Researchers in the US have used a modified measles virus to 'wipe out' myeloma

Media outlets, both traditional and social, are awash with the news that researchers in the US have apparently cured cancer with the measles virus – for example, the Washington Post, Daily Mail, Daily Mirror, Daily Telegraph and (with a much more measured headline) Reuters.

But while the story is dramatic – a 49-year old US woman’s myeloma blood cancer seems to have completely disappeared following treatment – the actual science is a lot more complex than simply injecting her with an armful of measles. A number of the stories implied that the woman had been treated with an extremely high dose of the regular measles vaccine, but we need to be absolutely clear here:

This treatment did not involve a standard measles vaccine or virus – the researchers used a genetically modified virus, and there’s no evidence that the regular measles or MMR jab can cure, prevent or cause any type of cancer.

In fact, we’ve been here before – the approach is similar (although different in certain key respects) to the modified HIV-type virus used to successfully treat a young girl with leukaemia. Overblown headlines about her treatment also flew round the social media world before the scientific truth had got its boots on.

It’s also similar in that this is just one single success story from a very early stage trial, and a lot more work needs to be done to prove that it could be a safe and effective treatment for cancer.

What is this virus treatment?

The researchers at the Mayo Clinic in the US, led by Dr Stephen Russell, are using an approach called ‘oncolytic virus therapy’, which is generating a lot of excitement in the cancer research community around the world. In fact, we’ve written about some of our work in this area a couple of times already.

Briefly, it involves treating patients with viruses that have been genetically engineered to specifically infect cancer cells, rather than causing the particular illness that they usually bring. When injected into the body, the viruses seek out and destroy the tumour cells, multiplying inside them to create even more cancer-killing viruses. At least, that’s the theory.

To date, researchers have created oncolytic viruses from a number of different types of modified virus, including the herpes virus (which causes cold sores), pox viruses and adenovirus (common cold). But while tests in cancer cells grown in the lab and animals have been remarkably successful, this promise unfortunately hasn’t yet translated into success in clinical trials with actual cancer patients.

What did they do?

In this study, published in the Mayo Clinic Proceedings (the clinic’s own peer-reviewed journal), Dr Russell and his team were building on previous research they’d done using a genetically modified version of a ‘crippled’ (attenuated) measles virus, used in some vaccines, which could kill cancer cells.

The virus also contained an extra gene swiped from the human thyroid gland, containing the instructions to make a protein that shuttles iodine from the bloodstream into cells. This addition meant that the researchers could track exactly which cells in the body the virus had infected, by injecting small amounts of radioactive iodine into the blood and then monitoring using a type of scan called SPECT-CT.

In this paper, the scientists describe the cases of two women, 49-year old Stacy Erholtz and another unnamed patient, who were part of a larger clinical trial started by the clinic a few years ago. Both had a type of blood cancer called myeloma that starts in the bone marrow – an ideal target for the measles virus, which particularly likes to infect bone marrow cells.

The women had received a range of treatments over nine and seven years, respectively, including a range of different chemotherapy drugs. Stacy had also had two bone marrow transplants. But while the treatments had held their cancers at bay for several years, they were now at the end of the road.

As part of an experimental, early-stage clinical trial, the researchers injected both patients with around 100 billion units of the measles virus – enough to vaccinate 10 million people if it had been a regular vaccine virus – over the course of an hour. Then they waited to see what would happen.

What were the results?

Almost straight away, the patients became feverish and unwell as their immune systems kicked into action against the massive virus load. They soon got better, and over the next few months the researchers watched as the levels of cancer cells in the patients’ bodies started to fall and their tumours shrank. For Stacy this was particularly noticeable as she had a large tumour on her forehead, which melted away as the virus got to work.

Although the initial responses were impressive, the two women had very different outcomes. Stacy’s cancer seemed to completely disappear, although according to Dr Russell in this video, her forehead tumour apparently came back after around 9 months but is now being controlled with radiotherapy.

However, the other woman was less lucky and after just two months her cancer had come back worse than before, although at the time of writing she is still alive. The researchers also managed to use the iodine-shuttling protein to see where the virus infection had taken hold in her body. It revealed that the virus had indeed infected all her tumours, even though it hadn’t managed to eradicate them.

Why did it work?

As we mentioned, many cancer-killing viruses have not been as successful in human trials as they have been in the lab. One reason that the measles virus might have worked in Stacy’s case is that it was injected at such high doses.

The Mayo Clinic team have been testing their modified measles virus over several years, and initially started testing doses around 100,000 times lower than in these two patients. This suggests that there may be some kind of ‘critical level’ of virus in the body that has to be reached before it can take effect – knowledge that may be useful for other virus researchers around the world.

One other thing to note about the two patients in this trial – neither of them had antibodies against the measles virus in their blood that might have ‘mopped it up’ and made it less effective. This may have been because they had not been exposed to the virus or vaccinated against it, or their previous cancer treatment could have wiped them out.

Today, many people are vaccinated against measles as children, which involves injecting a very small amount of non-infectious measles virus, so are likely to have antibodies against it. So one of the next steps for the Mayo Clinic team is to work out how to get round this problem – perhaps by only giving the treatment to people who don’t have measles antibodies, by masking the virus in some way (like our own researchers’ approach with adenovirus), or by modifying the virus so it looks suitably different from the real thing that it can’t be recognised by measles antibodies.

However, it’s certainly not a good reason to suggest skipping the measles or MMR vaccine in childhood – measles is an unpleasant disease at best and fatal at worst, and is still one of the leading global causes of death among young children.

Where next?

Stacy’s story is certainly an impressive result from an exciting field of research, and we look forward to seeing more results from the Mayo Clinic team’s trial as they come through.

But these are just two patients, only one of whom had a strong response to the therapy, and one success story does not make a miracle cure. We need to see results from many more patients to know whether the virus is safe and effective at treating cancer and that Stacy’s incredible outcome wasn’t just a fluke.

It’s also important to note that the measles virus approach won’t work for all cancers. Myeloma was chosen for this trial as the measles virus specifically targets the bone marrow. It would need significant genetic modifications before it could be persuaded to attack other types of cancer cells, and other oncolytic viruses are being designed to target different types of cancer.

In this short video about the research, Dr Russell is hopeful about the prospects for his modified measles virus, saying “We believe it can become a single shot cure.”

But despite the bold words and headlines, which might make you think that a measles-based cancer cure is just around the corner, the best approach to this new study is cautious optimism. It’s incredible science – and a fantastic outcome for one woman and her family – but (as ever) more work still needs to be done.

Kat