(Ivanhoe Newswire) – There are reasons vaccines aimed against HIV and many cancers do not work.

Researchers from the University of Missouri and Imperial College London find HIV, aggressive cancer cells, H. pylori – bacteria that cause stomach ulcers, and some parasitic worms carry the same carbohydrate sequences as many proteins produced in human sperm.

“It’s our major Achilles heel,” co-author Gary Clark, University of Missouri School of Medicine, was quoted as saying. “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.”
 

Early in life the body determines which cells and proteins belong in it, so it can detect the ones that do not belong. After that anything foreign is considered dangerous unless the immune system is specifically told to ignore those cells and proteins – this mainly happens during reproduction.

Aggressive tumor cells that defeat the immune system and HIV-infected immune cells that cause AIDS have the same sequence of carbohydrates. Researchers say vaccines probably don’t work against these diseases because the sequences shut down the specific immune response that lets the vaccines work; basically tricking the immune system into thinking they are harmless.

Researchers say the next step is to understand exactly how this interaction works, which could lead to new ways to treat or prevent cancers and other diseases.

“This work is creating an entirely new way of thinking about how we must combat viruses like HIV and aggressive tumor cells,” Clark was quoted as saying. “We must become more clever if we are ever going to solve the problems of cancer and AIDS.”

SOURCE: The Journal of Biological Chemistry, 2007; 282: 36593-36602