Scientists have genetically modified human mesenchymal progenitor cells to express a more potent version of the “longevity gene” FOXO3, producing rejuvenative effects in monkeys, mice, and human cells [1].
Making aging-resistant cells
Stem cell exhaustion is one of the mechanisms of aging. Replenishing the aging stem cell pool with new exogenous cells sounds like a good idea, but when new cells interact with an aging organism, they often experience accelerated aging and senescence [2]. To overcome this problem, in a new study published in Cell, scientists from China created genetically modified stem cells and injected them into cynomolgus monkeys.
The team started with wild-type human mesenchymal progenitor cells (MPCs), stem cells that can differentiate into several cell types and have a low immunogenic risk: they express few surface proteins that can be recognized by the immune system and secrete factors that actually calm immunity around them.
The MPCs were differentiated from human embryonic stem cells modified by a CRISPR-based editing system, which tweaked FOXO3, a transcription factor that orchestrates stress resistance and repair. FOXO3 is considered a promising “longevity gene,” since it extends lifespan and healthspan in animal models [3] and is associated with human longevity [4]. In stem cells, FOXO3 helps keep stem cells quiescent but competent, and it modulates inflammatory signaling.
In more technical terms, the researchers replaced two serine residues (Ser253 and Ser315) with alanine, eliminating the ability of these sites to be phosphorylated. Because phosphorylation at these sites normally promotes FOXO3 nuclear export and inactivation, this mutation keeps FOXO3 active for longer.
In vitro, the researchers confirmed that their senescence-resistant MPCs (SRCs) had a more youthful phenotype than wild-type MPCs (WTCs), exhibiting lower senescence and inflammation markers (SA-β-gal, IL-6, IL-8), longer telomeres, and more stable heterochromatin. SRCs were more competent at differentiation and more resistant to stressors, and they had their proliferation and tumor-suppressor programs upregulated.
Significant effects on monkeys
In the main experiment, cynomolgus monkeys were divided into four age groups. The three younger groups were used for studying natural aging in these animals and creating several bespoke clocks, which combined gene expression and DNA methylation patterns across multiple tissues to estimate each animal’s biological age. The last and oldest group (19-23 years) formed the intervention cohort and was further divided into subgroups that received a sham treatment, human WTCs, or human SRCs.
The treatment groups received bi-weekly IV infusions for 44 weeks, and upon the completion of the treatment, a large battery of tests was performed. The first part of it focused on the brain. Functionally, on a delayed-reward memory task, the SRC group performed significantly better than old controls, while the WTC group’s results were not clearly distinguishable from this control group’s.
SRCs preserved or even partially restored cortical thickness and volume in several brain regions, relative to age-matched controls. WTCs had weaker effects. Diffusion MRI revealed improved structural connectivity.
SRCs also reduced age-related myelin thinning and the levels of amyloid-β aggregates and p-Tau aggregates, both of which indicate Alzheimer’s disease. A single-cell clock showed an average reduction of biological age by about 2.5 years across hippocampal cell types following the SRC treatment.
This and other biological age measurements were compared to similarly aged untreated monkeys rather than the animals’ own baselines. In other words, the net age reversal, as measured by these metrics, was approximately 0.9 years less, as this is how long the experiment took to conduct.
The researchers also profiled 13 immune cell types. SRCs reversed more aging-related changes in gene expression than WTCs. Both treatments downregulated cellular senescence and apoptosis while upregulating DNA damage repair, autophagy, and lymphocyte differentiation and function. Both treatments also reduced the inflammation markers IL-6 and TNF-α in the plasma and CHIT1, a marker of microglial activation and neuroinflammation, in the cerebrospinal fluid (CSF).
Exosomes recapitulate many of the changes
In total, the team applied their bulk-tissue RNA-seq-based clock to 61 tissues from 10 organ systems. Generally, both WTCs and SRCs attenuated age-related trajectories, but SRCs had larger effects in most tissues, with an average biological age reduction of 3.3 years by SRCs compared to 2.8 years by WTCs.
Interestingly, the strongest effects were observed in reproductive tissues (ovary, testis, uterus, prostate, seminal vesicle, and epididymis). In tissues where transcriptomic aging was reversed, the methylation-based clock agreed with the transcriptomic one: according to it, SRCs made brains 5 years younger and skeletal muscle 4 years younger on average.
Because MPCs are thought to act largely via secreted factors, the researchers zoomed in on exosomes. Both in mice and in human cells, SRC-derived exosomes produced significant rejuvenation, lowering senescence markers and shifting gene expression profiles towards younger phenotypes.
Literature
[1] Lei, J., Xin, Z., Liu, N., Ning, T., Jing, Y., Qiao, Y., … & Liu, G. H. (2025). Senescence-resistant human mesenchymal progenitor cells counter aging in primates. Cell.
[2] Liu, J., Gao, J., Liang, Z., Gao, C., Niu, Q., Wu, F., & Zhang, L. (2022). Mesenchymal stem cells and their microenvironment. Stem cell research & therapy, 13(1), 429.
[3] Flachsbart, F., Dose, J., Gentschew, L., Geismann, C., Caliebe, A., Knecht, C., … & Nebel, A. (2017). Identification and characterization of two functional variants in the human longevity gene FOXO3. Nature communications, 8(1), 2063.
[4] Willcox, B. J., Donlon, T. A., He, Q., Chen, R., Grove, J. S., Yano, K., … & Curb, J. D. (2008). FOXO3A genotype is strongly associated with human longevity. Proceedings of the National Academy of Sciences, 105(37), 13987-13992.
