Cellular reprogramming is a technique that alters the expression profile of specific genes within a given cell type, allowing genes that had ceased to be expressed at a certain developmental stage to become active once again—thereby modifying the form and biology of the reprogrammed cell. Above all, the discovery of cellular reprogramming represented a paradigm shift in the field of regenerative medicine. The long-held view that embryonic development was a unidirectional process—in which pluripotent cells would differentiate and acquire a specific, irreversible cellular fate—was replaced by the understanding that this process is, in fact, malleable and even bidirectional. Reprogramming has revealed that adult or differentiated cells, such as those found in the skin, can be rejuvenated and returned to a state of pluripotency; from this state, they can self-renew and give rise to various other cell types, such as those of the liver, muscles, or skin.

This breakthrough has prompted a re-evaluation of aging—a phenomenon traditionally viewed as both unidirectional and inevitable. If a differentiated cell can be converted into a pluripotent cell—similar to those found in embryos—effectively returning it to its starting point, is it then possible to rejuvenate cells without necessarily going so far back in time? And what about an entire organism? Is it possible to slow down or even reverse the aging process?

In this seminar, I will discuss the latest advancements in *in vivo* partial reprogramming—pioneered by Dr. Juan Carlos Izpisua Belmonte—as well as my own involvement in these projects.