Sheep red blood cells armed with anti-CD20 single-chain variable fragments (scFvs) fused to a glycosylphosphatidylinositol (GPI) anchor: a strategy to target CD20-positive tumor cells

Development of a potent recombinant scFv antibody against the SARS-CoV-2 by in-depth bioinformatics study: Paving the way for vaccine/diagnostics development

BACKGROUND

The SARS-CoV-2 has led to a worldwide disaster. Thus, developing prophylactics/therapeutics is required to overcome this public health issue. Among these, producing the anti-SARS-CoV-2 single-chain variable fragment (scFv) antibodies has attracted a significant attention. Accordingly, this study aims to address this question: Is it possible to bioinformatics-based design of a potent anti-SARS-CoV-2 scFv as an alternative to current production approaches?

METHOD

Using the complexed SARS-CoV-2 spike-antibodies, two sets analyses were performed: (1) B-cell epitopes (BCEs) prediction in the spike receptor-binding domain (RBD) region as a parameter for antibody screening; (2) the computational analysis of antibodies variable domains (VH/VL). Based on these primary screenings, and docking/binding affinity rating, one antibody was selected. The protein-protein interactions (PPIs) among the selected antibody-epitope complex were predicted and its epitope conservancy was also evaluated. Thereafter, some elements were added to the final scFv: (1) the PelB signal peptide; (2) a GSGGGGS linker to connect the VH-VL. Finally, this scFv was analyzed/optimized using various web servers.

RESULTS

Among the antibody library, only one met the various criteria for being an efficient scFv candidate. Moreover, no interaction was predicted between its paratope and RBD hot-spot residues of SARS-CoV-2 variants-of-Concern (VOCs).

CONCLUSIONS

Herein, a step-by-step bioinformatics platform has been introduced to bypass some barriers of traditional antibody production approaches. Based on existing literature, the current study is one of the pioneer works in the field of bioinformatics-based scFv production. This scFv may be a good candidate for diagnostics/therapeutics design against the SARS-CoV-2 as an emerging aggressive pathogen.

Engineering bacterial surface interactions using DNA as a programmable material

The diverse surface interactions and functions of a bacterium play an important role in cell signaling, host infection, and colony formation. To understand and synthetically control the biological functions of individual cells as well as the whole community, there is growing attention on the development of chemical and biological tools that can integrate artificial functional motifs onto the bacterial surface to replace the native interactions, enabling a variety of applications in biosynthesis, environmental protection, and human health. Among all these functional motifs, DNA emerges as a powerful tool that can precisely control bacterial interactions at the bio-interface due to its programmability and biorecognition properties. Compared with conventional chemical and genetic approaches, the sequence-specific Watson-Crick interaction enables almost unlimited programmability in DNA nanostructures, realizing one base-pair spatial control and bio-responsive properties. This highlight aims to provide an overview on this emerging research topic of DNA-engineered bacterial interactions from the aspect of synthetic chemists. We start with the introduction of native bacterial surface ligands and established synthetic approaches to install artificial ligands, including direct modification, metabolic engineering, and genetic engineering. A brief overview of DNA nanotechnology, reported DNA-bacteria conjugation chemistries, and several examples of DNA-engineered bacteria are included in this highlight. The future perspectives and challenges in this field are also discussed, including the development of dynamic bacterial surface chemistry, assembly of programmable multicellular community, and realization of bacteria-based theranostic agents and synthetic microbiota as long-term goals.

Programming Cell-Cell Interactions through Non-genetic Membrane Engineering

The ability to direct targeted intercellular interactions has the potential to enable and expand the use of cell-based therapies for regenerative medicine, tissue engineering, and immunotherapy. While genetic engineering approaches have proven effective, these techniques are not amenable to all cell types and often yield permanent modifications with potentially long-lasting adverse effects, restricting their application. To circumvent these limitations, there is intense interest in developing non-genetic methods to modify cell membranes with functional groups that will enable the recognition of target cells. While many such techniques have been developed, relatively few have been applied to directing specific cell-cell interactions. This review details these non-genetic membrane engineering approaches-namely, hydrophobic membrane insertion, chemical modification, liposome fusion, metabolic engineering, and enzymatic remodeling-and summarizes their major applications. Based on this analysis, perspective is provided on the ideal features of these systems with an emphasis on the potential for clinical translation.

Engineering Reversible Cell-Cell Interactions with Lipid Anchored Prosthetic Receptors

Membrane-engineered cells displaying antigen-targeting ligands are useful as both scientific tools and clinical therapeutics. While genetically encoded artificial receptors have proven efficacious, their scope remains limited, as this approach is not amenable to all cell types and the modification is often permanent. Our group has developed a nongenetic method to rapidly, stably, and reversibly modify any cell membrane with a chemically self-assembled nanoring (CSAN) that can function as a prosthetic receptor. Bifunctional CSANs displaying epithelial cell adhesion molecule (EpCAM)-targeted fibronectin domains were installed on the cell membrane through hydrophobic insertion and remained stably bound for ≥72 h in vitro. These CSAN-labeled cells were capable of recognizing EpCAM-expressing target cells, forming intercellular interactions that were subsequently reversed by disassembling the nanoring with the FDA-approved antibiotic, trimethoprim. This study demonstrates the use of this system to engineer cell surfaces with prosthetic receptors capable of directing specific and reversible cell-cell interactions.

Targeting of mesenchymal stem cells to ovarian tumors via an artificial receptor

Background

Mesenchymal Progenitor/Stem Cells (MSC) respond to homing cues providing an important mechanism to deliver therapeutics to sites of injury and tumors. This property has been confirmed by many investigators, however, the efficiency of tumor homing needs to be improved for effective therapeutic delivery. We investigated the feasibility of enhancing MSC tumor targeting by expressing an artificial tumor-binding receptor on the MSC surface.

Methods

Human MSC expressing an artificial receptor that binds to erbB2, a tumor cell marker, were obtained by transduction with genetically modified adenoviral vectors encoding an artificial receptor (MSC-AR). MSC-AR properties were tested in vitro in cell binding assays and in vivo using two model systems: transient transgenic mice that express human erbB2 in the lungs and ovarian xenograft tumor model. The levels of luciferase-labeled MSCs in erbB2-expressing targeted sites were evaluated by measuring luciferase activity using luciferase assay and imaging.

Results

The expression of AR enhanced binding of MSC-AR to erbB2-expressing cells in vitro, compared to unmodified MSCs. Furthermore, we have tested the properties of erbB2-targeted MSCs in vivo and demonstrated an increased retention of MSC-AR in lungs expressing erbB2. We have also confirmed increased numbers of erbB2-targeted MSCs in ovarian tumors, compared to unmodified MSC. The kinetic of tumor targeting by ip injected MSC was also investigated.

Conclusion

These data demonstrate that targeting abilities of MSCs can be enhanced via introduction of artificial receptors. The application of this strategy for tumor cell-based delivery could increase a number of cell carriers in tumors and enhance efficacy of cell-based therapy.

Cell vehicle targeting strategies

Use of cells as therapeutic carriers has increased in the past few years and has developed as a distinct concept and delivery method. Cell-based vehicles are particularly attractive for delivery of biotherapeutic agents that are difficult to synthesize, have reduced half-lives, limited tissue penetrance or are rapidly inactivated upon direct in vivo introduction. Initial studies using cell-based approaches served to identify some of the key factors for the success of this type of therapeutic delivery. These factors include the efficiency of cell loading with a therapeutic payload, the means of cell loading and the nature of therapeutics that cells can carry. However, one important aspect of cell-based delivery yet to be fully investigated is the process of actual delivery of the cell payload in vivo. In this regard, the potential ability of cell carriers to provide site-specific or targeted delivery of therapeutics deserves special attention. The present review focuses on a variety of targeting approaches that may be utilized to improve cell-based therapeutic delivery strategies. The different aspects of targeting that can be applied to cell vehicles will be discussed, including physical methods for directing cell distribution, intrinsic cell-mediated homing mechanisms and the feasibility of engineering cells with novel targeting mechanisms. Development of cell targeting strategies will further advance cell vehicle applications, broaden the applicability of this delivery approach and potentiate therapeutic outcomes.