Gilead Just Broke Up with Assembly Bio's Hepatitis B Drug

That's like going to a buffet, loading up on the herpes and hepatitis delta stations, and walking right past the hepatitis B carving station without even picking up a plate. It's a deliberate choice, and it tells you something about where Gilead thinks the value is.

Why Gilead Might Be Cooling on HBV

Gilead isn't abandoning hepatitis B entirely. The company still sells Vemlidy (tenofovir alafenamide), its bread-and-butter HBV treatment. And at the 2025 EASL Congress, Gilead showed off early Phase 1a data for a therapeutic vaccine approach to achieving a functional cure.

The keyword there is "functional cure," which means getting the virus suppressed permanently so patients can stop taking pills. That's the holy grail. And Gilead appears to be betting that a vaccine approach, not another small-molecule antiviral like ABI-4334, is the way to get there.

It's a strategic pivot. Core inhibitors are useful tools, but they're incremental improvements on existing treatments. Gilead seems to be saying: we don't need another wrench. We need a whole new toolbox.

The Elephant in the Room: GSK

There's another reason Gilead might be rethinking its HBV playbook. GSK just changed the game.

GSK's bepirovirsen, an antisense oligonucleotide (a tiny molecule designed to silence the virus's genetic instructions), met its primary endpoints in not one but two Phase III trials. The B-Well 1 and B-Well 2 studies enrolled roughly 1,800 patients across 29 countries, and the drug achieved statistically significant rates of functional cure when added to standard antiviral therapy. GSK is planning global regulatory filings starting in Q1 2026.

If bepirovirsen gets approved, it would become the first finite treatment regimen for hepatitis B: a roughly 24-week course instead of lifelong pills. That changes the competitive math for everyone else in the space. Suddenly, your early-stage core inhibitor isn't competing against other experimental drugs. It's competing against a potential commercial product with Phase III data behind it.

For Gilead, investing further in ABI-4334 may have started to look like bringing a slingshot to a gunfight.

What Happens to Assembly Now?

Assembly Biosciences says it will seek a new partner before advancing ABI-4334 further. The company isn't in immediate financial trouble; its cash runway extends into 2028, thanks partly to that recent Gilead equity infusion. And the rest of the Gilead partnership remains intact, covering herpes and hepatitis delta programs.

Wall Street analysts still have a median price target of $45 on Assembly's stock (from 11 analysts), against a recent close of about $28.46. That implies significant upside, though it's worth noting the stock has bounced around quite a bit lately.

The bull case here centers on Assembly's broader pipeline. ABI-6250, the hepatitis delta entry inhibitor, has Phase 1a clearance and is targeting Phase 2 by late 2026. The herpes programs now have Gilead's full muscle behind them. ABI-4334 was one piece of a larger puzzle, and losing Gilead's backing on it hurts but doesn't break the company.

The Bigger Picture

Gilead's decision is really a signal about where the hepatitis B field is heading. The days of incremental antivirals are giving way to bolder bets: therapeutic vaccines, gene editing (Precision BioSciences has an FDA-cleared Phase I program targeting the virus's DNA directly), and antisense therapies like GSK's bepirovirsen.

For the roughly 254 million people living with chronic hepatitis B worldwide, that's actually encouraging news. The ambition level is rising. Companies aren't settling for "slightly better suppression." They want a cure.

But for Assembly Biosciences, the immediate reality is more mundane: they need to find someone willing to write a check for an early-stage drug in a space where the bar just got raised considerably. In biotech, timing is everything, and Gilead's exit suggests the window for core inhibitors as standalone plays may be closing.

The partnership isn't dead. But the hepatitis B chapter of it is over, and the next one won't write itself.