Illustration depicting innovative non-AAV viral vectors for gene therapyIntroduction

Gene therapy has made significant strides in recent years with various viral vectors being developed to deliver therapeutic genes to target cells. While adeno-associated viruses (AAVs) have been widely used, there is growing interest in exploring non-AAV viral vectors due to their unique advantages and capabilities. This news article highlights some of the innovative non-AAV viral gene delivery methods being developed, which were recently showcased at the American Society of Gene & Cell Therapy (ASCGT) 2024 meeting.

Innovative Non-AAV Viral Gene Delivery Methods

Human Bocavirus (HBoV) Vectors

Human Bocavirus Type 1 (HBoV1) effectively infects human airway epithelial cells, making it suitable for cystic fibrosis (CF) gene therapy. The hybrid vector CBN-1000, combining HBoV1 capsid with AAV2 genome elements, has shown potential in delivering CFTR genes to CF airway cells. CBN-1000 demonstrated efficient lung tropism, restoring CFTR protein levels and function in patient-derived cells. In vivo studies in ferrets and non-human primates confirmed its safety and efficacy, positioning CBN-1000 as a promising candidate for CF gene therapy. Read more

Helper-Dependent Adenovirus (HDAd) Vectors

Helper-dependent adenovirus (HDAd) vectors, especially the HDAd6/3+-cxcr4 platform, show promise for hematopoietic stem cell (HSC) gene therapy. Targeting receptors like CD46 and DSG2, this vector demonstrated superior transduction efficiency and safety in rhesus macaques. It aids in HSC mobilization and return to the bone marrow with minimal interaction with blood cells and reduced liver transduction. This resulted in high vector copy numbers in bone marrow cells, indicating successful and stable gene integration, making HDAd6/3+-cxcr4 a viable option for clinical translation. Read more

Foamy Viral Vectors

Foamy viral vectors (FVVs) are capable of delivering large genetic cargos, such as the factor 8 gene for hemophilia A treatment. In a mouse model, FVVs successfully expressed factor 8 in liver cells for up to a year. The study also explored the use of tolerogenic dendritic cells (DCs) to mitigate host immune responses, which is a significant challenge in gene therapy. Read more

Simian Virus 40 (SV40) Vectors

Simian Virus 40 (SV40) vectors offer a non-immunogenic alternative to AAV vectors. The SVec platform, developed by Amarna Therapeutics, has shown potential in gene replacement therapies for hemophilia B and primary hyperoxaluria type 1, as well as in inducing immune tolerance for autoimmune diseases like type 1 diabetes and multiple sclerosis. The ability to repeatedly administer SVec vectors without eliciting an immune response makes them highly attractive for clinical applications. Read more

Baculovirus Vectors

Baculovirus vectors, derived from insect viruses, can package and deliver large genetic cargos. By pseudo-typing baculovirus with proteins like VSV-G and complement regulatory domains, researchers have enhanced its transduction efficiency and persistence in mammalian tissues. This vector system allows for complex gene regulation and has demonstrated potential in delivering therapeutic genes to liver, muscle, and brain tissues in mice. Read more

Herpes Simplex Virus 1 (HSV-1) Vectors

HSV-1 vectors have been engineered to carry large or multiple genes by deleting cytotoxic viral genes and incorporating insulator elements to maintain transgene expression. These vectors have shown stable expression in muscle and brain tissues, making them suitable for treating diseases like Duchenne muscular dystrophy and neurodegenerative disorders. The novel insulator constructs further enhance transgene expression and durability. Read more

Lentiviral Vectors

Lentiviral vectors (LVs) are used for in vivo gene transfer to hepatocytes to treat homozygous familial hypercholesterolemia (HoFH). By optimizing the vector design to avoid LDLR expression during production, researchers achieved high infectious titers and therapeutic efficacy in a mouse model. The study demonstrated normalization of blood LDL cholesterol levels and prevention of atherosclerosis, highlighting the potential of LVs for liver-directed gene therapy. Read more

Alpha-Retrovirus-Based Virus-Like Particles (αVLPs)

Alpha-retrovirus-based virus-like particles (αVLPs) have been developed for delivering CRISPR-Cas9 genome editors into hematopoietic stem cells (HSCs). These αVLPs showed higher efficiency and lower cytotoxicity compared to existing systems, achieving high indel rates and maintaining cell viability. This approach holds promise for in vivo gene editing applications. Read more

Measles Virus (MeV) Vectors

A single-cycle measles virus (MeV) vector has been engineered to deliver gRNAs and Cas9 nuclease for gene editing. This vector achieved efficient on-target gene editing and limited off-target effects in human cells. The MeV vector platform offers a flexible and efficient method for gene knock-out and knock-in modifications, with potential applications in clinical gene editing. Read more

Anellovectors

Anelloviruses, which are commensal ssDNA viruses, have been vectorized to create anellovectors capable of evading the immune system and delivering DNA payloads to multiple tissues. In mouse models, anellovectors demonstrated effective DNA delivery and expression without triggering an immune response. This characteristic allows for repeated dosing, addressing a significant limitation of current viral gene therapies. Anellovectors hold promise for sustained gene therapy efficacy in various genetically-driven diseases. Read more

Self-Replicating RNA (srRNA) Vectors

Self-replicating RNA (srRNA) vectors co-encode viral replicase machinery, allowing for lower dosing and enhanced bioactivity. These vectors have shown potential in achieving protective antibody titers with minimal reactogenicity, broadening the therapeutic window for applications beyond vaccines, including protein replacement therapies. Read more

Integrase-Deleted Retrovector (IDRV)

Integrase-deleted retrovectors (IDRVs) offer transient gene expression without the risks associated with genomic integration. These vectors demonstrated high protein expression and cell kill activity in cancer cells, making them suitable for applications requiring transient expression such as immunotherapy and gene editing delivery. Read more

T4 Bacteriophage Nanoparticles

T4 bacteriophage nanoparticles have been engineered to display high-density vaccine antigens such as those for Dengue and Zika viruses. By optimizing genetic elements in the T4 genome, researchers achieved a significant increase in antigen production, making these nanoparticles a promising platform for developing effective and durable vaccines. Read more

Chimeric Adenoviral Vectors

Chimeric adenoviral vectors Ad5/3 and Ad5/21 have been developed to enhance transduction of human airway epithelial cells by altering receptor usage. These vectors showed improved transduction efficiency and cell-type specificity, making them potential candidates for delivering gene editing tools to airway progenitor cells for lung disease correction. Read more

Paramyxovirus-Like Particles

Paramyxovirus-like particles (VLPs) have been engineered to deliver functional proteins to cells, offering a safe and effective tool for therapeutic purposes. Paramyxovirus VLPs successfully packaged and delivered biologically active cargo such as Cre recombinase to target cells. Enhanced VLP production and delivery efficiency pave the way for their use in protein therapies, providing a versatile platform for therapeutic protein delivery. Read more

Papillomavirus Vectors

Papillomavirus vectors with natural tropism towards keratinocytes present a new candidate for gene therapy in skin diseases like Olmsted syndrome. Engineered papillomavirus vectors successfully disrupted the Trpv3 gene in keratinocytes, reducing disease phenotype in Olmsted syndrome models. This approach offers a promising new avenue for skin gene therapies, leveraging the virus’s natural properties for efficient gene delivery. Read more

Oncolytic Virus

Oncolytic immunotherapy using virus-mediated modalities is a promising anticancer approach, especially for treatment-resistant cancers. Oncolytic herpes simplex virus (oHSV) has clinical potential due to its natural tumor affinity and high gene insertion capacity. Genetic manipulation of the large oHSV genome is complex and can impact viral fitness and immune responses. Researchers developed bacterial artificial chromosome (BAC) and molecular scissor systems for precise genetic modifications, creating a novel oHSV-1 vector with a deletion of the neurovirulence factor ICP34.5, improving safety and maintaining replication capacity while introducing immunostimulatory factors to enhance antitumor immunity. This recombinant oHSV-1 showed high replication efficiency and over 90% cancer cell killing in vitro, significantly inhibiting tumor growth in mouse models. These findings highlight the potential of genetically modified oHSV-1 vectors for cancer treatment, with further studies underway. Read more

Advantages of Non-AAV Viral Vectors or Viruses Over AAV-Based Gene Therapy

Viral Vector Advantages Over AAV
Human Bocavirus (HBoV) Vectors Efficient lung tropism, increased genomic capacity, demonstrated safety and efficacy in ferrets and NHPs.
Helper-Dependent Adenovirus (HDAd) Vectors Target specificity (CD46, DSG2), high transduction efficiency, reduced off-target effects, minimal interaction with blood cells and liver.
Foamy Viral Vectors (FVVs) Large genetic cargo capacity, sustained expression, potential to mitigate host immune responses.
Simian Virus 40 (SV40) Vectors Non-immunogenic, effective for gene replacement and inducing immune tolerance in autoimmune diseases, repeated administration possible.
Baculovirus Vectors Large packaging capacity, enhanced transduction and persistence, broad tissue tropism.
Herpes Simplex Virus 1 (HSV-1) Vectors Large payload capacity, stable transgene expression, enhanced safety with deletion of cytotoxic viral genes.
Lentiviral Vectors (LVs) Stable integration, efficiency in liver cells, prevents atherosclerosis, normalization of blood LDL cholesterol levels.
Alpha-Retrovirus-Based Virus-Like Particles (αVLPs) High efficiency and low cytotoxicity, in vivo gene editing, maintains high cell viability.
Measles Virus (MeV) Vectors Efficient gene editing, flexible platform for various gene editing applications.
Anellovectors Immune evasion, broad tissue delivery, sustained efficacy, allows repeated dosing.
Self-Replicating RNA (srRNA) Vectors Lower dosing requirements, broadened therapeutic window, suitable for protein replacement therapies.
Integrase-Deleted Retrovector (IDRV) Transient expression, high protein expression, reduced risk of genomic integration, safer for therapeutic applications.
T4 Bacteriophage Nanoparticles High antigen density, durable vaccines, optimized for significant antigen production.
Chimeric Adenoviral Vectors Enhanced cell-type specificity, improved transduction efficiency, potential for lung disease correction.
Paramyxovirus-Like Particles (VLPs) Efficient protein delivery, versatile for various therapeutic protein deliveries.
Papillomavirus Vectors Natural tropism towards keratinocytes, effective for skin gene therapies, disease-specific applications.
Oncolytic Virus Natural tumor affinity, high gene insertion capacity, enhanced safety, immunostimulatory effects, significant efficacy in tumor growth inhibition.

Conclusion

The development of non-AAV viral vectors and viruses for gene therapy offers exciting new possibilities for treating a wide range of genetic and acquired diseases. Each vector type presents unique advantages and challenges, and ongoing research continues to optimize their safety, efficiency, and therapeutic potential. As these technologies advance, they hold the promise of transforming the landscape of gene therapy and improving patient outcomes.

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