VRC
Home
Research Laboratories
Biodefense Research Laboratory
Nancy Sullivan, Ph.D.
The research focus of the Biodefense Research
Laboratory comprises three areas: 1) development of vaccines and
antivirals against hemorrhagic fever viruses such as Ebola, Marburg
and Lassa, 2) studies of the mechanism of vaccine-induced immune
protection, and 3) basic research to understand the mechanism
of virus replication (entry) and neutralization.
Ebola and Marburg viruses have been identified
as the cause of several highly lethal outbreaks of hemorrhagic
fever for which there is no treatment or cure. Therefore, vaccine
studies are critically important for protection against infection.
We developed a highly effective vaccine strategy for Ebola virus
infection in non-human primates (Sullivan et al., Nature, 2000).
A combination of primary immunization with plasmid DNA and boosting
with adenoviral vectors containing Ebola genes generated protective
immunity in cynomolgus macaques. The vaccine yielded 100% protective
efficacy against Ebola infection and showed for the first time
that protective immune responses could be generated in primates.
The DNA vaccine is currently being tested in human trials conducted
by the VRC Clinical Trials Core Laboratory. Subsequently, our
laboratory has improved on earlier studies by demonstrating that
protective immunity can be generated with a single shot of the
adenoviral vector vaccine (Sullivan et al., Nature, 2003). Future
studies will precisely define the dose and composition of a clinical
Ebola vaccine product to be licensed for human use, and will also
apply similar strategies to the development of protective vaccines
against Marburg and Lassa viruses.
A second area of study in the Biodefense
Research Section is the analysis of vaccine-induced immune responses.
The mechanism of immune protection against Ebola virus infection
is as yet unknown. Studies using knock-out mice have reported
that NK-cells, cytolytic T-cells, or antibodies are each necessary
for protection in the mouse model of Ebola virus infection. Other
studies have shown using adoptive transfer that antibodies alone
or T-cells alone are sufficient for protective immunity. Collectively,
these investigations suggest that our understanding of immune
protection against Ebola remains limited. Moreover, the mouse
models of Ebola infection frequently fail to recapitulate important
components of pathogenesis and immunity that are observed in primates.
Therefore, we are using the studies of vaccine-induced protective
immunity in nonhuman primates to help elucidate the precise mechanism(s)
of immune protection against Ebola infection. Current studies
under investigation are being conducted in nonhuman primates and
utilize methods for selective inhibition of specific immunity
such as T- and B-cell depletion, inhibition of T-cell help, and
passive transfer of immune globulin. Using multicolor flow cytometry
we are able to evaluate with high precision the quantity and quality
of vaccine induced cellular responses by identifying distinct
subsets of lymphocytes that are present in protected animals,
and the kinetics with which they appear. Our goal is to combine
the methods described to define and characterize the components
required for immune protection against Ebola infection.
Our laboratory is also interested the basic
biology underlying Ebola virus pathogenesis, virus-host interactions,
and inhibition of virus replication. Ebola virus is a non-segmented
negative strand RNA virus with a simple genome containing seven
open reading frames. The virus replication cycle begins with binding
of the envelope glycoprotein, GP, to a putative cell surface receptor(s)
and entry into the host cell by fusion of viral and cell membranes.
Strategies to interrupt the virus life cycle can be targeted to
these early entry events or to later steps in the replication
cycle. We are currently investigating the molecular basis for
inhibition of virus entry by molecular inhibitors and neutralizing
antibodies, and of genome replication and transcription by siRNA
technology. We have developed and array of antibodies, both neutralizing
and non-neutralizing, that are useful for characterizing GP structural
changes and their functional consequences. We are using these
tools to dissect the molecular events underlying Ebola GP interactions
within the host. Our goal with these studies is to identify points
in the Ebola virus replication cycle that are vulnerable antiviral
and neutralization targets.
|