Modulating the Actions of NK Cell-Mediated Cytotoxicity Using Lipid-PEG (n) and Inhibitory Receptor-Specific Antagonistic Peptide Conjugates

Chemoenzymatic labeling to visualize intercellular contacts using lipidated sortase A

Methods to label intercellular contact have attracted attention because of their potential in cell biological and medical applications for the analysis of intercellular communications. In this study, a simple and versatile method for chemoenzymatic labeling of intercellularly contacting cells is demonstrated using a cell-surface anchoring reagent of a poly(ethylene glycol)(PEG)-lipid conjugate. The surfaces of each cell in the cell pairs of interest were decorated with sortase A (SrtA) and triglycine peptide that were lipidated with PEG-lipid. In the mixture of the two cell populations, the triglycine-modified cells were enzymatically labeled with a fluorescent labeling reagent when in contact with SrtA-modified cells on a substrate. The selective labeling of the contacting cells was confirmed by confocal microscopy. The method is a promising tool for selective visualization of intercellularly contacting cells in cell mixtures for cell-cell communication analysis.

Photoactivatable Materials for Versatile Single-Cell Patterning Based on the Photocaging of Cell-Anchoring Moieties through Lipid Self-Assembly

Versatile methods for patterning multiple types of cells with single-cell resolution have become an increasingly important technology for cell analysis, cell-based device construction, and tissue engineering. Here, we present a photoactivatable material based on poly(ethylene glycol) (PEG)-lipids for patterning a variety of cells, regardless of their adhesion abilities. In this study, PEG-lipids bearing dual fatty acid chains were first shown to perfectly suppress cell anchoring on their coated substrate surfaces whereas those with single-chain lipids stably anchored cells through lipid-cell membrane interactions. From this finding, a PEG-lipid with one each of both normal and photocleavable fatty acid chains was synthesized as a material that could convert the chain number from two to one by exposure to light. On the photoconvertible PEG-lipid surface, cell anchoring was activated by light exposure. High-speed atomic force microscopy measurements revealed that this photocaging of the lipid-cell membrane interaction occurs because the hydrophobic dual chains self-assemble into nanoscale structures and cooperatively inhibit the anchoring. Light-induced dissociation of the lipid assembly achieved the light-guided fine patterning of multiple cells through local photoactivation of the anchoring interactions. Using this surface, human natural killer cells and leukemia cells could be positioned to interact one-by-one. The cytotoxic capacity of single immune cells was then monitored via microscopy, showing the proof-of-principle for applications in the high-throughput analysis of the heterogeneity in individual cell-cell communications. Thus, the substrate coated with our photoactivatable material can serve as a versatile platform for the accurate and rapid patterning of multiple-element cells for intercellular communication-based diagnostics.

Chemical Reactive Anchoring Lipids with Different Performance for Cell Surface Re-engineering Application

Introduction of selectively chemical reactive groups at the cell surface enables site-specific cell surface labeling and modification opportunity, thus facilitating the capability to study the cell surface molecular structure and function and the molecular mechanism it underlies. Further, it offers the opportunity to change or improve a cell's functionality for interest of choice. In this study, two chemical reactive anchor lipids, phosphatidylethanolamine-poly(ethylene glycol)-dibenzocyclooctyne (DSPE-PEG₂₀₀₀-DBCO) and cholesterol-PEG-dibenzocyclooctyne (CHOL-PEG₂₀₀₀-DBCO) were synthesized and their potential application for cell surface re-engineering via lipid fusion were assessed with RAW 264.7 cells as a model cell. Briefly, RAW 264.7 cells were incubated with anchor lipids under various concentrations and at different incubation times. The successful incorporation of the chemical reactive anchor lipids was confirmed by biotinylation via copper-free click chemistry, followed by streptavidin-fluorescein isothiocyanate binding. In comparison, the cholesterol-based anchor lipid afforded a higher cell membrane incorporation efficiency with less internalization than the phospholipid-based anchor lipid. Low cytotoxicity of both anchor lipids upon incorporation into the RAW 264.7 cells was observed. Further, the cell membrane residence time of the cholesterol-based anchor lipid was evaluated with confocal microscopy. This study suggests the potential cell surface re-engineering applications of the chemical reactive anchor lipids.

Incorporation of Artificial Lipid-Anchored Proteins into Cultured Mammalian Cells

Exogenous lipid-anchored proteins can be incorporated into the plasma membranes of living mammalian cells, allowing the chemical structure of the incorporated protein and its lipid anchor to be controlled (and varied) to a much greater degree than is possible for proteins expressed by the cells themselves. This technology offers a variety of potential applications, including incorporating novel and complex protein constructs into cell surfaces and exploring structure-function relationships for biologically important lipid-anchored proteins such as glycosylphosphatidylinositol-anchored proteins. Here we describe detailed methods for stable incorporation of artificial lipid-anchored proteins into cultured mammalian cells under mild, nonperturbing conditions.

Biomolecular engineering for nanobio/bionanotechnology

Biomolecular engineering can be used to purposefully manipulate biomolecules, such as peptides, proteins, nucleic acids and lipids, within the framework of the relations among their structures, functions and properties, as well as their applicability to such areas as developing novel biomaterials, biosensing, bioimaging, and clinical diagnostics and therapeutics. Nanotechnology can also be used to design and tune the sizes, shapes, properties and functionality of nanomaterials. As such, there are considerable overlaps between nanotechnology and biomolecular engineering, in that both are concerned with the structure and behavior of materials on the nanometer scale or smaller. Therefore, in combination with nanotechnology, biomolecular engineering is expected to open up new fields of nanobio/bionanotechnology and to contribute to the development of novel nanobiomaterials, nanobiodevices and nanobiosystems. This review highlights recent studies using engineered biological molecules (e.g., oligonucleotides, peptides, proteins, enzymes, polysaccharides, lipids, biological cofactors and ligands) combined with functional nanomaterials in nanobio/bionanotechnology applications, including therapeutics, diagnostics, biosensing, bioanalysis and biocatalysts. Furthermore, this review focuses on five areas of recent advances in biomolecular engineering: (a) nucleic acid engineering, (b) gene engineering, (c) protein engineering, (d) chemical and enzymatic conjugation technologies, and (e) linker engineering. Precisely engineered nanobiomaterials, nanobiodevices and nanobiosystems are anticipated to emerge as next-generation platforms for bioelectronics, biosensors, biocatalysts, molecular imaging modalities, biological actuators, and biomedical applications.

Poly(ethylene glycol)-Lipid-Conjugated Antibodies Enhance Dendritic Cell Phagocytosis of Apoptotic Cancer Cells

A simple method for attaching immunoglobulin G (IgG) on the cell surface was successfully developed for enhancing phagocytosis of apoptotic tumor cells (ATCs) by dendritic cells (DCs) ex vivo. By conjugating with a poly(ethylene glycol) (PEG)-lipid, named the biocompatible anchor for the membrane (BAM), arbitrary IgG could be incorporated into the cell membrane. In particular, when IgG-BAM conjugates were prepared at the optimal molar ratio of IgG to BAM (1 to 20), almost all cells were efficiently modified with IgG by treatment with IgG-BAM. This simple method was successfully applied to four types of mammalian cells. Furthermore, treatment of ATCs with the IgG-BAM conjugate increased the phagocytosis ratio of ATCs by DCs two-fold when compared to no treatment. This phagocytosis-enhancing effect was nearly identical to treatment with a tumor-specific IgG. Thus, without employing the tumor-specific IgG, which is difficult to obtain for any tumor cells and is expensive, the present method could opsonize ATC with the use of arbitrary IgG. The results strongly indicate that IgG-BAM treatment represents a promising method for opsonizing ATC with human serum IgG, and that this approach will lead to objective clinical responses in DC vaccines.

Islet-encapsulation in ultra-thin layer-by-layer membranes of poly(vinyl alcohol) anchored to poly(ethylene glycol)-lipids in the cell membrane

The microencapsulation of islets of Langerhans (islets) in a semipermeable membrane, i.e., the creation of a bioartificial pancreas, has been studied as a safe and simple technique for islet transplantation without the need for immunosuppressive therapy. The total volume of the implant tends to increase after enclosure of the islets in the semipermeable membrane, which limits transplantation sites. Thus, ultra-thin membranes are required for clinical applications. Here, we propose a novel method to encapsulate islets in an ultra-thin membrane of poly(vinyl alcohol) (PVA) anchored to a poly(ethylene glycol) (PEG)-phospholipid conjugate bearing a maleimide group (Mal-PEG-lipids, PEG Mw: 5000) in the cell membranes of islets. When Mal-PEG-lipids were added to an islet suspension, they spontaneously formed a thin layer on cells of the outer layer of islets. The PEG-lipid layer on the islets was covered by a PVA monolayer, and the PVA membrane was further reinforced by using the layer-by-layer method with thiol/disulfide exchange reactions. No practical volume increase in islets was observed after microencapsulation by this method. In addition, encapsulation of the islet surface in PVA membranes did not impair insulin release in response to glucose stimulation.

Encapsulation of islets with ultra-thin polyion complex membrane through poly(ethylene glycol)-phospholipids anchored to cell membrane

The microencapsulation of islets of Langerhans (islets) has been studied as a safe and simple technique for islet transplantation without the need for immuno-suppressive therapy. However, thinner membranes are desired, because the increased total volume of the implant led to limited transplantation sites. Here, we propose a novel method for microencapsulation by polyion complex membrane formation on islets. Amino group-terminated poly(ethylene glycol)-conjugated phospholipids (PEG-lipids, M(w): 5000) spontaneously formed a thin layer on cells existing in the outer layer of islets when they were added to islet suspension. This layer-by-layer membrane could be further formed on the PEG-lipid layer through polyion complex formation between amino groups at the end of PEG chains, sodium alginate and poly(l-lysine). Islets could be microencapsulated by this method without volume increase. Encapsulation of the islet surface with PEG-lipids and polyion complex membranes did not impair the insulin release function in response to glucose stimulation. Our method is promising to encapsulate islets without affecting cell viability or increasing volume.