Summary. Our data show that alloSCT confers a downregulation of proliferation regulating genes and an increased expression in EMT- and ECM-genes in BM-MSC resulting in reduced ex vivo proliferation capacity. As this correlates with survival of patients and specifically with impaired engraftment of allogeneic hematopoiesis, we hypothesize that regeneration of the BM niche requires MSC proliferation to facilitate full hematopoietic recovery.