AML Vaccine Proves Feasible, Potentially Beneficial

A vaccine known as AST-VAC1 was successfully produced from most patients in a phase II trial of patients with acute myeloid leukemia.

A vaccine known as AST-VAC1 was successfully produced from most patients in a phase II trial of patients with acute myeloid leukemia (AML). The vaccine, a telomerase-based dendritic cell immunotherapy approach, produced encouraging clinical responses, according to results presented (abstract 7007) at the 2015 American Society of Clinical Oncology (ASCO) Annual Meeting, held May 29 to June 2, in Chicago.

“AST-VAC1 is an immunotherapeutic product that comprises mature dendritic cells,” said Hanna J. Khoury, MD, of Winship Cancer Center of Emory University in Atlanta. The cells are collected via leukapheresis and transfected with an mRNA encoding telomerase called hTERT, and a lysosomal sorting signal that “enhances immunostimulatory capacity,” Khoury said.

In this trial, 33 patients with AML were included, and the vaccine was successfully produced in 73%. In the full cohort, 51.5% were male, 84.8% were white, and the median age was 61 years. The median time from AML diagnosis to leukapheresis was 7 months.

A total of 21 patients received at least three vaccine doses (three in whom it was produced successfully were in florid relapse and did not receive vaccination). Thirteen patients received all 12 intended doses, and the mean number of doses received was 17.2.

Khoury said the vaccine was very well tolerated, with no grade 3/4 adverse events during leukapheresis period and two during vaccination; one of these, a case of idiopathic thrombocytopenic purpura, was believed to be related to the vaccine. Grade 1/2 adverse events included headache (five patients), fatigue (three patients), and others.

Of 19 patients in complete remission at the time of AST-VAC1 administration, 11 developed immune responses to hTERT. Eleven patients remained disease-free after a median follow-up of 52 months. In patients older than 60, four of seven were relapse-free after 54 months. “These values are encouraging compared to what is expected, historically, in these older patients,” Khoury said.

Michael R. Bishop, MD, of the University of Chicago Medical Center, who was the discussant for the session, said that “there is a great need for novel therapies for the treatment of AML.” He called the results with this vaccine encouraging and called for more trials comparing AST-VAC1 directly to other therapies, and also testing it in combination with other agents such as immune checkpoint inhibitors.

Khoury agreed, saying that these promising results still need confirmation in other validation studies.