Sanofi's Two-for-One Drug Just Went One-for-Two

Then there's the DUET trial (phase 2a, chronic rhinosinusitis with nasal polyps, or CRSwNP). This is the condition where polyps grow inside your nasal passages and make breathing miserable. Lunsekimig shrank those polyps significantly by week 24, measured via endoscopy. Patients also reported less nasal congestion and showed improvements on CT scans.

Safety was clean across the board. The most common side effects were the usual suspects: sore throats, upper respiratory infections, headaches, and injection-site reactions. Nothing alarming.

Sanofi's R&D chief, Houman Ashrafian, called the respiratory data "promising" for dual-targeting approaches. Phase 3 trials are already running in COPD.

So far, so great. Now for the other shoe.

The Skin Had Other Plans

The VELVET trial (phase 2b) tested lunsekimig in moderate-to-severe atopic dermatitis, the medical term for serious eczema. This was labeled an "exploratory" study, which in pharma-speak usually means "we're hopeful but hedging our bets." That hedge turned out to be wise.

Lunsekimig missed its primary endpoint: the percent change in EASI score (a standard measure of eczema severity) from baseline at 24 weeks. The drug simply didn't clear the bar for statistical significance.

Now, the story isn't entirely bleak. Secondary measures showed some improvement. More patients on lunsekimig achieved EASI-75 (a 75% or greater improvement in their eczema) compared to placebo. More also hit "clear or almost clear" skin on the vIGA-AD scale. But in clinical trials, secondary wins don't erase a primary miss. It's like getting an A on extra credit while failing the final exam; technically impressive, practically insufficient.

Why This Matters More Than You Think

This isn't just a story about one drug in three trials. It's a case study in the hardest bet in immunology: can a single bispecific platform conquer multiple diseases at once?

The respiratory system and the skin, despite both being playgrounds for type 2 inflammation, are very different battlefields. The airways and the epidermis have different cell populations, different tissue structures, and different ways of processing immune signals. What works in the lungs doesn't automatically translate to the skin. Lunsekimig just proved that the hard way.

For Sanofi specifically, the eczema miss stings. Dupixent generates enormous revenue, but patent cliffs loom on the horizon. A next-gen bispecific that could handle both respiratory and dermatology indications would have been the perfect succession plan. Instead, Sanofi now has a respiratory specialist on its hands (still valuable) but no clear heir to the Dupixent throne in eczema.

The Bispecific Reality Check

The broader industry should take notes. Bispecific antibodies are having a moment. The promise is tantalizing: one molecule, two targets, better outcomes. But the engineering challenges are real.

These molecules face problems that traditional antibodies don't. Their complex structures can misfold or clump together during manufacturing. They can trigger immune reactions. And the biggest issue of all: just because two targets matter in one disease doesn't mean the same combination matters equally in another. Biology isn't a vending machine where you insert the right molecular coins and collect your therapeutic prize every time.

Sanofi isn't the only company learning this lesson, but they're learning it publicly, across three simultaneous readouts.

What Happens Next

Sanofi will almost certainly double down on lunsekimig's respiratory franchise. The asthma and nasal polyps data are strong, phase 3 trials in COPD are underway, and the clean safety profile gives regulators less to worry about. Detailed data from all three trials will be presented at upcoming medical congresses.

The eczema question is murkier. Those positive secondary endpoints might justify further exploration, perhaps with different dosing, different patient populations, or combination approaches. But Sanofi hasn't signaled that yet, and the exploratory label on VELVET suggests the company wasn't betting the farm on dermatology in the first place.

Meanwhile, the rest of Sanofi's immunology pipeline keeps moving. DR-0201, a bispecific myeloid cell engager targeting CD20 for B-cell depletion (acquired from Dren Bio for up to $1.9 billion), is in phase 1 trials for inflammatory indications. An AI-powered collaboration with Earendil Labs, launched in January 2026, is hunting for new bispecific candidates in autoimmune disease.

The takeaway? Lunsekimig isn't dead; it's just been told where it belongs. Sometimes a drug designed to do everything ends up doing one thing really well. For Sanofi, that one thing might be enough to build a franchise. But the dream of a single molecule ruling both lungs and skin? That dream took a hit this week.

Biogen's Billion-Dollar Problem Has a Tiny, Twisted Solution

Biogen's newest deal isn't about a single drug; it's about fixing the delivery problem that's been holding back an entire class of genetic medicines. Alloy Therapeutics' shape-shifting ASO platform claims 50x better potency, and Sanofi already placed a $427M bet on it.