I think you'll agree this is an intriguing addition to the stable of potential methods to replace damaged mitochondria, and thus remove their contribution to aging and age-related disease: "Mitochondrial DNA [or mtDNA] mutations are the direct cause of several physiological disorders and are also associated with the aging process. The modest progress made over the past two decades towards manipulating the mitochondrial genome and understanding its function within living mammalian cells means that cures for mitochondrial DNA mutations are still elusive. Here, we report that transformed mammalian cells internalize exogenous isolated mitochondria upon simple co-incubation. We first demonstrate the physical presence of internalized mitochondria within recipient cells using fluorescence microscopy. Second, we show that xenogenic transfer of murine mitochondria into human cells lacking functional mitochondria can functionally restore respiration in cells lacking mtDNA." I'm sure you can speculate on how one would build therapies upon this basis, should it be made safe and reliable.