Human HSPCs clones balance stochastic diversification with cytokine-induced differentiation.

Hematopoietic stem and progenitor cells (HSPCs) balance self-renewal with on-demand differentiation of blood lineages. Modern bone marrow atlases specify static transcriptional states, but not HSPC dynamics, which are only partly understood, particularly in humans. Here, we introduce cHSPCTrack (clonal HSPC tracker), an in vitro framework for serially tracking clonal differentiation and fate acquisition from human HSPCs extracted from circulation. By following thousands of single-cell-derived clones stimulated by different cytokine combinations, cHSPCTrack reconstructs the balance between stochasticity and directed differentiation in human HSPCs. Single HSPCs stochastically yield multiple lineages under a uniform cytokine environment, with stimulatory inputs modulating differentiation probabilities by introducing biases toward preferred fates. In parallel, differentiation rates vary stochastically across and within clones. Clonal memory stabilizes the induction of a few genes per clone over otherwise archetypical differentiation trajectories. Within clones, multiple fates can interact with each other, as shown for clones mixing basophils, eosinophils, and mast cells with other fates. cHSPCTrack opens avenues for understanding hematopoietic clonal dynamics in health and disease.