BioSante Pharmaceuticals, Inc. announced positive results of a human clinical study that show that its GVAX Leukemia vaccine may be able to reduce or eliminate the last remaining cancer cells in some chronic myeloid leukemia (CML) patients taking the drug Gleevec (imatinib mesylate). BioSante owns the commercial rights to all GVAX vaccines as a result of acquisition in 2009 of Cell Genesys.
In 2010, approximately 5,050 new cases will be diagnosed with CML and approximately 470 people will die. The average person’s lifetime risk of getting CML is about 1 in 645. The average age at diagnosis of CML is around 66 years. Over half of cases are diagnosed in people 65 and older. This type of leukemia mainly affects adults, and is rarely seen in children.
Investigators used a vaccine made from CML cells irradiated to halt their cancerous potential and genetically altered to produce an immune system stimulator called GM-CSF. The treated cells also carry molecules, called antigens, specific to CML cells, which prime the immune system to recognize and kill circulating CML cells. All patients enrolled in the trial used Gleevec for at least one year and still had cancer cells present.
The GVAX Leukemia vaccine was given to 19 CML patients with measurable cancer cells, despite taking Gleevec for at least one year (range 13-53 months). Each patient was given a series of four vaccines administered in three-week intervals while remaining on a stable dose of Gleevec. After a median of 72 months of follow-up, the number of remaining cancer cells declined in 13 patients, eight of whom had increasing disease burden before vaccination. Twelve patients reached their lowest levels of residual cancer cells to date following vaccination. In seven patients, CML became completely undetectable.
Patients receiving the GVAX Leukemia vaccine experienced relatively few side effects that included injection site pain and swelling, occasional muscle aches and mild fevers.
Most patients with CML will need to remain on Gleevec therapy for the rest of their lives. More than 90 percent of them will achieve remission, but about 10 to 15 percent of patients cannot tolerate the drug long term. Gleevec, one of the first targeted cancer therapies with wide success in CML patients, destroys most leukemic cells in the body, but in most patients, some cancerous cells remain and are measurable with sensitive molecular tests. These remaining cells are a source of relapse, according to the investigators, especially if Gleevec therapy is stopped.
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