Biology Reference
In-Depth Information
Chapter
ProduCtIon oF VnPs, VlPs, And
ChIMerAS
Many viruses accumulate to high titers in their natural hosts; plant viruses,
for example, can be isolated in gram scales from a kilogram of infected leaf
material. Bacteriophages also accumulate to high titers (gram bacteriophage
per liter cell culture), and production of bacteriophages can be scaled up using
modern fermentation techniques. As diverse applications in nanotechnology
progress toward industrial practice and clinical trials, there is demand for
reliable and large-scale production of viral nanoparticles (VNPs). It is desired
that the expression system gives high flexibility, allowing production of
various mutant VNPs with altered surface properties such as modification of
amino acids, or chimeras (VNPs displaying foreign peptide sequences) with
ease, at low cost, and in a time-efficient manner. For safe use in materials
and medicine, it is generally desirable that the VNP be replication-deficient.
Various methods have been developed that allow extraction of the nucleic
acid from assembled particles to render them non-infectious. Alternatively,
the virus can be inactivated using physical methods such as UV irradiation.
However, these methods introduce additional steps in the manufacturing
process and can be cumbersome and inefficient.
Heterologous expression systems provide an attractive alternative for
the production of non-infectious particles. Heterologous expression systems
are highly efficient, extremely flexible, and allow the production of virus-like
particles (VLPs; particles that are devoid of genomic nucleic acid). Phages
and mammalian viruses are commonly expressed as VLPs in heterologous
systems. Plant viruses are expressed either in a heterologous system or in
the greenhouse in their natural hosts. Various production strategies and
assembly techniques are discussed in this chapter.
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