Human cytomegalovirus and glioblastoma

The timing of news about these related topics is interesting.

Common Virus May Serve As Target For Vaccine In Fight Against Deadly Brain Tumors (5/16/08)

A type of herpes virus called human cytomegalovirus (CMV) is found in up to 80 percent of Americans, though the virus normally produces very few clinical symptoms, is dormant, and usually undetectable in most people. However, more than 80 percent of patients newly diagnosed with the brain cancer glioblastoma multiforme (GBM) exhibit detectable CMV in their blood as well as in their tumors. The Duke team thought this might provide an opportunity to target brain tumors by going after the virus.

"Previous work has demonstrated the activation of this virus in patients with GBMs, so we took it one step further and tested a vaccine, in a small group of patients, that seems to show some efficacy in stalling the recurrence of these deadly tumors," said Duane Mitchell, M.D., Ph.D., a Duke researcher and lead investigator on the study. "We knew there was a connection between this virus and the brain cancer, and we were hoping to take advantage of that connection to treat one by treating the other."

The fact that glioblastoma multiforme and human cytomegalovirus occur together doesn't automatically mean that the latter "causes" the former, in the way that human papilloma virus (HPV) is known to cause cervical caner. Indeed, the fact that CMV is endemic, while GBM isn't, means that the story has to be more complicated. (The Wikipedia article even cites research (from 2003) that did not find a link between GBM and viral infection.)

However, the fact that a vaccine based on CMV seems to have some effect on GBM, means the relationship has to be more than fortuitous:

There were 21 patients enrolled in the trial, and the vaccine appears to have delayed the re-growth of tumors from a typical six to seven months after surgery to more than 12 months. Early results also show a lengthened overall survival among GBM patients, from about 14 months with standard treatment to greater than 20 months.

This still doesn't prove that CMV "causes" GBM. For instance, the tumor environment of GBM may simply be more supportive of the virus. But just having CMV more prevalent in GBM tumors makes it possible for a vaccine to work, because the vaccine causes the immune system to target cells that contain CMV.

Here's some other recent research that addresses the relationship. In fact, it shows just how CMV is tumorigenic.

Virus Mimics Human Protein To Hijack Cell Division Machinery (5/8/08)

Viruses are masters of deception, duping their host's cells into helping them grow and spread. A new study has found that human cytomegalovirus (HCMV) can mimic a common regulatory protein to hijack normal cell growth machinery, disrupting a cell's primary anti-cancer mechanism.

Writing in the May 9 issue of Science, researchers from the University of Wisconsin-Madison and Harvard Medical School report that a viral protein, called UL97, masquerades as a normal regulatory enzyme to modify a tumor-suppressing protein in human cells. Unlike the normal enzyme, which can be switched on and off by the cell as needed, the viral stand-in lacks an off switch and evades cellular control. The findings represent a previously unknown way that viruses can cause uncontrolled cell growth and division.

But this still doesn't address the question of why, if CMV is in 50% to 80% of the population, GBM is so rare. Or, indeed, why GBM is the only sort of cancer with which CMV seems to be associated. Whatever the relaltionship really is, it's apparently somewhat tenuous.

Update 6/4/08:

Here's another news report on the vaccine that just appeared. There will probably be more, since the results sound pretty encouraging.

Vaccine doubles brain cancer survival time

A vaccine that more than doubles the survival time of patients with the most common and aggressive form of brain cancer has been developed by scientists.

Early results from clinical trials suggest patients who received the vaccine lived for nearly three years after being diagnosed with glioblastoma multiforme.

Update, 7/16/08: More recent news story: Does Herpes Cause Brain Cancer? (7/3/08)


Further reading:

Phosphorylation of Retinoblastoma Protein by Viral Protein with Cyclin-Dependent Kinase Function – Research article in 5/9/08 Science about tumorigenicity of CMV

Tags: cancer, cytomegalovirus, glioblastoma