Engineered niches support the development of human dendritic cells in humanized mice

Anselmi, Giorgio; Vaivode, Kristine; Dutertre, Charles-Antoine; Bourdely, Pierre; Missolo-Koussou, Yoann; Newell, Evan; Hickman, Oliver; Wood, Kristie; Saxena, Alka; Helft, Julie; Ginhoux, Florent; Guermonprez, Pierre

Classical dendritic cells (cDCs) are rare sentinel cells specialized in the regulation of adaptive immunity. Modeling cDC development is both crucial to study cDCs and harness their potential in immunotherapy. Here we addressed whether cDCs could differentiate in response to trophic cues delivered by mesenchymal components of the hematopoietic niche where they physiologically develop and maintain. We found that expression of the membrane bound form of human FLT3L and SCF together with CXCL12 in a bone marrow mesenchymal stromal cell line is sufficient to induce the contact-dependent specification of both type 1 and type 2 cDCs from CD34+ hematopoietic stem and progenitor cells (HSPCs). Engraftment of these engineered mesenchymal stromal cells (eMSCs) together with CD34+ HSPCs creates an in vivo synthetic niche in the dermis of immunodeficient mice. Cell-to-cell contact between HSPCs and stromal cells within these organoids drive the local specification of cDCs and CD123+AXL+CD327+ pre/AS-DCs. cDCs generated in vivo display higher levels of resemblance with human blood cDCs unattained by in vitro generated subsets. Altogether, eMSCs provide a novel and unique platform recapitulating the full spectrum of cDC subsets enabling their functional characterization in vivo.