Human Stem Cells Retain 'Inflammatory Memory' Linked to Long-term Health
Recent research published in Nature reveals that human haematopoietic stem cells (HSCs)—the precursors responsible for blood cell production—possess a sophisticated mechanism for remembering past inflammatory stress. By utilizing advanced xenograft models and single-cell multiomics, scientists identified a distinct subset of these cells, termed 'HSC inflammatory memory' (HSC-iM). Unlike standard stem cells, these HSC-iM cells maintain a lasting molecular signature of previous immune challenges, which alters their behavior by promoting quiescence and limiting blood cell output.
This discovery is significant because it demonstrates that the body’s blood-forming system is not merely reactive but adaptive, carrying a biological record of past illnesses. The researchers observed this inflammatory memory in samples from patients recovering from COVID-19, those with sickle cell disease, and individuals experiencing natural ageing or clonal haematopoiesis. This suggests that the HSC-iM program is a fundamental physiological response that persists throughout a human lifetime, influencing how the immune system functions long after an initial infection or inflammatory event has subsided.
The implications of this finding extend to clinical diagnostics and long-term health management. The study found that when clonal haematopoiesis mutations occur within these memory-carrying cells, they can disrupt the protective quiescence of the HSC-iM subset, potentially accelerating disease progression or malignancy. Furthermore, the researchers discovered that the inflammatory program can be transmitted to differentiated immune cells, effectively 'priming' the immune system in ways that may be detrimental over time.
Crucially, the presence of the HSC-iM signature in circulating blood cells correlates with an increased risk of all-cause mortality. By identifying this subset, researchers have uncovered a potential biomarker for assessing an individual’s cumulative physiological stress. This insight provides a new framework for understanding 'inflammageing' and offers a promising avenue for developing targeted interventions to mitigate the long-term health impacts of chronic inflammation and age-related blood disorders.