

Cancer and the HIV virus may resist vaccines by dressing infected cells in the protein trappings of sperm, tricking bodies into thinking they're harmless.

The phenomenon, described today by researchers from the University of Missouri and Imperial College of London in the Journal of Biological Chemistry, could help explain why billions of dollars and decades of research have yet to produce a working vaccine against HIV, the virus that causes AIDS, or most forms of cancer.

When sperm are manufactured, their glycoproteins

\– compounds ubiquitous in cellular function – are tagged with chains of carbohydrates known as Lewis sequences. Human immune systems are generally friendly towards these sequences; they're probably what allow sperm to be accepted by female immune systems.

Unfortunately for us, HIV tells cells to produce Lewis sequence-tagged glycoproteins. The same thing happens in some especially aggressive cancers. Other invaders with Lewis sequences are schistosomes, a type of parasitic worm, and H. pylori, a common stomach bacteria. All are largely ignored by human immune systems.

“It’s our major Achilles heel,” said University of Missouri obstetrics professor and study co-author Gary Clark in a statement. "Reproduction is required for the survival of our species. Therefore we are

‘hard-wired’ to protect our sperm and eggs as well as our unborn babies from any type of immune response. Unfortunately, our results suggest that many pathogens and tumor cells also have integrated themselves into this protective system, thus enabling them to resist the human immune response.”

Clark and his colleagues next plan to how HIV and cancer write the

Lewis sequences. If researchers can understand the interaction's mechanics, they might be able to short-circuit it.

Expression of Bisecting Type and Lewisx/Lewisy Terminated N-Glycans on Human Sperm [Journal of Biological Chemistry]

New study suggests why vaccines directed against cancer, HIV don't work [Press Release]

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