Role of EGF Receptor Regulatory Networks in the Host Response to Viral Infections

In this review article, we will first provide a brief overview of EGF receptor (EGFR) structure and function, and its importance as a therapeutic target in epithelial carcinomas. We will then compare what is currently known about canonical EGFR trafficking pathways that are triggered by ligand binding, versus ligand-independent pathways activated by a variety of intrinsic and environmentally induced cellular stresses. Next, we will review the literature regarding the role of EGFR as a host factor with critical roles facilitating viral cell entry and replication. Here we will focus on pathogens exploiting virus-encoded and endogenous EGFR ligands, as well as EGFR-mediated trafficking and signaling pathways that have been co-opted by wild-type viruses and recombinant gene therapy vectors. We will also provide an overview of a recently discovered pathway regulating non-canonical EGFR trafficking and signaling that may be a common feature of viruses like human adenoviruses which signal through p38-mitogen activated protein kinase. We will conclude by discussing the emerging role of EGFR signaling in innate immunity to viral infections, and how viral evasion mechanisms are contributing to our understanding of fundamental EGFR biology.

Improved targeting of human CD4+ T cells by nanobody-modified AAV2 gene therapy vectors

Adeno-associated viruses (AAV) are considered non-pathogenic in humans, and thus have been developed into powerful vector platforms for in vivo gene therapy. Although the various AAV serotypes display broad tropism, frequently infecting multiple tissues and cell types, vectors for specific and efficient targeting of human CD4+ T lymphocytes are largely missing. In fact, a substantial translational bottleneck exists in the field of therapeutic gene transfer that would require in vivo delivery into peripheral disease-related lymphocytes for subsequent genome editing. To solve this issue, capsid modification for retargeting AAV tropism, and in turn improving vector potency, is considered a promising strategy. Here, we genetically modified the minor AAV2 capsid proteins, VP1 and VP2, with a set of novel nanobodies with high-affinity for the human CD4 receptor. These novel vector variants demonstrated improved targeting of human CD4+ cells, including primary human peripheral blood mononuclear cells (PBMC) and purified human CD4+ T lymphocytes. Thus, the technical approach presented here provides a promising strategy for developing specific gene therapy vectors, particularly targeting disease-related peripheral blood CD4+ leukocytes.

Expanding the understanding of viral tropism by characterizing the N-glycomic profiles of transducible cell lines and tissue types and Characterizing functional receptors that mediate the inhibitory relationship between 4-O-sulfated chondroitin sulfate and neurons

1: Glycosylation plays an important role in facilitating viral transduction by acting as preliminary cell surface receptors. For this reason, the structural determinants in glycans that dictate viral tissue tropism need to be extensively studied to improve the efficacy of gene therapy vectors in basic research and eventually the clinic. Elucidating the dependencies for viral transduction initiation and understanding how these structural nuances of glycans initiate virion specific tropic effects is paramount when considering how to use vectors to improve clinical outcomes for patients suffering from illnesses with few treatment options. The goal of this project was to use MALDI-TOF-MS to provide baseline N-glycan profiles of the cell lines and tissues used to test gene therapy vectors. In doing so these profiles will be valuable to the field by clarifying what structural determinants may influence viral tropism. It was discovered Neu5Ac sialic acid content differs qualitatively amongst the seven cell lines analyzed. These differences may play into why some cell lines such as CHO-K1 and COS-7 can transduce more preferentially with some AAV serotypes like AAV5. In addition, sialic acid differences were also assessed in three tissue types used in transduction assays. Abstract 2: After injury to the CNS, reactive astrocytes form a protective extracellular matrix to isolate damaged tissue. These astrocytes influence the surrounding tissue by upregulating the production of proteoglycans containing chondroitin sulfate. Due to the new cellular environment, chondroitin sulfate (CS) glycosaminoglycan chains are upregulated with predominately 4-O-sulated sulfation patterns. These sulfation patterns are known to inhibit axonal guidance, and ultimately neuronal regeneration. While the inhibitory effect of CS is well known, the mechanism by which these specific sulfation patterns may interact with receptors also known to have inhibitory effects on neuro-regeneration such as protein tyrosine phosphatase σ is unknown. To characterize these interactions reductive amination was used to immobilize these CS chains onto solid beads. Chondroitin sulfate was isolated from the organs of an ARSB null mouse model which lacks the N-acetylgalactosamine-4-sulfatase (arylsulfatase B, ARSB) which is involved in the degradation of glycosaminoglycans (GAGs). Disruption of arylsulfatase B leads to the production of CS chains with 4-O-sulfated non-reducing ends exclusively. Key findings indicate that purified GAG chains retain their ligand specificity after being covalently immobilized onto solid supports, and that these systems can be utilized to characterize the relationship between inhibitory forms of CS and protein tyrosine phosphatase σ.

Stability of Recombinant Mosaic Adeno-Associated Virus Vector rAAV/DJ/CAG at Different Temperature Conditions

The nanometer size and biological characteristics of recombinant adeno-associated virus vectors (rAAV) make them particularly useful as gene therapy vectors and they have been successfully used in this role. Our latest research revealed that the rAAV/DJ/CAG mosaic vector offers highly efficient targeted gene delivery to melanoma cells metastasized to the lungs and that the transduction is temperature dependent. In order to further explore the ability of the rAAV/DJ/CAG vector to deliver highly selective transduction, this study was designed to identify the transduction stability of rAAV/DJ/CAG under various conditions. The temperatures used in this study ranged from −196 ° (liquid nitrogen) to 90 °, and the effect of temperature fluctuations (freeze-thaw, cooling-heating cycles) was also studied. This research also investigated the effects of UV radiation (ultraviolet) on the rAAV/DJ/CAG activity. Changes in the transduction efficiency were assessed via fluorescence microscopy imaging and the qPCR method. Under the test conditions, the transduction efficiency was reduced by approx. 35%, on average. High temperatures (70 °/90 °) and UV light proved to have the most detrimental impact. Changes in the stability of the rAAV/DJ/CAG structure are manifested by variations in the number of genome copies (gc) and GFP+ cells. Temperature fluctuations resulted in differences in the number of gc while maintaining a similar number of GFP+ cells, which may indicate specific changes in the rAAV/DJ/CAG structure, triggering disorders or degradation in the vector entry. This study provides interesting insights into rAAV/DJ/CAG, and the implications of these findings provide a basis for developing new protocols in cancer gene therapy.

Structural study of AAVrh.10 Receptor and Antibody Interactions

Recombinant Adeno-associated virus (rAAV) vectors are one of the leading tools for the delivery of therapeutic genes in human gene therapy applications. For a successful transfer of their payload, the AAV vectors have to circumvent potential pre-existing neutralizing host antibodies and bind to the receptor of the target cells. Both these aspects have not been structurally analyzed for AAVrh.10. Here, cryo-electron microscopy (cryo-EM) and three-dimensional image reconstruction were used to map the binding site of sulfated N -Acetyllactosamine (LacNAc, previously shown to bind AAVrh.10) and a series of four monoclonal antibodies (MAbs). LacNAc was found to bind to a pocket located on the side of the 3-fold capsid protrusion, that is mostly conserved to AAV9 and equivalent to its galactose-binding site. As a result, AAVrh.10 was also shown to be able to bind to cell surface glycans with terminal galactose. For the antigenic characterization, it was observed that several anti-AAV8 MAbs cross-react with AAVrh.10. The binding sites of these antibodies were mapped to the 3-fold capsid protrusions. Based on these observations, the AAVrh.10 capsid surface was engineered to create variant capsids that escape these antibodies while maintaining infectivity. Importance Gene therapy vectors based on Adeno-associated virus rhesus isolate 10 (AAVrh.10) have been used in several clinical trials to treat monogenetic diseases. However, compared to other AAV serotypes little is known about receptor binding and antigenicity of the AAVrh.10 capsid. Particularly, pre-existing neutralizing antibodies against capsids are an important challenge that can hamper treatment efficiency. This study addresses both topics and identifies critical regions of the AAVrh.10 capsid for receptor and antibody binding. The insights gained were utilized to generate AAVrh.10 variants capable of evading known neutralizing antibodies. The findings of this study could further aid the utilization of AAVrh.10 vectors in clinical trials and help the approval of the subsequent biologics.

Assessment of genome packaging in AAVs using Orbitrap-based charge detection mass spectrometry

Adeno-associated viruses (AAV) represent important gene therapy vectors with several approved clinical applications and numerous more in clinical trials. Genome packaging is an essential step in the bioprocessing of AAVs and needs to be tightly monitored to ensure the proper delivery of transgenes and the production of effective drugs. Current methods to monitor genome packaging have limited sensitivity, a high demand on labour, and struggle to distinguish between packaging of the intended genome or unwanted side-products. Here we show that Orbitrap based charge detection mass spectrometry allows the ultra-sensitive quantification of all these different AAV bioprocessing products. A protocol is presented that allows the quantification of genome packed AAV preparations in under half an hour, requiring only micro-liter quantities of typical AAV preparations with ~1013 viral genome copies per millilitre. The method quickly assesses the integrity and amount of genome packed AAV particles to support AAV bioprocessing and characterization of this rapidly emerging class of advanced drug therapies.

Ultra-sensitive AAV capsid detection by immunocapture-based qPCR following factor VIII gene transfer

Adeno-associated virus (AAV)-based gene therapy vectors are replication-incompetent and thus pose minimal risk for horizontal transmission or release into the environment. In studies with AAV5-FVIII-SQ (valoctocogene roxaparvovec), an investigational gene therapy for hemophilia A, residual vector DNA was detectable in blood, secreta, and excreta, but it remained unclear how long structurally intact AAV5 vector capsids were present. Since a comprehensive assessment of vector shedding is required by regulatory agencies, we developed a new method (termed iqPCR) that utilizes capsid-directed immunocapture followed by qPCR amplification of encapsidated DNA. The limit of detection for AAV5 vector capsids was 1.17E+04 and 2.33E+04 vg/mL in plasma and semen, respectively. Acceptable precision, accuracy, selectivity, and specificity were verified; up to 1.00E+09 vg/mL non-encapsidated vector DNA showed no interference. Anti-AAV5 antibody plasma concentrations above 141 ng/mL decreased AAV5 capsid quantification, suggesting that iqPCR mainly detects free capsids and not those complexed with antibodies. In a clinical study, AAV5-FVIII-SQ capsids were found in plasma and semen but became undetectable within nine weeks after dose administration. Hence, iqPCR monitors the presence and shedding kinetics of intact vector capsids following AAV gene therapy and informs the potential risk for horizontal transmission.

Improved systemic AAV gene therapy with a neurotrophic capsid in Niemann–Pick disease type C1 mice

Niemann–Pick C1 disease (NPC1) is a rare, fatal neurodegenerative disease caused by mutations in NPC1, which encodes the lysosomal cholesterol transport protein NPC1. Disease pathology involves lysosomal accumulation of cholesterol and lipids, leading to neurological and visceral complications. Targeting the central nervous system (CNS) from systemic circulation complicates treatment of neurological diseases with gene transfer techniques. Selected and engineered capsids, for example, adeno-associated virus (AAV)-PHP.B facilitate peripheral-to-CNS transfer and hence greater CNS transduction than parental predecessors. We report that systemic delivery to Npc1m1N/m1N mice using an AAV-PHP.B vector ubiquitously expressing NPC1 led to greater disease amelioration than an otherwise identical AAV9 vector. In addition, viral copy number and biodistribution of GFP-expressing reporters showed that AAV-PHP.B achieved more efficient, albeit variable, CNS transduction than AAV9 in Npc1m1N/m1N mice. This variability was associated with segregation of two alleles of the putative AAV-PHP.B receptor Ly6a in Npc1m1N/m1N mice. Our data suggest that robust improvements in NPC1 disease phenotypes occur even with modest CNS transduction and that improved neurotrophic capsids have the potential for superior NPC1 AAV gene therapy vectors.

ImmTORTM to amplify the efficacy and reduce immunogenicity of biologics

In recent months as vaccines against the SARS-CoV-2 virus continue to rollout across the globe, there has been a renewed interest in ways to activate or ignite the immune system. For a vaccine to be effective, it must be immunogenic and specific to provoke the body's defenses to mount an effective response that protects the host from disease. However, there are other situations wherein the immune system mounts an unwanted immune response that can be detrimental to health, either directly, by causing an autoimmune disease, or indirectly, by compromising the safety and/or efficacy of biologic drugs. In these scenarios, it would be desirable to have a ‘tolerogenic vaccine’ that could selectively and effectively mitigate these unwanted immune responses. ImmTORTM, a nanoparticle technology, is being developed to address the issue of immunogenicity for gene therapy vectors and other biologic drugs. By targeting antigen-presenting cells, ImmTORTM has the potential to amplify the efficacy of biologic therapies and unlock the full potential of such treatments to improve the lives of those who suffer from serious and debilitating diseases.