PR1 peptide vaccine may benefit many patients with myeloid leukemia, chronic myeloid leukemia and myelodysplastic syndrome, findings from an early clinical trial suggest.
As Dr. Muzaffar Qazilbash told Reuters Health by email, “This vaccine was able to induce a leukemia-specific immune response in more than half of the treated patients. These leukemia-specific T cells were probably responsible for the durable clinical responses seen in the study.”
For the study, online September 22 in Leukemia, Dr. Qazilbash of MD Anderson Cancer Center in Houston, Texas, and colleagues studied 66 HLA-A2+ patients. As well as establishing whether the vaccine was tolerated, the team sought to determine whether vaccination with the HLA-A2-restricted peptide would lead to its recognition on myeloid leukemia cells by cytotoxic T lymphocytes (CTLs) that preferentially kill leukemia and contribute to cytogenetic remission.
The patients received three to six PR1 vaccinations subcutaneously every three weeks at dose levels of 0.25, 0.5 or 1.0 mg.
Of the 53 evaluable patients with active disease, 12 (24%) had objective clinical responses. This was complete in eight, partial in one and three showed immunological improvement. Response was seen in all three disease types, but was most prominent in those with a low disease burden.
Nine of 25 patients with immune response, defined as a doubling of PR1-CTL in peripheral blood, had a clinical responders, significantly more than was the case in non-responders (3 of 28).
No grade 3 or 4 toxicity was observed and there was no association between grade 1 or grade 2 toxicity and vaccine dose level.
After a median follow-up of 10 years, 26 patients (39%) are still alive. Of the 14 patients who are in remission, 10 (71%) had an immune response to the vaccine.
“PR1 vaccine,” he added, “may also be used in patients who have achieved a complete remission after standard therapy, but are at a high risk of relapse.”
Dr. Peter Maslak, chief of the Immunology Laboratory Service at Memorial Sloan Kettering Cancer Center in New York, told Reuters Health by email, “This is a novel vaccine approach for patients with myeloid malignancies which demonstrates the ability to induce specific T cell immunity which, in some cases, translates to meaningful clinical responses.”
“Such studies provide ‘proof of hypothesis’ as we investigate incorporating non-transplant, immune-based strategies into current treatment regimens,” said Dr. Maslak, who was not involved in the work.
SOURCE: http://bit.ly/2ezHGZT