Human Embryonic Stem Cells Differentiate into Functional Natural Killer Cells with the Capacity To Mediate Anti-Tumor Activity.
Authors: Kaufman Dan S. , Woll Petter S. , Martin Colin H. , Miller Jeffrey S. 
Published: April 2020

Abstract
Hematopoiesis from human embryonic stem cells (hESCs) follows developmental kinetics similar to what is observed during normal human ontogeny. Myeloid, erythroid and megakaryocytic progenitors can be routinely generated from hESCs. However, little is known about the ability of hESCs to differentiate into the lymphoid lineage. Natural killer (NK) cells are important mediators of donor anti-host alloreactivity seen after allogeneic transplant for myeloid leukemias. Our studies use a two-step culture method to demonstrate efficient generation of functional NK cells from hESCs. CD34+ and CD34+CD45+ hESC-derived hematopoietic progenitor cells were co-cultured with inactivated AFT024 stromal cells in medium supplemented with IL-7, IL-15, SCF and FL. Generation of NK cells was established by phenotypic and functional analysis. CD34+ umbilical cord blood (UCB) cells were utilized as a positive control. After 14 days of culture of CD34+ hESC-derived cells, more than 90% of the cells express CD45, a pan-hematopoietic cell marker, but few CD56+ cells are observed. At 21 days of culture a distinct CD56+CD45+ cell population develops (14.9%), which increases to 37.5% of cells after 28 days of culture. Similar results are observed for CD34+CD45+ hESC-derived cells, characterizing that both CD34+ and CD34+CD45+ cell populations contain hematopoietic progenitors with NK cell developmental potential. Limiting dilution analysis of hESC-derived progenitor cells demonstrates CD34+ hESC-derived cells have a low NK cell progenitor frequency. However, sorting for CD34+CD45+ hESC-derived cells significantly increased the NK cell cloning frequency (1.92% ± 1.20%) to a level comparable to the frequency observed for CD34+ UCB cells cultured in the same manner (3.57% ± 1.68%). The hESC-derived NK cells also express receptors known to regulate NK cell cytolytic activity, including killer-Ig-like receptors (KIRs), C-type lectin-like receptors (CD94 and NKG2A) and natural cytotoxicity receptors (NKp30, NKp44, and NKp46). Furthermore, hESC-derived NK cells also express CD16, an Fc-receptor typically expressed on more mature NK cells. The expression of KIRs is significantly higher for the hESC-derived NK cells compared to the UCB-derived NK cells. This may lead to future strategies to generate selective alloreactive NK cell populations for therapy. To investigate the functional properties of the hESC-derived NK cells, cytolytic activity was tested against K562 erythroleukemia cells and Raji B-lymphoblastoid cells. hESC-derived NK cells effectively killed K562 cells, with activity similar to that seen with UCB-derived NK cells. As expected, Raji cells were resistant to direct cytotoxicity by both hESC and UCB-derived NK cells. However, treatment of Raji cells with anti-CD20 antibody results in effective antibody-dependent cell-mediated cytoxicity by the hESC-derived NK cells. The hESC-derived NK cells also demonstrate ability to upregulate production of cytokines such as IFN-γ upon stimulation. Furthermore, we also find that hESC-derived progenitors also have T cell and/or B cell potential based on cells that express Ikaros, Rag1, and IL7Rα. These results demonstrate that the CD34+ and CD34+CD45+ hESC-derived cell populations contain lymphoid progenitor cells that can develop into both innate and adaptive immune cells. The ability to generate functional NK cells that can target and lyse human tumor cells via two distinct mechanisms suggests potentially novel anti-cancer therapy applications of hESCs.