3. Partial Cellular Reprogramming May Rejuvenate, but Requires Control of Identity and Cancer Risk

Adult somatic cells can be converted to embryonic-like pluripotent cells (induced pluripotent stem cells) via the expression of several transcription factors, treatment with chemical cocktails and by other methods (73). Organismal rejuvenation with this method remains a major challenge. Partial reprogramming aims to capture the reset component of reprogramming while avoiding full dedifferentiation and loss of cellular identity. Cyclic or targeted expression of Yamanaka factors can ameliorate some age-associated phenotypes in mice, and related approaches can restore function in specific tissues such as the retina (61, 74). Reprogramming within adult organisms aims to reduce regulatory drift (one component of the deleteriome), while leaving structure and function largely intact. The central challenge is control, as reprogramming must be cell-type-specific, temporally limited, and carefully monitored, because excessive or misdirected resetting can impair function or raise tumor risk. If these constraints are met, partial reprogramming could become a tool to restore youthful regulatory states across multiple tissues.