Anti-Tau Immunotherapy Programs

Anti-Tau Immunotherapy Programs

Overview

Anti-Tau Immunotherapy Programs

Overview

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Anti-Tau Immunotherapy Programs</th>
</tr>
<tr>
<td class="label">Antibody</td>
<td>Company</td>
</tr>
<tr>
<td class="label">JNJ-63742057</td>
<td>Janssen</td>
</tr>
<tr>
<td class="label">Lu AF87908</td>
<td>Lundbeck</td>
</tr>
<tr>
<td class="label">ACI-35</td>
<td>AC Immune</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">N-terminal antibodies</td>
<td>Block extracellular tau</td>
</tr>
<tr>
<td class="label">Mid-region antibodies</td>
<td>Bind intracellular tau</td>
</tr>
<tr>
<td class="label">Phospho-tau antibodies</td>
<td>Target pathological tau</td>
</tr>
<tr>
<td class="label">Active vaccines</td>
<td>Induce anti-tau antibodies</td>
</tr>
<tr>
<td class="label">Small molecules</td>
<td>Inhibit aggregation</td>
</tr>
</table>

Anti-tau immunotherapy represents one of the most actively pursued disease-modifying strategies for Alzheimer's disease and related tauopathies. These approaches aim to target pathological tau protein through monoclonal antibodies or active vaccination, with the goal of clearing existing tau pathology and preventing the spread of tau pathology throughout the brain["@tau_immunotherapy_overview"][@tau_antibody_mechanisms].

Despite significant investment and numerous clinical trials, anti-tau immunotherapy programs have largely failed to demonstrate clinical efficacy. However, the trials have generated important insights into tau biology, biomarkers, and the challenges of treating neurodegenerative diseases. This page provides an overview of the various anti-tau antibody and vaccine programs that have been or are currently being developed.

Tau Biology and Therapeutic Target

Tau Protein Normal Function

Tau is a microtubule-associated protein encoded by the MAPT gene. In its normal state, tau plays essential roles in neuronal biology:

• Microtubule stabilization: Tau binds to microtubules and promotes their polymerization
• Axonal transport: Facilitates transport of vesicles and organelles along axons
• Synaptic function: Modulates synaptic plasticity and neuronal signaling
• Neuronal health: Supports neuronal viability through various mechanisms

Tau Pathological Transformation

In Alzheimer's disease and tauopathies, tau undergoes pathological transformation:

Hyperphosphorylation:

• Abnormal phosphorylation at multiple sites (>80 potential sites)
• Reduces tau's ability to bind microtubules
• Promotes tau misfolding and aggregation

• Formation of paired helical filaments (PHFs)
• Assembly into neurofibrillary tangles (NFTs)
• Progressive accumulation correlates with cognitive decline

• Tau propagates between neurons in a prion-like manner
• Pathological tau appears in connected brain regions over time
• Forms the basis for staging of tau pathology (Braak staging)

Therapeutic Rationale

Anti-tau immunotherapy is based on several hypotheses:

Anti-Tau Monoclonal Antibodies

N-Terminal Targeting Antibodies

The largest class of anti-tau antibodies target the N-terminal region of tau, based on the hypothesis that N-terminal antibodies can intercept extracellular tau and prevent propagation.

Gosuranemab (BIIB092)

Developer: Biogen

Mechanism:

• Humanized IgG1 targeting amino acids 6-23 of tau
• Binds to extracellular tau released from neurons
• Intended to prevent tau propagation

• Phase I: Completed, showed safety and target engagement
• Phase II TANGO trial: Did not meet primary endpoints in AD
• Phase II in PSP: Did not meet primary endpoints
• Status: Discontinued

• Target engagement demonstrated (CSF tau reductions)
• No clinical benefit despite biomarker effects
• Highlighted disconnect between biomarker engagement and clinical outcomes

Tilavonemab (ABBV-8E12)

Developer: AbbVie

Mechanism:

• Humanized antibody targeting N-terminal tau
• Similar mechanism to gosuranemab

• Phase I: Completed successfully
• Phase II in PSP: Did not meet primary endpoints
• Phase II in AD: Did not meet primary endpoints
• Status: Discontinued

• Autopsy study confirmed brain penetration and target engagement
• Mechanism of action validated but insufficient clinical efficacy
• Suggested that earlier intervention might be needed

Semorinemab

Developer: Roche

Mechanism:

• Humanized antibody targeting the mid-region of tau
• Different epitope than N-terminal antibodies

• Phase II trials in AD
• Results did not meet primary endpoints
• Status: Discontinued

• Mid-region targeting did not provide advantage
• Consistent with failures of other anti-tau approaches

Other N-Terminal Antibodies

Approaches in Development

Different Epitopes:

• Mid-region targeting
• C-terminal targeting
• Phospho-tau specific antibodies (e.g., targeting pSer396/404)

• Antibody engineering for improved brain penetration
• Bispecific antibodies
• Trojan horse approaches

• Anti-tau + anti-amyloid combination
• Anti-tau + small molecule combinations

Tau Vaccination Approaches

Active vaccination approaches aim to stimulate the patient's own immune system to produce anti-tau antibodies[@tau_vaccine_approaches]:

ACI-35 (Lipidated Phospho-Tau Vaccine)

Developer: AC Immune / Janssen

Mechanism:

• Liposome-based vaccine containing phosphorylated tau peptides
• Elicits antibodies targeting pathological phosphorylated tau
• Designed to specifically target disease-relevant tau forms

• Phase I/II trials in early AD
• Showed safety and immunogenicity
• Antibodies recognized pathological tau species
• Status: Ongoing development

• Could provide continuous antibody production
• Lower cost than repeated antibody infusions
• Phospho-tau specificity may improve safety

Other Vaccine Approaches

• AADvac1 (Axon Neuroscience): Active vaccine targeting pathological tau
• ABV-5: Various approaches in early development
• DNA-based vaccines: Alternative delivery methods

• Immune response variability
• Need for adjuvant to enhance response
• Risk of autoimmune reactions
• Antibody titer maintenance

Biomarkers in Anti-Tau Trials

Tau PET Imaging

Tau PET has become essential for anti-tau clinical trials[@tau_pet_biomarkers]:

Tracers:

• [^18F]flortaucipir (AV-1451): Most widely used
• [^18F]PI-2620: Alternative tracer
• Others in development

• Patient selection (tau-positive subjects)
• Baseline pathology assessment
• Monitoring tau accumulation during treatment
• Correlation with clinical outcomes

• Off-target binding in certain brain regions
• Limited sensitivity to early tau changes
• Cannot distinguish functional effects from mere binding

Cerebrospinal Fluid Biomarkers

Measures:

• Total tau (t-tau)
• Phosphorylated tau (p-tau181, p-tau217)
• Tau oligomers
• Neurofilament light (NfL) for neurodegeneration

• Many anti-tau antibodies reduce CSF tau
• Biomarker changes do not consistently predict clinical benefit
• Disconnect between target engagement and clinical outcomes

Blood Biomarkers

Emerging blood-based biomarkers:

• p-tau217, p-tau181: Highly specific for AD pathology
• NfL: Neurodegeneration marker
• Tau fragments: Potential specific markers

Challenges and Lessons Learned

Why Have Anti-Tau Programs Failed?

Multiple factors likely contribute to the lack of clinical efficacy:

Timing:

• Patients may have too much established tau pathology
• Need to treat earlier in disease course

• Antibody brain penetration may be insufficient
• May not reach all relevant tau species

• Multiple tau strains with different properties
• Different forms of pathological tau (soluble, insoluble)
• Tau may not be primary driver of neurodegeneration in established disease

• Tau may be downstream of other processes (e.g., amyloid)
• Neuronal loss may be too advanced to reverse

What Have We Learned?

Biomarkers:

• Target engagement can be demonstrated
• Biomarker changes do not reliably predict clinical benefit
• Need better biomarkers for patient selection and response

• Earlier disease stages may be needed
• Tau-positive patient selection is important
• Longer trials may be needed

• Anti-tau alone may be insufficient
• May need to address amyloid first
• Multiple targets may be necessary

Future Directions

Active Programs

Despite failures, several programs continue:

• ACI-35 vaccine: Phospho-tau specific approach
• JN-63742057: Different epitope targeting
• Combination approaches: Anti-tau + anti-amyloid

New Mechanisms

Tau Degradation:

• PROTAC approaches (protein degradation)
• Autophagy-inducing approaches

• Acetylation modulators
• Phosphorylation inhibitors

• Antisense oligonucleotides targeting MAPT
• RNA interference approaches

Precision Medicine Approaches

• Tau strain identification
• Personalized targeting based on pathology
• Biomarker-driven patient selection

Comparison of Anti-Tau Approaches

See Also

• [Tau Protein](/proteins/tau)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• [Tauopathies](/diseases/tauopathies)
• [Gosuranemab](/therapeutics/gosuranemab)
• [Tilavonemab](/therapeutics/tilavonemab)
• [Semorinemab](/therapeutics/semorinemab)

References

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