Human Stem Cell-Derived Thymic Epithelial Cells Enhance Human T Cell Development in a Xenogeneic Thymus.

ABSTRACT Background Generation of thymic tissue from pluripotent stem cells would provide therapies for acquired and congenital thymic insufficiency states. Objective We aimed to generate human thymic epithelial progenitors from human embryonic stem cells (hES-TEPs) and to assess their thymopoietic function in vivo. Methods We differentiated hES-TEPs by mimicking developmental queues with FGF8, Retinoic Acid, Sonic Hedgehog, Noggin and BMP4. We assessed their function in reaggregate cellular grafts under the kidney capsule and in hybrid thymi by incorporating them into fetal swine thymus (SwTHY) grafts implanted under the kidney capsules of immunodeficient mice that received human hematopoietic stem and progenitor and stem cells (hHPSCs) intravenously. Results Cultured hES-TEPs expressed FOXN1 and formed colonies expressing EpCAM and both cortical and medullary thymic epithelial cell (TEC) markers. In thymectomized immunodeficient mice receiving hHSPCs, hES-TEPs mixed with human thymic mesenchymal cells supported human T cell development. Hypothesizing that support from non-TEC thymic cells might allow long-term function of hES-TEPs, we injected them into SwTHY tissue, which supports human thymopoiesis in NSG mice receiving hHSPCs. hES-TEPs integrated into SwTHY grafts, enhanced human thymopoiesis and increased peripheral CD4+ naive T cell reconstitution. Conclusion We have developed and demonstrated in vivo thymopoietic function of hES-TEPs generated with a novel differentiation protocol. The SwTHY hybrid thymus model demonstrates beneficial effects on human thymocyte development of hES-TEPs maturing in the context of a supportive thymic structure.