Like it or not, your body gradually loses its capacity for producing blood as you age -- that's why immune deficiencies, leukemia and other blood conditions become more likely with time. Scientists may have found a way to turn back the clock, though. They've found a way to rejuvenate blood by reprogramming the stem cells that create it. The team effectively "resets" the stem cells by turning them into iPS cells, which can generate any kind of cell. When they once again form blood stem cells, it's as if they were brand new.