The tree · Broken proteins and waste
An antibody clears amyloid from the brain and slows the decline of Alzheimer's disease
Amyloid is a protein that misfolds and piles up between brain cells with age, and in Alzheimer's disease it piles up faster. Antibodies that stick to it and get the immune system to clear it were first shown to work in mice in 1999, failed in people for twenty years, and in 2022 one of them, lecanemab, slowed the decline of people with early Alzheimer's by about a quarter over eighteen months in a trial of nearly eighteen hundred people. The United States regulator gave it full approval on 6 July 2023, and a second antibody followed in 2024. The effect is modest, the drug needs frequent brain scans, and some patients bleed or swell in the brain; so it is in clinical use, not wide use. It has needed infusions, but on 2026-07-13 the United States regulator approved an under-the-skin weekly autoinjector as the starting dose too, so a whole course can now be given at home.
What would count
A person given an antibody against amyloid afterwards has measurably less of it in the brain on a scan, and in a controlled trial such people decline more slowly on a pre-stated measure of thinking and function than those on placebo, in a peer-reviewed report. The animal rung is amyloid cleared from a living animal's brain. For the clinic rung: a regulator's full approval, not an accelerated one, for Alzheimer's disease. For wide use: available by prescription in several countries and taken by a substantial share of eligible patients.
Who settles it: Peer-reviewed trial reports; the regulator's approval record; published uptake figures for the wide-use rung.
Where it stands
In clinical use. Reached 6 July 2023, on the record of fda.gov. Next rung within 5 to 20 years. The year the model reads for it is 2023, the year it reached the clinic; what has happened is not drawn.
When it reaches the clinic: the project's estimate
This is the one thing on this page that is a judgment rather than a record. It is already in the clinic, so the model reads a known year; the estimate below is for the rungs still above it and feeds nothing. Set 16 October 2026, a first pass awaiting an outside review.
| Rung | No earlier than | Most likely | No later than | |
|---|---|---|---|---|
| In wide use | 2028 | 2035 | 2055 |
Why. Wide use needs a form that does not require infusions and frequent scans (an under-the-skin version was approved in 2025 for maintenance), lower prices, and clinics able to give it. The likely year assumes those come together in the mid 2030s; the earliest assumes the next generation of antibodies, with fewer brain-swelling events, arrives sooner; the latest allows for the drugs staying a specialist treatment given to a small share of patients. [Note 2026-10-17, from the weekly reading of that date: the first sentence above names infusions as a bar to wide use and says the under-the-skin form was approved in 2025 for maintenance only. Since 2026-07-13 it is also approved as a starting dose (eisai-2026, the companies' own release), so that bar no longer holds. The frequent brain scans, the price and the absence of any published uptake figure stand. The years are unchanged; John may want to weigh whether the earliest and likely wide-use years (2028, 2035) should move at the next review.]
Changes to this record
- 17 October 2026, description: The effect is modest, the drug needs infusions and brain scans, and some patients bleed or swell in the brain; so it is in clinical use, not wide use. became The effect is modest, the drug needs frequent brain scans, and some patients bleed or swell in the brain; so it is in clinical use, not wide use. It has needed infusions, but on 2026-07-13 the United States regulator approved an under-the-skin weekly autoinjector as the starting dose too, so a whole course can now be given at home.. [reading 2026-10-17] 'The drug needs infusions' stopped being true on 2026-07-13, when the companies announced the United States approval of the autoinjector as a starting dose. Scans, price and the lack of uptake figures stand, so the stage stays at clinical use. Source: Ltd. and Inc., 13 July 2026.
- 17 October 2026, estimate.why: (nothing; a dated note added at the end of the reasoning; no year changed) became [Note 2026-10-17, from the weekly reading of that date: the first sentence above names infusions as a bar to wide use and says the under-the-skin form was approved in 2025 for maintenance only. Since 2026-07-13 it is also approved as a starting dose (eisai-2026, the companies' own release), so that bar no longer holds. The frequent brain scans, the price and the absence of any published uptake figure stand. The years are unchanged; John may want to weigh whether the earliest and likely wide-use years (2028, 2035) should move at the next review.]. [reading 2026-10-17] A dated note that one of the estimate's stated bars to wide use has been removed; no year changed. Source: Ltd. and Inc., 13 July 2026.
The last readings
- 17 October 2026 Left for the author
Nothing dated 2026-10-10 to 2026-10-17 bears on the wide-use test: no new regulator's record, no peer-reviewed trial report and no published uptake figure was found in the window, and the only uptake material seen was company sales guidance (Eisai's fiscal 2026 Leqembi revenue target of about 143.5 billion yen, from its 2026-05-15 earnings presentation) and a post-authorisation registry study of lecanemab-treated patients that began recruiting in mid 2026 (ClinicalTrials.gov NCT07762092), neither of which counts people treated or eligible. Two records older than the window are not in the leaf: on 2026-07-13 Eisai and Biogen announced that the United States regulator approved the under-the-skin autoinjector form of lecanemab (Leqembi Iqlik) as a starting dose, 500 mg once a week, with a United States launch planned for late 2026-08, so the whole course can now be given at home; and a Cochrane overview reported in 2026-04 (seen only in a German news report dated 2026-04-16) concluded the two antibodies offer little clinical benefit against their risks. Neither meets the wide-use test, so the verdict is flagged rather than noted or moved. Left for the author, resolved on 17 October 2026: The estimate's "why" says an under-the-skin version was approved in 2025 for maintenance only; as of 2026-07-13 the regulator has approved it for starting treatment as well, which removes the "needs infusions" condition the estimate names as a bar to wide use. I would add a dated line to the leaf's description or notes recording the 2026-07-13 approval (the Eisai and Biogen release, with the regulator's own notice still to be found), and let the author decide whether the earliest and likely wide-use years (2028, 2035) should move. The frequent brain scans and the price still stand, and no uptake figure has changed, so the stage does not move. The 2026-04 Cochrane overview was seen only through a news report and should not be logged until its own page is read. Rewriting the estimate is the author's call, and I could not open any of these pages to check them. To log in the publications log once its page has been read, as the reading's rule asks: FDA Approves LEQEMBI IQLIK (lecanemab-irmb) Subcutaneous Injection as an Initiation Dose for Early Alzheimer's Disease (Company press release, 2026-07-13; https://www.biospace.com/press-releases/fda-approves-leqembi-iqlik-lecanemab-irmb-subcutaneous-injection-as-an-initiation-dose-for-early-alzheimers-disease).source 1, source 2, source 3, source 4, source 5, source 6
What the story so far says about it
On the record
Notes
The branch's own line on what would move it asks for a kind of waste cleared throughout the body, not one organ; this leaf is one organ and one protein, and the branch's notes say so. It is on the tree because it is the first approved drug that removes an age-related protein deposit from a person and changes the course of the disease, and because the twenty years of failure before it are the best record the tree has of how long such a drug takes.
Not yet verified
These facts in the record were written from memory or from a secondary source and have not yet been checked against the paper, the regulator's record or the registry. Nothing here is presented as settled until it is cleared, by checking it and either deleting the line or correcting the record.
- That uptake of both antibodies has been slow is supported by trade coverage (2025-11-10); the patient counts (tens of thousands) and the number eligible (millions) were not found in a primary source.
- A Cochrane overview of the two Alzheimer's antibodies, reported in 2026-04 (seen only in a German news report of 2026-04-16), concluded that they offer little clinical benefit against their risks; the overview's own page was not opened, so it is not logged.