What happened

Shares of Celldex Therapeutics (CLDX -2.05%) were skyrocketing 28.4% as of 10:47 a.m. EDT on Monday. The big jump came after the company announced positive data from its ongoing phase 1b clinical study evaluating CDX-0159 in treating two of the most common types of hives. 

So what

With the huge gain for the biotech stock today, you'd expect Celldex's phase 1b clinical results to be really great. And they were. 

The company said that 18 of the 19 patients who received a single full dose of CDX-0159 experienced a complete response. The other patient in the group had a "marked partial response," according to the company. 

Person scratching arm.

Image source: Getty Images.

Patients with cold urticaria (a skin reaction after exposure to cold temperatures) had a median duration of response of 77+ days. Patients with symptomatic dermographism (hives that occur after light scratching of the skin) had a median duration of response of 57+ days. Celldex said that CDX-0159 was "generally well tolerated" by patients in the study.

More clinical testing will be needed before the safety and efficacy of CDX-0159 can be proved. However, lead investigator Marcus Maurer with Charite–Universitatsmedizin in Germany stated, "These early stage results are stunning and represent a major breakthrough for patients with inducible urticarias where current treatment options have been unable to provide relief from often severe symptoms."

Now what

Celldex will continue evaluating CDX-0159 in the phase 1b study. CEO Anthony Marucci said that the company plans to expand clinical testing of the drug into prurigo nodularis (a chronic inflammatory skin disease) later in 2021. Celldex also expects to target additional indications in the future.