The vaccine was created by taking a glycoprotein antigen from the rabies virus and inserting it into Vaccinia virus, the same one used for smallpox inoculation.
To see if the treatment could be effective, they grew balls of cancer cells in a laboratory, some with low amounts of P-glycoprotein, and others with high.
Developed using technology from partner Seattle Genetics, the drug is a monoclonal antibody containing a toxic chemotherapy that attacks cancer cells if they express glycoprotein NMB, or GPNMB.
They knew a drug called XR9576 could block P-glycoprotein and sensitise individual cancer cells to chemotherapy, but they did not know if the drug would be successful against whole tumours, which can be very difficult to treat.