Bacteriophage vector systems

Researchers have expanded upon the natural diversity generated by the immune system. In 1989 a novel vector system based on the bacteriophage lambda was used to express a synthetic combinatorial library of Fab fragments of the mouse antibody repertoire in Escherichia coli [22]. This system allowed rapid and easy identification of monoclonal Fab fragments that bind a given antigen, in a form suitable for genetic manipulation. For example. 

At a minimum, hosts and vectors shall be comparable in containment to Escherichia coliK- 2 with a non-conjugative plasmid or bacteriophage vector. AppendixI-II describes the data to be considered and mechanism for approval of Host-Vector 1 systems. 

Pierce J.C., Sauer B., and Sternberg N. 1992. A positive selection vector for cloning high molecular weight DNA by the bacteriophage PI system Improved cloning efficacy. Proc. Natl. Acad. Sci. 89 2056-2060. 

Two other bacteriophage systems have also been investigated as potential phage-display vectors, namely bacteriophage T4 [131], where a C-terminal extension on fibritin encoded by gene wac (whisker s antigen control) could be displayed, and P4 [132], where a deca-peptide was successfully inserted and presented near the N-terminus of the capsid decoration component, Psu. Their relative usefulness cannot yet be evaluated. 

Within each host cell system, several independent isolates and laboratory variant strains are available, and the efficiency of expression can vary between them for reasons that are not always understood. For example, there are several independently isolated strains of E. coli, which vary in their ability to express the same protein using the same vector. Thus, it is routine to test several strains for optimal production, and this is usually achieved by screening a bank of available strains. In addition, notably in the E. coli system, there are several mutant strains which may be used to increase product yield and improve fermentation characteristics. Such mutants may have deficiencies in proteases, resulting in increased stability of the expressed protein (Kresze, 1991), cell-wall mutations permitting better secretion characteristics (Le and Trotta, 1991), or resistance to bacteriophages which can lyse bacteria leading to losses and delays in large-scale fermentation. 

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