Bioengineered human microtissue model of healthy and leukemic bone marrow

Acute leukemias represent the most frequent type of cancer (∼30%) in children and young adults. The lack of robust systems for in vitro culture of primary leukemia samples is a significant barrier for the development of effective genetic and chemical screens for novel therapeutic targets in pediatric leukemia. In vitro systems, including engineered tissues and organ-on-a-chip systems, are of increasing interest in the stem cell and cancer fields. In vitro models of the bone marrow (BM) have yet to gain momentum, largely due to their reduced throughput, technical complexity, and heterogeneity of starting stromal cell populations. In this work, we present a bioengineered, human, induced pluripotent stem cell (iPSC)-derived bone marrow tissue model (eBM), comprised of osteoblasts, mesenchymal stromal cells, and endothelial cells within a decellularized bone scaffold. This model was developed to include both healthy BM-derived hematopoietic stem and progenitor cells (HSPCs) and acute lymphoblastic leukemia (ALL) blasts. We first demonstrate the ability of our eBM tissue model to support ALL blast maintenance in vitro over 4 weeks, with survival of patient-derived xenograft samples significantly higher (5-10 fold expansion) than in monolayer controls. Acute leukemias are known to alter their microenvironmental niche, and in many cases, use the stroma to protect malignant clones during treatment. In this modular eBM model, the combination of all supporting populations (osteoblasts, endothelium, and mesenchymal stromal cells) was crucial in supporting difficult-to-culture ALL donor cells, likely because of the continuous, responsive secretion of hematopoietic regulatory factors (i.e. osteopontin, IL-7, CXCL8). We propose that this novel model system will advance studies of the human BM during malignant transformation and in the development of personalized therapeutics.