'It is amazing,' Prof Essand gleams in wonder. 'It's better than anything else. Tumour cell lines that are resistant to every other drug, it kills them in these animals.'
Yet as things stand, Ad5[CgA-E1A-miR122]PTD – to give it the full gush of its most up-to-date scientific name – is never going to be tested to see if it might also save humans. Since 2010 it has been kept in a bedsit-sized mini freezer in a busy lobby outside Prof Essand's office, gathering frost.
A million pounds (1.6 million US dollars) is needed to advance the research
The Uppsala virus isn't unique. Since the 1880s, doctors have known that viral infections can cause dramatic reductions in tumours. In 1890 an Italian clinician discovered that prostitutes with cervical cancer went into remission when they were vaccinated against rabies, and for several years he wandered the Tuscan countryside injecting women with dog saliva. In another, 20th-century, case, a 14-year-old boy with lymphatic leukaemia caught chickenpox: within a few days his grotesquely enlarged liver and spleen had returned to ordinary size; his explosive white blood cell count had shrunk nearly 50-fold, back to normal.
But it wasn't until the 1990s, and the boom in understanding of genetics, that scientists finally learnt how to harness and enhance this effect. Two decades later, the first results are starting to be discussed in cancer journals.