Stem cell transplants offer a lot of promise for treating or curing patients who’ve exhausted their therapeutic options. However, there are some potential risks associated with putting stem cells into the human body such as cancer and infection. But scientists and clinicians are working hard to reduce the risk of stem cell therapies by testing them in animals and in early stage clinical trials.
There was good news recently when scientists at the City of Hope reported that they’ve developed a vaccine that could make stem cell transplants safer.
The vaccine helps the immune system fight cytomegalovirus (CMV), which affects 50-80% of adults in the US. CMV typically lies dormant in the human body, but it can be activated in immunocompromised people, pregnant women, and patients receiving stem cell transplants. Once activated, CMV can cause nasty infections and even hepatitis (liver inflammation). There are anti-viral drugs that patients suffering from CMV flare-ups can take, but these drugs are very toxic and can sometimes do more harm than good.
CMVPepVax to the rescue!
In a report published in the Lancet Haematology, the group at City of Hope described a CMV vaccine called CMVPepVax that’s both safe and effective in protecting patients receiving stem cell transplants from CMV flare-ups. They tested the vaccine in a phase 1 clinical trial in 36 patients receiving stem cell treatments for cancer or other diseases. Half of the group received two doses of the vaccine at different time points (28 and 56 days), and the other half didn’t get the vaccine.
After three months, the researchers compared the group that received the vaccine to the control group and saw striking differences. Patients who got CMVPepVax had a boosted immune response against CMV, lower occurrence of CMV flare-ups, and reduced need for anti-viral drugs.
First author on the study, Ryotaro Nakamura, commented:
“Overall, people who received the vaccine had more robust immune recovery than those in the observation group. I was surprised because I didn’t expect to see such a dramatic difference between the two groups in such a small sample study.”
But wait, there’s more good news!
Even more exciting was the observation that patients receiving the vaccine were less likely to experience a relapse of their disease (leukemia was given as an example) and had a lower risk of death.
Senior author on the paper Don Diamond explained,
“We didn’t anticipate this to happen. Yet we found this striking signal from the data, which told us that those in the vaccine arm of the trial were less likely to relapse of their disease and less likely to develop problems that would lead to non-relapse mortality. In the future, the CMVPepVax vaccine may prove useful not only for patients receiving stem cell transplants, but also for recipients of solid organ transplants or other immunodeficiency diseases.”
Hold your horses
Of course, with any exciting breakthrough such as this, it’s wise to not count your chickens too early. In a City of Hope press release, both Nakamura and Diamond said that these results need to be replicated in a larger phase 2 trial before they can conclude that the vaccine works.
The trial is currently underway. It’s a larger, double-blind study that will compare patients receiving CMVPepVax to a placebo group. It’s the authors’ hope that the results from this trial will support their earlier phase 1 results and also shed light on why the vaccine protects against leukemia relapse.
“We want to get confirmation to see whether lightning strikes twice with these effects. The current phase 2 trial, funded by the National Cancer Institute, will tell us whether the protective effects are really valid. If they are, it would be quite exciting.”
The results of this phase 2 trial will be especially important given the recent news about the failure of Chimerix Inc.’s antiviral CMV drug. The company’s stock took a huge hit today after they reported that their oral antiviral CMV drug didn’t reduce infection in stem cell transplant patients in a late-stage study.