Three dimensional platforms for ex vivo hematopoietic cell bioprocesses

Abstract

Umbilical cord blood (UCB) has been shown as a convenient source of hematopoietic stem cells (HSCs) for autologous or allogeneic HSC transplantation in the treatment of leukemia and many other hematological diseases. However, widespread application of cord blood is hampered by the low stem cell number in a single cord unit. One possible approach to solve this problem is ex vivo expansion. Three dimensional (3D) culture systems and bioreactors are developed to recapitulate the bone marrow microenvironment in vitro to enhance cell-cell and cell-niche interactions and mimic the biologic and mechanical function of bone marrow niche. Two different potential 3D platforms for culturing HSCs and abnormal hematopoietic cells are presented in this thesis; electrospun nanofiber scaffold (NFS) and hollow fiber bioreactor (HFBR). Electrospun NFS created a nano-scale 3D architecture mimicking the native bone marrow structure in vitro. It effectively enhanced the adherence of both abnormal leukemia cells and normal HSCs. Yet NFS only proved to enhance growth of normal hematopoietic cells but inhibit leukemia cell proliferation. Nevertheless, cells cultured on NFS showed enhanced cell-matrix interaction, which demonstrate that NFS provides a better mimicry of bone marrow microstructure. Electrospun NFS is therefore useful as a matrix coating for enhancing HSC expansion and its potential application for leukemic cells can be further explored. The HFBR showed excellent feasibility as a bone marrow mimetic in vitro system for hematopoiesis. Larger number of stromal cells cultured inside the HFBR formed a 3D and bone marrow mimetic architecture for hematopoietic cell culture. Successful and extensive expansion of both HSCs and leukemic cells are achieved in hollow fiber bioreactor while preserving the differentiation ability of HSCs. Interaction between hematopoietic cells and stromal cells is also significantly enhanced in the HFBR. Ex vivo expanded cord blood HSCs in the HFBR successfully engrafted into mice models, demonstrating its potential clinical utility in the future. This thesis successfully demonstrates that NFS and HFBR can recreate a closer mimicry of the bone marrow microenvironment, which provide significant improvements for in vitro studies of leukemic and hematopoietic cell functions. The NFS and HFBR can provide different sets of tools to study insights of hematopoiesis in vitro.