We have used a combinatorial immunoglobulin
library approach to obtain monoclonal antibodies from
nonimmune adult mice, thereby establishing the principles of
(i) accessing naive combinatorial antibody libraries for predetermined
specificities and (ii) increasing the affinity of the
selected antibody binding sites by random mutagenesis. A
combinatorial Fab library expressing immunoglobulin Ip and it
light-chain fragments on the surface of filamentous phage was
prepared from bone marrow of nonimmunized, adult BALB/c
mice with the multivalent display vector pComb8. Phage
displaying low affinity Fabs (binding constants, 104-1O M-')
binding to a progesterone-bovine serum albumin conjugate
were isolated from the library. Random mutagenesis of the
heavy- and light-chain variable regions expressed in the monovalent
phage display vector pComb3 was performed by errorprone
PCR, and subsequently clones with improved affinity for
the hapten conjugate were selected. We demonstrate that
antibodies with desirable characteristics from a nonimmune
source may be selected and affinity maturation may be achieved
by using the twin vectors pComb8 and pComb3, thus opening
the route to obtaining specific antibodies from a generic library
and bypassing immunization