FSL constructs: a simple method for modifying cell/virion surfaces with a range of biological markers without affecting their viability

Differential recognition of lipid domains by two Gb3-binding lectins

The two lectins LecA from Pseudomonas aeruginosa and the B-subunit of Shiga toxin from Shigella dysenteriae (StxB) share the glycosphingolipid globotriaosylceramide (Gb3) as receptor. Counterintuitively, we found that LecA and StxB segregated into different domains after recognizing Gb3 at the plasma membrane of cells. We hypothesized that the orientation of the carbohydrate head group of Gb3 embedded in the lipid bilayer differentially influences LecA and StxB binding. To test this hypothesis, we reconstituted lectin-Gb3 interaction using giant unilamellar vesicles and were indeed able to rebuild LecA and StxB segregation. Both, the Gb3 fatty acyl chain structure and the local membrane environment, modulated Gb3 recognition by LecA and StxB. Specifically, StxB preferred more ordered membranes compared to LecA. Based on our findings, we propose comparing staining patterns of LecA and StxB as an alternative method to assess membrane order in cells. To verify this approach, we re-established that the apical plasma membrane of epithelial cells is more ordered than the basolateral plasma membrane. Additionally, we found that StxB recognized Gb3 at the primary cilium and the periciliary membrane, whereas LecA only bound periciliary Gb3. This suggests that the ciliary membrane is of higher order than the surrounding periciliary membrane.

AGI-134: a fully synthetic α-Gal glycolipid that converts tumors into in situ autologous vaccines, induces anti-tumor immunity and is synergistic with an anti-PD-1 antibody in mouse melanoma models

Background

Treatments that generate T cell-mediated immunity to a patient’s unique neoantigens are the current holy grail of cancer immunotherapy. In particular, treatments that do not require cumbersome and individualized ex vivo processing or manufacturing processes are especially sought after. Here we report that AGI-134, a glycolipid-like small molecule, can be used for coating tumor cells with the xenoantigen Galα1-3Galβ1-4GlcNAc (α-Gal) in situ leading to opsonization with pre-existing natural anti-α-Gal antibodies (in short anti-Gal), which triggers immune cascades resulting in T cell mediated anti-tumor immunity.

Methods

Various immunological effects of coating tumor cells with α-Gal via AGI-134 in vitro were measured by flow cytometry: (1) opsonization with anti-Gal and complement, (2) antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells, and (3) phagocytosis and antigen cross-presentation by antigen presenting cells (APCs). A viability kit was used to test AGI-134 mediated complement dependent cytotoxicity (CDC) in cancer cells. The anti-tumoral activity of AGI-134 alone or in combination with an anti-programmed death-1 (anti-PD-1) antibody was tested in melanoma models in anti-Gal expressing galactosyltransferase knockout (α1,3GT^−/−) mice. CDC and phagocytosis data were analyzed by one-way ANOVA, ADCC results by paired t-test, distal tumor growth by Mantel–Cox test, C5a data by Mann–Whitney test, and single tumor regression by repeated measures analysis.

Results

In vitro, α-Gal labelling of tumor cells via AGI-134 incorporation into the cell membrane leads to anti-Gal binding and complement activation. Through the effects of complement and ADCC, tumor cells are lysed and tumor antigen uptake by APCs increased. Antigen associated with lysed cells is cross-presented by CD8α+ dendritic cells leading to activation of antigen-specific CD8+ T cells. In B16-F10 or JB/RH melanoma models in α1,3GT^−/− mice, intratumoral AGI-134 administration leads to primary tumor regression and has a robust abscopal effect, i.e., it protects from the development of distal, uninjected lesions. Combinations of AGI-134 and anti-PD-1 antibody shows a synergistic benefit in protection from secondary tumor growth.

Conclusions

We have identified AGI-134 as an immunotherapeutic drug candidate, which could be an excellent combination partner for anti-PD-1 therapy, by facilitating tumor antigen processing and increasing the repertoire of tumor-specific T cells prior to anti-PD-1 treatment.

Rapid one-step biotinylation of biological and non-biological surfaces

We describe a rapid one-step method to biotinylate virtually any biological or non-biological surface. Contacting a solution of biotin-spacer-lipid constructs with a surface will form a coating within seconds on non-biological surfaces or within minutes on most biological membranes including membrane viruses. The resultant biotinylated surface can then be used to interact with avidinylated conjugates, beads, vesicles, surfaces or cells.

Engineering the Surface of Therapeutic "Living" Cells

Biological cells are complex living machines that have garnered significant attention for their potential to serve as a new generation of therapeutic and delivery agents. Because of their secretion, differentiation, and homing activities, therapeutic cells have tremendous potential to treat or even cure various diseases and injuries that have defied conventional therapeutic strategies. Therapeutic cells can be systemically or locally transplanted. In addition, with their ability to express receptors that bind specific tissue markers, cells are being studied as nano- or microsized drug carriers capable of targeted transport. Depending on the therapeutic targets, these cells may be clustered to promote intercellular adhesion. Despite some impressive results with preclinical studies, there remain several obstacles to their broader development, such as a limited ability to control their transport, engraftment, secretion and to track them in vivo. Additionally, creating a particular spatial organization of therapeutic cells remains difficult. Efforts have recently emerged to resolve these challenges by engineering cell surfaces with a myriad of bioactive molecules, nanoparticles, and microparticles that, in turn, improve the therapeutic efficacy of cells. This review article assesses the various technologies developed to engineer the cell surfaces. The review ends with future considerations that should be taken into account to further advance the quality of cell surface engineering.

Obtaining control of cell surface functionalizations via Pre-targeting and Supramolecular host guest interactions

The use of mammalian cells for therapeutic applications is finding its way into modern medicine. However, modification or "training" of cells to make them suitable for a specific application remains complex. By envisioning a chemical toolbox that enables specific, but straight-forward and generic cellular functionalization, we investigated how membrane-receptor (pre)targeting could be combined with supramolecular host-guest interactions based on β-cyclodextrin (CD) and adamantane (Ad). The feasibility of this approach was studied in cells with membranous overexpression of the chemokine receptor 4 (CXCR4). By combining specific targeting of CXCR4, using an adamantane (Ad)-functionalized Ac-TZ14011 peptide (guest; KD = 56 nM), with multivalent host molecules that entailed fluorescent β-CD-Poly(isobutylene-alt-maleic-anhydride)-polymers with different fluorescent colors and number of functionalities, host-guest cell-surface modifications could be studied in detail. A second set of Ad-functionalized entities enabled introduction of additional surface functionalities. In addition, the attraction between CD and Ad could be used to drive cell-cell interactions. Combined we have shown that supramolecular interactions, that are based on specific targeting of an overexpressed membrane-receptor, allow specific and stable, yet reversible, surface functionalization of viable cells and how this approach can be used to influence the interaction between cells and their surroundings.

Biomedical applications of glycosylphosphatidylinositol-anchored proteins

Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) use a unique posttranslational modification to link proteins to lipid bilayer membranes. The anchoring structure consists of both a lipid and carbohydrate portion and is highly conserved in eukaryotic organisms regarding its basic characteristics, yet highly variable in its molecular details. The strong membrane targeting property has made the anchors an interesting tool for biotechnological modification of lipid membrane-covered entities from cells through extracellular vesicles to enveloped virus particles. In this review, we will take a closer look at the mechanisms and fields of application for GPI-APs in lipid bilayer membrane engineering and discuss their advantages and disadvantages for biomedicine.

Directing and Potentiating Stem Cell-Mediated Angiogenesis and Tissue Repair by Cell Surface E-Selectin Coating

Stem cell therapy has emerged as a promising approach for treatment of a number of diseases, including delayed and non-healing wounds. However, targeted systemic delivery of therapeutic cells to the dysfunctional tissues remains one formidable challenge. Herein, we present a targeted nanocarrier-mediated cell delivery method by coating the surface of the cell to be delivered with dendrimer nanocarriers modified with adhesion molecules. Infused nanocarrier-coated cells reach to destination via recognition and association with the counterpart adhesion molecules highly or selectively expressed on the activated endothelium in diseased tissues. Once anchored on the activated endothelium, nanocarriers-coated transporting cells undergo transendothelial migration, extravasation and homing to the targeted tissues to execute their therapeutic role. We now demonstrate feasibility, efficacy and safety of our targeted nanocarrier for delivery of bone marrow cells (BMC) to cutaneous wound tissues and grafted corneas and its advantages over conventional BMC transplantation in mouse models for wound healing and neovascularization. This versatile platform is suited for targeted systemic delivery of virtually any type of therapeutic cell.

Ultra-Fast Glyco-Coating of Non-Biological Surfaces

The ability to glycosylate surfaces has medical and diagnostic applications, but there is no technology currently recognized as being able to coat any surface without the need for prior chemical modification of the surface. Recently, a family of constructs called function-spacer-lipids (FSL) has been used to glycosylate cells. Because it is known that lipid-based material can adsorb onto surfaces, we explored the potential and performance of cell-labelling FSL constructs to "glycosylate" non-biological surfaces. Using blood group A antigen as an indicator, the performance of a several variations of FSL constructs to modify a large variety of non-biological surfaces was evaluated. It was found the FSL constructs when optimised could in a few seconds glycosylate almost any non-biological surface including metals, glass, plastics, rubbers and other polymers. Although the FSL glycan coating was non-covalent, and therefore temporary, it was sufficiently robust with appropriate selection of spacer and surface that it could capture anti-glycan antibodies, immobilize cells (via antibody), and withstand incubation in serum and extensive buffer washing, making it suitable for diagnostic and research applications.

Cell surface glycoengineering improves selectin-mediated adhesion of mesenchymal stem cells (MSCs) and cardiosphere-derived cells (CDCs): Pilot validation in porcine ischemia-reperfusion model

Promising results are emerging in clinical trials focused on stem cell therapy for cardiology applications. However, the low homing and engraftment of the injected cells to target tissue continues to be a problem. Cellular glycoengineering can address this limitation by enabling the targeting of stem cells to sites of vascular injury/inflammation. Two such glycoengineering methods are presented here: i. The non-covalent incorporation of a P-selectin glycoprotein ligand-1 (PSGL-1) mimetic 19Fc[FUT7(+)] via lipid-protein G fusion intermediates that intercalate onto the cell surface, and ii. Over-expression of the α(1,3)fucosyltransferse FUT7 in cells. Results demonstrate the efficient coupling of 19Fc[FUT7(+)] onto both cardiosphere-derived cells (CDCs) and mesenchymal stem cells (MSCs), with coupling being more efficient when using protein G fused to single-tailed palmitic acid rather than double-tailed DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine). This non-covalent cellular modification was mild since cell proliferation and stem-cell marker expression was unaltered. Whereas coupling using 19Fc[FUT7(+)] enhanced cell capture on recombinant P-selectin or CHO-P cell surfaces, α(1,3)fucosylation was necessary for robust binding to E-selectin and inflamed endothelial cells under shear. Pilot studies confirm the safety and homing efficacy of the modified stem cells to sites of ischemia-reperfusion in the porcine heart. Overall, glycoengineering with physiological selectin-ligands may enhance stem cell engraftment.

Fluorescence molecular painting of enveloped viruses

In this study, we describe a versatile, flexible, and quick method to label different families of enveloped viruses with glycosylphosphatidylinositol-modified green fluorescent protein, termed fluorescence molecular painting (FMP). As an example for a potential application, we investigated virus attachment by means of flow cytometry to determine if viral binding behavior may be analyzed after FMP of enveloped viruses. Virus attachment was inhibited by using either dextran sulfate or by blocking attachment sites with virus pre-treatment. Results from the FMP-flow cytometry approach were verified by immunoblotting and enzyme-linked immunosorbent assay. Since the modification strategy is applicable to a broad range of proteins and viruses, variations of this method may be useful in a range of research and applied applications from bio-distribution studies to vaccine development and targeted infection for gene delivery.

PEGylation of vesicular stomatitis virus extends virus persistence in blood circulation of passively immunized mice

We are developing oncolytic vesicular stomatitis viruses (VSVs) for systemic treatment of multiple myeloma, an incurable malignancy of antibody-secreting plasma cells that are specifically localized in the bone marrow. One of the presumed advantages for using VSV as an oncolytic virus is that human infections are rare and preexisting anti-VSV immunity is typically lacking in cancer patients, which is very important for clinical success. However, our studies show that nonimmune human and mouse serum can neutralize clinical-grade VSV, reducing the titer by up to 4 log units in 60 min. In addition, we show that neutralizing anti-VSV antibodies negate the antitumor efficacy of VSV, a concern for repeat VSV administration. We have investigated the potential use of covalent modification of VSV with polyethylene glycol (PEG) or a function-spacer-lipid (FSL)-PEG construct to inhibit serum neutralization and to limit hepatosplenic sequestration of systemically delivered VSV. We report that in mice passively immunized with neutralizing anti-VSV antibodies, PEGylation of VSV improved the persistence of VSV in the blood circulation, maintaining a more than 1-log-unit increase in VSV genome copies for up to 1 h compared to the genome copy numbers for the non-PEGylated virus, which was mostly cleared within 10 min after intravenous injection. We are currently investigating if this increase in PEGylated VSV circulating half-life can translate to increased virus delivery and better efficacy in mouse models of multiple myeloma.