

Cell-cell interactions via non-covalent click chemistry

Metabolic glycoengineering with unnatural sugars became a valuable tool for introducing recognition markers on the cell membranes via bioorthogonal chemistry. By using this strategy, we functionalized the surface of tumor and T cells using complementary artificial markers based on both β-cyclodextrins (β-CDs) and adamantyl trimers, respectively. Once tied on cell surfaces, the artificial markers induced cell-cell adhesion through non-covalent click chemistry. These unnatural interactions between A459 lung tumor cells and Jurkat T cells triggered the activation of natural killer (NK) cells thanks to the increased production of interleukin-2 (IL-2) in the vicinity of cancer cells, leading ultimately to their cytolysis. The ready-to-use surface markers designed in this study can be easily inserted on the membrane of a wide range of cells previously submitted to metabolic glycoengineering, thereby offering a simple way to investigate and manipulate intercellular interactions.

Enhanced Endothelial Cell Delivery for Repairing Injured Endothelium via Pretargeting Approach and Bioorthogonal Chemistry

Arterial wall injury often leads to endothelium cell activation, endothelial detachment, and atherosclerosis plaque formation. While abundant research efforts have been placed on treating the end stages of the disease, no cure has been developed to repair injured and denude endothelium often occurred at an early stage of atherosclerosis. Here, a pretargeting cell delivery strategy using combined injured endothelial targeting nanoparticles and bioorthogonal click chemistry approach was developed to deliver endothelial cells to replenish the injured endothelium via a two-step process. First, nanoparticles bearing glycoprotein 1b α (Gp1bα) proteins and tetrazine (Tz) were fabricated to provide a homogeneous nanoparticle coating on an injured arterial wall via the interactions between Gp1bα and von Willebrand factor (vWF), a ligand that is present on denuded endothelium. Second, transplanted endothelium cells bearing transcyclooctene (TCO) would be quickly immobilized on the surfaces of nanoparticles via TCO:Tz reactions. In vitro binding studies under both static and flow conditions confirmed that our novel Tz-labeled Gp1bα-conjugated poly(lactic-co-glycolic acid) (PLGA) nanoparticles can successfully pretargeted toward the injured site and support rapid adhesion of endothelial cells from the circulation. Ex vivo results also confirm that such an approach is highly efficient in mediating the local delivery of endothelial cells at the sites of arterial injury. The results support that this pretargeting cell delivery approach may be used for repairing injured endothelium in situ at its early stage.

Advanced Bottom-Up Engineering of Living Architectures

Bottom-up tissue engineering is a promising approach for designing modular biomimetic structures that aim to recapitulate the intricate hierarchy and biofunctionality of native human tissues. In recent years, this field has seen exciting progress driven by an increasing knowledge of biological systems and their rational deconstruction into key core components. Relevant advances in the bottom-up assembly of unitary living blocks toward the creation of higher order bioarchitectures based on multicellular-rich structures or multicomponent cell-biomaterial synergies are described. An up-to-date critical overview of long-term existing and rapidly emerging technologies for integrative bottom-up tissue engineering is provided, including discussion of their practical challenges and required advances. It is envisioned that a combination of cell-biomaterial constructs with bioadaptable features and biospecific 3D designs will contribute to the development of more robust and functional humanized tissues for therapies and disease models, as well as tools for fundamental biological studies.

Biomedical applications of copper-free click chemistry: in vitro, in vivo, and ex vivo

Recently, click chemistry has provided important advances in biomedical research fields. Particularly, copper-free click chemistry including strain-promoted azide-alkyne cycloaddition (SPAAC) and inverse-electron-demand Diels-Alder (iEDDA) reactions enable fast and specific chemical conjugation under aqueous conditions without the need for toxic catalysts. Click chemistry has resulted in a change of paradigm, showing that artificial chemical reactions can occur on cell surfaces, in cell cytosol, or within the body, which is not easy with most other chemical reactions. Click chemistry in vitro allows specific labelling of cellular target proteins and studying of drug target engagement with drug surrogates in live cells. Furthermore, cellular membrane lipids and proteins could be selectively labelled with click chemistry in vitro and cells could be adhered together using click chemistry. Click chemistry in vivo enables efficient and effective molecular imaging and drug delivery for diagnosis and therapy. Click chemistry ex vivo can be used to develop molecular tools to understand tissue development, diagnosis of diseases, and therapeutic monitoring. Overall, the results from research to date suggest that click chemistry has emerged as a valuable tool in biomedical fields as well as in organic chemistry.

Cell membrane engineering with synthetic materials: Applications in cell spheroids, cellular glues and microtissue formation

Biologically inspired materials with tunable bio- and physicochemical properties provide an essential framework to actively control and support cellular behavior. Cell membrane remodeling approaches benefit from the advances in polymer science and bioconjugation methods, which allow for the installation of un-/natural molecules and particles on the cells' surface. Synthetically remodeled cells have superior properties and are under intense investigation in various therapeutic scenarios as cell delivery systems, bio-sensing platforms, injectable biomaterials and bioinks for 3D bioprinting applications. In this review article, recent advances in the field of cell surface remodeling via bio-chemical means and the potential biomedical applications of these emerging cell hybrids are discussed. STATEMENT OF SIGNIFICANCE: Recent advances in bioconjugation methods, controlled/living polymerizations, microfabrication techniques and 3D printing technologies have enabled researchers to probe specific cellular functions and cues for therapeutic and research purposes through the formation of cell spheroids and polymer-cell chimeras. This review article highlights recent non-genetic cell membrane engineering strategies towards the fabrication of cellular ensembles and microtissues with interest in 3D in vitro modeling, cell therapeutics and tissue engineering. From a wider perspective, these approaches may provide a roadmap for future advances in cell therapies which will expedite the clinical use of cells, thereby improving the quality and accessibility of disease treatments.