WT1 and leukemia: To gain deeper insight into this issue, firstly, we investigated the effect of MSCs on the proliferative, secretory, and cytotoxic potential of clonal CD8+ cytotoxic T-lymphocytes (CTLs) specific for the leukemia-associated antigens WT1 and tyrosine-protein kinase transmembrane receptor 1 (ROR1) [10, 11], as well a switchable CAR T-cell system redirected against the AML marker CD123 currently tested in a phase I clinical trial [12–15].