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Complete remission in myeloid leukemia patients with Peptide vaccine

The University of Texas M D Anderson Cancer Center offers these news items presented at the annual meeting of the American Society of Hematology (ASH). - Researchers from The University of Texas M. D. Anderson Cancer Center are reporting the first study to show that vaccination with a peptide that is abnormally expressed on myeloid leukemia cells can produce a complete molecular remission in some patients.

The experimental vaccine produced an immune response in 60 percent of patients tested - or 20 of 33 evaluable patients, according to their study, which is being presented at the annual meeting of the American Society of Hematology.

Of those 20 patients who mounted an immune response against their cancer, 14 had an overall survival of four years, and none of the 13 patients who did not have such a response lived that long, they say. Three patients are in "molecular remission" in which there is no evidence of the disease remaining.

"These are very promising results in a group of patients who were quite sick, and who normally would live for just months," says the study's lead investigator, Jeffrey Molldrem, M.D., an associate professor in the Department of Blood & Marrow Transplantation.

"Not only can we say that some of these patients had an immune response, but they also went into remission, and that has never been demonstrated to occur after peptide vaccination before. And for patients who showed an immune response but did not go into remission, progression of their cancer was slowed down compared to patients who did not have an immune response to the vaccine," he says. "Of course, we have much more research to do, especially in testing greater numbers of patients within each disease group."

Nearly all of these patients had either active or relapsed acute myelogenous leukemia (AML) or refractory chronic myelogenous leukemia (CML) - forms of leukemia in which there is a dangerous accumulation of immature cells in the bone marrow - or they had high-risk myelodysplastic syndrome (MDS), a precancerous bone marrow disorder.

The vaccine is made from the PR1 peptide, a small part of a protein found on the inside of leukemia cells. Delivery of the vaccine induces immune cells that recognize the PR1 peptide, which are recruited to the bone marrow that contains leukemia," says Molldrem. "The PR1 peptide is naturally present in normal bone marrow cells and since the target protein is overexpressed on leukemia cells, it directs immune T-cells to kill the leukemia and leave normal cells alone."

Like many vaccines used to induce immunity against infections, this one appears to create an immune system "memory" for the PR1 peptide, conferring long-lasting protection. "Patients only get the vaccine three times, yet we have been able to measure an immune response in patients four years after treatment," says Molldrem.

Contact: Nancy Jensen
[email protected]
713-794 1584
University of Texas M. D. Anderson Cancer Center

Cell Genesys Releases GVAX Cancer Data

05.16.2005 - Biotechnology company Cell Genesys Inc. said Monday that data from a mid-stage clinical trial showed the company's GVAX cancer vaccine lowered residual indications of leukemia by up to 69 percent in eligible patients.

In the trial, newly diagnosed leukemia patients were treated with chemotherapy, and if responsive, they then received bone marrow stem cell transplantation and the GVAX vaccine. In the trial, which enrolled 54 patients, 21 patients became eligible for the first dose of the GVAX vaccine after achieving remission through chemotherapy, and completing stem cell transplantation.

Researchers then looked for levels of WT-1, a leukemia-associated genetic marker which is detectable in more than 95 percent of patients with active acute myelogenous leukemia, and found that 11 of 16 patients had declines of WT-1 in the blood and 12 out of 20 patients had WT-1 declines in the bone marrow.

Cell Genesys also reported that 73 percent of those 11 patients who showed a decrease in WT-1 in the blood after one vaccination lived relapse free for two years. None of the patients whose levels of WT-1 failed to decline post-vaccination survived two years without a relapse.

"We are encouraged by the results of our ongoing Phase 2 study of GVAX vaccine in acute leukemia, particularly the observed correlation between vaccine-associated immune response, WT-1 response and relapse-free survival," stated Joseph J. Vallner, president and chief operating officer of Cell Genesys.

In 19 patients who achieved undetectable levels of WT-1 following a series of vaccinations after transplantation, the two-year survival rate was 89 percent versus the 17 percent survival rate who did not have undetectable levels.

Six patients in the trial have remained in complete remission from 16 months to 29 months post-transplant. All six patients had a vaccine-associated WT-1 decline, or undetectable levels at the time of vaccination, the company said. Cell Genesys said that to date, there have been no serious side effects related to the vaccine therapy.

Acute myelogenous leukemia is a type of cancer that occurs when infection-fighting white blood cells do not mature fast enough, and leave the body susceptible to anemia and infection.

Cell Genesys shares fell 10 cents to close at $5.85 on the Nasdaq.

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