CD38 and leukemia: CD34 and CD38 staining were used to then subdivide the leukemia cells in leukemic stem cells (Q1‐Leukemia Stem Cells, CD34+, CD38 low) and leukemia progenitors (Q2‐Leukemia Progenitors, CD34+, CD38 high) (Figure S10f, Supporting Information).[67] An increasing FBS concentration is known to usually decrease the interaction between nanoparticles and cells.[68] Hence, as expected, the total uptake was lower at 25% FBS (Figure S10g, Supporting Information) than what was observed in 10% FBS (Figure S10a–d, Supporting Information, Patient 1).