|PhD ceremony:||S. Jacobs|
|When:||September 27, 2021|
|Supervisor:||prof. dr. G. (Gerald) de Haan|
|Co-supervisors:||dr. L. Bystrykh, dr. M.E. Belderbos|
|Where:||Academy building RUG|
Leukemia is clonally heterogenous, consisting of multiple groups of cells with distinct (epi-)genetic alterations, which may alter essential cell functions. Clonal heterogeneity is thought to drive leukemia evolution, therapy resistance and relapse. To improve treatment of leukemia patients and prevent relapse, we need to extend our knowledge of clonal heterogeneity in leukemia. Here, we used cellular barcoding of patient-derived leukemia cells to trace their clonal behavior in murine xenografts. Cellular barcoding relies on the viral integration of synthetic DNA sequences of fixed length into the genome of the leukemia cells. Upon cell division, barcodes are inherited by a cell’s progeny. As a result, the barcode composition in a given cell population reflects the number of clonogenic cells and their relative fitness. First, to optimize reliability of barcode detection, we compared different data-analysis pipelines. We showed that the number of counted barcode clones can differ several-fold depending on the selected data-analysis strategy, and provide a method for optimization. Second, applying this method to murine xenografts transplanted with pediatric leukemia samples, we demonstrate that these mice harbor tens to hundreds of leukemia clones, which are asymmetrically distributed across the murine body. As a consequence, approximately half of the leukemia clones remained undetected when only one anatomical location is analyzed. Moreover, barcodes allowed for the identification of chemotherapy-resistant leukemia clones in mice. Combining cellular barcoding with other clone tracing methods will further improve our understanding of clonal heterogeneity in leukemia and potentially result in the development of new and improved treatment strategies of leukemia patients.