BIIB080 (formerly known as MAPTRx) is an antisense oligonucleotide (ASO) therapeutic developed by Biogen in collaboration with Ionis Pharmaceuticals that targets the MAPT gene to reduce production of tau protein. This novel approach aims to treat Progressive Supranuclear Palsy (PSP) and other tauopathies by directly addressing the underlying cause of tau pathology rather than just managing symptoms.
BIIB080 is a gapmer antisense oligonucleotide designed to bind to MAPT messenger RNA (mRNA) and induce RNase H-mediated degradation. This reduces the translation of tau protein from the MAPT gene, thereby lowering total tau production in the brain.
The first-in-human study evaluated safety, tolerability, and pharmacokinetics of BIIB080 in healthy volunteers and patients with Alzheimer's disease.
Key Findings:
A study specifically in patients with PSP (Richardson syndrome and other variants) to evaluate:
Study Design Elements:
New exploratory analyses from the Phase 1b long-term extension study in Alzheimer's disease were published in Nature Aging (February 2026)[1], providing additional evidence for BIIB080's disease-modifying potential:
Key Findings:
The convergence of biomarker reduction (CSF tau, tau PET) with clinical outcome trends provides encouraging evidence for BIIB080's potential in PSP and other tauopathies.
| Approach | Mechanism | Stage | Advantages | Limitations |
|---|---|---|---|---|
| BIIB080 (ASO) | Reduce tau production | Phase 1/2 | Direct targeting of root cause | Invasive delivery |
| Anti-tau antibodies | Passive immunization | Phase 3 | Less invasive | Peripheral clearance |
| Tau aggregation inhibitors | Prevent fibril formation | Phase 1/2 | Oral small molecule | Efficacy unclear |
| Microtubule stabilizers | Preserve neuronal transport | Phase 2 | Targets downstream effects | Limited specificity |
Tau is a microtubule-associated protein encoded by the MAPT (Microtubule-Associated Protein Tau) gene located on chromosome 17q21.31[2]. In the healthy brain, tau functions to stabilize microtubules, which are essential for axonal transport and neuronal connectivity. Six tau isoforms are expressed in the adult human brain, ranging from 352 to 441 amino acids, generated through alternative splicing of exon 2, exon 3, and exon 10.
The tau protein contains multiple phosphorylation sites (approximately 85 serine/threonine residues and 5 tyrosine residues) that regulate its binding to microtubules. Under physiological conditions, tau phosphorylation is tightly regulated by a balance between kinases (such as GSK-3β, CDK5, and MAPK) and phosphatases (including PP2A). This dynamic regulation allows tau to respond to cellular signals and maintain microtubule stability[3].
In Alzheimer's disease and related tauopathies, tau becomes hyperphosphorylated and aggregates into neurofibrillary tangles (NFTs), neuropil threads, and dystrophic neurites. This pathological transformation involves:
The progression of tau pathology follows a predictable pattern in AD, beginning in the entorhinal cortex and hippocampus (Braak stages I-III) before spreading to adjacent cortical regions (Braak stages IV-VI). This hierarchical spread correlates with cognitive decline[3:1].
Tau pathology exhibits prion-like properties, with aggregated tau capable of spreading between neurons and brain regions[3:2]. This propagation occurs through:
Understanding these propagation mechanisms has important implications for therapeutic development, as interventions that block tau transmission could potentially slow disease progression.
Antisense oligonucleotides are single-stranded DNA analogs that can modulate gene expression through multiple mechanisms[4]. BIIB080 employs RNase H-dependent degradation, which requires:
BIIB080 utilizes a "gapmer" design consisting of a central DNA "gap" flanked by modified RNA nucleotides[5]:
This 5-10-5 gapmer configuration represents the optimal balance between RNase H activation and target binding affinity established through years of ASO development.
The delivery of ASOs to the central nervous system presents unique challenges[6]. BIIB080 uses intrathecal administration to bypass the blood-brain barrier:
Alternative approaches under investigation include:
The first-in-human study of BIIB080 employed a classic dose-escalation design to evaluate safety, tolerability, and pharmacokinetics:
Part A (Healthy Volunteers):
Part B (Alzheimer's Disease Patients):
Dose Levels Evaluated:
The ongoing Phase 1b/2a study (NCT04144191) specifically enrolls patients with PSP:
Study Population:
Study Design:
Endpoints:
The 2026 Nature Aging publication reported 18-month follow-up data from the Phase 1b long-term extension[1:1]:
Cognitive Outcomes:
Biomarker Correlations:
Progressive Supranuclear Palsy (PSP) is a 4R tauopathy characterized by:
Unlike AD where 3R and 4R tau isoforms are both present in NFTs, PSP predominantly involves 4R tau isoforms. The tau aggregates in PSP exhibit distinct morphological characteristics:
This isoform specificity has implications for therapeutic targeting, as interventions that reduce total tau production (like BIIB080) would be expected to reduce all tau forms.
PSP represents a significant unmet medical need:
An effective tau-reduction therapy could address the fundamental pathological driver of PSP, potentially slowing or halting disease progression.
The tau targeting field has evolved to include multiple therapeutic modalities:
| Therapeutic Category | Examples | Mechanism | Development Stage |
|---|---|---|---|
| ASOs | BIIB080 | Reduce tau production | Phase 1/2 |
| Anti-tau antibodies | Gosuranemab, Tilavonemab | Clear extracellular tau | Phase 2 |
| Tau aggregation inhibitors | LMTM, methylene blue | Prevent fibril formation | Phase 3 |
| Microtubule stabilizers | Davunetide, BMS-986241 | Preserve tau function | Phase 2 |
| Kinase inhibitors | Tau-aggregation inhibitors | Reduce phosphorylation | Preclinical |
Comparing ASO and antibody approaches reveals distinct profiles:
ASO Advantages:
Antibody Advantages:
Multiple companies are developing tau-targeting ASOs:
The FDA's accelerated approval pathway may be relevant for BIIB080 in PSP:
Biomarker-Based Approval:
Regulatory History:
Confirmatory trials for PSP would likely require:
PSP may qualify for orphan drug designation:
Future studies may explore combination strategies:
Continued biomarker development is critical:
Preventive intervention in at-risk populations:
Development timeline considerations:
Intrathecal administration requires lumbar puncture, which may limit patient access and compliance. Research into alternative delivery methods including focused ultrasound for BBB opening is ongoing.
While CSF tau reduction is a promising pharmacodynamic marker, validation of clinical endpoints remains necessary to confirm disease modification.
Early intervention may be critical - treating patients before extensive tau accumulation could yield better outcomes.
Exploratory analyses of clinical outcomes from the BIIB080 phase 1b study in mild Alzheimer's disease. 2026. ↩︎ ↩︎
MAPT gene and tau isoforms in neurodegenerative disease. 2024. ↩︎
Tau biology and propagation in neurodegenerative disease. 2023. ↩︎ ↩︎ ↩︎
Antisense oligonucleotides for neurological disorders. 2024. ↩︎
RNase H-mediated antisense oligonucleotide cleavage mechanisms. 2024. ↩︎