Combinatorial Phage Antibody Libraries
91
in the form of an aerosol directly into
the lungs of infected mice at the time of
peak viral replication, it was able to reduce
the viral titer by a factor of 5000. These
Fndings suggest that recombinant human
monoclonal ±abs may prove useful in the
therapy of RSV disease and other respira-
tory conditions in which virus replication
occurs largely in the luminal lining of the
respiratory tract.
The HSV-speciFc antibody was selected
from a library constructed from a different
HIV-1-positive donor whose serum had
demonstrable antibody titers to HSV-1 and
-2. Even though only one heavy-chain se-
quence was recovered by panning against
both viruses, all the antibodies studied re-
acted well with HSV-1 and -2. Only one
clone, ±ab 8, which recognizes the HSV
envelope glycoprotein D, was able to con-
sistently neutralize the virus in a plaque-
reduction assay. HSV ±ab 8 has also been
shown to both completely prevent plaque
development in cell monolayers 72 h post
infection, establishing that the ±ab can
neutralize after attachment of the virus to
the host cell, and to protect mice against
vaginal challenge with the virus.
The Floviruses, which cause hemor-
rhagic fever, are characterized by their
extreme lethality (up to
80% of those in-
fected die) and have gained much media at-
tention in recent years. Human ±ab phage
display libraries were constructed from
the bone marrow from two donors who
recovered from infection with Ebola virus
during the 1995 outbreak in Kikwit, Demo-
cratic Republic of the Congo. Initially, only
weakly binding ±abs could be selected by
radiation-inactivated infected cell lysates.
By contrast, soluble Ebola virus glycopro-
tein (SGP) and irradiated whole virions
were used to select ±abs with high afFnity
to both SGP and nucleoprotein (NP). Of
these antibodies, ±ab KZ52, which binds
to GP, had the greatest reactivity against
live Ebola virus–infected Vero cells as
shown by immunofluorescence. ±ab KZ52
was engineered as a whole IgG1 molecule
and, signiFcantly, neutralized Ebola virus
at 0.4
µ
gmL
1
in a plaque reduction as-
say. IgG1 KZ52 was also shown to protect
guinea pigs from lethal Ebola Zaire virus
challenge. KZ52 protected at 25 mg kg
1
was administered 1 h prior to (preexpo-
sure) or 1 h following (postexposure) virus
challenge. Although sterilizing protection
was not observed, plasma viremia was
reduced by approximately three orders
of magnitude. Whether human recombi-
nant monoclonal antibodies against the
Floviruses will be useful as prophylactic
agents remains unknown.
Prion diseases such as scrapie and
bovine spongiform encephalopathy (‘‘mad
cow disease’’) are fatal disorders of pro-
tein conformation, which are characterized
by progressive degeneration of the central
nervous system. Mad cow disease has had
enormous negative impact on the beef and
cattle industry in the United Kingdom, and
worldwide restrictions have been placed
on the import of beef from the United
Kingdom. The insidious transmissibility
of prion diseases and the lack of a reliable
and sensitive diagnostic test for prions
has created a demand for highly sensi-
tive agents to accurately diagnose prion
protein in animals, animal products, and
in humans. The molecular basis of prion
propagation is generally believed to be that
the pathogenic or ‘‘scrapie’’ form of the
prion protein (PrP
Sc
)
acts as a template to
convert the normal cellular prion protein
(PrP
C
)
to the PrP
Sc
form. Although the pri-
mary amino acid sequences of PrP
C
and
PrP
Sc
are identical, numerous structural
studies suggest that the conversion of PrP
C
to PrP
Sc
involves an extensive conforma-
tional change with substantial acquisition
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