86
Combinatorial Phage Antibody Libraries
the antigen (e.g. an infectious agent).
Preparing combinatorial antibody libraries
from immune individuals is advantageous
in that the antibody gene repertoires
of these donors have been biased in
favor of antibodies binding to particular
antigens in the course of a natural immune
response.
In
addition,
if
the
subject
has been challenged with the antigen
on
multiple
occasions,
the
available
antibodies will probably be of high afFnity
following rounds of afFnity maturation.
Combinatorial antibody libraries prepared
from a single immune donor can provide
ag
l
im
p
s
eo
rar
o
u
g
h‘
s
n
a
p
s
h
o
t
’o
f
an individual’s antibody repertoire. This
allows a unique opportunity to examine the
human humoral immune response to any
number of pathogens at the monoclonal
level. However, one large caveat should
be borne in mind. Library construction
shuffles heavy and light chains so that in
theory no knowledge of heavy–light chain
pairing
in vivo
is available. In practice,
many heavy chains may be combined with
light chains related to those to which it was
paired
in vivo,
but this is extremely difFcult
to prove for any given case.
One application has been to obtain mon-
oclonal antibodies with antiviral activity, in
particular, those antibodies that are best
able to neutralize viruses by binding to
their surface and diminishing or eliminat-
ing their ability to infect host cells. (There
are additional and very important effec-
tor functions of antibodies, such as their
ability to recruit complement and effector
cells, but this topic is outside the scope of
this review.) In the next section, we will fo-
cus on antibody-mediated neutralization,
with the acknowledgement that effector
functions of antibodies have been found to
play a critical role in Fghting infectious dis-
eases. Indeed, all neutralizing antibodies
(of the appropriate isotype) have effector
function capability.
Another potential application of anti-
body immune libraries is to attempt to
understand what deFciencies might exist
in the antibody response against cer-
tain pathogens, or the nature of immune
pathologies in certain tissues. ±or example,
if mostly nonneutralizing antibodies are
elicited against a virus, to which epitopes
do they bind? What isotypes of antibod-
ies are elicited, how long are the third
complementarity-determining regions in
the heavy chains (CDR H3s), and what is
the degree of somatic mutation? In another
example, an antibody library may be con-
structed from peripheral blood in a tumor
or at a site of autoimmune inflammation,
so that antibodies selected against these tis-
sues might identify potentially therapeutic
or pathologic speciFcities.
There is no doubt that there are many
human
antibody
speciFcities
of
great
diagnostic and therapeutic potential that
may be cloned from immune donors.
When making antibody libraries from
immune sources, however, the
donor
a
n
dt
i
s
s
u
es
o
u
r
c
es
h
o
u
l
db
ec
a
r
e
f
u
l
l
y
chosen. The primary prognostic indicator
is demonstrable serum antibody reactivity
with the antigen to be studied. Serum
antibody levels are thought to be predictive
of
antibody
secretion,
which
in
turn
reflects the level of speciFc RNA in plasma
cells, and it is this factor that will largely
dictate the composition of the library.
Although speciFc antibodies have been
isolated from libraries constructed from
donors with comparatively low serum
titers, libraries prepared from donors with
higher titers tend in general to yield a more
diverse panel of ±abs. To clone human
antibody genes from reverse-transcribed
cDNA, human primer sets have been
described, which allow the creation of very
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