New research on the involvement of immune system problems in ageing and how it might be fixed - works in mice....

There's a whole load of research being done into improving the quality of our lives as we get older... In fact there are clinical trials (for us humans) currently going on now to reduce some of the bad effects of the more ordinary senescent cells. And yet there is so little written about these effects and the consequences in science fiction... there's a large empty expanse in the genre where such stories and discussions should be... with a few exceptions.
Off the top of my head:
The Trouble with Lichen John Wyndham
Blood Music Greg Bear

There is loads of sf about, or involving, the effects of extended lifespans and immortality, though most of it is not science- focussed.