Down under, two teams of scientists took what may be a giant step in immune rebooting in June when they discovered the mother of all thymus cells -- the so-called epithelial progenitor. Grafted into mice, the stem cell grew into a fully formed thymus to replace the pea-sized original, which plays an integral role in generating HIV-fighting T cells -- but eventually loses its punch to age or worse.

Researchers believe that the newfound stem cell might be used to grow thymuses in humans, whose immune systems are strikingly similar to those of Mickey and Minnie. "If it worked, it could speed up the reconstitution of the naïve T-cell pool in PWAs," Treatment Action Group's Richard Jefferys said. "Although thymus transplants have been tried before, they tend to be rejected by the immune system as foreign. If you could build a thymus from someone's own cells, it would get around this problem." Tell that to President Bush, who has stemmed the tide of stem-cell science for "pro-life" reasons.