The team behind Leyden Labs has done this before, which is most of why it just raised €40 million with the Gates Foundation in the room. The Leiden company is a direct descendant of Crucell, the Dutch vaccine maker that Johnson and Johnson bought for roughly €1.75 billion in 2011, and its lead antibody, CR9114, was discovered more than a decade ago by chief scientific officer Jaap Goudsmit, who calls it the most broadly neutralising anti-influenza antibody identified to date. The new money is a bet that the right place to use an antibody like that is not the bloodstream, where vaccines do their work and then wait, but the nose, where the virus actually arrives.

The round brings together the European Innovation Council Fund, the Dutch state investor Invest-NL with a €10 million cheque, the Gates Foundation Strategic Investment Fund and Singapore’s ClavystBio, a syndicate the company says spans Europe, the United States and Asia. It follows Leyden’s selection for the EIC’s STEP Scale Up programme, the instrument Brussels uses to back companies it considers important for European technological readiness, and it adds Ben Verwaayen, the former chief executive of BT and Alcatel-Lucent, to the supervisory board. This is not the company’s first trip to the well: it raised €30 million from the EIC Fund and Invest-NL in October 2025, a $70 million Series B earlier that year, and a €20 million European Investment Bank venture-debt facility before that, taking total backing past €300 million since its founding in 2020.

The thesis is about geography, the geography of your airway

The science is easier to grasp as a question of location than of chemistry. Injected vaccines and systemic antibodies generate protection in the body broadly, and then rely on the immune system to meet a virus that has usually already established itself. Airborne viruses, influenza and coronaviruses among them, enter through the nose and mouth, so Leyden’s Mucosal Protection Platform delivers broadly protective antibodies straight to the respiratory mucosa, the tissue at that first point of contact. The antibodies are designed to target conserved regions that whole viral families share, the parts that mutate slowly, so the protection is meant to keep working even as a given strain evolves and slips past the immunity left by last year’s shot.

The lead programme, PanFlu, is built around CR9114, repositioned from a conventional systemic antibody into something sprayed locally. Leyden’s argument is that systemic antibody prophylaxis for influenza has always foundered on dose, cost and logistics, and that concentrating the antibody at the site of entry lowers the practical barriers to giving it to people before a season rather than after an infection. The approach is pitched as particularly relevant for the immunocompromised, the people for whom a vaccine is least reliable precisely because it asks for a working immune response the patient may not have. A spray that does not depend on the body mounting its own defence is, for that group, a different category of protection.

What Leyden has so far is safety, not proof of prevention, and the company is direct about the distinction. Across two Phase 1 trials in 143 healthy volunteers, intranasal dosing was found safe and tolerable and the antibody was detected locally in the nasal cavity after administration. None of that data measured whether the spray actually stops anyone from getting sick. The efficacy case still rests on preclinical and non-human-primate work, which leaves the only question that matters, prevention of infection in humans, as the next test the programme has to pass.

A field that suddenly has money and rivals

Leyden is no longer alone in this corner, which is usually a sign the corner is real. London’s RQ Bio just raised $115 million in a Series A for a long-acting antibody designed to protect against influenza for an entire season after a single dose, and the strategic money is moving too: MSD’s $9.2 billion acquisition of Cidara was driven in part by its late-stage flu-prevention candidate, while Moderna is pushing an mRNA alternative to traditional flu vaccines. The nasal niche specifically is filling up, with NorthLinks Bio launching on $34 million from RA Capital to advance a host-directed intranasal antiviral. Competition validates the thesis and crowds the eventual market in the same breath.

The Gates Foundation’s presence points at the part of the round that is not really about commercial return. Its investment is tied to access strategies for low- and middle-income countries, the places where a self-administered spray that needs no cold-chain heroics and no functioning immune system would matter most, and where the economics of a premium antibody usually mean it never arrives. That global-access angle is doing real work in the syndicate, pairing patient public capital from the EIC and Invest-NL with a foundation whose interest is reach rather than margin, which is a coalition European biotech assembles more often than the continent gets credit for.

So the money is in, the safety data is in, and the team has the lineage to be taken seriously by exactly the investors who would know. What is not in is the only figure that decides the company: whether antibodies sprayed into a nose can stop a virus that has already arrived there. Leyden has spent six years and more than €300 million getting to the edge of that answer. The next trials are where it finds out if the geography was the insight or just an elegant place to spend the money.