- There is a saying in the world of cancer researchers:
Don't mention"cancer" and "cure" in the same sentence.
Perhaps that truism should benoted here.
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- Nevertheless, cancer researchers in Boston have begun
the first trials ofa general purpose cancer vaccine, a treatment designed
to stimulate the bodyto subdue most types of cancer with its own immunity
defenses. The vaccinerelies on the fact that roughly 85 percent of all
human cancer cells expressan enzyme called telomerase that normal cells
do not. While researchers have conducted more than one hundred trials ofcancer-specific
vaccines -- with some notable though preliminary successes-- a general
cancer vaccine has never been attempted in humans.
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- The researchers, working at the Dana Farber Cancer Institute
in Boston,will attach part of an enzyme found in most cancers to cells
from apatient's own immune system. The resulting complex will be injected
into thepatient, where the group hopes it will prod immunity components
called Tlymphocytes to seek out and destroy cancer cells.
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- Lead researcher Dr. Bob Vonderheide is careful not to
overstate hisexpectations, however. "At this point it's an interesting
idea that we want to test. There's noguarantee," Vonderheide, also
on the faculty of Harvard Medical School, toldUnited Pres International.
"The number one question for this upcoming trialis: Will we be able
to get over the threshold necessary to achieve aclinical response in a
safe way?"
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- Dr. Jeffrey Schlom, a cancer vaccine researcher at the
National CancerInstitute, Bethesda, Md., explained the fundamental difference
in a vaccineapproach to cancer treatment. In chemotherapy, he said, "it's
like putting a nerve gas over abattlefield. It's just going to go everywhere
and all those people who arenot wearing gas masks are going to die. And
if you are wearing a gas maskyou're resistant and you'll go on to fight.
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- "When you're dealing with immunology you're giving
these dendritic cells,"which activate the T cells against the tumor,
he continued. "You're dealingmore like hand-to-hand combat in a battle.
So if you have evenly matched oroverwhelming force you can overcome the
tumor. If you have a thousand(times) more tumor cells than your T cells
you're not going to do very well.So it may be a numbers game."
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- Vonderheide's phase I trial will treat up to 18 patients
whose cancershave metastasized, or spread -- those with stage IV breast
or prostatecancer, leukemia or lymphoma -- and who have exhausted other
therapyoptions. Like all phase I clinical trials, the team will emphasize
testingthe vaccine's safety and leave true efficacy studies to phase II
and IIItrials later.
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- The investigators will take blood from a patient, then
isolate, mix andultimately attach the dendritic cells to a part of the
telomerase enzymecalled the telomerase catalytic subunit, or hTERT.
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- The researchers are crafting a custom vaccine for each
patient. The process is costly and takes about a week. The dendritic cell-hTERT
complexwill then be injected under the skin of the volunteer patients every
otherweek for a month and a half. The researchers hope that the speciallystimulated
T lymphocytes will seek out and destroy telomerase-rich cancercells.
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- Telomerase protects the ends of chromosomes from the
inevitable frayingthat occurs when a growing cell splits into two daughters.
Its lack innormal adult cells contain imposes a natural lifespan. But if
by mistake acell manufactures much of the enzyme, that cell can become
what researcherscall immortal -- cancerous -- and divide indefinitely.
While Vonderheide's approach is logical, other researchers in the fieldare
even more cautious in their hope for a cure.
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- Dr. Elie Gilboa of Duke University's Center for Genetic
and CellularTherapies told UPI, "By itself, telomerase (subunit attached
to dendriticcells) would not be fully or sufficiently effective."
Gilboa, who did the first animal research with the technique, found a"significant"
response by tumors to a telomerase-dendritic cell experimentin mice. However,
he does not believe the response was enough to eventuallyjustify an approved
vaccine unless further strides are made in thetechnique.
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- For example, the numbers game described by Schlom could
tip in favor ofthe vaccine if, as Gilboa noted, researchers can grow both
dendritic cellsand T lymphocytes outside the body, and in greater numbers.
Vonderheide expects to grow large numbers of cells in a subsequentexperiment.
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- Durham, N.C.-based Gilboa did say there's no question
that if thetechnique works, large factories would be built to make the
custom vaccines.The road from clinical trial to market -- if indeed the
vaccine makes itthat far -- is probably at least seven years away. NCI's
Schlom himself is concerned about possibly triggering a reaction tothe
body's own telomerase-containing stem cells, he said.
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- However, the approach "is just so new and so different
that one just hasto do it and see," he told UPI. "I don't know
of any so-called universalcancer antigen, other than perhaps telomerase."
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- The Damon Runyon-Walter Winchell Foundation and the CaP
Cure Foundationare funding the three-year, $2,000,000 experiment.
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- c. 2001 by United Press International. All rights reserved
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