Viral vectors adenovirus

Viruses are infectious particles formed by nucleic acid, proteins, and in some cases lipids. As viruses (for example, retro- and adenoviruses) transfer viral genes into cells with high efficiency, modified forms are sometimes used as vectors for gene transfer. However, procedures using virus-based vectors are often significantly more complicated and time-consuming than other transfection methods. In addition, viral vectors are potentially hazardous, and biological safety issues need to be considered carefully. Therefore, techniques that combine... 

Most vaccine vectors developed to date are viral based, with poxviruses (as well as picorna viruses and adenoviruses) being used most. In general, such recombinant viral vectors elicit both... 

Additional viruses that may prove of some use as future viral vectors include adeno-associated virus and herpes virus. Adeno-associated virus is a very small, single-stranded DNA virus its genome consists of only two genes. It does not have the ability to replicate autonomously and can do so only in the presence of a co-infecting adenovirus (or other selected viruses). 

Gene Therapies. The types of vectors that have been used or proposed for gene transduction include retrovirus, adenovirus, adeno-associated viruses, other viruses (e.g., herpes, vaccinia, etc.), and plasmid DNA. Methods for gene introduction include ex vivo replacement, drug delivery, marker studies, and others and in vivo, viral vectors, plasmid vectors, and vector producer cells. 

Viral Vectors. The direct administration of a viral vector (e.g., retrovirus, adenovirus, adeno-associated virus, herpes, vaccinia) to patients. 

Peptides can also help overcome the most significant drawback to using liposome vectors when compared to viral vectors, which is lower transfection efficiency. Additional benefits include promotion of compaction, assisting cellular uptake of the DNA. Even peptides derived from viruses themselves can be used to compensate this deficit (e.g., adenovirus p protein and the HIV TAT). 

There is a wide variety of vectors used to deliver DNA or oligonucleotides into mammalian cells, either in vitro or in vivo. The most common vector systems are based on viral [retroviruses (9, 10), adeno-associated virus (AAV) (11), adenovirus (12, 13), herpes simplex virus (HSV) (14)] andnonviral [cationic liposomes (15,16), polymers and receptor-mediated polylysine-DNA] complexes (17). Other viral vectors that are currently under development are based on lentiviruses (18), human cytomegalovirus (CMV) (19), Epstein-Barr virus (EBV) (20), poxviruses (21), negative-strand RNA viruses (influenza virus), alphaviruses and herpesvirus saimiri (22). Also a hybrid adenoviral/retroviral vector has successfully been used for in vivo gene transduction (23). A simplified schematic representation of basic human gene therapy methods is described in Figure 13.1. 

This is in contrast to viruses, where the virus particles also show active transport when present in the cytosol after fusion with the plasma membrane or endosomal membrane [60-62], This is due to the ability of specific proteins of the virus particle to bind motor proteins. Single-particle tracking reveals that the quantitative intracellular transport properties of internalized non-viral gene vectors (e.g., polyplexes) are similar to that of viral vectors (e.g., adenovirus) [63]. Suk et al. showed that over 80% of polyplexes and adenoviruses in neurons are subdiffusive and 11-13% are actively transported. However, their trafficking pathways are substantially different. Polyplexes colocalized with endosomal compartments whereas adenovirus particles quickly escaped endosomes after endocytosis. Nevertheless, both exploit the intracellular transport machinery to be actively transported. 

However, a variety of issues have implications for the use of viral vectors in gene therapy. Obvious potential concerns are the immune and inflammatory responses to viral vectors. Patients who received VEGF-121 via an adenoviral vector had increased levels of serum antiadenoviral neutralizing antibodies, but there was no report on an inflammatory response in these patients (27). The use of adenovirus-mediated gene therapy in treating brain tumors has been reported to lead to active brain inflammation as well as persistent (up to three months after treatment) transgene expression (30). 

HEK-293 cells, derived from human embryo kidney, were transformed with human type 5 adenovirus (Graham et al., 1977). These cells exhibit epithelial morphology and can be adapted to suspension growth in serum-free media. In addition, this cell line is easily transfected and has been explored for viral vector production for gene therapy and for obtaining human recombinant proteins with normal glycosylation profiles. 

Table 21.3 shows the clinical studies that have been conducted worldwide, with their different applications, showing that therapies intended for monogenic disease treatment are the second most assessed group, after therapies for tumor treatment. The most used vectors in gene therapy clinical studies are viral vectors (68%), and among those, retroviruses and adenoviruses are the viruses of choice. Synthetic vectors were used in 25% of the studies performed, and about 16% correspond to the use of naked plasmid DNA (Table 21.4). 

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