3105 – ENHANCED OUTPUT OF PRIMITIVE HEMATOPOIETIC CELL PHENOTYPES IN TERATOMAS GENERATED FROM HUMAN INDUCED PLURIPOTENT STEM CELLS (HIPSCS) IN MORE PERMISSIVE IMMUNODEFICIENT MICE

Abstract

Investigation of human hematopoietic stem cells (HSCs) has been revolutionized by advances in cell separation and clonal tracking of cells produced in transplanted patients and immunodeficient mice. However, methods able to expand them significantly remain elusive. iPSCs are of continuing interest as an alternative source, although robust conditions that support iPSC generation of human HSC either in vitro or in vivo have also not yet been identified. To determine whether the use of a more compatible in vivo host environment might offer an improvement, we compared the outputs of teratomas generated from human iPSC transplanted (± irradiated mouse fibroblasts engineered to produce human FLT3-L, SCF and IL3) into immunodeficient NOD-Rag1-null- IL2Rgc-null mice with a c-kit deficiency with or without a transgenic source of human IL3, GM-CSF and SCF (NRG-W41± 3GS mice). 6-8 week teratomas generated in the NRG-W41-3GS mice contained 40-fold more human CD34+CD45+ cells than those produced in NRG-W41 mice with yields up to 7 × 106 CD45+ cells. Co-injection of human growth factor-producing mouse fibroblasts further increased the production of human CD34+CD45+ ∼6-fold in the NRG-W41-3GS mice that extended to the phenotypically early GPI80+ and CD49f+ cells within the CD45+CD34+CD38-CD45RA-CD90+ subset. However, despite their display of short-term granulopoietic and erythroid differentiation potential in vitro, no evidence of in vivo engrafting potential was detected. These experiments suggest a persisting failure of conditions in the teratomas to support the acquisition of certain functional properties that primitive human cells require to engraft and set the stage for their future identification.