Viruses are perhaps the biological entity most effective at introducing new genes into living cells. Having adapted over millions of years as intracellular parasites that take advantage of cells’ genetic machinery to reproduce, viruses are considered experts at integration and reapplication, traits which make them highly amenable to human manipulation. It is possible to remove the pathogenic or disease-causing portions of a virus, turning its ability to infiltrating its host’s cells into a tool that scientists can use to introduce other material into that cell. These properties make viruses an exceptional vector or transmission method for gene therapies.
Viral-vector-based gene therapy can take two forms. In ex vivo therapies, cells from the patient are collected in a process called apheresis and introduced to engineered viruses that alter its genome. These modified cells are then returned to the patient. In vivo therapy by contrast involves administering the modified virus directly into the patient, typically via direct injection, effecting its alterations in their living body. These methods usually use different kinds of virus: lentiviruses (LV) for ex vivo and adeno-associated viruses (AAV) for in vivo, but they rely on the same biological quirk: their ability to integrate into the host genome and wait, a characteristic which is they lacked would make them not nearly as useful for gene therapy.
Producing a viral vector has several steps:
- A specific plasmid or set of plasmids must be created or selected from a library. These plasmids combine the genes for viral proteins with the gene of interest, sometimes referred to as the GOI or transgene, which provides the specific genetic payload being targeted by the project. These plasmids enable the cells they transfect to produce viral particles with the GOI integrated into, or even replacing most of, the virus’s normal genome. The specifics of this step depend on the type of virus being used as the vector.
- A cell culture, such as the commonly used mammalian Human Embryonic Kidney HEK293 line, suitable for propagating the virus must be established.
- The cell culture must then be transfected with the plasmid.
- The transfected cell culture then produces the engineered virus, complete with the integrated GOI.
- Once they have been produced the viral particles must be harvested and purified from the culture, stored appropriately, and distributed to the end users.
What distinguishes this process from older virus-based gene therapy protocols is that there is no need to have virus particles on hand to infect the culture medium; instead, this is achieved via plasmid transfection. The virus’s genetic material is introduced directly into the host cells, reducing potential errors as the cell starts producing these viral particles. Once purified the engineered viral particles are ready for use.
Gibco offers products to facilitate every step of this process, from creation of a suitable plasmid to storing and packaging complete gene-therapy virus products. Invitrogen’s GeneArt gene synthesis service in particular offers a cost-effective, timesaving, and resource-saving method for obtaining custom DNA constructs for use in gene therapy, made to order with 100% sequence accuracy and an optimized expression profile. GeneArt takes the guesswork out of what might be the most fraught and challenging part of viral vector-based gene therapy creation and delivers highly pure and homogeneous plasmids and the documentation needed for regulatory compliance. Combined with the rest of Gibco’s viral vector portfolio, GeneArt assures higher production titers, more virus particles in less volume, and flexible systems that can adapt to practitioner needs, regardless of whether the cell culture used if of mammalian or insect origin and across use cases. Gibco tools are already proving their mettle in the challenging field of CAR-T associated gene therapy.
The GibcoTM portfolio of viral vector products is manufactured in GMP-compliant settings, safety tested, and backed by regulatory documentation to support the whole sequence of gene therapy research, testing, and manufacture, from plasmid creation all the way to measuring experimental results. Gibco offers instrumentation, software, consumables, and dedicated testing, regulatory, and quality control support for every step in the viral vector process. Gibco also offers protocols, handbooks, e-learning resources, and workflows for adeno-associated and lentiviral research to guide new researchers on the way to becoming experts in this challenging field.
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