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Single‐cell RNA sequencing reveals developmental heterogeneity among early lymphoid progenitors

Single‐cell RNA sequencing is a powerful technology for assessing heterogeneity within defined cell populations. Here, we describe the heterogeneity of a B220+CD117intCD19−NK1.1− uncommitted hematopoietic progenitor having combined lymphoid and myeloid potential. Phenotypic and functional assays revealed four subpopulations within the progenitor with distinct lineage developmental potentials. Among them, the Ly6D+SiglecH−CD11c− fraction was lymphoid‐restricted exhibiting strong B‐cell potential, whereas the Ly6D−SiglecH−CD11c− fraction showed mixed lympho‐myeloid potential. Single‐cell RNA sequencing of these subsets revealed that the latter population comprised a mixture of cells with distinct lymphoid and myeloid transcriptional signatures and identified a subgroup as the potential precursor of Ly6D+SiglecH−CD11c−. Subsequent functional assays confirmed that B220+CD117intCD19−NK1.1− single cells are, with rare exceptions, not bipotent for lymphoid and myeloid lineages. A B‐cell priming gradient was observed within the Ly6D+SiglecH−CD11c− subset and we propose a herein newly identified subgroup as the direct precursor of the first B‐cell committed stage. Therefore, the apparent multipotency of B220+CD117intCD19−NK1.1− progenitors results from underlying heterogeneity at the single‐cell level and highlights the validity of single‐cell transcriptomics for resolving cellular heterogeneity and developmental relationships among hematopoietic progenitors.