Celldex Releases Phase 1 Results For Its Bispecific Antibody CDX-622 Showing Drug Was Well Tolerated, Showed Favorable Pharmacokinetics, And Led To Rapid, Sustained Reductions In Serum Tryptase, Confirming Effective Mast Cell Inhibition

Author: Benzinga Newsdesk | October 30, 2025 03:14pm

Celldex (NASDAQ:CLDX) announced today positive data from the ongoing Phase 1 study of CDX-622, a novel bispecific antibody that targets two non-redundant, complementary pathways implicated in inflammation and fibrosis—mast cell depletion via stem cell factor (SCF) starvation and neutralization of the alarmin thymic stromal lymphopoietin (TSLP). CDX-622 was well tolerated, exhibited a good pharmacokinetic profile and induced rapid and sustained reductions in serum tryptase, indicative of mast cell inhibition and depletion. The data were presented by Diego Alvarado, PhD, Vice President of Research at Celldex, in an oral presentation at the CIA (Collegium Internationale Allergologicum) Biennial Symposium in Dubrovnik, Croatia.

"Celldex continues to lead the field in therapeutic targeting of mast cells, presenting promising data today from the first stem cell factor neutralizing antibody to be studied in humans," said Tibor Keler, PhD, Executive Vice President and Chief Scientific Officer of Celldex Therapeutics. "Combining this unique approach of mast cell depletion with the blockade of a validated and critical inflammation pathway driven by TSLP could potentially deliver profound clinical benefit for patients with inflammatory and fibrotic disorders where both mast cells and TSLP play a pathogenic role."

"The data presented today demonstrate that CDX-622 has a long half-life with no measurable immunogenicity observed to date—two critical hurdles for bispecific antibodies," continued Dr. Keler. "We are very pleased with the safety profile and the sustained dose dependent reductions in serum tryptase we observed over a 12 week period following a single dose. Based on these data, we have progressed this study to the next phase of development and are now testing multiple ascending doses of CDX-622. We expect to complete this study next year and plan to initiate a Phase 1b proof of mechanism study in patients with mild to moderate asthma, where we will be able to assess the impact of dual neutralization of SCF and TSLP, which could support broad development in a number of clinical indications with significant unmet need."

Key presentation highlights:

• CDX-622 potently neutralizes TSLP and soluble SCF and leads to mast cell reduction in preclinical models.
• CDX-622 preferentially inhibits the soluble form of SCF over the membrane form, which may lead to differential impact on KIT-dependent processes.
• In a GLP toxicology study, the No-Observed-Adverse-Effect-Level (NOAEL) was the highest dose level tested (75 mg/kg) and led to profound mast cell depletion in the tissues.
• In healthy participants, CDX-622 was well tolerated with no dose limiting toxicities, serious adverse events, or infusion reactions and no emergent events related to systemic KIT inhibition.
• CDX-622 exhibited mAb-like pharmacokinetics (serum half-life of approximately 18 days at 9 mg/kg) without any evidence of antidrug antibodies (ADA).
• A single dose of CDX-622 resulted in a rapid and sustained decrease (~50%) in circulating tryptase consistent with systemic mast cell inhibition and depletion

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