AST-VAC1 (hTERT-DC, formerly GRNVAC1) is an investigational immunotherapy being developed as a cancer vaccine by Asterias Biotherapeutics to treat acute myeloid leukemia (AML).
How AST-VAC1 works
AML is frequently associated with high levels of a protein called telomerase in cancer cells. Telomerase, also called telomerase reverse transcriptase (TERT), is an enzyme that extends the protective cap on the end of chromosomes. If the enzyme is highly expressed, the cells survive and turn into cancer. Several cancer therapies have been designed to block this enzyme.
AST-VAC1, as an anti-cancer vaccine, aims to help the immune system recognize cells expressing telomerase as a target to be destroyed.
The immune system uses a type of cell called a T-cell to identify and kill abnormal or infected cells, such as cancer cells. T-cells recognize their target via antigens that are expressed on their surface. These antigens must be presented to the T-cells by another type of immune cell called a dendritic cell (DC).
AST-VAC1 consists of the patient’s own DCs containing the mRNA for human telomerase, called hTERT-DC, and a protein to enhance the ability to stimulate an immune response, called LAMP.
For the treatment, the patient undergoes a procedure called leukapheresis where a large volume of blood is drawn from the patient, filtered to collect white blood cells (which includes the DCs), and then returned to the patient’s bloodstream over a period of six hours. The collected DCs are treated so they take the mRNA for hTERT and the LAMP protein inside themselves. This product is AST-VAC1.
When a patient is injected with a dose of AST-VAC1, the hTERT-DCs stimulates the body’s own T-cells to target and kill the cancerous cells expressing telomerase.
AST-VAC1 in clinical trials
AST-VAC1 has been investigated in an open-label, multi-center, Phase 2 clinical trial (NCT00510133). The trial’s main objective was to determine whether enough AST-VAC1 could be produced from the patient’s blood. A secondary goal was to assess the safety and tolerability of the vaccination.
Patients received a total of 12 AST-VAC1 doses, once weekly for six weeks. This was followed by a four-week break and then one dose ofAST-VAC1 every other week for 12 weeks. The trial took place at multiple sites across the U.S. and patients were monitored for up to five years following the first vaccination.
A total of 33 patients were enrolled in the trial, however, only 21 patients successfully received AST-VAC1 produced from their own cells. The results for those treated were positive and were published in the scientific journal Cancer.
In 58 percent of patients who were treated, a successful immune response was induced, confirming that AST-VAC1 could be a viable treatment option. This was supported by 57 percent of AST-VAC1-treated patients experiencing a prolonged period of progression-free survival.
A total of 19 patients were in complete remission (with no symptoms of the cancer) at the start of the study, and at follow-up 11 patients (58 percent) were still in complete remission. This included four of seven patients over the age of 60 (57 percent) maintaining remission after 4.5 years on average.
According to Asterias, this is much higher than what is seen in other studies, where the percentage of patients remaining in remission is much lower with 20 to 40 percent, and only 10 to 20 percent in patients over age 60.
Following these positive results, Asterias intends to initiate a Phase 3 clinical trial to support a biologics license application (BLA) to the U.S. Food and Drug Administration (FDA).
Additional information
In general, the treatment was well-tolerated, with only one patient experiencing a severe adverse event that may have been related to AST-VAC1. Other adverse events included low blood platelet and neutrophil (a type of white blood cell) count, injection site reactions, diabetes mellitus, bone pain, redness of the skin, rash, and vitiligo.
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