Researchers report that engineered human stem cells can slow and in some cases partially reverse signs of aging across multiple organs in primates, without causing tumors or obvious harmful side effects. In experiments on aged cynomolgus macaques, regular intravenous injections of senescence-resistant human mesenchymal progenitor cells produced improvements in brain, bone, immune, vascular and reproductive systems, and reduced molecular markers of biological age.
The team, from the Chinese Academy of Sciences and Capital Medical University, published the results in Cell. They created senescence-resistant cells (SRCs) by genetically modifying human mesenchymal progenitor cells—a type of stem cell that can give rise to bone, cartilage and fat—so the cells keep an active form of the longevity-associated gene FOXO3. The modification alters specific phosphorylation sites to maintain FOXO3 activity, helping cells resist aging-related decline while avoiding uncontrolled growth.
In the trial, aged macaques comparable to 60–70-year-old humans received intravenous SRC injections every two weeks for 44 weeks at a dose of 2 million cells per kilogram of body weight. A control group received unmodified cells. Treatment was well tolerated: animals showed no signs of immune rejection, no weight loss and no tumor formation or other evident adverse effects.
Improvements were recorded across 10 major physiological systems and 61 tissue types. Observed benefits included reduced fibrosis, better lipid metabolism, and signs of regeneration in the brain, bones, blood vessels and reproductive organs. Cognitive measures improved alongside MRI evidence of reduced brain atrophy, thicker cortical layers and stronger hippocampal connectivity. Bone density rose and periodontal degeneration decreased. Immune system measures shifted toward patterns seen in younger animals, and reproductive tissues showed preserved germ cells and more youthful gene expression profiles.
At the molecular level, biological age estimates based on transcriptomic and DNA methylation aging clocks fell by an average of 3.3 years. Some tissues showed larger effects: hippocampal cells appeared nearly 42% younger by the study’s measures, and ovarian and blood cell profiles were rejuvenated by up to 45%. Neurons and oocytes showed reductions in biological age equivalent to about 5–7 years.
The researchers traced much of the therapeutic effect to exosomes—tiny vesicles released by the SRCs that carry proteins, RNA and other signaling molecules. In follow-up lab tests, these exosomes revived aging human cells in vitro and reduced degeneration in mouse models, suggesting the possibility of cell-free therapies derived from SRCs.
The findings demonstrate in primates that systemic aspects of aging can be slowed and partially reversed in a multi-organ way, and they provide a proof of principle for further development. The authors and outside experts note important caveats: long-term safety, the durability of benefits, and ethical and translational challenges remain to be addressed before human clinical use. Future work will need to clarify how long effects last, whether similar results occur in humans, and which components of the therapy are most responsible for the benefits.
