Celldex Barzolvolimab Fails PN Phase 2: AD Readout in Doubt

Celldex Therapeutics (CLDX) discontinued development of barzolvolimab in prurigo nodularis after the drug missed its primary and key secondary endpoints in a Phase 2 trial, despite achieving what the company called “profound systemic mast cell depletion.” The news, reported after market close on July 21, sent shares down roughly 7% in extended trading before recovering to close at $35.42 on July 23 with volume of 856,000 shares.

What the trial showed

Barzolvolimab is an anti-KIT monoclonal antibody designed to deplete mast cells. The Phase 2 trial tested whether that depletion would translate into clinical benefit for prurigo nodularis, a chronic skin disease characterized by intense itching and hard nodules.

The answer was no. The 140-patient trial missed its primary endpoint: the proportion of patients achieving a 4-point or greater improvement on the WI-NRS (Worst Itch Numeric Rating Scale) from baseline to Week 12. The miss was not close (p=0.868 for the 150mg dose; p=0.428 for the 300mg dose). Key secondary endpoints also missed. Barzolvolimab produced significant reductions in serum tryptase, confirming mast cells were being depleted as intended. But clinical outcomes, including itch severity and skin lesion clearance, were no different from placebo. Celldex reported no improvement through extended treatment to Week 24.

The disconnect matters. If mast cell depletion does not improve symptoms, it raises the question of whether mast cells are actually a primary driver of the disease, or just a downstream participant. For a framework on reading clinical trial endpoints and spotting a miss before the market does, see our guide to reading a clinical trial press release.

Why the atopic dermatitis readout is now in doubt

Celldex has a separate Phase 2 trial of barzolvolimab in atopic dermatitis expected to read out in Q4 2026. TD Cowen noted the PN failure “somewhat weakens the argument” for the AD program because both diseases share components of pruritic pathology hypothesized to be mast-cell-driven.

The risk is read-across: if mast cell depletion does not work in one pruritic skin disease, investors will discount the odds it works in another. Celldex was “disappointed” the study did not confirm a promising signal from an earlier intravenous Phase 1b trial, and TD Cowen flagged the switch from IV to subcutaneous delivery as a factor.

What remains: the CSU program

The core thesis now rests on Phase 3 data in chronic spontaneous urticaria (CSU) and cold urticaria, expected September through October 2026. Barzolvolimab has shown strong efficacy and a tolerable safety profile in CSU, where mast cells have a more established role. Analysts view this as the thesis-defining readout.

Wells Fargo maintained an Overweight rating but lowered its price target to $48. Morgan Stanley also maintained Overweight with a $40 target. The analyst consensus is that CSU, not PN or AD, determines whether barzolvolimab becomes a commercial product.

One safety signal worth monitoring: Celldex disclosed an investigator’s diagnosis of aseptic meningitis as a serious adverse event, though the company “strongly disagreed” with the diagnosis and suggested it may have been a viral neuroinflammatory event. This is not confirmed but adds uncertainty.

What to watch next

The CSU Phase 3 readout in September or October is the next major catalyst. If positive, barzolvolimab still has a path to market in a well-established mast-cell-driven indication. If the AD readout follows in Q4 and also disappoints, the mast cell depletion thesis narrows significantly.

For Celldex, the stock at $35.42 is telling you the market still believes in CSU. The PN failure is a setback, but not the end of the program.

Source: Celldex press release via GlobeNewswire | Fierce Biotech