Insect Cell Culture- General Information
The utilization of insect cell culture for heterologous protein expression has steadily
increased over the last several decades. It has become a common expression system for
both basic research and large-scale commercial applications. Currently, some of the
common uses of insect cell expression include the research driven gene expression for
protein crystallography-small molecule interaction, and FDA regulated GMP protein
production. These regulated applications can include subunit vaccine production as well
as the in vitro diagnostic and in vivo therapeutic markets. A key factor to the popularity
of insect cell expression is the ability of insect cells to produce relatively large quantities
of posttranslationally modified eukaryotic proteins in a relatively short period of time.
Most insect cell-produced proteins have been expressed by employing the Baculovirus
Expression Vector System (BEVS); however, other technologies that make stable
transfected insect cells are gaining in popularity.
Many types of viruses infect insects, with the most common belonging to the family
Baculoviridae. The most popular invertebrate expression vector system is based on the
nuclear polyhedrosis virus ( AcNPV ), an insect baculovirus
isolated from the Alfalfa looper that replicates in the nucleus of over 30 lepidopteran
insect cell lines.
The baculovirus expression vector system has been used to express
genes derived from viruses, fungi, bacteria, plants, and animals.
In this system, foreign
genes placed under the control of the strong polyhedrin promoter of the AcNPV are
usually expressed at high levels in cultured lepidopteran insect cells.
constitute one of the largest known groups of viruses, and they are capable of infecting
over 500 species of insects, and more recently, these viruses have shown the ability to
make ideal vectors for a variety of mammalian cell lines.
The most widely used
lepidopteran cells for BEVS are the Sf9 and Sf21 cell lines isolated from ovarian tissue of
the fall army worm,
, and the High Five cell line, designated BTI-
Tn-5B1-4, originally established from the
embryonic tissue. Sf9 cells are
a sub-clone of the Sf21 cells and were selected for their faster growth rate and higher cell
densities than the Sf21 cells.
frugiperda cells, either Sf9 or Sf21 are preferred
for virus expansion. Sf21 cells can compare favorably, in terms of heterologous protein
expression, to both High Fives and the Sf9 cell lines in certain situations.
The BEVS technology, developed by Max Summers, Gale Smith and colleagues at Texas
A&M University, has unique biological advantages over bacterial, yeast or mammalian
protein expression systems. A major advantage is the quick turnaround time for the
expression of recombinant proteins that show biological activity, antigenicity, and
immunogenicity similar to authentic natural proteins. Also, the vectors are not dependent