In Vitro Generation of Human XCR1⁺ Dendritic Cells from CD34⁺ Hematopoietic Progenitors

Abstract

Dendritic cells (DCs) are a heterogeneous population of professional antigen-presenting cells which play a key role in orchestrating immune defenses. Most of the information gained on human DC biology was derived from studies conducted with DCs generated in vitro from peripheral blood CD14⁺ monocytes (MoDCs) or from CD34⁺ hematopoietic progenitors. Recent advances in the field revealed that these types of in vitro-derived DCs strikingly differ from the DC subsets that are naturally present in human lymphoid organs, in terms of global gene expression, of specialization in the sensing of different types of danger signals, and of the ability to polarize T lymphocytes toward different functions. Major efforts are being made to better characterize the biology and the functions of lymphoid organ-resident DC subsets in humans, as an essential step for designing innovative DC-based vaccines against infections or cancers. However, this line of research is hampered by the low frequency of certain DC subsets in most tissues, their fragility, and the complexity of the procedures necessary for their purification. Hence, there is a need for robust procedures allowing large-scale in vitro generation of human DC subsets, under conditions allowing their genetic or pharmacological manipulation, to decipher their functions and their molecular regulation. Human CD141⁺CLEC9A⁺XCR1⁺ DCs constitute a very interesting DC subset for the design of immunotherapeutic treatments against infections by intracellular pathogens or against cancer, because these cells resemble mouse professional cross-presenting CD8α⁺Clec9a⁺Xcr1⁺ DCs. Human XCR1⁺ DCs have indeed been reported by several teams to be more efficient than other human DC subsets for cross-presentation, in particular of cell-associated antigens but also of soluble antigens especially when delivered into late endosomes or lysosomes. However, human XCR1⁺ DCs are the rarest and perhaps the most fragile of the human DC subsets and hence the most difficult to study ex vivo. Here, we describe a protocol allowing simultaneous in vitro generation of human MoDCs and XCR1⁺ DCs, which will undoubtedly be extremely useful to better characterize the functional specialization of human XCR1⁺ DCs and to identify its molecular bases.