PROJECT SUMMARY

Familial Platelet Disorder (FPD) is an autosomal dominant disorder, caused by germline RUNX1 mutations that are passed down within families. These inherited mutations are present throughout a person’s life in virtually every cell in the body. FPD is associated with life-long bleeding disorders, platelet dysfunction, and a risk of developing blood cancers, most commonly myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). To date, 210 FPD families are known within the U.S., with an expectation of ~5515 FPD families worldwide. The germline mutation in the single allele of RUNX1 reduces function of RUNX1 protein and alters expression of the target genes, including those involved in growth and differentiation of stem (primitive) cells. RUNX1 mutations in FPD individuals are not sufficient to cause aggressive leukemia, but they do establish a preleukemic state that predisposes patients to develop overt leukemia following the acquisition of secondary mutations in several genes, including the wild-type RUNX1 allele, BCOR, TET2, STAG2, and ASXL1. Before progressing to overt leukemia, the FPD patients develop clonal hematopoiesis (CH) more frequently and earlier than the healthy population. CH occurs when a single blood stem cell with the acquired mutations dominates all other stem cells in the blood and bone marrow in the absence of leukemia. However, how the expansion of CH clones and clonal evolution leads to aggressive leukemia in FPD individuals is not yet understood.

We propose that in FPD the surrounding bone marrow microenvironment (niche) exerts inflammatory stress to primitive hematopoietic stem and progenitors (HSPCs) to provide them a growth advantage and promote their clonal hematopoiesis, eventually leading to the disease evolution. Our hypothesis is based on the following evidence. Several studies have shown that inflammation contributes to the development of MDS and AML. Inflammatory and immune dysregulation may also have a role in disease progression in patients with CH. A recent NIH clinical study suggests that many individuals in families with FPD have inflammatory conditions such as skin allergies, arthritis, and eczema, which raise the concern whether inflammation may also contribute to the FPD phenotype and leukemia transformation. Accordingly, we found FPD patients have high levels of secreted inflammatory cytokines and growth factors in the bone marrow microenvironment. Further, we found that in FPD stromal microenvironment itself is defective in function and leads to increased growth and differentiation defects of primitive HSPCs. These results suggest that the bone marrow niche contributes to the clinical characteristics of FPD and has a role in clonal evolution. This highlights the importance of studying ways to disrupt the microenvironment-driven signaling cues to suppress clonal evolution in FPD. Therefore, we will identify the mechanism by which inflammatory stress impacts functions of primitive FPD cells and niche cells simultaneously using new “co-culture” models. We will also determine how blocking inflammatory stress impacts CH in FPD. By unraveling how inflammation drives this clonal selection process, we can identify effective therapies to prevent or delay leukemia initiation, clonal hematopoiesis, and leukemia progression. These inhibitors may also rescue growth and differentiation defects of HSPCs and niche cells to design better surveillance strategies. The aims proposed here are unique as they will identify clinically actionable pathways using orthogonal approaches. To accomplish the proposed goals, we have gathered a multidisciplinary team with expertise in bioengineering, bioinformatics, single cell analysis, and initiating clinical trials. A support from the joint RUNX1 Research Program-EvanMDS foundation is critical to help us move this field forward, catalyze future funding from the NIH, and fulfill the unmet need of improving outcomes for FPD patients.