The UK immunotherapy company Vaccitech has announced promising initial results from a phase IIa trial of a therapeutic vaccine that could offer a new way to treat advanced prostate cancer.
In the open-label trial, the University of Oxford spin-off enrolled 23 patients with advanced castration-resistant prostate cancer. The patients received the company’s viral vector vaccine in combination with the approved checkpoint inhibitor nivolumab, which is branded as Opdivo.
According to the results, serum levels of prostate-specific antigen — a biomarker that is elevated in prostate cancer — at least halved in 22% of participants at any time point. The levels dropped to zero in one patient at 24 weeks.
The company reported that the combination treatment had comparable safety to nivolumab alone, with no serious adverse events attributable to the vaccine.
The therapeutic vaccine candidate is designed to make the immune system target 5T4, a protein present on the surface of cancer cells.
It is formed from two recombinant viruses — the chimpanzee adenovirus Oxford 1 vector ChAdOx1 and the modified vaccinia Ankara MVA — that both produce the 5T4 protein but are modified and weakened so they cannot replicate inside the body like normal viruses.
Once injected, the viruses help the immune system learn to target the 5T4 protein and kill cancerous cells.
Vaccitech’s CEO, Bill Enright, told me that its cancer vaccine “is at the cutting-edge of immunotherapy.”
“We look forward to generating additional clinical data that further establishes our approach in oncology and infectious disease.”
While early-stage, the company says its trial results compare favorably to the 9% response rate of a previously reported study, which tested the benefits of the checkpoint inhibitor drug Keytruda in 243 patients with advanced prostate cancer.
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