CELLDEX (CLDX) REPORTS POSITIVE PHASE 3 RESULTS FOR BARZOLVOLIMAB IN CSU

Celldex Therapeutics ($CLDX) announced positive topline results from its two Phase 3 studies of barzolvolimab in chronic spontaneous urticaria (CSU).

Both EMBARQ-CSU1 and EMBARQ-CSU2 met their primary endpoints and all key secondary endpoints at both doses studied.

The two trials enrolled a combined 1,939 patients across 43 countries and more than 500 clinical sites.

What is CSU?

Chronic spontaneous urticaria is an inflammatory condition characterized by recurring hives, itching and sometimes angioedema, or swelling beneath the skin, without an identifiable external trigger.

Mast cells play a central role in CSU by releasing histamine and other inflammatory substances.

Barzolvolimab is a monoclonal antibody designed to target KIT, a receptor that is important to mast-cell function and survival.

By inhibiting KIT, barzolvolimab is designed to reduce mast-cell activity and mast-cell numbers.

The Phase 3 Program

Patients in EMBARQ-CSU1 and EMBARQ-CSU2 received:

• 150 mg barzolvolimab every 4 weeks

• 300 mg barzolvolimab every 8 weeks

• Placebo

The primary endpoint was change from baseline at Week 12 on UAS7 — Weekly Urticaria Activity Score, which measures the severity of hives and itching over seven days.

EMBARQ-CSU1 — Week 12

• Placebo: -10.7

• 150 mg: -20.2

• 300 mg: -20.5

EMBARQ-CSU2 — Week 12

• Placebo: -11.4

• 150 mg: -20.2

• 300 mg: -19.7

Both doses in both trials achieved statistical significance versus placebo at p<0.00001.

Complete Response: No Hives and No Itch

Celldex also reported the percentage of patients reaching UAS7=0, meaning patients reported no hives and no itching during the measurement period.

Week 12

EMBARQ-CSU1

• Placebo: 9.3%

• 150 mg: 42.4%

• 300 mg: 42.1%

EMBARQ-CSU2

• Placebo: 12.6%

• 150 mg: 45.7%

• 300 mg: 44.0%

Responses continued through Week 24.

Week 24

EMBARQ-CSU1

• Placebo: 15.4%

• 150 mg: 49.0%3

• 00 mg: 45.1%

EMBARQ-CSU2

• Placebo: 17.6%

• 150 mg: 54.0%

• 300 mg: 48.4%

At Week 24, between approximately 45% and 54% of barzolvolimab-treated patients reported no hives and no itch, depending on dose and study.

Patients Previously Refractory to Omalizumab

The Phase 3 program also included patients whose CSU was refractory to omalizumab (Xolair), an existing biologic treatment for CSU.

At Week 12, complete response rates among these patients ranged from 41.7% to 55.3% across the two barzolvolimab doses and studies.

Placebo complete response rates were 9.3% and 15.1%.

Angioedema

Celldex also evaluated patients experiencing angioedema, the deeper swelling that can accompany CSU.

Among patients with angioedema at baseline, complete resolution at Week 12 was reported in:

EMBARQ-CSU1

• Placebo: 33.8%

• 150 mg: 62.7%

• 300 mg: 66.3%

EMBARQ-CSU2

• Placebo: 33.7%

• 150 mg: 74.3%

• 300 mg: 66.2%

Safety

Celldex reported that barzolvolimab was well tolerated through the 24-week placebo-controlled period and that the safety profile was consistent with previous studies.

The company plans to provide more detailed Phase 3 results, including additional safety data, at an upcoming medical meeting.

Patients in the EMBARQ studies continue treatment through Week 52, and a Phase 3b long-term extension study is also underway.

What Comes Next

Celldex plans to submit a Biologics License Application (BLA) to the FDA in 2027.

A BLA is the formal application through which a company asks the FDA to approve a biologic medicine for commercial use.

Barzolvolimab is also being studied in other mast-cell-related diseases, including cold urticaria, symptomatic dermographism, prurigo nodularis and atopic dermatitis.

Source: Celldex Therapeutics, September 22, 2026.