My work focuses on employing the cellular barcoding method to better understand the (sub)clonal evolution of normal human HSC and of leukemia. We have recently shown that xenografted patient-derived leukemia is highly polyclonal, consisting of hundreds of clonogenic cells (Belderbos et al, Blood 2017). Current work focuses on the potential heterogeneity between these cells, in terms of genetic mutations, localization and/or responses to chemotherapy. Answering these questions is of great importance, to increase our understanding of normal and pathological hematopoiesis, to optimize therapeutic strategies that use HSC and to expand the spectrum of diseases for which HSC can be a safe and effective treatment strategy.
Hematopoiesis involves the tightly regulated process of blood cell production, which is maintained by a small number of hematopoietic stem cells (HSC). Currently, the number of HSC that actively participate in hematopoiesis is unknown. Resolving the exact number of clonogenic cells that contribute to each of the given blood cell lineages at any given time is important for a better understanding of normal and malignant hematopoiesis, and for the optimization of therapeutic strategies that use HSC transplantation to treat patients with hematologic, immunologic and genetic diseases.
An important reason for our lack of knowledge on the frequency of HSC and the biology of their clonal offspring, is the lack of unique markers to discriminate “true” HSC from other long-term proliferating cells. To address this issue, we have developed a genetic barcoding approach, allowing the clonal progeny of individual HSC to be tracked over time. In this approach, cells are lentivirally labeled with unique, heritable and identifiable genetic “barcodes”. Upon cell division, each daughter cell inherits the same barcode. The barcode composition of a given population thus reflects the frequency and clonal output of individual clonogenic cells.