EurekAlert! passes on news of more progress towards the safe reconstruction of an age-damaged or otherwise dangerously malfunctioning immune system: "researchers found a way to transplant new blood-forming stem cells into the bone marrow of mice, effectively replacing their immune systems. Many aspects of the technique would need to be adapted before it can be tested in humans ... When those barriers are surmounted, the benefits are potentially big. ... [researchers] mice with molecules that latch on to specific proteins on the surface of the blood-forming stem cells, effectively destroying the cells. That technique eliminated the blood-forming stem cells without otherwise harming the mice. ... It is essentially a surgical strike against the blood-forming stem cells ... When they transplanted new blood-forming stem cells into the mice, those cells took up residence in the bone marrow and established a new blood and immune system." This is one of a number of lines of research aimed at the goal of rebuilding the immune system. You might recall trials of another method aimed at curing type 1 diabetes, for example.