Cancer vaccines produce encouraging
results
SAN FRANCISCO -- May
14, 2001 (Cancer Digest) -- The long-sought goal of vaccinating
patients against their own cancers received a boost from a pair
of studies presented at this week's American Society of Clinical
Oncology meeting.
While taking different
routes to the treatment approach, both depend on removing cells
from the patient's body and treating them in the laboratory before
re-infusing them back into the patient where it is hoped the
modified cells will stimulate the immune system to attack the
cancer.
Early results of a
trial conducted by a Stanford University Medical Center team
led by Dr. Lawrence Fong indicate that a vaccine made from genetically-altered
immune cells resulted in a dramatic regression of cancer in some
patients with end-stage colorectal disease.
"The study demonstrates
that a protein expressed in common malignancies can be vaccinated
against and may ultimately be applicable to many patients,"
Fong said in a release.
The vaccine was produced
in a two-step process designed to boost the ability of a patient's
immune system to attack cancer cells. Researchers first used
a drug to expand by 20 times the number of dendritic cells within
a patient, and then extracted the cells from the patient's blood.
The dendritic cells
-- rare, specialized cells that tell the immune system what to
look for -- were then altered to display a protein known as carcinoembryonic
antigen (CEA) that is overexpressed by most gastrointestinal
cancer cells. The genetically engineered CEA protein was also
designed to be slightly different from the natural protein so
that it could be more easily "seen" by the body's immune
system cells.
When the altered dendritic
cells were injected back into patients, they stimulated a potent
immune response that targeted CEA proteins on cancer cells.
In the trial, 12 patients
with either advanced colorectal or lung cancer were tested. In
two patients, all tumors regressed. One patient has remained
cancer-free for almost a year, while cancer recurred after ten
months in the second patient in a different location. Cancer
stabilized for six months in two other colorectal cancer patients,
but then recurred. None of the patients experienced side effects.
"We do not know
if the patient who remains cancer free will stay in remission,
but having results like this with immune therapy in colorectal
cancer has not been seen before. It's very promising," says
Fong.
He added that CEA is
also over expressed in lung and breast cancer. He expects to
test the vaccine next in patients with colorectal cancer who
are less ill and have stronger immune systems.
In a larger vaccine
trial, researchers collaborating from eight research centers
took a different approach to stimulating an immune system attack
on cancer cells.
Aimed at treating non-small-cell
lung cancer (NSCLC) the early results of the trial show the therapy
has the power to halt, and even reverse cancer growth in patients
who failed to respond to all other treatments.
In this trial, study
leader Dr. John Nemunaitis, of U.S. Oncology in Dallas says preparation
of the vaccine is done overnight at the patient's hospital. The
patient's own tumors are harvested and genetically engineered
to secrete granulocyte-macrophage colony stimulating factor (GM-CSF),
a cytokine that may play a key role in stimulating an immune
response against the patient's tumor.
In 80 patients, 20
had early stage NSCLC and 60 had advanced NSCLC. Eleven patients
have completed the vaccine treatment, called GVAX, which takes
approximately six months to complete. All patients in the study
will receive a total of six vaccinations.
Of three patients with
advanced NSCLC who completed the vaccine therapy, the cancer
completely disappeared and has not recurred for nine months in
one patient; the cancer was halted in another; and the third
showed a mixed result, with some tumors shrinking as others continued
to grow.
The cancer has not
recurred in three other patients with early-stage NSCLC who had
their tumors surgically removed. All have remained cancer-free
for at least three months. Disease in the other five patients
has advanced.
"GVAX has produced
one of the most dramatic responses I have seen with an experimental
agent," Nemunaitis said in a prepared statement. "The
results so far are definitely encouraging and the agent is demonstrating
activity, but we don't yet know whether it is an anomaly that
one patient had a complete response or whether it indicates a
potential range of benefit from modest to a high response."
|