Uncovering human yolk sac-derived innate lymphoid-biased multipotent progenitors prior to hematopoietic stem cell formation (scRNA-Seq)

Hematopoietic stem cell (HSC)-independent lymphopoiesis has been elucidated in murine embryos. However, our understanding regarding human embryonic counterparts remains limited. Here, we unveiled the presence of human yolk sac-derived lymphoid-biased progenitors (YSLPs) expressing CD34, IL7R, LTB and IRF8 at Carnegie Stage 10, much earlier than the first HSCs emergence. The number and lymphopoietic potential of these progenitors were both significantly higher in yolk sac than embryo proper at this early stage. Importantly, single-cell/bulk culture and CITE-seq have elucidated the tendency of YSLP differentiating into innate lymphoid cells and dendritic cells. Notably, lymphoid progenitors in fetal liver before and after HSCs seeding displayed distinct transcriptional features, with the former closely resembling those of YSLPs. Overall design: 7-AAD– cells from one CS10 YS (in vivo) were sorted for scRNA-seq (10X Genomics). All generated CD45+ cells from cultured CS12b-YS were sorted for scRNA-seq (10X Genomics). The generated cells from cultured CS12a-YS, CS12a-EP, CS12a-YS (CD45+CD127+) and CS12a-YS (CD45+CD127–) were combined with the following CITE-Seq antibodies: CD56, CD117, CD11b, CD161, CD5 and CD1a. Cells were individually hashtagged per group and pooled together.