Hematopoietic stem cell state and fate in trained immunity.

Trained immunity serves as a de facto memory for innate immune responses, resulting in long-term functional reprogramming of innate immune cells. It enhances resistance to pathogens and augments immunosurveillance under physiological conditions. Given that innate immune cells typically have a short lifespan and do not divide, persistent innate immune memory may be mediated by epigenetic and metabolic changes in long-lived hematopoietic stem cells (HSCs) in the bone marrow. HSCs fine-tune their state and fate in various training conditions, thereby generating functionally adapted progeny cells that orchestrate innate immune plasticity. Notably, both beneficial and maladaptive trained immunity processes can comprehensively influence HSC state and fate, leading to divergent hematopoiesis and immune outcomes. However, the underlying mechanisms are still not fully understood. In this review, we summarize recent advances regarding HSC state and fate in the context of trained immunity. By elucidating the stem cell-intrinsic and extrinsic regulatory network, we aim to refine current models of innate immune memory and provide actionable insights for developing targeted therapies against infectious diseases and chronic inflammation. Furthermore, we propose a conceptual framework for engineering precision-trained immunity through HSC-targeted interventions.