I. Mechanisms of progression and relapse in T-cell acute lymphoblastic leukemia

T-ALL is an aggressive malignancy of thymocytes that affects thousands of children and adults in the United States each year. Patients with relapse disease are largely unresponsive to additional therapy and have a very poor prognosis with 70% of children and 92% of adults ultimately succumbing to disease. Thus, there is a clinical imperative for identifying the molecular mechanisms that cause leukemia cells to re-emerge at relapse. Utilizing a novel zebrafish model of relapse T-ALL, large-scale transgenesis platforms, and unbiased bioinformatics approaches, we have uncovered new oncogenic drivers associated with aggression, therapy resistance and relapse. Large subsets of these genes exert important roles in regulating human T-ALL proliferation, apoptosis and response to therapy. Discovering novel relapse-driving oncogenic pathways will likely identify new drug targets for the treatment of T-ALL.

II. Functional consequences of tumor cell heterogeneity in embryonal rhabdomyosarcoma

ERMS is a common soft-tissue sarcoma of childhood that phenotypically recapitulates fetal muscle development arrested at early stages of differentiation. Our laboratory has developed a transgenic zebrafish model of kRASG12D-induced ERMS that mimics the molecular underpinnings of human ERMS and has utilized fluorescent transgenic zebrafish to label ERMS cell subpopulations based on myogenic factor expression. From this work, we have identified functionally distinct classes of tumor cells contained within the ERMS mass. Importantly, we have identified that myf5-GFP+ cells, akin to normal muscle stem cells, drive continued tumor growth and relapse. Building on the dynamic live cell imaging available in the zebrafish ERMS model, our laboratory has undertaken chemical genetic approaches to identify drugs that kill relapse-associated, self-renewing myf5-GFP+ ERMS cells. Subsets of these drugs are currently being assessed for regulating growth of human ERMS.

III. Optimized cell transplantation using immune compromised fish

Cell transplantation into immune compromised mice has become an important tool to study stem cell biology, regeneration, and cancer processes including cellular heterogeneity, self-renewal, growth, metastatic progression, and therapy responses. Despite the great utility of mouse xenograft models that exhibit variable defects in T, B and Natural Killer (NK) cells, transplantation experiments in mice are expensive, performed on a small scale, and engraftment difficult to directly visualize. Using genome-engineering techniques and optically clear adult zebrafish, we have developed immune compromised zebrafish models by knocking out a series of genes required for immune cell differentiation. Subsets of these models allow engraftment of normal stem cells and cancers in the allogeneic transplant setting. We are currently optimizing transplantation approaches and refining the genetic models to permit xenograft transplantation of human cells. The long-term goal is to establish immune compromised zebrafish as the next generation of high-throughput, low cost models for efficient human xenograft transplantation.