Research by Steven Reiner, MD, Professor, Abramson Family Cancer Research Institute and Department of Medicine, and his colleagues at the University of Pennsylvania School of Medicine has been selected by the prestigious journal Science as one of the top breakthroughs of 2007. The landmark discovery, published last March, demonstrated how cells of the immune system solve the problem of eliminating an infection without being depleted in the process.

At the end of each year Science publishes its Breakthroughs issue, in which it describes the top-ten scientific breakthroughs, from all fields and journals – from astrophysics to zoology – as chosen by its editorial staff. This year, Reiner’s research made the list at number seven.

When cells of the immune system are recruited to fight infection, their success is usually accompanied by their own elimination. In order to defend us against future infections, however, the immune system must also have a way of preserving the most useful cells. Reiner and his lab discovered that when immune cells divide, their daughter cells differ in their inheritance of proteins from the mother cell and this determines their decision to fight to the death in eliminating an infection, or to live to fight another day in case the infection returns.

The researchers found that the immune cells, by designating some daughter cells for immediate deployment to fight disease and other daughter cells to fight future infections, gives the body the ability to respond to the same infection over and over – sometimes even faster and better than it does the first time around.

The researchers studied the immune response to bacteria called Listeria. Using a special dye, the investigators were able to track the T-cells’ first divisions upon infection. The researchers demonstrated that the first two daughter cells inherited different amounts of important proteins and that this unequal inheritance destined the two daughter cells to different fates that would accomplish both short-term and long-term protection against infection.

“These findings may change the way we think about vaccines,” says Reiner. “We've always known the important end result – that more than one type of cell is needed – but not how to generate cell diversity. Ironically, the immune system has simply recycled the strategy of other stem cells in our body – knowing this could improve our strategy for developing vaccines to prevent both infections and cancer.”