Newsletter · · Ashutosh Agarwal

Biogen's Tau Drug Misses Its Goal and Heads to Phase 3 Anyway - The Neuro & Alzheimer's Pipeline - Week of July 12, 2026

Neuroscience and Alzheimer's newsletter for the week of July 12, 2026. Ahead of AAIC, Biogen's anti-tau drug missed its Phase 2 endpoint yet advances to Phase 3, as the sell-side pivots toward IV brain-shuttle delivery and blood tests become the first diagnostic ordered.

The Neuro & Alzheimer's Pipeline

Week of July 12, 2026: Biogen's Tau Drug Misses Its Goal and Heads to Phase 3 Anyway

Two weeks ago a Voyager executive told us on a podcast that Biogen's tau drug had "just read out" and we'd see the numbers at a July conference. Well, here comes the conference, the Alzheimer's Association International Conference (AAIC), the field's biggest annual meeting, opens in London this coming Tuesday, July 14. And thanks to a very candid sell-side roundtable, we now know the punchline before the slides go up: the drug missed its main goal in the mid-stage trial, and Biogen is pushing it into a large, expensive final-stage program anyway. That is the whole story of tau in one sentence: the science everyone believes in, colliding with data that refuses to cooperate. Below, what the podcasts actually said, who said it, and why it matters for the names you follow.

TL;DR

  • Biogen's anti-tau drug missed the primary endpoint of its Phase 2 trial, yet the company is advancing it to Phase 3, full data lands Tuesday at AAIC in London. Sell-side analysts are split on whether the miss is a fatal mess or a messy-but-real proof of concept, and they flag that Biogen's spinal-injection delivery may be the real problem, not the biology. Watch Tuesday.
  • The smart-money bet is shifting toward "brain-shuttle" tau drugs you can give by IV, analysts named Denali and Arrowhead as the more interesting long-term plays versus Biogen's every-six-months spinal tap. A Sofinnova investor separately flagged Lilly's blood-brain-barrier transport deal with BioArctic, pointing the same direction.
  • Still no operator color on the marketed drugs, three weeks running with zero hard numbers on Lilly's Kisunla launch or Eisai/Biogen's Leqembi and its new under-the-skin version. What we did get: two top clinicians confirming the blood test is now the first thing they order, and a blunt UK academic explaining exactly why Britain's health service won't pay for these drugs.

What's new

The big one: Biogen's tau drug missed, and they're going to Phase 3 anyway. On Biotech Hangout (July 10), sell-side analysts Paul Matteis, Eric Schmidt and Josh Schimmer, with Matt Herper of STAT guesting (all PUNDIT/ANALYST), previewed AAIC. The headline, from Matteis: "the big thing at AAIC coming on Tuesday is Biogen is going to show full data for their anti-tau [drug]… The study missed its primary endpoint, but Biogen is moving it to phase three." (This is BIIB080, the tau antisense drug that a Voyager executive told us two weeks ago had "just read out.") The oddity that has everyone scratching their heads: the trial's main measure was a dose-response, the drug was supposed to work better at higher doses, but "it sounds like the lowest dose did the best." For a drug that works by switching off the gene that makes tau, that backwards result "doesn't really make sense," Matteis said. His theories: at higher doses you may get "idiosyncratic safety stuff" from the drug in the brain, or the delivery (a spinal injection) is just so variable patient-to-patient that the amount actually reaching the brain is all over the map. Why it moves numbers: this is tau's first real swing in a big, marketed name, and it's a miss, but a miss the company is spending heavily to chase. The stock reaction Tuesday will hinge on whether the full curves look "interesting" or "super messy."

Why the analysts still can't quit tau, and where the better bet may be. Same podcast, Matteis (PUNDIT) made the bull case for the target even as he panned the trial design: "tau has the strongest scientific rationale for a disease-modifying target in Alzheimer's. It correlates with progression. It also precedes progression… you can stage the disease based on tau aggregation. And we know the antibodies don't really work because they don't actually lower intracellular tau." That last point is the crux, the marketed amyloid antibodies clear gunk outside the cell; tau's damage is inside the neuron, which is far harder to reach. Biogen's answer is to inject the drug into the spinal fluid, which Matteis flagged as "its whole other challenge." His alternative:

"The more interesting play [is] the brain-shuttle approaches, like Denali and Arrowhead, which can be given IV… and just have a different kind of risk-benefit profile and maybe a much lower efficacy bar given ease of use."

Eric Schmidt (PUNDIT) added the cold-eyed investor framing: "the Biogen bull case has become this broader pipeline optionality thesis", meaning don't buy the stock for tau, buy it for the "lower-risk, more proximal" assets like its two lupus drugs and felzartamab. And a very human coda from Schmidt: he and Matteis "both have PTSD from Alzheimer's now, and it's just hard to have much faith in any phase two program." Why it matters: the desk consensus is drifting away from spinal-injection tau drugs toward IV "brain-shuttle" delivery, a read-through that lifts Denali and Arrowhead into the conversation and quietly pressures Biogen's approach.

A blue-chip investor lays out the "it's all a combination" thesis, and two Lilly deals to watch. On Business Of Biotech (July 6), Sofinnova partner Dr. Maha Radhakrishnan, a former Biogen and BMS drug-development executive now investing in the field (PUNDIT/investor, but an unusually operator-flavored one), argued Alzheimer's will never be a one-drug disease: "we all know that Alzheimer's is a very heterogeneous pathology… It's not amyloid alone. It's not tau alone. It's a combination of multifactors, vascular, microglia, anything else. So at the end of the day, it's going to be a combination approach." She singled out two Lilly moves as evidence the frontier is opening up: a collaboration "on the Gamma Secretase Modulator Program to really understand what a modulator could do different from… the amyloid-lowering therapy approach," and a separate deal with Sweden's BioArctic (the company behind Eisai's Leqembi) "to look at the blood-brain transport technology to bring in a new target." Why it matters: the BioArctic tie-up is the same "get the drug across the blood-brain barrier by IV" theme the sell-side flagged as the future of tau, Lilly is buying optionality on it. And "combination therapy" is bullish for the whole diagnostic-and-drug complex, because you can't combine what you can't measure.

The best plain-English defense of the amyloid drugs, from someone with no stock to sell. On The Naked Scientists Podcast (July 7), Edinburgh neuroscientist Prof. Tara Spires-Jones (OPERATOR/academic) cut through the noise on whether Leqembi and Kisunla actually work. Her answer: yes, unambiguously, "these two drugs did succeed in their primary endpoints of their Phase 3 clinical trials, so they unequivocally work to slow disease progression." She even called out a widely-shared Cochrane review that pooled every old amyloid trial together as bad science, "comparing apples and oranges." But she was equally blunt about the catch: "they're only slowing the disease progression by about 35 or 40%. So you're still getting worse, just more slowly." Add rare but real brain bleeding, brain swelling, "and rarely even death," plus a price of "tens of thousands of pounds a year per person," and you get the payer verdict in one line: the drugs are approved by the UK regulator, "but the NHS won't pay for them because of this cost-benefit issue." Why it matters: this is the cleanest steel-man of both sides you'll hear, from a credible scientist, and a concrete data point that a major national health system is walking away on cost. That is the bear case for the marketed franchises, stated without spin.

Two top clinicians confirm the blood test is now the front door. On Brain Talk | Being Patient (July 7), UCSF's Dr. Gil Rabinovici, one of the field's leading imaging and clinical experts (OPERATOR/trialist), described how diagnosis actually works now at a top center: after history, basic bloods and an MRI, "if we suspect that may be Alzheimer's disease… we actually often start with a blood test, a P-Tau 217," and only then move to a PET scan if needed. He put the accuracy bar high: blood tests can now, "with 90% accuracy, determine whether people have plaques and tangles in their brain," which he called a "game changer" that will "democratize diagnosis" because PET scans exist only in "major urban areas, academic centers." He reached for the same analogy a different clinician used two weeks ago, the amyloid antibodies as the "AZT" of Alzheimer's (the first, toxic, so-so HIV drug that nonetheless "opened the door" to the combinations that made HIV livable). And on tau specifically: "the more tau you have in the brain, the faster the progression," and where the tau sits predicts which symptoms come next. Why it matters: pTau-217 as the automatic first test is the volume thesis for blood diagnostics, and tau-PET as a prognosis tool is a distinct, sticky demand driver for the imaging names.

The debate

Does under-the-skin dosing + cheap blood tests + broadening coverage turn anti-amyloid into a multi-billion-dollar franchise, or do modest benefit, brain-bleed risk, and diagnostic bottlenecks keep uptake weak while the tau bets stay unproven?

Bull: The drugs work, a serious academic with no financial stake just said so on the record, and dismissed the loudest counter-argument (that pooled review) as bad statistics. The diagnostic plumbing is arriving fast: a blood test is now the first thing a top center orders, at "90% accuracy," cheap enough to "democratize" a diagnosis that used to require a scanner in a big city. And the science is broadening, not narrowing, Lilly is buying blood-brain-transport technology and a new-mechanism (gamma-secretase modulator) program, exactly the combination-therapy future a blue-chip investor laid out this week.

Bear: Slowing decline "by about 35 or 40%" means the patient still gets worse, and a national health service just decided that isn't worth "tens of thousands of pounds a year" plus a bleeding-and-swelling risk. Tau, the target that's supposed to be the real prize, just missed its primary endpoint in Biogen's trial, and the leading asset needs a spinal injection every six months. Even the analysts who love the tau story admit they have "PTSD" from Phase 2 Alzheimer's data and are now valuing Biogen for its lupus drugs instead. And three weeks in, not one operator will put a number on how the marketed drugs are actually selling.

Net: the week tilted the narrative toward "it's a combination disease, and the future is IV-delivered tau plus better diagnostics", but the one hard tau data point we got was a miss, and the one hard payer data point was a no. Tuesday's AAIC readout is the referee.

Stocks in play

  • BIIB (Biogen), Bull: tau has the strongest disease-modifying rationale of any AD target, and Biogen owns a dated Phase 3-bound program; "broader pipeline optionality" (two lupus drugs, felzartamab) offers lower-risk upside regardless. Bear: the tau trial missed its primary endpoint with a backwards dose-response; delivery is an every-six-months spinal injection analysts openly doubt commercially; no Leqembi launch color, again. Next catalyst: full tau data at AAIC, Tuesday July 14. (Biotech Hangout, July 10)
  • DNLI (Denali) / ARWR (Arrowhead), Bull: IV "brain-shuttle" tau delivery is where the sell-side thinks the puck is going, "a much lower efficacy bar given ease of use" versus spinal injection. Bear: still early; named as a thesis, not on the back of new data this week. Next catalyst: none dated on the podcasts. (Biotech Hangout, July 10)
  • LLY (Lilly), Bull: buying the future, a gamma-secretase modulator program and a BioArctic blood-brain-transport deal position it for the combination-therapy era; the "match vs. forest fire" amyloid-triggers-tau logic favors treating early. Bear: zero Kisunla launch color for a third straight week; the whole category faces the same 35–40% benefit-vs-cost math. Next catalyst: watch AAIC for donanemab/pipeline updates. (Business Of Biotech, July 6)
  • RHHBY (Roche), Bull: the "combination approach, brain-shuttle IV delivery" theme is squarely Roche's lane (its own trontinemab uses that concept); flagged by name as a serious player. Bear: no direct trontinemab/bepranemab coverage this week. Next catalyst: AAIC. (Business Of Biotech, July 6)
  • QTRX (Quanterix), C2N, Roche Elecsys, LabCorp/Quest, Bull: pTau-217 is now the automatic first test at a top academic center, at "90% accuracy," positioned to "democratize" diagnosis; combination therapy makes measurement even more essential. Bear: no vendor was named individually this week; reimbursement and the "who discloses a positive result" bottleneck remain unresolved. Next catalyst: AAIC diagnostic sessions. (Brain Talk, July 7)
  • LNTH (Lantheus), GEHC (GE HealthCare), Bull: tau-PET is emerging as a prognosis tool ("the more tau… the faster the progression"), a demand driver distinct from simple diagnosis. Bear: Rabinovici stressed PET is inaccessible for most patients, and blood tests are explicitly the cheaper front door, a long-run substitution risk. Next catalyst: AAIC imaging data. (Brain Talk, July 7)
  • GSK, Bull: a natural-experiment study in Wales showed the shingles vaccine cut dementia risk "up to 20%" over seven years, a wildly cheap potential prevention read-through for Shingrix if it holds. Bear: association, not proof; Spires-Jones herself was initially "quite skeptical." Purely a watch-item. (The Naked Scientists, July 7)
  • BMS / Karuna, Seaport Therapeutics, Bull: the Sofinnova partner is hunting muscarinic (M1/M4) psychiatry assets and namechecked Karuna (the KarXT/Cobenfy originator) and the newly-public Seaport as portfolio companies, a live, funded psychiatry pipeline beyond Alzheimer's. Bear: commentary, no new clinical data. (Business Of Biotech, July 6)

Read-throughs

  • Brain-shuttle / IV delivery (DNLI, ARWR, RHHBY): the clearest new theme of the week. The sell-side thinks the winning tau (and next-gen amyloid) drugs will cross the blood-brain barrier by simple IV, not spinal injection, and Lilly's BioArctic deal shows big pharma paying up for the technology. If Biogen's spinal-injection tau data disappoints Tuesday, expect this thesis to get louder. (Biotech Hangout, July 10; Business Of Biotech, July 6)
  • Blood diagnostics (QTRX, C2N, Roche, LabCorp/Quest): the thread advanced from "how is the test used" to "it's the first test used." Rabinovici's UCSF workflow now starts with pTau-217; the science backs it up, a basic-science guest on Science Straight Up (July 5), UT Southwestern's Dr. Lukasz Joachimiak (OPERATOR/academic), described the two blood markers that matter, a drop in amyloid-beta and a rise in phosphorylated tau, "pretty diagnostic" as a ratio, plus neurofilament light as a general brain-damage signal. (Brain Talk, July 7; Science Straight Up, July 5)
  • PET imaging (LNTH, GEHC): tau-PET is quietly becoming the "how fast will this progress" tool, not just a yes/no plaque scan, a research-and-clinical demand pillar that survives even as blood tests take share at the front door. (Brain Talk, July 7)
  • Payers (US and UK): no US coverage news, but a hard UK data point: the NHS will not reimburse the amyloid antibodies on cost-benefit grounds despite regulatory approval. That is the reimbursement bear case made concrete, and a reminder that approval and payment are two very different battles. (The Naked Scientists, July 7)
  • Immune / microglia targets (TREM2, complement): Spires-Jones noted that of 75+ gene variants nudging Alzheimer's risk, "the vast, vast majority… are expressed in the immune cells in the brain," not neurons, the scientific backbone for the microglia and immune-modulation bets. Early, but the rationale keeps compounding. (The Naked Scientists, July 7)
  • Vaccines (active immunization): the cheap-and-scalable dream isn't dead, Spires-Jones is still studying brains from people given an amyloid vaccine and sees benefits "even 14 years later," though the field moved to expensive antibodies over autoimmune-risk fears. A long-run structural watch-item. (The Naked Scientists, July 7)
  • Huntington's (Skyhawk): flagged but skipped, Biotech Hangout had Skyhawk's Huntington's data on the docket and chose to spend the time on AAIC instead. On the radar, no detail. (Biotech Hangout, July 10)
  • Infusion centers / specialty pharmacy (OPCH): no coverage this week.

What changed vs last week

Last week we flagged Biogen's tau drug BIIB080 as a dated "July conference" catalyst, courtesy of Voyager's Al Sandrock. This week we learned what's actually in the box: a primary-endpoint miss that Biogen is chasing into Phase 3 anyway, with full data this Tuesday at AAIC in London. The tau story got richer (a blue-chip investor's combination-therapy thesis, Lilly's two frontier deals, the sell-side's pivot toward IV brain-shuttle delivery) but the tau data got worse. The diagnostics thread advanced a notch, from "is the blood test good enough" to "it's the first test we order," confirmed by a leading UCSF clinician at 90% accuracy. The AZT-of-Alzheimer's analogy resurfaced yet again, now from Rabinovici. And a genuinely new bear brick landed: the UK's NHS won't pay for these drugs, stated plainly by an academic with no dog in the fight. What did not change: still zero operator numbers on Kisunla starts, Leqembi/IQLIK persistence, or US payer friction, a three-week blank on the metrics that actually move the marketed names. AAIC next week should finally break that silence.