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Minnesota Medicine
Published
monthly by the Minnesota Medical Association
February 2002/Volume 85
New
Directions in Vaccine Research
Developments in molecular medicine
have expanded the reach of vaccines.
By Dan Emerson
Success sometimes breeds complacency—that certainly has been the case
with public attitudes toward vaccines and the infectious diseases vaccines
have brought under control. During the second half of the 20th century, a
series of vaccine breakthroughs, beginning with Jonas Salk’s development of
the polio vaccine, greatly reduced the threat of infectious disease and
lengthened the average human life span. It wasn’t until the bioterrorism
threat of 2001 that the public’s attitude changed. Suddenly, there was a
heightened sense of urgency regarding researchers’ efforts to develop
vaccines against anthrax, smallpox, and other infectious diseases. “Up
until the anthrax attacks, most people in the current generation didn’t
have a true appreciation for the devastation that infectious diseases cause,”
says Gregory Poland, M.D., who has headed the Mayo Clinic’s 20-person
Vaccine Research Group since it was established in 1988. “They had the
feeling that everything that can be known about infectious disease is
known, that we are safe.”
Recent disease outbreaks—anthrax, smallpox, HIV, Lyme disease—have
proven that statement false, Poland points out. “The list goes on and on,”
he says. Although public interest in vaccine research may have been minimal
before September 11, researchers’ dedication and drive to defeat a variety
of bacterial and viral infections have never faltered. Efforts to improve
existing vaccines’ safety and efficacy continue. And the range of effects
scientists seek to achieve with vaccines has expanded; many of the vaccines
being developed today are designed to treat diseases rather than prevent
them.
Applying New Technology
The new generation of vaccines is derived from traditional vaccines that
have been enhanced by new developments in molecular medicine and
biotechnology. The most effective types of vaccines are “live” viruses that
have been weakened (attenuated) so as not to cause disease. Such vaccines
are effective because of the way they present themselves to the immune
system, according to Stephen Russell, M.D., a cancer researcher and
director of molecular medicine at Mayo Clinic. “If you just give protein or
a ‘killed’ virus to [an organism] it will be fairly rapidly eliminated. But
to eliminate something that is alive, the immune system really has to get
its teeth in it to eliminate it. It provides much more effective, lasting
immunity.” The attenuated viral vaccine used to protect against polio,
measles, mumps, rubella, and yellow fever are “classic examples,” of this,
Russell says.
In recent years, the method of using attenuated viruses to trigger a
T-cell immune response has been dramatically enhanced by the advent of
genetic engineering, which may make it possible to change virtually every
virus, Poland says. “We can add another gene or change one of the viral
genes so it works in a slightly different way.” The current vaccines
against hepatitis B virus and Lyme disease, for example, are the products
of recombinant DNA technology.
A major component of Mayo’s vaccine development effort involves using
genomics and proteomics—which have developed as a result of recent advances
in molecular biology and mass spectrometry—to learn about individual
response to vaccines. “This suite of tools has allowed us to begin to try
to understand the biology of vaccine nonresponse or aberrant response,”
Poland says. He explains that research at Mayo is attempting to answer what
he calls a “simple, clinical question.” In a population such as a school
community, Poland says, about 10 percent of those who receive a vaccine may
not respond to it, 80 percent receive good protection, and 10 percent show
a spectacular immune response. And in some cases, a vaccine can cause a
health problem or disease. “We believe most, if not all, of that difference
in response is genetically mediated,” Poland says.
Within the past five years, Poland and other Mayo scientists have
published a series of papers on measles vaccine and HLA (human leukocyte
antigens) genes showing the genes’ importance in determining individuals’
response to the vaccine. In the future, scientists may be able to detect
which patients will not respond to a specific vaccine and which will
experience serious side effects. They could then use that information to
develop more effective vaccines.
Funding is one of the most crucial variables in achieving those goals,
Poland contends. “At this stage, it’s almost entirely dollar-driven;
genomics and proteomics are very expensive.” For example, Mayo researchers
are just about to begin a gene study to determine whether the measles
vaccine may be involved in causing autism in children—a current topic of
controversy, especially in England. They will study microarray gene
expression profiles, which are small glass slides (or “chips”) to which are
attached DNA fragments representing all 60,000 human genes. “At the DNA
level, we’ll look at what happens to those genes when they are exposed to
vaccines.” Testing one child costs about $5,000.
Treating Cancer with Vaccines
Defeating cancer is another major focus of current vaccine research.
Scientists are experimenting with vaccines to treat several types of
cancer, including kidney, colon, pancreatic, and ovarian cancer, and
melanoma. The vaccines use a patient’s own cancer cells to help spur his or
her immune system to target and destroy other cancer cells. For years,
researchers tried to stimulate immune reactions against cancers using whole
cancer cells, with limited success. In recent years, scientists have been
able to isolate proteins from the surface of melanoma cells. Injected into
the body, these antigens provoke the immune system into producing killer
T-cells directed against the cancer.
In working to develop an immunotherapy program for malignant melanoma,
some Mayo Clinic researchers have been developing tumor-specific, peptide-based
vaccines (peptides are protein fragments that provoke the immune response)
and also conducting experiments on in vivo vaccine generation. They are
injecting various immune-modulating agents into the patient to boost
pre-existing immune responses— in effect, they’re building vaccines to
attack patients’ own tumors. In one study, Mayo researchers are using
cytokines—substances produced by immune cells that enhance the immune
response—as adjuvants to vaccines.
“Over the last four years we’ve been able to translate a lot of this
research from preclinic mouse experiments to ongoing clinical trials at
several sites,” says Svetomir Markovic, M.D., Ph.D., a Mayo senior
associate consultant and assistant professor in the departments of
Hematology and Oncology. Trials are underway at some of the 280
institutions of the North Central Cancer Treatment Group and at Mayo’s
sites in Rochester, Arizona, and Florida.
Methods of in vivo vaccine generation present several advantages,
Markovic says. “There is no need for artificial processing of tumor cells
and antigens. The ‘vaccines’ are created specifically for the patient’s own
tumor. Tumors are not all identical; each of those cells are somewhat
different, and a vaccine can only be effective against a limited number of
targets. With these interventions, we’re broadening the target range the
immune system is capable of recognizing.”
At the University of Minnesota, researchers have developed vaccines for
humans diagnosed with melanoma or renal cell carcinoma. For several years,
Matthew Mescher, Ph.D., professor and director of the Center for Immunology
at the University of Minnesota, has focused on understanding how cytotoxic
T-lymphocytes are able to recognize and kill virus-infected cells or cancer
cells. Mescher and his colleagues discovered that in order for the T-cells
to recognize the molecules specific to a virus-infected cell or a tumor
cell, the molecules have to be displayed on a surface that is about the
size of a cell. “Exposing T-cells to the purified molecules called antigens
doesn’t activate the T-cells, but if you put them on a cell-sized surface,
they will recognize them and respond to them.”
To make a vaccine, researchers peel the outer membranes off tumor cells
removed from the patient, then attach them to cell-sized beads. The
membrane-coated beads are then injected into the patient. Exposure to the
beads mobilizes the immune system against the introduced material and the
cancer cells.
Mescher is now testing the safety of the vaccines on humans, in
collaboration with university researchers Julie Curtzinger, Ph.D., Jeffrey
Miller, M.D., and Ian Okazaki, M.D. Working with mice, they found that the
combination of the chemotherapy drug Cytoxan plus the vaccine rid the mice
of tumors. Researchers theorize that although Cytoxan does not attack the
cancer cells directly, it does seem to help the immune system fight the
cancer. “It may help bring the immune system back into balance,” Okazaki
says. “Cancer patients often have too many suppressor cells; Cytoxan
hopefully restores the ability of immune cells to respond to the
vaccination.”
Based on the successful experiments in mice, the researchers have begun
Phase I clinical trials. About six months ago, they began treating patients
with late-stage melanoma and renal carcinoma in a small-scale trial with
about 60 patients.
Finding New Uses for the Measles Vaccine
In 1998, when Russell came to the Mayo Clinic from England’s Cambridge
University, one of his first projects was to determine whether or not the
vaccine strain of the measles virus would be effective as an oncolytic
agent. For several decades, there have been anecdotal reports of cancer
patients whose tumors disappeared after they contracted measles. In the
1950s and 1960s, it was standard protocol to test any newly isolated virus
for therapeutic activity in humans with cancer. However, at that time,
scientists were not skilled at growing or purifying viruses, says Russell.
“They might extract a crude form from saliva or tissue culture and
administer that to patients. They saw occasional responses, but, often
after the tumor responded, the patient went on to get very sick.” With the
advent of effective chemotherapy, those efforts were largely
discontinued.
Recently, there’s been a resurgence of interest in the cancer-fighting
potential of viruses. “It really is an untapped resource of new agents
known to have strong activity against cancer; we just have to learn how
best to use it,” Russell says. “The biggest impediment to its successful
use is the immune system. After the first dose, the patient’s system is
going to mount an antibody response to eliminate the virus before it
reaches tumors. A lot of effort is currently being directed at trying to
overcome that barrier.”
The naturally occurring strain of measles virus does not damage tumor
cells; however, the Edmonston B strain (MVE—measles virus Edmonston), first
isolated in 1954, does. Nearly all of the measles vaccines currently in use
were derived from that strain. “It’s interesting that while the vaccines
subsequently developed from that strain must have changed over the years,
they still provide very good protection against currently circulating
strains of measles,” Russell notes.
In its attenuated form, MVE induces protective immunity when administered
by immunizations. The Mayo researchers introduced MVE into at least six
types of myeloma cell lines. It reproduced and caused the myeloma cells to
fuse together in abnormal cell masses, which eventually died. In contrast,
the wild type measles virus produced little, if any, cell growth
abnormality or inhibition.
In 1999, the Mayo researchers discovered that the MVE strain is able to
effectively kill tumor cells in tissue culture without causing significant
damage to normal cells, Russell says. “It’s very selective in its ability
to damage tumor cells.” Then they duplicated the findings in laboratory
mice. Nearly every tumor tested showed the desired response—regression or,
in some cases, total disappearance of large tumors. The response occurred
and ran its course in periods of one to three weeks.
The Mayo group has also begun an open clinical trial using off-the-shelf
measles vaccine to treat non-Hodgkins lymphoma. Adele Fielding, M.D, an
expert in that form of cancer, is the study’s principal investigator.
Robert Cattaneo, M.D., whom Mayo recruited from the University of Zurich in
1999, has provided vital expertise in re-engineering the measles virus. One
key change was introducing a marker gene into the virus. The protein marker
made from that gene is secreted into the blood, allowing the researchers to
determine whether the virus is growing or disappearing by sampling the
level of the marker in the blood. It eliminates the need to monitor the
virus by periodically collecting tissue samples.
Russell and his colleagues are also in the process of writing a protocol
for treatment of ovarian cancer with the measles vaccine and hope to begin
that dose escalation study by late this year. They are also developing a
process to manufacture the re-engineered measles vaccine at Mayo and
completing the toxicology studies required for approval by the FDA and the
National Institutes of Health’s Recombinant DNA Advisory Committee. “We’re
hopeful; clearly, this is an agent that has potency against a majority of
the cancer types we have looked at,” Russell says. A number of other groups
are also working to develop viruses that will destroy tumors, but Russell
and his colleagues are the only group developing a measles vaccine for that
purpose.
Developing an AIDS Vaccine
Approximately 20 years after the discovery of AIDS, not one HIV vaccine
has been fully tested. But recent progress in animal trials has made
researchers more confident they are nearing a breakthrough. With an
estimated 36 million people living with HIV, dozens of vaccine prototypes
are being developed around the world.
For the past five years, Ashley Haase, M.D., a University of Minnesota
Regents Professor, head of the microbiology department, and director of the
university’s biomedical genomics center, has been focusing on models of
heterosexual transmission of the simian immuno-deficiency virus (SIV) in
rhesus monkeys.
“There appears to be a staged dissemination; the virus appears to
replicate at the portal of entry for a week or so before it is disseminated
within the lymphatic system,” Haase explains. “The question is, what can we
do to elicit a strong muscosal response at the portal of entry that might
contain the virus before it is spread?”
Haase and Patrick Schlievert, Ph.D., a professor of microbiology at the
university, are using a mutated form of a protein involved in toxic shock
syndrome to develop a vaccine with the ability to cross mucosal surfaces
and enter the bloodstream in the same way that the toxic shock bacteria do
when they enter the body through the vagina. The researchers have developed
a nontoxic mutant protein that, in rabbits and monkeys, has the same
“mucosal transport” property and amplifies the immune response
approximately 10-fold. Haase explains that the researchers use that protein
to enable other things to cross mucosal surfaces. Haase reports
“encouraging results” in eliciting an immune response. A new round of
experiments began in January, in collaboration with the National Institutes
of Health–supported regional primate center at the University of Wisconsin
in Madison, where the actual experiments are conducted.
In 1969, the surgeon general of the United States announced that the war
against infectious disease had been won. Subsequent events have long since
proven the fallacy of that pronouncement. The natural ability of viruses
and bacteria to mutate, making them impervious to existing vaccines, poses
new risks to mankind. But Mayo’s Poland expresses an optimism widely held
among scientists: “In the next five to 10 years, we will see an explosion
in the number of vaccines available to protect against diseases and an
increase in the speed with which we can go to from discovery to
licensure.”
Dan Emerson is a freelance writer living in Minneapolis.
Improving the Anthrax Vaccine
One year before the September 11 terrorist
attacks, Mayo Clinic researchers began a federally funded effort to improve
the efficacy and cost-effectiveness of the anthrax vaccine. Now they are
launching a large (nearly 500 patients at Mayo, 1,600 nationwide) clinical
trial to study whether the effectiveness of the vaccine can be maintained
if the anthrax vaccine is administered intramuscularly rather than
subcutaneously and if the number of doses is decreased, according to
Gregory Poland, M.D., director of Mayo’s Vaccine Research Group. Although
Poland would not say that the effort has accelerated in the wake of
September 11, the attacks have had some effect. “Certainly we all feel
pressure to get the trial started,” says Poland, who has been a U.S. Department
of Defense consultant since the late 1980s and a member of the Armed Forces
Epidemiological Board. He chaired its Infectious Disease Committee in the
period immediately after the Gulf War.
The anthrax vaccine was first licensed for use in 1970. Studies have found
the vaccine to be both safe and effective, and more than 2 million doses of
anthrax vaccine have been administered to more than 500,000 members of the
U.S. armed services since March 1998. Although there have been
production-related delays in vaccinating U.S. forces, the Department of
Defense’s goal is to have all service personnel vaccinated by 2005.
However, administration of the vaccine has been controversial. About 400
military personnel, concerned about the vaccine’s safety, have chosen to
resign rather than be vaccinated.
One drawback to the vaccine is that it must be administered in six doses
over 18 months. “Not a very feasible schedule to deploy,” Poland notes. The
vaccine also causes side effects—localized reactions that range from tenderness
to flu-like symptoms in between 5 and 35 percent of those vaccinated. The
researchers want to test the hypothesis that administering the vaccine
intramuscularly will reduce or eliminate side effects. In the randomized,
double-blind study, some participants will receive the vaccine
subcutaneously, others intramuscularly. Some will receive six doses of the
vaccine, and some will receive a combination of vaccine and placebo doses.
Researchers will measure antibody responses and side effects.—D.E.
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