The tree · branch 6 of 8

Replacing lost cells and parts

The reserve of cells that replace lost tissue runs out with age, tissue goes unreplaced and organs fail. The route around that is to supply the parts: stem cells, organs from gene-edited animals, organs grown outside the body.

Of the twelve published hallmarks of ageing, this branch groups one: the reserve of cells that replace lost tissue running out.

Where this branch stands

required: the year cannot arrive until this branch is handled; handled when 2 treatments are in the clinic

2029handled, in the middle run
1of 7 in the clinic already
in clinical usefurthest stage reached

One treatment under this branch is in the clinic already (a person's own cells are grown outside the body and used to rebuild a worn joint surface, 2016); the branch counts as handled when one morereaches it, and in each run of the model that year is drawn from the ranges below. Across all the runs, the middle year this branch is handled is 2029.

7 treatments and tools

listed by how soon each could reach its next rung

An organ from a gene-edited pig keeps a person alive First human clinic likely 2032, 2028 to 2045
Next rung within 1 to 5 years. Pigs' organs are the right size for people, and gene editing can take out the pig genes that make a human body reject them at once and add human ones that calm the rest.
Cells grown from stem cells restore a lost organ function in people First human clinic likely 2028, 2027 to 2036
Next rung within 1 to 5 years. The promise of stem cells was always this: grow the cells an organ has lost and put them back. Insulin-making cells were grown from embryonic stem cells in bulk in 2014 and cured diabetic mice; in June 2025 a Vertex Pharmaceuticals trial reported that twelve people with type 1 diabetes given an infusion of such cells into the liver all had their blood sugar back in the target range a year later, and ten of them no longer needed insulin.
A person's own cells are grown outside the body and used to rebuild a worn joint surface In clinical use in the clinic since 2016
Next rung within 5 to 20 years. Cartilage, the smooth surface that lets a joint glide, does not heal; a hole in it is for life and is where osteoarthritis starts.
A printed or lab-grown organ works in a person for a year First human clinic likely 2045, 2032 to 2100
Next rung within 5 to 20 years. Take a few of a person's own cells, grow them on a scaffold shaped like the organ, and put the result in.
Heart muscle grown from stem cells is grafted onto a person's failing heart First human clinic likely 2038, 2031 to 2070
Next rung within 5 to 20 years. A heart that has lost muscle to a heart attack does not grow it back, and heart failure is among the commonest ways an old person dies.
An old animal's blood-making stem cells are made young again, and its immune system with them Shown in animals clinic likely 2048, 2036 to 2100
Next rung more than 20 years away, if ever. The stem cells in bone marrow that make every blood and immune cell change with age: more of them come to favour the inflammatory cells of the innate immune system and fewer the T and B cells that learn new threats, which is one reason old people respond poorly to vaccines and infections.
A human organ is grown inside an animal and transplanted into a person Idea only clinic likely 2060, 2040 to not this century long shot
Next rung more than 20 years away, if ever. Between a pig's organ and an organ grown in a dish lies a third idea: grow a human organ inside a pig, from a person's own cells, so that it is the right size, has its own blood supply, and is not rejected.

What would move this

the next test each treatment needs, and the branch's own line

A regulator's approval of an organ from a gene-edited animal or an organ grown from a person's own cells for use outside a trial, or a stem cell therapy restoring a lost function in a controlled trial.

An organ from a gene-edited pig keeps a person alive Next rung: in clinical use. A regulator somewhere has approved it, or it is in routine use in a named clinical setting, so a doctor can give it to a patient outside a trial. Settled by the transplant centre's own release naming the patient, the peer-reviewed case report, and the regulator's trial clearance or approval record.
Cells grown from stem cells restore a lost organ function in people Next rung: in clinical use. A regulator somewhere has approved it, or it is in routine use in a named clinical setting, so a doctor can give it to a patient outside a trial. Settled by the peer-reviewed trial report; the trial registry; the regulator's approval record for the clinic rung.
A person's own cells are grown outside the body and used to rebuild a worn joint surface Next rung: in wide use. Available to the general public in at least one country without joining a trial, and taken up by many people. Settled by the peer-reviewed trial report; the regulator's approval record; published use figures for the wide-use rung.
A printed or lab-grown organ works in a person for a year Next rung: in clinical use. A regulator somewhere has approved it, or it is in routine use in a named clinical setting, so a doctor can give it to a patient outside a trial. Settled by peer-reviewed reports with follow-up of a year or more; a regulator's approval record if an engineered organ is approved.
Heart muscle grown from stem cells is grafted onto a person's failing heart Next rung: in clinical use. A regulator somewhere has approved it, or it is in routine use in a named clinical setting, so a doctor can give it to a patient outside a trial. Settled by the peer-reviewed report; the trial registry; the regulator's approval record for the clinic rung.
An old animal's blood-making stem cells are made young again, and its immune system with them Next rung: first human. At least one person has had it, with a public record of that result. Settled by peer-reviewed reports; the trial registry and report when a first person is treated; the regulator's approval record for the clinic rung.
A human organ is grown inside an animal and transplanted into a person Next rung: shown in animals. Shown to work in a living animal, in a peer-reviewed report. Settled by peer-reviewed reports; the transplant centre's report and the regulator's record for the later rungs.

Its history

the handled year, computation by computation

The year was first computed on 17 October 2026, with this branch handled in the middle run by 2029. Every estimate under it is still a first pass. From the second computation on, this section charts the branch's handled year run by run, so a reader who sees the year at the top move can tell which branch moved it.

What the story so far says about it

the promises, the self-experiments and the papers that bear on this branch

Promised, in public

December 2013Methuselah Foundation: Ninety-year-olds as healthy as fifty-year-olds by 2030, through tissue engineering and regenerative medicine. Verdict: not yet due, due 2030.

Tried on themselves, in public

2013Dave PascoeRunning. A claim about one person is a story, not a record, and it moves nothing on this branch.
2021Bryan Johnson, BlueprintRunning. A claim about one person is a story, not a record, and it moves nothing on this branch.

On the record

27 May 2026Stem-Cell-Derived Biologic Ventricular Assist Tissue in Heart FailureZimmermann and 7 others.
7 October 2024Implausibility of radical life extension in humans in the twenty-first centuryOlshansky and 3 others.
16 March 2017Autologous Induced Stem-Cell–Derived Retinal Cells for Macular DegenerationMandai and 38 others.
3 January 2023Hallmarks of aging: An expanding universeLópez-Otín and 4 others.
6 June 2013The Hallmarks of AgingLópez-Otín and 4 others.
22 June 2022Genetically Modified Porcine-to-Human Cardiac XenotransplantationGriffith and 12 others.
12 May 2022Foreword to the Aubrey de Grey and Charles Brenner debate (Let's Talk Longevity newsletter)Gobel.
15 June 2004Escape Velocity: Why the Prospect of Extreme Human Life Extension Matters NowGrey.
15 April 2006Tissue-engineered autologous bladders for patients needing cystoplastyAtala and 4 others.

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