CD9 and Buschke-Ollendorff syndrome: Regarding B cells and their blood longitudinal monitoring after LT, we report that CD19+CD24hiCD38hi transitional B cells are correlated with CD9 expression and that the frequency of CD9+ B cells >6.6% at 24 months post-LT allows us to distinguish between patients who will develop BOS within 3 years post-LT and those who will keep a stable graft function (27).