indicate normal function. Today, functional assays such as with tetramer staining, intracellular cytokine staining, and degranulation assays, are becoming more readily available and allow us to functionally interrogate lymphocyte subpopulations. These assessments, if validated as predictors of infection and relapse, will not only help elucidate the impact of various graft-intrinsic and extrinsic factors on the kinetics of immune recovery, but may also help us identify those patients at highest risk for these complications. The article by Jacobson et al. [4] challenges us further to identify what factor or factors may be responsible for the apparent delay in adaptive immunity observed in their patients undergoing UCB transplantation. The tools now exist to better assess immune function and perhaps overcome this brick wall, previously limiting our ability to understand the myriad of factors negatively influencing immune reconstitution. What are ‘‘brick walls’’ anyway? As we are told by Randy Pausch in The Last Lecture, ‘‘Brick walls . are there to give us a chance to show how badly we want something . brick walls are there to stop the other people!’’ [Not us!] It’s time to remove this wall and finally figure out how to enhance the pace of immune reconstitution . and win the race.’’