Researchers at the University of Texas M. D. Anderson Cancer Center found that a peptide vaccine can improve immune response in leukemia patients.
Immune response to the PR1 vaccine was associated with an 8.7 month event-free survival compared with 2.4 months for non-responders.
The researchers also found that the blood counts also improved in 36 percent of the responders compared with 10 percent of non-responders.
Muzaffar Qazilbash, the lead researcher, Associate professor in M. D. Anderson's Department of Stem Cell Transplantation and Cellular Therapy said that they were amazed by the 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" said Qazilbash.
The PR1 vaccine is derived from two myeloid leukemia-associated antigens, proteins that are either over expressed or abnormally expressed in cancer cells.
The vaccine selectively kills three types of leukemia - myelodysplastic syndrome, acute myelogenous leukemia and chronic myelogenous leukemia.
The study was conducted over 66 patients where 53 had active disease and 13 were in remission when they entered the trial.
Among the 53 with one of the three types of active leukemia, 25 had an immune response and 28 did not.
Nine out of 25 responders had some type of clinical response compared with three of the 28 non-responders.
Qazilbash said that in phase I trials, patients were heavily pretreated with other therapies.
"We had good accrual and a reasonably long follow-up of almost three years," Qazilbash adds "For a Phase I/II, that's a fair number of patients."
"Immunotherapy works best for low level of diseases so patients with low leukemia burden may get the maximum benefit," he further added.
The study was presented at the 49th Annual Meeting of the American Society of Hematology.