Download Human Immunoglobulin as a Treatment for West Nile Virus Infection

E D I T O R I A L C O M M E N TA R Y
Human Immunoglobulin as a Treatment for West Nile
Virus Infection
Amy Guillet Agrawal1 and Lyle R. Petersen2
1
Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; 2Division of Vector-Borne Infectious Diseases, Center
for Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado
(See the article by Ben-Nathan et al. on pages 5–12.)
During the West Nile virus outbreak in
Israel in 2000, a woman with chronic lymphocytic leukemia who was comatose as
a result of West Nile virus encephalitis recovered after treatment with intravenous
immunoglobulin (IVIG) [1]. Antibody titers against West Nile virus were 1:1600
in Israeli IVIG; in contrast, North American IVIG preparations had no detectable
West Nile virus antibody [1, 2]. A second
patient, a lung transplant recipient, also
recovered from West Nile virus encephalitis after treatment with Israeli IVIG [3].
Six other subsequently treated patients
have had variable outcomes: 2 improved,
2 had no improvement, and 2 eventually
died [4] (C. Isada, oral communication;
R. Babecoff, written communication).
These anecdotal reports, although inconclusive, have stimulated interest in the use
of passive immunization for treating severe West Nile virus disease.
The article on the efficacy of human
immunoglobulin in treating West Nile virus infection in mice by Ben-Nathan et al.
[5] is provocative, in that it suggests that
Received 12 May 2003; accepted 14 May 2003; electronically
published 23 June 2003.
Reprints or correspondence: Dr. Lyle R. Petersen, Div. of
Vector-Borne Infectious Diseases, Centers for Disease Control
and Prevention, PO Box 2087 (Foothills Campus), Fort Collins,
CO 80522 ([email protected]).
The Journal of Infectious Diseases 2003;188:1–4
This article is in the public domain, and no copyright is claimed.
0022-1899/2003/18801-0001
IVIG might ameliorate or abort established West Nile virus infection. In the series of experiments described, BALB/c
mice were infected intraperitoneally with
either 20 or 200 times the LD50 (100 or
1000 pfu). They received 1 of 6 treatments: nonimmune mouse serum, immune mouse serum with ELISA titers
against West Nile virus of 1:3200, Omrix
IVIG with ELISA titers of 1:1600, IVIG
from US donors with ELISA titers of 1:
10, pooled plasma from Israeli donors
(titers not described but presumed to be
less than concentrated immunoglobulin),
or pooled plasma from US donors. In
protection experiments in which the antibody-containing treatments were given
shortly before and after infection, the results were unequivocal—any treatment
containing specific antibody produced
100% survival, and treatments without
specific anti–West Nile virus antibody
provided no protection (100% mortality;
table 1).
In subsequent experiments, the infected
mice were treated with 1–5 injections of
specific anti–West Nile Virus antibody,
with a clear dose- and time-dependent relationship to survival (table 1). Importantly, all treatments were started during
the viremic phase, before virus entered the
brain. It was established that virus entry
into the brain occurred on day 3 after injection with the 1000-pfu inoculum and
on days 6–8 after injection with the 100pfu inoculum in untreated West Nile virus–infected control mice. Finally, highdose antibody treatment administered 1
and 2 days or 2 and 3 days after injection with the 100-pfu inoculum afforded
complete protection; however, antibody
administered 3 and 4 days after infection yielded only 50% survival, although
those mice that died survived longer than
controls.
Evidence suggests that West Nile virus
may be more susceptible to antibody-mediated immunity than to cell-mediated
immunity. Clearance of primarily neurotropic viruses is not dependent on cytolytic T cell activity, in contrast to nonneurotropic viruses [11, 12]. Neurons, as
terminally differentiated cells, do not express major histocompatibility complex
class I, which would subject them to lysis
by CD8 T cells and nonreplacement [12].
Animal data support this concept. In the
1970s, Camenga et al. [6] challenged mice
with West Nile virus, gave them cyclophosphamide 1 day later to suppress both
the humoral and T cell–mediated arms of
immunity, and then administered immune serum or immune syngeneic spleen
cells at varying times (table 1). One injection of immune serum at day 5 or 6
resulted in 82% survival, and 1 injection
at day 8 or 10 resulted in 22% survival,
compared with 3% survival in controls.
EDITORIAL COMMENTARY
• JID 2003:188 (1 July) • 1
Table 1. Summary of published animal studies that used immunoglobulin for protection against or treatment of experimental flaviviral
infection.
Survival in indicated
treatment group, %
Source
Flavivirus
Animal(s)
Ben-Nathan et al. [5]
WNV
BALB/c mice: 4 weeks old
Camenga et al. [6]
WNV
BALB/c mice: 4–8 weeks old
Diamond et al. [7]
Tesh et al. [8]
Mathews and Roehrig [9]
WNV
WNV
SLEV
mMT mice (B cell deficient)
Golden hamsters: 10–11 weeks old
BALB/c mice
Kriel and Eibl [10]
TBEV
BALB/c mice
NOTE.
a
b
Day virus
was found
in brain
b
3–8
6
4
ND
4
4
Time of a
treatment
Specific
anti-WNV
antibody
Nonspecific
antibody
Untreated
infected
control
⫺1, 1, and 3
1
1 and 2
1, 2, and 3
1–5
3 and 4
1 or 2
5 or 6
8 or 10
⫺1 and 1
⫺1
1
4
1
3
100
64
75
92
100
50
94
82
22
100
100
100
30
190
25–30
0
ND
ND
ND
ND
ND
0
ND
ND
0
ND
ND
ND
ND
ND
0
0
0
ND
0
0
3
ND
ND
ND
ND
0
0
0
0
ND, not determined; SLEV, St. Louis encephalitis virus; TBEV, tickborne encephalitis virus; WNV, West Nile virus.
Day(s) after infectious challenge on which treatment was administered.
Virus found in brain on day 3 after challenge with 1000 pfu of WNV and on days 6–8 after challenge with 100 pfu of WNV.
Notably, virus was detectable in the brain
at day 6. Immune syngeneic spleen cells
rescued 87% of mice at day 2 but only
13% at day 4; survival among controls was
12% [6].
Diamond et al. [7] have described the
effects of immunoglobulin in several different mouse models of West Nile virus
infection. In a B cell knockout model, a
single plaque-forming unit of West Nile
virus given by footpad inoculation constitutes the LD50. All mice given specific
immunoglobulin 1 day before and 1 day
after infectious challenge with a lethal inoculum of West Nile virus (100 pfu) survived, compared with none of the controls
(table 1). In wild-type mice, immune serum produced results similar to those reported by Ben-Nathan et al. [5]; after inoculation with 100 pfu of West Nile virus,
immune serum produced 80% survival if
administered at 24 h and 50% survival if
administered at 4 days, versus 20% survival in control animals (M. S. Diamond,
unpublished data).
Xiao et al. [13] established a model of
West Nile virus encephalitis in Syrian
golden hamsters. After intraperitoneal in-
oculation, moderate viremia was detected
for the first 5 days after infection. Natural
antibody levels increased by day 5, and
viremia became undetectable by day 7. By
day 5, neuronal degeneration was evident,
and by days 7–8, degeneration had localized to the deeper layers of the cerebral
cortex, Purkinje cells in the cerebellum,
and the brain stem. Death occurred in
∼50%–70% of the infected animals between 7 and 14 days after infection. In
another study using the same model, hamsters (18 weeks old) treated with exogenous immune serum 24 h before infection
were completely protected from viremia
and death (table 1) [8]. However, if antibody administration was delayed 48 h
after infection, no survival effect was seen
(R. B. Tesh, unpublished data).
Finally, in recent experiments, golden
hamsters and BALB/c mice were given Israeli IVIG, IVIG from US donors, or saline
on day 1 and 2 after intraperitoneal injection with West Nile virus. Older hamsters (18 weeks old) showed no survival
benefit with IVIG, but younger hamsters
(4–5 weeks old) had 100% survival when
Israeli IVIG was used and 20% survival
2 • JID 2003:188 (1 July) • EDITORIAL COMMENTARY
when US IVIG was used. Among BALB/
c mice, 90% of those given Israeli IVIG
survived, compared with 10% of those
given US IVIG (J. D. Morrey, unpublished
data).
The results of Ben-Nathan et al. [5] and
other groups showing clear-cut protection
by IVIG when animals are treated before
or shortly after infectious challenge with
West Nile virus provide support for the
potential usefulness of IVIG in the treatment of acute West Nile virus infection in
humans. Passive immunization of humans
for treatment of other viral infections has
precedent. Examples include parvovirus in
patients with human immunodeficiency
virus [14]; chronic echovirus meningoencephalitis in children [15–17]; disseminated vaccinia infection [18]; Junin virus,
the agent of Argentine hemorrhagic fever
[19]; and cytomegalovirus pneumonitis in
bone marrow transplant recipients [20].
A critical question is whether IVIG is
effective when cerebral infection has been
established. Successful treatment of animals challenged with St. Louis encephalitis
and tickborne encephalitis viruses, flaviviruses related to West Nile virus, was pos-
sible several days after infection; however,
the therapeutic effect decreased rapidly
once virus was found in brain (table 1) [9,
10]. Other neurotropic viruses are amenable to treatment with antibody [21–23].
Studies by Griffin and coworkers [12, 21]
indicated an important role for antibody
in the clearance of neuroadapted Sindbis
virus after well-established brain infection.
Virgin and Tyler and their associates [22,
23] successfully treated reovirus brain infection with intraperitoneally administered antibody up to 7 days after infectious
challenge. In the preantibiotic era, horse
serum treatment for meningitis caused by
Neisseria meningitidis significantly reduced
mortality [24]. The efficacy of antibody
therapy for cerebral infection depends on
passage of IgG through the blood-brain
barrier. Studies in humans without inflamed meninges show that IgG enters at
very low levels [25]. Entry is enhanced,
however, once inflammation is present. In
a study of patients who developed aseptic meningitis as a complication of highdose IVIG therapy for autoimmune disease, IgG levels of 1.5–7 times the upper
limit of normal were seen in cerebrospinal
fluid [26].
There are several limitations to the
study by Ben-Nathan et al. [5]. One concern is that success was shown in animal
models when antibody was given during
the viremic phase; however, nearly all patients with West Nile virus infection are
no longer viremic when they present, and
most have already developed IgM antibody [27, 28]. Another limitation was that
even the lower infecting dose used by BenNathan et al. [5] produced 100% mortality
in untreated mice. But the infectious inoculum from a mosquito bite is far less,
and most persons infected remain asymptomatic. It would be of interest to see how
long after an infectious inoculum is injected IVIG can produce a survival benefit,
particularly when the inoculum is low.
Another potential limitation was the
choice of infecting strain. Whereas other
recent work investigating the efficacy of
antibody against West Nile virus in animal
models has used contemporary strains
from the US outbreak [7, 8], Ben-Nathan
et al. [5] used a 1954 strain. Although the
establishment of an LD50 still ensures adequate virulence, differences in strain may
produce different responses to treatment.
In work screening other compounds in
vitro, Morrey et al. [29] found an up to
30-fold difference in EC50 (the amount of
a compound required to abrogate 50% of
the cytopathic effect produced by a virus)
for some compounds when they used a
recent New York strain, compared with the
1937 Uganda strain of West Nile virus.
Finally, the efficacy of antibody therapy
demonstrated in animal models may not
translate directly to humans. As an example from the preantibiotic era, the
mouse model of pneumococcal infection
showed that treatment with horse serum
was only effective when given within 12
h, but when this therapy was transferred
to humans for this otherwise untreatable
disease, it was very effective when given
within 4 days [24].
Current candidate agents for treatment
of severe West Nile virus disease include
ribavirin, interferon (IFN)–a2b, and hightiter anti–West Nile virus immunoglobulin. Ribavirin has some activity at very
high doses in vitro [29, 30]. Patients who
received ribavirin during the 2000 West
Nile virus outbreak in Israel had increased
mortality; however, this was likely due to
the fact that ribavirin was administered to
sicker patients [31]. If the high levels required for any antiviral activity in vitro are
extrapolated to levels achievable in human
cerebrospinal fluid, extraordinarily high
intravenous doses (on the order of 4 g/
day) would be required achieve levels between the in vitro EC50 and the EC90 for
oligodendroglial cells [30]. Such doses are
associated with significant, although reversible, hemolytic anemia.
IFN-a2b is active in vitro against West
Nile virus [32] but has not been tested in
an animal model of West Nile virus. Its in
vitro activity and broad immunostimulatory activity [33] have prompted several
clinical trials involving flaviviral diseases.
In an outbreak of St. Louis encephalitis in
Louisiana, IFN-a2b was used expediently
in a nonrandomized open-label fashion.
The first 17 patients in the outbreak were
treated with supportive care only; the next
15 patients were treated with IFN-a2b
[34]. Neither group experienced mortality.
Although the mean neurological score improved in the treated group and worsened
in the untreated group by week 3, these
results must be interpreted with considerable caution, because the study was not
randomized, there was no placebo group,
and the scoring scale was applied in an
unblinded fashion [34]. An open-label
study examining the effect of IFN-a2b
versus supportive care for West Nile virus
infection is ongoing (J. J. Rahal, written
communication). A large, double-blind,
placebo-controlled study failed to find a
difference in mortality or functional outcome resulting from the use of IFN-a2b
for treatment of Japanese encephalitis, a
related flavivirus, in Vietnam [35].
Although studies such as that by BenNathan et al. [5] suggest that flaviviral infections are at least partially treatable with
passive immunity, if antibody is going to
work at all, it must be administered early.
The side-effect profile of IVIG compares
favorably with that of the other 2 main
candidate therapies (ribavirin and IFN),
and, without a human trial, there will be
no way to know whether the results in
animals will translate to a significant benefit in humans. The high mortality seen
among persons with West Nile virus encephalitis and the long-term morbidity
among survivors [36, 37] provide impetus
for such a trial. Patients with established
neurological disease or who are at high risk
for progression to severe disease but who
have not yet developed encephalomyelitis
would be candidates for any effective therapy. Risk factors for progression of disease
are advanced age or immunosuppression,
although the type of immunosuppression
is not yet well defined [31, 36, 38]. If IVIG
or any agent is found to be effective, rapid
diagnosis will become far more important
to identify potentially treatable patients
EDITORIAL COMMENTARY • JID 2003:188 (1 July) • 3
early in the course of disease. The unpredictability of flaviviral outbreaks other
than Japanese encephalitis complicates
planning of human clinical trials; if the
high incidence of severe West Nile virus
illness observed in 2002 in North America
is repeated in coming years, there may exist a unique opportunity to determine
whether early treatment of West Nile virus infection with specific antibody is
beneficial.
10.
11.
12.
13.
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