Cellular Reprogramming (Yamanaka Factors)

The key experiment: Sinclair et al. (Nature 2020, Harvard University) intermittently expressed OSK (Oct4, Sox2, Klf4) in retinal cells of aged mice. The result was extraordinary — recovery of vision lost with age, restoration of nerve axonal regeneration, and reversal of biological age measured by epigenetic clocks.

Proposed mechanism: partial reprogramming 'rejuvenates' the epigenome without altering cellular identity. Yamanaka demonstrated that the epigenetic clock is reversible: DNA methylation and histone marks associated with ageing can be selectively erased. If reprogramming is transient, cells recover their young pattern without losing differentiated function.

Leading companies developing human partial reprogramming: Altos Labs (funded by Bezos, Yuri Milner): team led by Hal Barron and Juan Carlos Izpisúa. Calico (Alphabet/Google): previously led by Hal Barron. Retro Biosciences (funded by Sam Altman): focus on cellular reprogramming and plasmapheresis. NewLimit (Brian Armstrong of Coinbase): massive screening of reprogramming factors. Iduna Therapeutics: spin-off of Sinclair's lab, first biotech with OSK in clinic.

Pending challenges: precise control of temporal dosing (overshoot causes tumorigenesis), delivery method (AAV viral vector vs modified mRNA), tissue specificity, scalability. First human clinical trials are expected for 2026-2028 — initially in localised pathologies (vision, inner ear) before systemic applications.