This application addresses broad challenge Area (11) "Regenerative Medicine" and specific Challenge Topic 11-HL-101* "Develop cell-based therapies for cardiovascular, lung and blood diseases". Bone marrow and Hematopoietic Stem Cell (HSC) transplantation are the best proof of concept on the feasibility of regenerative medicine therapies through the adoptive transfer of progenitors to replace damaged or non-functional tissues. Since the development of embryonic stem (ES) cells, investigators have studied their potential to generate hematopoietic components, and several reports have shown the ability of ES cells to differentiate to hematopoietic cells. However, methods to direct their development towards defined lineages with confidence and reproducibility have not been developed. This is crucial to the use of hematopoietic components derived from human ES or other pluripotential cells for therapeutic purposes. We propose to selectively direct the development of human ES cells to hematopoiesis towards myeloid development, focusing on conditions to generate osteoclasts. These experiments will test the hypothesis that myeloid cells of human origin derived from modified human ES and induced pluripotent stem (iPS) cells would localize to the right bone microenvironments, providing experimental systems for targeted delivery of biological mediators using osteoclasts as cellular vectors. This project will provide important basic and practical data on conditions to drive human hematopoietic development along the myeloid lineage from ES cell lines and their outcome for therapeutic approaches. Our interest in studying osteoclasts is based in multiple reasons. First, osteoclasts have important functions that could be modulated by the genetic modification of cells with unlimited regenerative potential, as hES and iPS cells. Second, osteoclasts are derived from a myeloid progenitor which has not been fully described in humans and that we have been studying in murine systems for the past six years. Third, their localization make osteoclasts excellent vehicles for the potential manipulation of microenvironments with important outcomes for the development of innovative therapies for the precondition of bone marrow microenvironments to facilitate and support of donor hematopoietic engraftment. Finally, there is evidence demonstrating that osteoclasts can be generated in vitro from ES cells. Three related aims are considered for this proposal: Aim 1. Generation of hematopoietic myeloid progenitors and mature osteoclasts from human ES cell lines. In this aim we will work on defined hES cell development systems while evaluating and modifying methods to efficiently generate hematopoietic progenitors from hES cell lines. We will test the developing cells by phenotypic characterization followed by in vitro functional characterization From these progenitors we will subsequently test their potential to derive mature and functional osteoclasts in defined in vitro conditions. Aim 2. Generation of human ES cell lines expressing reporter genes under the control of myeloid specific promoters and validation of their expression in vitro. We will test the conditions to insert specific genes in hES cells with restricted expression in the myeloid system, including mature osteoclasts. We will evaluate their expression by studies of hematopoiesis in vitro. This will be important to validate the hypothesis that we could utilize similar strategies expressing functionally relevant genes for adoptive therapies. Aim 3. Development of animal transplantation models to assess engraftment of human hematopoietic progenitors and in vivo generation of osteoclasts. We have shown that conditional ablation of osteoblasts modify hematopoietic niches allowing engraftment of exogenously transferred hematopoietic progenitors without additional pre conditioning. We will develop immunodeficient animals in which we will be able to eliminate osteoblasts and then test the ability of these mice to accept human hematopoietic grafts utilizing some of the reporter systems developed in aim 2 to track osteoclast development in vivo. Combined, these experiments will test the hypothesis that myeloid cells of human origin derived from modified human pluripotent stem cells can localize to the right bone microenvironments, and will provide experimental systems for delivery strategies using osteoclasts as therapeutic vectors. PUBLIC HEALTH RELEVANCE: This project will design novel regenerative therapy approaches using osteoclasts as cellular vectors to deliver signals to the bone marrow microenvironment. Using these methods we propose to modulate properties of the bone marrow compartment to increase its ability to engraft hematopoietic progenitors, and to increase the potential of hematopoietic progenitors to progress towards active hematopoiesis. This research will provide important strategies to improve regenerative potential for hematopoietic recovery and bone tissue repair. In addition, these techniques can be adapted for developing novel venues to control the metastasis and establishment of tumors into bone.