Ex Vivo out-Competition of Leukemia Stem Cells By Healthy Hematopoietic Stem Cells for Autologous Transplantation from Leukemia Patients

Allogeneic hematopoietic stem/progenitor cell transplantation (alloHSCT) from genetically similar donors can be curative for a variety of hematologic malignancies, including high risk leukemia. Unfortunately, Graft versus Host Disease (GvHD), an immune reaction of donor cells against the host, occurs in 30-60% of recipients. GvHD results in mortality as high as 50% or more, largely dependent on the degree of genetic similarity between donor and recipient. While broad immunosuppressants are given to prevent and treat GvHD, this further carries a higher risk of cancer relapse, delayed immune reconstitution, increased infections, and other toxicities. Additionally, large racial disparities exist in finding an appropriate donor for alloHSCT, and most minority patients are not able to find a suitable match. Less suitable matches, if found at all, cause more severe GvHD in these minority populations. GvHD is eliminated if a patient's own bone marrow can be used (autologous HSCT); however, this is not possible for leukemia patients due to the presence of leukemia stem cells (LSCs). Our research reveals a path toward changing this.

We previously investigated self-renewal, the process whereby stem cells regenerate and multiply. Using a mouse model, we studied the effect of Pten deletion combined with β-catenin activation. We showed that double mutant mice exhibit a novel phenotype including expansion of HSCs without extensive differentiation. Overall, PTEN/PI3K/Akt and Wnt/β-catenin pathways were shown to cooperatively interact to drive HSC expansion by inducing proliferation while simultaneously inhibiting apoptosis and blocking differentiation. Utilizing these concepts, we have developed an ex vivo expansion protocol for normal, functional HSCs generating serially transplantable HSCs with engraftment equivalent to a one-hundred-fold greater dosage of uncultured HSCs.

Using 1) a leukemia mouse model demonstrating that healthy HSPCs can be separated from leukemia causing LSCs, 2) an ex vivo HSC expansion system that depletes murine LSCs while increasing HSCs in bone marrow (BM) from this animal model, and 3) an ex vivo system that expands human HSCs, we are conducting preclinical testing of the ability of healthy HSCs to be expanded from leukemia patient BM while depleting LSCs-ultimately with the goal of allowing autoHSCT and eliminating risk of GvHD in these patients. The project is expected to demonstrate, in principle, that at least some patient samples contain normal, healthy HSPCs, which can be at least maintained and likely expanded using our ex vivo system; however, LSCs are expected to be depleted with culture.

No relevant conflicts of interest to declare.