Contact: Wendy Brown, WSU Department of Veterinary Microbiology and Pathology, 509/335-6067, wbrown@vetmed.wsu.edu
WSU Researchers Invent Technique to Speed Development of Vaccines
PULLMAN, Wash.-A team of Washington State University scientists
has devised a method that could lead to the development of vaccines
against some of the most troubling infectious diseases we
face-diseases that have so far been difficult or impossible to
vaccinate against.
The new method allows researchers to rapidly screen large numbers
of pathogen proteins, called antigens, for their ability to prompt
an immune response in a host. Proteins with that ability are good
candidates for use in vaccines. The method will be especially
valuable in the quest for vaccines against persistent diseases such
as malaria, sleeping sickness and syphilis.
"It's very slick," said immunologist Wendy Brown, who led the
research effort. "Now we have a high-throughput way of finding
antigens from any pathogen, as long as you have the genome
sequence. To me this was a huge breakthrough, because I've been
spending my whole career trying to figure out ways to do this."
The research team included scientists at WSU and at the Rocky
Mountain Laboratories of the National Institutes of Health. Their
paper was published in the March 20 issue of the Journal of
Immunological Methods and is available online at
http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T2Y-4RPD1TP-2-F&_cdi=4931&_user=137179&_orig=browse&_coverDate=03%2F20%2F2008&_sk=996679998&view=c&wchp=dGLbVzW-zSkWb&md5=c5df3cf715d25fc2884d90f4959ba3b3&ie=/sdarticle.pdf.
A vaccine works by showing the body's immune system a pathogen or
part of a pathogen (usually a protein) so that it can develop
cellular memory and antibodies that will recognize and attack the
pathogen in the future. A key step in the development of a vaccine
is identifying which protein(s) to use. Until now, screening
pathogen proteins to find those few that might be good candidates
has been laborious, time-consuming, and in the case of persistent
diseases, not very successful. Brown said prior methods required
about three months to produce and purify a single protein to test.
With her new method she is able to screen dozens of proteins within
a few weeks.
Brown's group worked with Anaplasma, a bacterium that causes
severe anemia in cattle. Anaplasma is the most common
tick-borne pathogen of cattle worldwide and costs an estimated $100
million per year in lost animals and lowered productivity in the
United States alone.
The new method starts with the pathogen's DNA. Previous work by WSU
scientists had determined the whole genome sequence of
Anaplasma. By comparing that sequence with the genome
sequences of better-known microbes, Brown's team was able to
pinpoint genes that code for proteins that stick out of the
pathogen's cell membrane. Brown reasoned that since those proteins
are exposed on the surface of the cell, they should be visible to
antibodies and immune system cells, and therefore could be a good
way to target the pathogen.
Once the genes were isolated, Brown's team made the proteins they
coded for by using chemical 'machinery' derived from E. coli
bacteria. They then purified each protein to get rid of any E.
coli proteins that were present. They did that by using a
chemical that would specifically bind to the Anaplasma
proteins. Brown attached the chemical to tiny synthetic beads and
then poured the protein mixture over the beads. Anaplasma
proteins stuck to the beads, while E. coli proteins did not
and were discarded. This purification step represented a big
advance over other methods, which have been plagued by
contamination with irrelevant proteins.
Each purified test protein was then presented to T cells from cows
that had previously been exposed to Anaplasma outer membrane
proteins. T cells are the immune system's "memory cells." In the
body, when they recognize an antigen they have seen before, they
trigger antibody production by other immune system cells. In
Brown's test, if the T cells recognized a protein, they started
dividing and making interferon.
Using the new procedure, Brown's team found T cells responded to
about 20 proteins, including many that had never before been shown
to stimulate a T cell response. The researchers are now testing
whether any of these might form the basis for an effective vaccine
against Anaplasma.
Brown said the new technique also will be a boon to researchers
working on vaccines against pathogens that are highly contagious or
especially deadly, such as the Ebola virus and the bacterium that
causes anthrax. She is using it to screen proteins from
Coxiella, a bacterium that causes Q fever and is considered
a possible bioterrorism threat.
"If you have the genome, you don't have to touch the organism. You
can just start expressing all these proteins and test them," Brown
said.