Adenovirus-Based Targeting in Myoblasts Is Hampered by Nonhomologous Vector Integration

Recombinant Viral Vectors for Therapeutic Programming of Tumour Microenvironment: Advantages and Limitations

Viral vectors have been widely investigated as tools for cancer immunotherapy. Although many preclinical studies demonstrate significant virus-mediated tumour inhibition in synergy with immune checkpoint molecules and other drugs, the clinical success of viral vector applications in cancer therapy currently is limited. A number of challenges have to be solved to translate promising vectors to clinics. One of the key elements of successful virus-based cancer immunotherapy is the understanding of the tumour immune state and the development of vectors to modify the immunosuppressive tumour microenvironment (TME). Tumour-associated immune cells, as the main component of TME, support tumour progression through multiple pathways inducing resistance to treatment and promoting cancer cell escape mechanisms. In this review, we consider DNA and RNA virus vectors delivering immunomodulatory genes (cytokines, chemokines, co-stimulatory molecules, antibodies, etc.) and discuss how these viruses break an immunosuppressive cell development and switch TME to an immune-responsive “hot” state. We highlight the advantages and limitations of virus vectors for targeted therapeutic programming of tumour immune cell populations and tumour stroma, and propose future steps to establish viral vectors as a standard, efficient, safe, and non-toxic cancer immunotherapy approach that can complement other promising treatment strategies, e.g., checkpoint inhibitors, CAR-T, and advanced chemotherapeutics.

Selective killing of lung cancer cells using carcinoembryonic antigen promoter and double suicide genes, thymidine kinase and cytosine deaminase (pCEA-TK/CD)

The application of gene therapy in cancer treatment is limited by non-specific targeting. In the present study, we constructed a recombinant plasmid, containing a carcinoembryonic antigen (CEA) promoter and double suicide genes thymidine kinase (TK) and cytosine deaminase (CD), henceforth referred to as pCEA-TK/CD. Our results showed that the CEA promoter can specifically drive target gene expression in CEA-positive lung cancer cells. In the presence of prodrugs 5-flucytosine and ganciclovir, pCEA-TK/CD transfection decreased inhibitory concentration 50 and increased apoptosis and cyclomorphosis. Our result suggests that gene therapy using pCEA-TK/CD may be a promising new approach for treating lung cancer.

Genomic integration of adenoviral gene transfer vectors following transduction of fertilized mouse oocytes

Adenoviral vectors (AdV) are popular tools to deliver foreign genes into a wide range of cells. They have also been used in clinical gene therapy trials. Studies on AdV-mediated gene transfer to mammalian oocytes and transmission through the germ line have been reported controversially. In the present study we investigated whether AdV sequences integrate into the mouse genome by microinjecting AdV into the perivitelline space of fertilized oocytes. We applied a newly developed PCR technique (HiLo-PCR) for identification of chromosomal junctions next to the integrated AdV. We demonstrate that mouse oocytes can be transduced by different recombinant adenoviral vectors (first generation and gutless). In one transgenic mouse line using the first generation adenoviral vector, the genome has integrated into a highly repetitive cluster located on the Y chromosome. While the transgene (GFP) was expressed in early embryos, no expression was detected in adult transgenic mice. The use of gutless AdV resulted in expression of the transgene, albeit the vector was not transmitted to progeny. These results indicate that under optimized conditions fertilized mouse oocytes are transduced by AdV and give rise to transgenic founder animals. Therefore, adequate precautions should be taken in gene therapy protocols of reproductive patients since transduction of oocytes or early embryos and subsequent chromosomal integration cannot be ruled out entirely.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.