The Harvard group focused on a process called telomere shortening. Most cells in the body contain 23 pairs of chromosomes, which carry our DNA. At the ends of each chromosome is a protective cap called a telomere. Each time a cell divides, the telomeres are snipped shorter, until eventually they stop working and the cell dies or goes into a suspended state called "senescence". The process is behind much of the wear and tear associated with ageing.
At Harvard, they bred genetically manipulated mice that lacked an enzyme called telomerase that stops telomeres getting shorter. Without the enzyme, the mice aged prematurely and suffered ailments, including a poor sense of smell, smaller brain size, infertility and damaged intestines and spleens. But when DePinho gave the mice injections to reactivate the enzyme, it repaired the damaged tissues and reversed the signs of ageing.
What does this mean? It means that we are in all probability now just 10-20 years away from radically extending the average human life (to the maximum of 100-120) and possibly only around 25 or so years away from extending the maximum lifespan (to ???). In other words, we are now knocking at the gates of immortality.
What's even better is that this technique, if it works, would also regenerate ageing damage. In other words, this is not merely lengthened life, but also lengthened youth. We'll have done an end-run around the Tithonys dilemna, and the huge numbers of elderly such a process would generate will be healthy enough to support themselves, and thus be a gain for rather than a drain on the economy.
There is also no obvious reason why this technique will be particularly expensive. Right now, we aren't geared up for mass production of human telomerase, but it shouldn't be a matter of more than 10 or so years past our decision to search for a tecnnique of mass production for it to be cheaply synthesizable. Note that we already routinely synthesize (or grow in other animals) numerous other human hormones, most famously insulin (which was once very expensive but is today fairly cheap to obtain).
There might be bad side effects. We didn't evolve to live 100 or more years. But so far, this looks like unadulterated good news to me.