Yamanaka factors are promising, but at the same time rather dangerous, as one of them (cMyc) is a powerful oncogene.
Hence, the search for safer alternatives. What the Yamanaka factors do is not just rejuvenation, but also de-differentiation of cells, with the latter being undesirable in clinical settings. (Though desirable for stem cell production.) It is possible that these two effects can be separated and rejuvenation can be achieved without de-differentiation.
