“Scientists working with Yamanaka factors have shown that aged cells can partially regain youthful characteristics, resetting biological age markers and restoring damaged cellular functions, and partial cellular reprogramming may reverse key hallmarks of aging without fully turning cells into stem cells.”

The core scientific statement is supported by real, peer-reviewed primary literature. Ocampo and colleagues reported that partial reprogramming by short-term cyclic expression of Oct4, Sox2, Klf4 and c-Myc ameliorates cellular and physiological hallmarks of aging and prolongs lifespan in a progeria mouse model , and stated that partial reprogramming by short-term expression of the Yamanaka factors has the capacity to rejuvenate cellular phenotypes of aging in mouse and human cells . An independent commentary noted that the effect occurred without teratoma formation, cancer development, or increased mortality even after 35 cycles of doxycycline administration . Functional restoration has also been demonstrated. Ectopic expression of Oct4, Sox2 and Klf4 in mouse retinal ganglion cells restored youthful DNA methylation patterns and transcriptomes and promoted axon regeneration , with the beneficial effects requiring the DNA demethylases TET1 and TET2, indicating that mammalian tissues retain a record of youthful epigenetic information . In normally aging (non-progeroid) mice, long-term partial reprogramming produced rejuvenating effects in tissues such as kidney and skin and at the organismal level, with treatment duration determining the extent of benefit , and these effects were associated with a reversion of the epigenetic clock along with metabolic and transcriptomic changes . In human cells in culture, transient reprogramming rejuvenated multiple cellular attributes including the transcriptome by around 30 years as measured by a transcriptome clock, with the epigenome rejuvenated to a similar extent including H3K9me3 levels and the DNA methylation ageing clock . Researchers described 13 days of transient reprogramming as a "sweet spot" for partial rejuvenation of the methylome , which underlines how narrow the effective window is. On the "without fully turning cells into stem cells" element: analysis of cellular age during human iPSC reprogramming found that partial reprogramming reduces the epigenetic age of cells, and that loss of somatic gene expression and reduction in epigenetic age follow different kinetics, suggesting a possible safe window where rejuvenation is achieved with minimized cancer risk . Translation to humans has only just begun. Life Biosciences received FDA clearance for ER-100, described as the first cellular rejuvenation therapy using epigenetic reprogramming to enter human clinical trials , and the Phase 1 first-in-human study (NCT07290244) will enroll people with open-angle glaucoma and non-arteritic anterior ischemic optic neuropathy to assess safety, tolerability, immune responses and visual measures . The therapy uses a cocktail based on three of the four original Yamanaka factors: OCT-4, SOX-2 and KLF-4 . This is a localized eye treatment for specific diseases, not systemic rejuvenation. ## METHODOLOGY AND CONTEXT - **Model systems**: Almost all evidence is transgenic mice (doxycycline-inducible OSKM cassettes), non-human primates for the eye program, and cultured human fibroblasts. There is no published evidence of whole-body rejuvenation in a living human. - **Delivery**: Nearly all mouse work uses genetically engineered animals, not a treatment that can currently be given to an existing human body. - **Endpoints**: Predominantly molecular markers such as DNA methylation clocks and transcriptomic signatures, plus some functional readouts (axon regeneration, visual acuity, glucose tolerance, wound healing, lifespan in progeroid mice). - **Safety**: The literature is explicit that dose and duration control is the central problem. One review states that there are still cancer-associated risks, with partial reprogramming associated with teratoma formation and cancer in vivo, and that overly dedifferentiated cells can be malignant , noting that extended reprogramming of cardiomyocytes in vivo in mice for 12 days results in excessive dedifferentiation and cell death . A 2026 landscape summary lists loss of cell identity, tumorigenesis if reprogramming runs too long, and immune responses to delivery vectors as safety concerns, with regulators wanting staged dosing in accessible tissues before systemic rejuvenation claims . - **Durability**: In the vision work, significant vision improvements remained for one month after switching off OSK, after which the benefit gradually diminished while remaining better than baseline . Effects are not permanent resets.