Human Pluripotent Stem Cell-Derived Blood Cells for Therapies

It has now been twenty years since human embryonic stem cells (hESCs) were first isolated and described in 1998. In the next decade, induced pluripotent stem cells (iPSCs) were produced first from mouse somatic cells and then from human cells. Since these landmark advances, hESCs and iPSCs have been utilized to advance our understanding of basic human developmental biology and cellular plasticity. These lessons are crucial to fulfill the goal to use human pluripotent stem cells to derive new cellular therapies to better treat and repair organs and tissues damaged by disease, trauma or aging. Clinical trials are underway to utilize differentiated cells derived from hESCs or iPSCs for treatment of retinal disease, spinal cord injury, diabetes, cardiac failure, and other disorders. Production of therapeutic blood cells such as transplantable hematopoietic stem cells (HSCs) from hESCs and iPSCs remains a key goal. However, despite intensive research efforts by our group and many others, there remain challenging to achieve long-term multi-lineage engraftment in vivo with HSCs derived from unmodified hESCs/iPSCs. More successful approaches have used genetic modification or teratoma formation, though these strategies cannot be directly translated to clinical cell products. Reasons for this continued challenge and novel solutions such as use of a Runx1 genetic reporter system will be discussed. In contrast to production of transplantable HSCs, the ability use hESCs/iPSCs to produce functional lymphocytes with anti-tumor and anti-viral activity has been quite successful. Our group has defined methods to efficiently differentiate and expand clinical-scale quantities of natural killer (NK) cells. These hESC/iPSC-derived NK cells have phenotypic and genetic profiles similar to NK cells isolated from peripheral blood. Additionally, hESC/iPSC-derived NK cells are able to kill diverse tumor cells in vitro and in vivo. The hESCs/iPSCs also serve as a versatile platform to engineer genetic enhancements to produce NK cells with improved anti-tumor activity. For example, we have produced hESC/iPSC-derived NK cells that express novel chimeric antigen receptors (CARs) that are able to better target tumors that are more refractory to NK cell-mediated killing. This optimized NK-CAR construct utilizes the NKG2D transmembrane domain, 2B4 co-stimulatory domain, and the CD3ζ signaling domain to activate key NK cell-specific intracellular signaling pathways and increase NK cell survival and expansion in vivo. In one direct comparison between CAR-expressing-iPSC-derived NK cells and "conventional" CAR-expressing T cells, demonstrates the CAR-NK cells have similar ability to kill ovarian tumors in vivo, but with less toxicity, suggesting a safer approach. We have engineered other modifications into iPSC-NK cells to enhance NK cell targeting, proliferation, expansion and survival -- all key qualities to improve in vivo anti-tumor activity. These studies demonstrate that hESC/iPSC-provide an ideal platform to produce standardized, targeted, "off-the-shelf" cellular immunotherapies to treat refractory hematological malignancies and solid tumors. Finally, iPSC-derived NK cells are now being produced at clinical scale under current good manufacturing practices (cGMP) conditions with clinical trials scheduled to start by the end of 2018.