In vivo recombined antibody libraries
To circumvent the earlier limits imposed by the transformation
step, some libraries have been constructed using
in vivo recombination or combinatorial infection to generate
highly diversifi ed repertoires of either synthetic or
naive antibody fragments. A synthetic Fab library was
constructed using two vectors, each with a different antibiotic
selectable marker. One is a plasmid derived from
pUC19, and the second is a phage vector (fdDOG). The
heavy and light chain antibody sequences were cloned
into this vector [29]. The vectors are then incorporated
into the same cell by a simple phage rescue strategy, and
cells are sub sequently coinfected by the chloramphenicol-
resistant phage P1. P1 provides the Cre recombinase
which recognizes the loxP sites fl anking the heavy and
light chain antibody sequences and recombines them
within the cell. The constructed library was predicted
to contain ~1010 recombinants, and these recombinants
were being detected on the basis of their resistance to all
three antibiotics. Recently, a single vector system which
also used Cre recombinase has been described [30]. A
phagemid vector containing both VH and VL segments