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Vaccine Causes Response in Leukemia Patients

CancerWise - March 2008

An experimental vaccine for patients with leukemia produced an immune response in 60% of patients with myeloid leukemias and myelodysplastic syndrome (MDS) and also extended survival without relapse, according to new clinical trial results.

Significance of results

"We did not expect dramatic responses in this clinical trial and were pleasantly surprised to see the clinical responses and improved event-free survival," says Muzaffar Qazilbash, M.D., an associate professor in M. D. Anderson's Department of Stem Cell Transplantation and Cellular Therapy. Qazilbash presented the results at the 49th annual meeting of the American Society of Hematology in December.

The results of the Phase I/II clinical trial laid the groundwork for more in-depth studies, including a national Phase III clinical trial.

Goal of the study

The Phase I/II trial, which ran from 2000 to 2006, involves a vaccine made from the PR1 peptide, a small part of a protein found on the inside of leukemia cells.

The trial was designed to assess the vaccine's safety and its ability to elicit an immune response.

Primary results

An immune response to the PR1 vaccine was seen in 60% of patients and was associated with an 8.7 month, event-free survival compared with 2.4 months for patients who did not have an immune response to the vaccine.

Clinical responses, ranging from improvements in blood counts to complete cytogenetic (chromosomal) remission, were observed in 36% of the responders, compared with 10% of non-responders.

Out of 66 patients on the trial, 53 had active disease and 13 were in remission when they entered the trial.

Of the 53 who had one of the three types of active leukemia, 25 (47%) had an immune response and 28 did not. Nine out of 25 responders (36%) had some type of clinical response compared with three of the 28 non-responders (10%).

Among the 13 in remission at the start of the trial, four remained in remission for a median time of 30.5 months.

"We had good accrual and a reasonably long follow-up of almost three years," Qazilbash says, "For a Phase I/II, that's a fair number of patients."

Additional results

Toxicity was limited to low-grade side effects at the injection site, such as redness, swelling and some pain.

Background

The PR1 vaccine is derived from two myeloid leukemia-associated antigens, proteins that are either overproduced or present in cancer cells. When PR1 brings about an immune response, PR1-specific T lymphocytes are produced that selectively kill three types of leukemia: MDS, acute myelogenous leukemia (AML) and chronic myelogenous leukemia (CML).

To be eligible for PR1, patients must be positive for a specific molecule called HLA-A2. Qazilbash says about 40% of the general population is HLA-A2 positive.

The PRI vaccine was developed by Jeffrey Molldrem, M.D., a professor in
M. D. Anderson's Department of Stem Cell Transplantation and Cellular Therapy. Molldrem co-founded The Vaccine Company in 2003, which licensed the technology from M. D. Anderson in 2004. M. D. Anderson has an equity interest in the company. The arrangements are managed in accordance with the institution's conflict-of-interest policies.

What’s next?

Phase II clinical trials of the vaccine for CML and MDS are planned or under way at M. D. Anderson. A national Phase III clinical trial is being conducted for AML.

– Adapted by Darcy De Leon from an M. D. Anderson news release

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© 2014 The University of Texas MD Anderson Cancer Center