Modulation of Myelopoiesis Progenitors Is an Integral Component of Trained Immunity

Trained innate immunity fosters a sustained favorable response of myeloid cells to a secondary challenge, despite their short lifespan in circulation. We thus hypothesized that trained immunity acts via modulation of hematopoietic stem and progenitor cells (HSPCs). Administration of β-glucan (prototypical trained-immunity-inducing agonist) to mice induced expansion of progenitors of the myeloid lineage, which was associated with elevated signaling by innate immune mediators, such as IL-1β and granulocyte-macrophage colony-stimulating factor (GM-CSF), and with adaptations in glucose metabolism and cholesterol biosynthesis. The trained-immunity-related increase in myelopoiesis resulted in a beneficial response to secondary LPS challenge and protection from chemotherapy-induced myelosuppression in mice. Therefore, modulation of myeloid progenitors in the bone marrow is an integral component of trained immunity, which to date, was considered to involve functional changes of mature myeloid cells in the periphery. [Display omitted] •Trained immunity (TI) modulates hematopoietic progenitors in bone marrow•TI is associated with adaptations in cell metabolism in progenitors•TI increases expansion of hematopoietic progenitors and myelopoiesis•TI promotes beneficial responses to systemic inflammation and chemotherapy Modulation of hematopoietic stem and progenitor cells during trained immunity allows a sustained response of myeloid cells to a secondary challenge despite their short lifespan in circulation.