Combinatorial Phage Antibody Libraries
95
targeted mutagenesis and codon optimiza-
tion. In addition, to mimic the afFnity
maturation seen in a secondary response
in
vivo
, antibodies selected from both nonim-
mune and semisynthetic repertoires can
be genetically manipulated
in vitro
to im-
prove their afFnity and/or modify their
speciFcity. ±or example, it is possible to in-
crease the afFnity of these clones through
the random mutagenesis of selected CDRs
of the heavy chain followed by reselection
against antigen. Additionally or alterna-
tively, one can take a particular heavy or
light chain and ‘‘cross’’ or reclone it into
a light- or heavy-chain library respectively
in the hope that it will pair with a more
suitable partner. These strategies can often
improve binding constants by more than
two orders of magnitude, thus enabling
high-afFnity antibodies to be generated
from naive sources.
Several companies are now in exis-
tence, which engineer and screen naive
combinatorial antibody libraries that have
been optimized to be very large and di-
verse. ±ully human monoclonal antibodies
have been selected against therapeutically
relevant targets. In fact, Knoll Pharma-
ceuticals and the Cambridge Antibody
Technologies Group have developed the
Frst human antibody using phage li-
braries, which has been approved for
human use and is marketed by Abbott
Laboratories under the name Humira
03/brieFng/3930B1
02
A-Abbott-Humira.
pdf).
5
Summary
In the short time since their inception,
combinatorial phage antibody libraries
have been rapidly established as one of the
most efFcient routes to the generation of
human monoclonal antibodies. Libraries
prepared from immunized sources allow
the selection of antibodies generated dur-
ing a natural immune response. Moreover,
the antibodies generated will normally be
of high afFnity following rounds of se-
lection
in vitro
. Despite the scrambling of
light and heavy-chain pairs inherent to
library construction, antibodies selected
from immune libraries have repeatedly
been shown to be broadly reflective of the
donor’s serological reactivity. In addition,
efFcient selection procedures permit the
isolation of antibodies occurring at very
low frequencies in the library. Hence, li-
brary technology grants the investigator
previously unavailable access to the hu-
man antibody response. SigniFcantly, the
problem of eliciting human antirodent re-
sponses, an enormous limitation to early
therapeutic applications for rodent mon-
oclonal antibodies, has been overcome as
fully human antibody libraries are now
readily available.
Libraries
constructed
from
immune
donors have already yielded a number of
antibodies highly efFcient in virus neu-
tralization. Detailed information on the
antibody response to infectious pathogens
obtained through antibody libraries may
be applied in the design and assessment
of candidate vaccines as well as in eluci-
dating the mechanisms by which viruses
are neutralized by antibodies.
Unimmunized libraries, whether de-
rived from
naive repertoires or from
synthetic antibody sequences, have al-
most unlimited potential to generate an-
tibody speciFcities against any antigen.
In some cases, these libraries have gen-
erated antibodies with afFnities similar
to those found in a secondary immune
response
in vivo
. The resulting antibod-
ies – having already been cloned at the
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