PCL consists in introducing a somatic adult or senescent cell nucleus or entire cell with enlarged membrane pores in an (activated) oocyte and to withdraw this treated cell before its de-differentiation and first cell division occurs. Thus, the progressive rejuvenation capability of the oocyte is used only temporarily in order to obtain a partial natural rejuvenation. PCL permits to envisage a chosen degree of partial rejuvenation in changing the duration of the introduction of the treated cell in the oocyte. Using PCL cell de-differentiation and its age reprogramming might be, at least partially, separable. Thus the existence of an isolated ageing clock would be confirmed at least during a certain part of the cellular evolution and involution.