The South San Francisco biotech turning one antibody, one obscure protein, and one unfashionable disease into a Phase 3 trial - and a quietly persuasive case that big pharma might be moving slow.
The office on Haskins Way looks like any other Bay Area biotech: glass, lanyards, a coffee machine that nobody fully understands. Inside, a quiet team is running a pivotal trial that, if it works, will change the standard of care for tens of thousands of people who have been managing a bleeding disorder with IV infusions two or three times a week.
The company is Star Therapeutics. The molecule is called VGA039. The bet is that a once-monthly shot can do what twice-weekly factor infusions do today - only better, and from the comfort of a couch.
It affects an estimated one in a hundred people globally. In the United States alone, more than 50,000 patients have a confirmed diagnosis. Many more do not. The current treatments are decades old, expensive, and inconvenient: factor concentrates given through an IV, often multiple times a week, often for life.
Hemophilia, for comparison, has been getting better drugs for years. VWD has been waiting in line. Star noticed the line and decided to skip it.
Before Star, Rosenthal helped build True North Therapeutics into an $825 million sale to Bioverativ, and before that, iPierian into a $725 million BMS acquisition. Four MIT and Harvard degrees, two exits, and a habit of recognizing biology that other people miss. In 2018, he started something different.
The premise was simple, in the way the best biotech premises sound simple in retrospect: build one company around one piece of novel biology, but design that biology so it could become the source of multiple medicines, in multiple indications, through multiple subsidiaries. Star calls it a pipeline-in-a-product. Most biotechs build a pipeline. Star builds the engine that builds them.
The first two spinouts: Vega Therapeutics, focused on hematology, and Electra Therapeutics, focused on immunology. Both built around antibodies that target biology nobody else was targeting. Both quietly accumulated data while the rest of the industry was still chasing GLP-1s and CAR-Ts.
Von Willebrand factor is the protein that helps your blood clot. When it does not work, you bleed. The conventional fix is to add more of the missing factor - hence the IV infusions, twice or three times a week, forever.
VGA039 goes a different direction. Instead of replacing what is missing, it dials down a natural inhibitor of clotting called Protein S. Less brake, more grip. The result is restored clotting without giving the body an external factor at all.
The delivery is the second half of the story. VGA039 is designed for once-monthly subcutaneous injection. That is a sentence written for regulators. The translation: a small shot you give yourself, at home, once a month - instead of a needle that goes into a vein two or three times a week, often at a clinic.
First-in-class monoclonal antibody targeting Protein S, restoring clotting at the regulatory layer instead of replacing a missing factor.
Designed for once-monthly subcutaneous injection - the kind a patient can self-administer at home.
Mechanism is type-agnostic, with potential to address all major VWD subtypes plus other bleeding indications.
FDA Fast Track + Orphan Drug designation. Pivotal trial enrolling in 2025-2026.
Star has raised in waves, and each wave has been bigger than the last. The Series D in 2025 was the biggest signal yet that crossover investors think a Phase 3 readout could be a public-market event.
The Series D was co-led by Sanofi Ventures, the venture arm of one of the largest hematology franchises in the world, and Viking Global Investors, a crossover fund whose involvement typically signals a credible path to public markets. New investors included Janus Henderson, Frazier Life Sciences, and GordonMD Global Investments.
Strategics put money in when the biology is plausible. Crossovers put money in when the timing is plausible. Both did, on the same round, on the same day.
That is the line on the website, and it is mostly accurate. The more honest version: Star is trying to prove that one carefully chosen target, antibody-engineered, can carry a small company through approval - and that the same chassis can be used again, in another disease, by a sister company down the hall.
If VGA039 works, the model works. If the model works, Electra is next. And then the question becomes how many times Star can repeat the trick before someone decides it is a category.
Pull back from the boardroom and the term sheet, and the company comes into focus at the level of a single person. A teenager with type 3 VWD whose evenings are organized around an IV pole. A mother who has trained herself to find a vein because the home health nurse is unreliable. A retired teacher who has run out of patience with the routine.
For all of them, the difference between a twice-weekly infusion and a once-monthly shot is not incremental. It is structural. It is the difference between organizing your week around a bleeding disorder and not.
Back on Haskins Way, the team is preparing dosing logistics, watching the early data, and trying not to talk too loudly about a Phase 3 that has not yet read out. That part is appropriate. The hard work is still ahead. The trial is not the answer. But it is the right question, finally being asked.
Five years from now, two outcomes are possible. Either VGA039 fails - and Star will have to argue, again, that its model produces second and third shots on goal that justify a third and fourth try. Or VGA039 works - and a small company in South San Francisco will have rewritten how a common, undertreated, mostly invisible disease gets managed.