Immobilization of insect cells

Abstract

The production of baculoviruses and recombinant proteins in insect cell culture has been mostly carried out in culture systems with freely-suspended cells. Suspended culture systems usually suffer from a number of disadvantages, such as the fluid mechanical cell damage from agitation and air-sparging, low cell and product concentrations, and low productivity. Another limitation is that the method is only suitable for the growth of non anchorage-dependent cell (e.g., Sf-9 cells). These drawbacks can be eliminated with the exploitation of cell immobilization techniques, such as the attachment of cells on solid surfaces, entrapment of cells in polymer gels, and encapsulation of cells in artificial membranes. With immobilized cells, a 10-fold or more increase in the cell and production concentrations can be achieved (e.g., Dean et al., 1987; Reiter et al., 1991; and Park & Stephanopoulos, 1992). The technology will also allow for simpler cellmedium separation and product purification processes. In addition, immobilization of cells in porous supports and microencapsules could also prevent the cell from mechanical damage due to mechanical agitation and gas sparging. There have been extensive studies on immobilization of animal cells and its application in large-scale production of mammalian cells and associated products, such as hybridoma cells in the production of monoclonal antibodies (Reuveny, 1985; Heath and Belfort, 1987). The development of immobilized insect cell culture, however, is still in its infant stage. This is not surprising since it is only recently that insect cell culture has been recognized as an important tool in the biotechnology industry (Luckow and Summers, 1988). Other factors responsible for the fewer studies on insect cell immobilization may be related to the type of insect cells used for large-scale production and the mechanism of virus and recombinant protein production. The cell lines used predominantly in baculovirus and recombinant protein production, i.e., those derived from Spodopterafrugiperda insect, Sf-21 and Sf-9, grow well in suspension, which undermines the advantages of immobilized culture. On the other hand, production of cell products involves viral infection and subsequent lysis of the cell. Immobilized cell culture can thus only be used for one batch operation. With the development of anchorage-dependent insect cells for virus and protein production, and processes of producing secreted cell products without cell lysis, immobilization technology will become more attractive for large-scale production. In this chapter, we will primarily focus on techniques for animal cell immobilization in particulate supports, including microcarrier beads and microcapsules, with emphasis on their applications in insect cell culture. Typical immobilization materials and methods, immobilized cell bioreactors and the major concerns associated with each technique will be addressed. The review will conclude with an outline of the studies conducted in our laboratory on insect cell immobilization techniques.