Impact of adenovirus life cycle progression on the generation of canine helper-dependent vectors

Cell Bank Origin of MDCK Parental Cells Shapes Adaptation to Serum-Free Suspension Culture and Canine Adenoviral Vector Production

Phenotypic variation in cultured mammalian cell lines is known to be induced by passaging and culture conditions. Yet, the effect these variations have on the production of viral vectors has been overlooked. In this work we evaluated the impact of using Madin-Darby canine kidney (MDCK) parental cells from American Type Culture Collection (ATCC) or European Collection of Authenticated Cell Cultures (ECACC) cell bank repositories in both adherent and suspension cultures for the production of canine adenoviral vectors type 2 (CAV-2). To further explore the differences between cells, we conducted whole-genome transcriptome analysis. ECACC's MDCK showed to be a less heterogeneous population, more difficult to adapt to suspension and serum-free culture conditions, but more permissive to CAV-2 replication progression, enabling higher yields. Transcriptome data indicated that this increased permissiveness is due to a general down-regulation of biological networks of innate immunity in ECACC cells, including apoptosis and death receptor signaling, Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling, toll-like receptors signaling and the canonical pathway of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling. These results show the impact of MDCK source on the outcome of viral-based production processes further elucidating transcriptome signatures underlying enhanced adenoviral replication. Following functional validation, the genes and networks identified herein can be targeted in future engineering approaches aiming at improving the production of CAV-2 gene therapy vectors.

CAV-2 Vector Development and Gene Transfer in the Central and Peripheral Nervous Systems

The options available for genetic modification of cells of the central nervous system (CNS) have greatly increased in the last decade. The current panoply of viral and nonviral vectors provides multifunctional platforms to deliver expression cassettes to many structures and nuclei. These cassettes can replace defective genes, modify a given pathway perturbed by diseases, or express proteins that can be selectively activated by drugs or light to extinguish or excite neurons. This review focuses on the use of canine adenovirus type 2 (CAV-2) vectors for gene transfer to neurons in the brain, spinal cord, and peripheral nervous system. We discuss (1) recent advances in vector production, (2) why CAV-2 vectors preferentially transduce neurons, (3) the mechanism underlying their widespread distribution via retrograde axonal transport, (4) how CAV-2 vectors have been used to address structure/function, and (5) their therapeutic applications.

Combining Gene Transfer and Nonhuman Primates to Better Understand and Treat Parkinson's Disease

Parkinson’s disease (PD) is a progressive CNS disorder that is primarily associated with impaired movement. PD develops over decades and is linked to the gradual loss of dopamine delivery to the striatum, via the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). While the administration of L-dopa and deep brain stimulation are potent therapies, their costs, side effects and gradual loss of efficacy underlines the need to develop other approaches. Unfortunately, the lack of pertinent animal models that reproduce DA neuron loss and behavior deficits—in a timeline that mimics PD progression—has hindered the identification of alternative therapies. A complementary approach to transgenic animals is the use of nonhuman primates (NHPs) combined with the overexpression of disease-related genes using viral vectors. This approach may induce phenotypes that are not influenced by developmental compensation mechanisms, and that take into account the personality of animals. In this review article, we discuss the combination of gene transfer and NHPs to develop “genetic” models of PD that are suitable for testing therapeutic approaches.

CAV-2--why a canine virus is a neurobiologist's best friend

Canine adenovirus type 2 (CAV-2) vectors are powerful tools for fundamental and applied neurobiology due to their negligible immunogenicity, preferential transduction of neurons, widespread distribution via axonal transport, and duration of expression in the mammalian brain. CAV-2 vectors are internalized in neurons by the selective use of coxsackievirus and adenovirus receptor (CAR), which is located at the presynapse in neurons. Neuronal internalization and axonal transport is mediated by CAR, which potentiates vector biodistribution. The above characteristics, together with the ∼30kb cloning capacity of helper-dependent (HD) CAV-2 vectors, optimized CAV-2 vector creation, production and purification, is expanding the therapeutic and fundamental options for CNS gene transfer.

Evaluation of helper-dependent canine adenovirus vectors in a 3D human CNS model

Gene therapy is a promising approach with enormous potential for treatment of neurodegenerative disorders. Viral vectors derived from canine adenovirus type 2 (CAV-2) present attractive features for gene delivery strategies in the human brain, by preferentially transducing neurons, are capable of efficient axonal transport to afferent brain structures, have a 30-kb cloning capacity and have low innate and induced immunogenicity in preclinical tests. For clinical translation, in-depth preclinical evaluation of efficacy and safety in a human setting is primordial. Stem cell-derived human neural cells have a great potential as complementary tools by bridging the gap between animal models, which often diverge considerably from human phenotype, and clinical trials. Herein, we explore helper-dependent CAV-2 (hd-CAV-2) efficacy and safety for gene delivery in a human stem cell-derived 3D neural in vitro model. Assessment of hd-CAV-2 vector efficacy was performed at different multiplicities of infection, by evaluating transgene expression and impact on cell viability, ultrastructural cellular organization and neuronal gene expression. Under optimized conditions, hd-CAV-2 transduction led to stable long-term transgene expression with minimal toxicity. hd-CAV-2 preferentially transduced neurons, whereas human adenovirus type 5 (HAdV5) showed increased tropism toward glial cells. This work demonstrates, in a physiologically relevant 3D model, that hd-CAV-2 vectors are efficient tools for gene delivery to human neurons, with stable long-term transgene expression and minimal cytotoxicity.

Canine helper-dependent vectors production: implications of Cre activity and co-infection on adenovirus propagation

The importance of Cre recombinase to minimize helper vector (HV) contamination during helper-dependent adenovirus vectors (HDVs) production is well documented. However, Cre recombinase, by inducing DNA double-strand breaks (DSBs), can cause a reduced proliferation and genotoxic effects in cultured cells. In this work, Cre-expressing cell stability, co-infection and their relation to adenovirus amplification/HV contamination were evaluated to develop a production protocol for HD canine adenovirus type 2 (CAV-2) vectors. Long-term Cre expression reduced the capacity of MDCK-E1-Cre cells to produce CAV-2 by 7-fold, although cell growth was maintained. High HDV/HV MOI ratio (5:0.1) led to low HV contamination without compromising HDV yields. Indeed, such MOI ratio was sufficient to reduce HV levels, as these were similar either in MDCK-E1 or MDCK-E1-Cre cells. This raises the possibility of producing HDVs without Cre-expressing cells, which would circumvent the negative effects that this recombinase holds to the production system. Here, we show how Cre and MOI ratio impact adenovirus vectors yields and infectivity, providing key-information to design an improved manufacturing of HDV. Potential mechanisms to explain how Cre is specifically impacting cell productivity without critically compromising its growth are presented.