Abstract 28 A Novel Chemically Defined Culturing System to Support Hematopoietic Stem Cell Expansion

INTRODUCTION: Hematopoietic stem cells (HSCs) are known to be multipotent and can reconstitute the entire blood and immune system following HSC transplantation (HSCT). However, the current HSCTs have many unresolved issues including difficulties in finding donors for bone marrow transplantation, preparing a sufficient HSC dose in cord blood transplantation, and the risk of graft-versus-host disease (GvHD) for all allogeneic HSCTs. In recent years, there have been substantial efforts to research and understand the biology of HSCs to develop cell therapy products that meet these challenges and provide an alternative to traditional HSCTs. Several culturing methods have been developed to stimulate HSC expansion ex vivo, but the use of biological materials, such as albumin, has not been ideal for pharmaceutical manufacturing, and it has been difficult inhibiting differentiation of HSCs into lineage-committed cells while culturing in a cytokine-filled medium. We have developed a novel albumin-free culturing system that supports proliferation of long-term HSCs ex vivo by replacing cytokines and albumin with chemical agonists and a caprolactam-based polymer. OBJECTIVES: The objective of this study is to characterize our expanded cell population as part of an analysis to determine whether the population reconstitutes bone marrow and is therefore suitable for development of a cell therapy product. METHODS: Here we report the in vitro and in vivo characterization of proliferated HSCs using our novel culturing system compared with a nicotinamide system which is known to support HSC proliferation ex vivo. A colony forming assay, cell surface marker analysis using a flow cytometer, and in vivo repopulating analysis using the NOD/Shi-scid IL-2Rγ(null) (NOG) mouse were conducted. RESULTS: Surface marker analysis of the proliferated population shows more than 70% remaining as undifferentiated CD34(+). Of which, a higher number of CD201+CD90+CD45RA- exists compared with the nicotinamide-cultured population. Colony forming unit assays indicate that our proliferated cell population contains a higher number of multipotent progenitors. The repopulating cell assay also shows that the proliferated cells have bone marrow reconstitution capability in bone marrow-ablated NOG mice. DISCUSSION: We believe that our chemically defined culturing system can selectively proliferate HSCs while restraining their differentiation and will contribute to the development of novel HSC therapy products.