Differentiation of Human Induced Pluripotent Stem Cells (iPS Cells) and Embryonic Stem Cells (ES Cells) into Dendritic Cell (DC) Subsets.

Induced pluripotent stem cells (iPS cells) are engineered stem cells, which exhibit properties very similar to embryonic stem cells (ES cells; Takahashi and Yamanaka, 2016). Both iPS cells and ES cells have an extraordinary self-renewal capacity and can differentiate into all cell types of our body, including hematopoietic stem/progenitor cells and dendritic cells (DC) derived thereof. This makes iPS cells particularly well suited for studying molecular mechanisms of diseases, drug discovery and regenerative therapy ( Grskovic et al., 2011 ; Bellin et al., 2012 ; Robinton and Daley, 2012). DC are the major antigen presenting cells of the immune system and thus they are key players in modulating and directing immune responses ( Merad et al., 2013 ). DC patrol peripheral and interface tissues (e.g., lung, intestine and skin) to detect invading pathogens, and upon activation they migrate to lymph nodes to activate and prime lymphocytes. DC comprise a phenotypically heterogeneous family with functionally specialized subsets (Schlitzer and Ginhoux, 2014). Generally, classical DC (cDC) and plasmacytoid DC (pDC) are distinguished, exhibiting a classical and plasma cell-like DC morphology, respectively. cDC recognize a multitude of pathogens and secrete proinflammatory cytokines upon activation, while pDC are specialized to detect intracellular pathogens and secrete type I interferons ( Merad et al., 2013 ; Schlitzer and Ginhoux, 2014). cDC are further divided into cross-presenting cDC1 and conventional cDC2, in the human system referred to as CD141+ Clec9a+ cDC1 and CD1c+ CD14- cDC2. Human pDC are characterized as CD303+ CD304+ ( Jongbloed et al., 2010 ; Joffre et al., 2012 ; Swiecki and Colonna, 2015). To investigate subset specification and function of human DC, we established a protocol to generate cDC1, cDC2 and pDC in vitro from human iPS cells (or ES cells) ( Sontag et al., 2017 ). Therefore, we differentiated iPS cells (or ES cells), via mesoderm commitment and hemato-endothelial specification, into CD43+ CD31+ hematopoietic progenitors. Subsequently, those were seeded onto inactivated OP9 stromal cells with FLT3L, SCF, GM-CSF and IL-4 or FLT3L, SCF and GM-CSF to specify cDC1 and cDC2, or cDC1 and pDC, respectively.