Anti-Amyloid & Disease-Modifying Therapies

Anti-amyloid monoclonal antibodies — lecanemab, donanemab, and the (since-withdrawn) aducanumab — represent the first disease-modifying treatments for Alzheimer disease and a fundamental shift in AD pharmacotherapy. By targeting and clearing β-amyloid plaques, these agents slow the rate of cognitive decline by approximately 25-35% in early symptomatic AD over 18 months. They have transformed early AD treatment but introduce new risks (ARIA — amyloid-related imaging abnormalities), require infrastructure for safe administration, and have prompted complex conversations about benefit, risk, and patient selection. This page covers the current anti-amyloid landscape, mechanism, clinical use, and emerging anti-tau therapies.

Amyloid Biology and Disease

  • Amyloid precursor protein (APP) cleaved by β-secretase + γ-secretase → Aβ peptides (Aβ40, Aβ42).
  • Aβ42 is the more pathogenic species; aggregates into oligomers, fibrils, plaques.
  • Plaques and oligomers cause synaptic dysfunction, neuroinflammation, neuronal loss.
  • Apolipoprotein E (APOE) ε4 allele: major risk factor; ε4/ε4 homozygotes have substantially elevated AD risk.
  • APP/PSEN1/PSEN2 mutations: rare autosomal dominant familial AD.

Anti-Amyloid Monoclonal Antibodies

Lecanemab (Leqembi / Leqembi IQLIK)

  • Mechanism: humanized IgG1 monoclonal antibody targeting soluble Aβ protofibrils.
  • Initiation dosing: 10 mg/kg IV every 2 weeks (Leqembi).
  • Maintenance dosing: Leqembi IQLIK (subcutaneous formulation) was FDA-approved in 2025 for maintenance therapy after initial IV induction — given as a weekly SC injection rather than continuing biweekly IV infusions. This has changed the long-term treatment workflow and reduced infusion-center burden.
  • Indication: early symptomatic AD (MCI due to AD or mild AD dementia) with biomarker-confirmed amyloid pathology.
  • Pivotal trial (CLARITY-AD): 27% slowing of cognitive decline (CDR-SB) over 18 months.
  • FDA-approved 2023; first traditional FDA approval (Aducanumab was accelerated approval). Subcutaneous maintenance approved 2025.

Donanemab (Kisunla)

  • Mechanism: humanized IgG1 monoclonal antibody targeting pyroglutamate-modified Aβ in plaques.
  • Dosing: 700 mg IV every 4 weeks for 3 doses, then 1400 mg every 4 weeks until amyloid clearance confirmed by PET → can discontinue.
  • Indication: similar to lecanemab.
  • Pivotal trial (TRAILBLAZER-ALZ2): 35% slowing of cognitive decline (iADRS).
  • FDA-approved 2024.
  • Unique feature: can discontinue after amyloid clearance (typically 12-18 months).

Aducanumab (Aduhelm) — Withdrawn

  • Removed from market by manufacturer 2024 due to commercial failure.
  • Historic significance as first FDA-approved anti-amyloid therapy (2021).

Patient Selection

Inclusion Criteria

  • Mild cognitive impairment due to AD OR mild dementia due to AD.
  • Biomarker confirmation of amyloid pathology is required. CSF Aβ42/40 ratio or amyloid PET remain the established confirmatory tests. Plasma biomarkers (especially p-tau217 and the p-tau217 ratio) are increasingly used for triage and in selected clinical workflows, but should not be presented as a blanket interchangeable substitute for CSF or PET without local validation and protocol — refer to local center practice.
  • MMSE typically 22-30 (mild range).
  • Stable on other AD therapies (donepezil, memantine).
  • Cognitive impairment well-documented.

Exclusion / Caution

  • Moderate-severe dementia.
  • Significant other neurologic disease.
  • Severe cerebrovascular disease.
  • Microhemorrhages (>4 on baseline MRI).
  • Anticoagulation (relative contraindication; ICH risk).
  • Multiple prior cerebral microhemorrhages.

ARIA (Amyloid-Related Imaging Abnormalities)

ARIA-E (Edema)

  • Vasogenic edema in cortex; usually asymptomatic.
  • ~12-13% incidence with lecanemab; ~24% with donanemab.
  • Higher rate in APOE ε4 homozygotes.
  • Symptoms (when present): headache, confusion, visual changes, seizures.
  • Management: temporary discontinuation; usually resolves within weeks.

ARIA-H (Hemorrhage)

  • Microhemorrhages; superficial siderosis.
  • ~17% lecanemab; ~31% donanemab.
  • Most asymptomatic.
  • Rare severe intracerebral hemorrhage.

ARIA Management

  • Baseline brain MRI required (within 1 year before initiation).
  • Lecanemab surveillance MRI: per the FDA safety communication (December 2024), obtain MRI before the 3rd, 5th, 7th, and 14th infusions — this is earlier and more frequent than the original label schedule and reflects observed early ARIA-E timing.
  • Donanemab surveillance MRI: per donanemab protocol (typically before doses 2, 3, 4, and 7).
  • If ARIA present:
    • Asymptomatic, mild radiographic ARIA: usually continue with closer follow-up MRI.
    • Moderate symptoms or moderate radiographic ARIA: hold dose; recheck MRI.
    • Severe symptoms or severe radiographic ARIA: discontinue.
  • APOE ε4 homozygotes: higher ARIA risk; FDA labeling explicitly notes this and recommends discussion before initiation.

APOE Testing

  • APOE ε4/ε4 homozygotes: highest ARIA risk; FDA labeling notes.
  • APOE ε4 heterozygotes: intermediate risk.
  • Discussion of risk and shared decision-making.
  • Genotyping increasingly considered before therapy.

Infrastructure Requirements

  • IV infusion capability.
  • Brain MRI access for surveillance.
  • Standardized protocols for ARIA detection and management.
  • Emergency response capability for severe events.
  • Trained staff for infusion reactions.
  • Multidisciplinary team (neurology, radiology, pharmacy, nursing).

Cost and Access

  • Annual drug cost: ~$26,000 (lecanemab); similar for donanemab.
  • Plus infusion, MRI surveillance, monitoring costs.
  • CMS coverage for FDA-approved use under traditional approval pathway.
  • Coverage for biomarker testing variable.
  • Emerging plasma biomarkers may reduce cost barriers.

Emerging and Investigational

Other Anti-Amyloid Approaches

  • Solanezumab: failed in trials.
  • Gantenerumab: failed in trials.
  • BACE inhibitors: largely failed (CV safety issues, cognitive worsening).
  • γ-Secretase modulators: investigational.
  • Vaccines (active immunization): early-phase trials.

Anti-Tau Approaches

  • Anti-tau antibodies in trials (tilavonemab, semorinemab, zagotenemab — most have failed).
  • Tau-targeted ASOs in early trials.
  • Tau aggregation inhibitors: in development.
  • Rationale: tau correlates with cognitive decline better than amyloid.

Other Targets

  • Anti-inflammatory approaches.
  • NLRP3 inflammasome modulators.
  • Multiple gene therapy approaches in development.
  • Microbiome modulation.

Combination Approaches

  • Anti-amyloid + anti-tau: emerging concept.
  • Anti-inflammatory + amyloid: emerging.

Practical Clinical Considerations

  • Realistic expectations: SLOWING decline, not reversal or cure.
  • ~25-35% slowing of cognitive trajectory over 18 months.
  • Functional benefit may be subtle.
  • Best in early disease.
  • Lifelong treatment uncertain (donanemab discontinuation after amyloid clearance is a novel model).
  • Shared decision-making essential — discuss benefit, risk, cost, infrastructure burden.

🔍 Did You Know?

The recognition that APOE ε4 homozygotes are at substantially higher risk of ARIA has transformed the patient selection conversation in anti-amyloid therapy. APOE ε4 homozygotes — approximately 2% of the population — have the highest baseline risk for AD (~10-15× compared to ε3/ε3) but also paradoxically the highest risk of ARIA on anti-amyloid therapy. In CLARITY-AD, ARIA-E occurred in ~5% of APOE ε4 non-carriers but ~32% of APOE ε4 homozygotes; ARIA-H also higher. The mechanism likely involves the more severe baseline cerebral amyloid angiopathy in APOE ε4 carriers — clearance of vascular amyloid by anti-amyloid antibodies destabilizes vessel walls. The clinical implications are profound: APOE ε4 testing should be discussed before anti-amyloid therapy, particularly for homozygotes who face a genuinely different risk-benefit calculation. The FDA labeling for lecanemab and donanemab specifically addresses APOE ε4 status and emphasizes informed consent. For APOE ε4 homozygotes considering anti-amyloid therapy, the conversation must include: (1) substantially higher ARIA risk, (2) need for closer MRI monitoring, (3) careful baseline assessment for microhemorrhages, (4) realistic expectations about benefit-risk. Some specialists are hesitant to recommend anti-amyloid therapy to APOE ε4 homozygotes given the higher risk; others proceed with intensive monitoring. The lesson generalizes: pharmacogenomic risk stratification is becoming standard in modern AD care, and personalized medicine in dementia is rapidly maturing. For practicing neurologists, APOE testing in patients considering anti-amyloid therapy is increasingly standard, alongside biomarker confirmation of amyloid pathology.

Pitfalls and Pearls

  • Lecanemab (Leqembi): anti-Aβ protofibrils; IV every 2 weeks; 27% slowing.
  • Donanemab (Kisunla): anti-Aβ plaque; IV every 4 weeks; 35% slowing; can discontinue after amyloid clearance.
  • Aducanumab (Aduhelm): withdrawn from market.
  • Patient selection: MCI or mild AD with biomarker-confirmed amyloid.
  • ARIA-E (edema): ~12-13% lecanemab, ~24% donanemab.
  • ARIA-H (hemorrhage): ~17% lecanemab, ~31% donanemab.
  • APOE ε4 homozygotes: higher ARIA risk; discuss carefully.
  • APOE testing: increasingly standard before anti-amyloid therapy.
  • Surveillance MRI: required protocol; ARIA detection.
  • Baseline MRI: required; microhemorrhages or stigmata of CAA may exclude.
  • Anticoagulation: relative contraindication.
  • Infrastructure: IV infusion, MRI access, multidisciplinary team needed.
  • Cost: ~$26,000/year drug + infrastructure costs.
  • Expectations: slowing of decline, not reversal; modest individual benefit.
  • Biomarker confirmation: CSF, amyloid PET, or plasma; required.
  • Continue symptomatic AD meds: AChE inhibitors, memantine; do not stop.
  • Anti-tau therapy: investigational; promising but not yet approved.

References

  1. van Dyck CH, Swanson CJ, Aisen P, et al. Lecanemab in early Alzheimer’s disease (CLARITY-AD). N Engl J Med. 2023;388(1):9-21.
  2. Sims JR, Zimmer JA, Evans CD, et al. Donanemab in early symptomatic Alzheimer disease: the TRAILBLAZER-ALZ 2 randomized clinical trial. JAMA. 2023;330(6):512-527.
  3. Cummings J, Apostolova L, Rabinovici GD, et al. Lecanemab: appropriate use recommendations. J Prev Alzheimers Dis. 2023;10(3):362-377.
  4. Cogswell PM, Barakos JA, Barkhof F, et al. Amyloid-related imaging abnormalities with emerging Alzheimer disease therapeutics: detection and reporting recommendations. AJNR Am J Neuroradiol. 2022;43(9):E19-E35.
  5. Honig LS, Sabbagh MN, van Dyck CH, et al. Updated safety results from phase 3 lecanemab study in early Alzheimer’s disease. Alzheimers Res Ther. 2024;16(1):105.
  6. Selkoe DJ, Hardy J. The amyloid hypothesis of Alzheimer’s disease at 25 years. EMBO Mol Med. 2016;8(6):595-608.