New Findings
1.
Potential for AAV as a vector for Hemophilia A gene therapy
Adeno-associated virus has been a candidate
virus for vector gene therapy for many years for several reasons.
First, it is not associated with any human diseases. Cells
carrying provirus precursor don't express new cell surface antigens, so
immunogenicity is also minimized. Finally, experiments have shown
that AAV has the potential for long-term transgene expression from both
integrated and episomal forms.
Recently, AAV utility as a viral delivery
system in long-term gene expression of coagulation factor IX has been demonstrated
in
vivo. Now, Gnatenko, et al, have successfully packaged B-domain
deleted fVIII into an adeno-associated viral vector, with detectable secretion
of functionally active factor VIII in vitro. This finding provides
the first evidence that AAV is an adaptable virus for fVIII delivery, and
given its potential as a
recombinant viral vector and its recent success in factor
IX delivery in vivo, it provides a new approach toward hemophilia A.
see reference #1
2.
Parvovirus B19 Associated acute cerebellar ataxia
PVB19 has been known to cause such
CNS diseases as meningitis and encephalitis, but PVB19-associated acute
cerebellar ataxia had never been reported. Last year, however, a
two year old boy was diagnosed with acute cerebellar ataxia. He was
seroposititve for IgM and IgG antibodies against PVB19 but he tested negative
for antibodies in the cerebral spinal fluid (CSF). Similarly, PCR
tests were positive for PVB19 in the blood serum but not in the CSF.
Because acute cerebellar ataxia is a disease of the central nervous system,
and because tests showed that PVB19 had not infected the cells of the nervous
system, it is probable that PVB19-associated acute cerebellar ataxia does
not involve direct viral invasion. One possible mechanism is that
it is a post infectious allergic reaction.
see reference #2
3.
Role of PVB19 in Pathogenesis of Giant Cell Arteritis
Recent findings suggest that PVB19
may play a role in the pathogenesis of Giant Cell Arteritis (GCA).
GCA is a systemic vasculitis of unknown etiology that involves large and
medium sized vessels. Study of the possible association between PVB19
and GCA was motivated by several factors, including: 1-B19 was been shown
to occur in epidemic cycles like those of GCA, 2-B19 has been associated
with other forms of systemic vasculitis, 3-that B19 is capable of persistent
and recurrent infection, and 4-that it appears to be associated with inflammatory
rheumatic disease.
The study found that there was a highly
significant correlation between the presence of B19 in DNA (as evidenced
by PCR analysis) and histological evidence of GCA, including symptoms of
systemic vasculitis and inflammatory arthritis. This correlation
is based on the demonstration of B19 DNA in the involved tissue and on
the recent finding that the cellular receptor for B19 is also expressed
on endothelial cells. It is possible that the correlation is not
etiologic, however, and further research is necessary to confirm these
findings.
see reference #3
4.
Fetal Hematological Parameters for Fetal PVB19 Infection Prognosis
Fetal parvovirus B19 infection causes
fetal anemia, non immune hydrops foetalis and fetal thrombocytopenia, which
in severe cases can lead to birth defects or death of the fetus.
Although detection of fetal PVB19 infection is easily obtained by PCR analysis
of amniotic fluid, there is presently no way of predicting which cases
will lead to severe outcomes, such as birth malformations and death.
Additionally, intrauterine transfusions have been shown to be an effective
treatment in only some cases. Attempts have recently been made to
use fetal hematological parameters, such as the severity of the fetal anemia,
to develop parameters that will help predict the outcome of the infection
and to give insight as to when blood transfusions will be an effective
treatment.
So far, there has been no success
in developing such parameters. In a recent study, the severity of
anemia of the fetuses who died was similar to that of the fetuses who had
favorable outcomes.
see reference #4
5.
Risk Factors for PVB19 Infection in Pregnancy
PVB19 infection during pregnancy greatly
increases a woman's risk of fetal death. Thus, recent studies have
attempted to determine the risk factors for PVB19 infections and to quantify
the importance of previously hypothesized risk factors for infection, including
family structure, housing density, length and type of education, and socioeconomic
status. PVB19 infection is transmitted primarily though respiratory
secretions, so study of contact patterns in outlining the risk factors
for PVB19 infection are especially important. One study in Denmark
attempted to outline the risk factors for both past and acute PVB19 infection.
In terms of risk factors for past
and acute infection, the Denmark study found that women with many siblings
and an interval to the nearest sibling of less than two years were more
likely to have been infected as children. Also, the number of children
already born in the household increased the pregnant woman's risk of both
past and acute infection. Finally, pregnant women with children aged
5-7 years were at the greatest risk, which is consistent with the theory
that children during early school years represent a particularly great
risk for infection. The intensity of child exposure in the woman's
workplace is another risk factor for acute and past infection, with school
teachers and after-school-club personnel being at highest risk. Contrary
to previous beliefs, socioeconomic factors, such as household crowding,
did not pose as a significant risk factor. In general, susceptible
pregnant women are at highest risk of PVB19 infection during epidemics,
especially if she has a high level of contact with children.
see reference #5
6.
Involvement of PVB19 in Acute Fulminant Liver Failure
Recent studies are investigating the
possible involvement of parvovirus B19 infection in liver injury.
Previous detection of PVB19 DNA in livers from patients requiring transplantation
for acute fulminant liver failure (AFLF) of unknown etiology suggested
the possibility that PVB19 infection plays a role in the development of
the disease. The presence of globoside, the B19 receptor, on human
liver cells also supports the hypothesis that PVB19 could be infecting
liver cells. A recent study used immune adherence PCR to detect the
presence of B19 virions in liver cells of patients with AFLLF. This
finding, together with the PCR analysis detecting viral mRNA encoding the
structural capsid protein in liver tissue, argue strongly for the involvement
of B19 virus in the development of acute fulminant liver failure.
see reference #6
7.
Role of PVB19 in Systemic Sclerosis
Recent studies suggest that PVB19
infection of bone marrow cells may be involved in the development of systemic
sclerosis (SSc), a connective tissue disease characterized by skin and
visceral organ involvement. Preliminary observations detected the
presence of B19 viremia in 4% of SSc patients, compared to a rate of 0.6%
in healthy blood donors. Also, the presence of anti-B19 IgG, but
not anti-B19 IgM, in the serum of B19 DNA positive SSc patients suggest
a persistent PVB19 infection. Now, a more recent study has discovered
the presence of B19 infection in bone marrow from a significant percentage
of SSc patients compared with that of a control group. Although these
preliminary observations suggest a possible role of B19 infection in SSc,
further studies are necessary to confirm the hypothesis.
see reference #7
8.
PVB19-Associated Disease in Bone Marrow Transplantation
Recent studies suggest that PVB19
can persist in immunocompromised patients and produce severe clinical illness.
A retrospective study was recently undertaken to evaluate the incidence
of parvovirus B19-associated infections in bone marrow transplant patients
and its impact on transplant related morbidity and mortality. PCR
analyses of blood and tissue specimens of patients who had developed infections
or complications after a bone marrow graft tested positive for B19 infection
a significant percentage of the time. This finding suggests that
parvovirus B19-associated infections are more common in immunocompromised
patients (such as those receiving bone marrow transplants) than was previously
anticipated.
see reference #8
9.
Progress in Adeno-Associated Virus Type-2 Vector Production
Although vectors derived from human
parvovirus AAV-2 are among the most promising gene delivery vector vehicles
currently being developed, they have the drawback that they are limited
in their clinical application due to the laborious work required to prepare
high titer and pure AAV-2 stocks. Recent improvements to the basic
manufacturing protocol, however, is resulting in the production of significantly
higher quality and quantity of viral stocks. New techniques include:
1-modification of conventional transfection/infection protocols, 2-development
of helper virus-free vector production, and 3-use of vector producer cell
lines. Future techniques may utilize a combination of these techniques
for rAAV manufacturing. While each of the strategies have many benefits,
each one also has a number of drawbacks that may still complicate the use
of large-scale AAV-2 vector manufacturing. Further research and will
be required for the development of an ideal AAV-2 vector production method
that is fully suitable to clinical requirements.
see reference #9
10.
Viral Safety of SD-Treated Plasma
Solvent/detergent (SD) treatment of
plasma and plasma proteins is highly efficient in inactivating lipid-enveloped
viruses. Non-lipid-enveloped viruses like parvovirus B19, on the
other hand, are not effected by SD-treatment of plasma. PVB19 is
a blood-borne pathogen, and there is thus a great risk of infection involved
when blood transfusions are given. A recent study in Norway, however,
showed that in populations where B19 is endemic, an epidemiological equilibrium
exists such that specific viral antibodies against PVB19 are present
in the plasma and that they serve to neutralize the B19 viral particles
that may be present. Thus, although the SD-treated plasma itself
does nothing to affect PVB19, the SD-treated plasma is nonetheless safe
with respect to transmission of infection with B19 in areas where B19 is
endemic.
see reference #10
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