Acute myeloid leukemia (AML) development often involves a preleukemic stage, making the prevention of cancer by targeting pre-oncogenic cells a key goal in cancer research. However, these cells are notoriously difficult to define and capture, leading to limited success in preemptive antileukemic therapies to date. Our research focuses on myeloid leukemia in children with Down syndrome (ML-DS), which evolves through a stepwise clonal process starting from fetal hematopoiesis and progressing through a preleukemic stage known as transient leukemia (TAM). In 20-30% of cases, TAM pro­gresses to ML-DS following the acquisition of secondary mutations, with GATAl mutant cells persisting despite cytarabine treatment. These minimal residual disease (MRD) cells are critical to the development of ML-DS, making them a prime target for research and therapeutic intervention. This PhD project will explore the potential of immunotherapy, an efficient therapeutic option for cancer cell targeting and surveillance, which remains unexplored for TAM and ML-DS. By employing flow cytometry-based cell enrichment followed by single-cell transcriptomics and proteomics, the project aims to characterize persistent clones and develop suitable immuno­therapeutic strategies, such as CAR T-cells. These cellular immunotherapeutic approaches will be evaluated using preclinical patient-derived xenograft models. The anticipated outcomes of this research will not only enhance our understanding of the stepwise evolution of ML-DS, but will also pioneer the elimination of persisting AML clones through immunotherapy, marking a significant advancement in cancer treatment.