"Notably, none of the cell transplant recipients developed tumors (n = 16)."
https://www.cell.com/cell/fulltext/S0092-8674(25)00571-9?_re...
Would they get cancer if they lived for 400 years? Maybe not either. Their immune systems are very good, better than ours.
(We humans don't really want to acknowledge that some other animals may have better immune systems, or any other systems, at their disposal.)
On the other end of the scale, mice die of cancer while not even three years old, because their immune systems are really bad at fighting cancer cells.
Cancer in mammals seems to be a function of failing immune systems rather than raw age in numbers. In some species, including us humans, weakening of the immune system goes hand in hand with aging. But in others it does not.
If cancer really is an inevitability, then whales, who have both livespan limits longer than that of humans, and enormous bodies with a staggering amount of living cells, would be full of cancer. They aren't.
Clearly, humans must have better innate cancer suppression than mice, and whales must have better innate cancer suppression than humans.
There are some hints that this may come down to programmed cell death and DNA repair mechanisms (i.e. the p53 pathway) more than the immune system tweaks - with immune response being the "last resort" of cancer suppression. But we also don't know enough about the immune system to be able to examine it the same detail we can examine the DNA repair pathways.
Our evolutionary biology doesn't "care" if we get cancer. Just that we have healthy children and can rear them for one or two generations. That was a (locally) optimal algorithm.
We have plenty of in-built checks and protections in our molecular biology, and they are sufficient to expand the species.
The implanted stem cells, however, were human. (The fact that that the treatments did not cause "fever or substantial changes in immune cell levels (lymphocytes, neutrophils, and monocytes), which are commonly monitored for xenograft-related immune responses," is itself surprising.)
> promises of extending life have always fallen short of hype, and odds are this will too
Correct, though I'd say because this is early-stage medical research. Not because it's targeting longevity. I'd be similarly sceptical of an N = 16 early-stage drug trial for the flu.
In terms of replicatability, it is also not always the sample size, it is the effect size. Small samples do affect ability to generalize, but the point is that sample size isn't everything.
Which effect size do you find lacking?
As well as the undeniable benefit to individuals, a cure for aging would unleash a whole new bunch of problems that have been kept in check through the mechanism of people dying off regularly. A society of immortals could be quite alien to us.
Good example is vitamin supplementation. There isn't a downside. It's just a fuck-up we can't synthesise vitamin C. (There may be path-dependent benefits, e.g. our jaw muscles getting smaller thereby permitting a larger brain. But we don't need to be vitamin C restricted anymore.)
Every action in the known universe (and surely in some unknown ones too) results in a trade-off. This is maybe the only precept on software architecture that doesn't "depends" on anything and is closer to natural law.
Human body isn't exactly bottlenecked by energy availability. Calories are getting cheaper and cheaper, with obesity rates as a testament to that.
There are old people who remain lucid and active well into their nineties, not getting dementia or cancer - through some combination of good luck, good genes and good lifestyle choices. They live a good life - until a stroke cripples them, or the heart fails them, or a very mundane illness like flu puts them in bed and they never quite recover from it. If that couldn't happen to them, how many more good years would that buy them?
Any treatment that addresses the aging-associated systematic decline in bodily functions should be extremely desirable. Even if it wouldn't help everyone live longer, it would help a lot of people live better lives nonetheless.
We are consistently sold ideas that do not meet expectation, the catch is expected.
"Hey everyone we discovered X breakthrough!" It only has Y constrains or consequences which make it not so useful, or at worst, harmful later.
"The super stem cells prevent age-related bone loss while rejuvenating over 50% of the 61 tissues analyzed." (including the brain).
What do people die of when they die of 'old age'? There's the 3 pillars: cancer, cardiovascular, neurodegenerative. These are often (but not always) metabolic diseases; i.e. cardiovascular death often arises from kidney insufficiency. If you can regenerate the liver, kidney, etc. indefinitely, a large vector of metabolic disease is probably diminished or disappears.
In the paper, monkeys restored brain volume. They reduced the levels of senescent cells to youthful levels. They increased bone mass. This reduces or eliminates many of the threats that inflict casualties among the centenarian population.
Sure, something else could come up that the monkeys start dying from instead. But, given the way humans and monkeys die of old age—by reducing or eliminating all known threats—it's hard to see how this wouldn't extend lifespan.
Unclear from the study what the stem cells are doing to address either problem.