Study of the Efficacy and Safety of RPH-104 in Adult Subjects With Schnitzler Syndrome

The study will include a screening period (up to 28 days), a double blind, placebo controlled treatment period (14 days), followed by an 8 week safety follow up period after the second dose of study drug.

Subjects with an established diagnosis of Schnitzler Syndrome (SchS) will participate in a Screening period of up to 28 days after signing an informed consent form (ICF). Subjects will be advised to schedule the Day 0 visit with the study staff as soon as the symptoms of SchS flare occur during the Screening period.

If the subject does not meet the inclusion/exclusion criteria at the site visit during the screening period, other screening visits are allowed within this period until the subject meets the study criteria.

A total of 14 subjects will be randomly assigned to 1 of 2 treatment groups (in a 1:1 ratio) to receive a double blind, single subcutaneous (SC) injection of study drug (80 mg RPH-104 or matching placebo) on Day 0. On Day 14, subjects will receive a second dose of randomized treatment as well as an additional dose of 80 mg RPH-104 or placebo based on response to treatment, such that responders (SDAS = 0) will receive a dose of placebo, and non responders defined as no response (no change in SDAS) or partial responders (SDAS ≥ 1, and activity reduction by 1 or more points of SDAS compared to baseline) will receive an 80 mg RPH 104 dose. (Schnitzler Disease Activity Score includes the PGA score and C-reactive protein (CRP) result: If the PGA and CRP grades are not of the same severity, the higher severity level of either PGA or CRP will be used to determine the SDAS)

The study will be stopped after Data and Safety Monitoring Board (DSMB) review if:

1. Death is reported in 2 subjects assigned to the RPH 104 treatment arm or after receiving RPH 104 on Day 14 (i.e., non responder to the Day 0 study drug dose). 2. Two subjects assigned to the RPH 104 treatment arm or after receiving RPH 104 on Day 14 (ie, non responder to the Day 0 study drug dose) report liver function test abnormalities which meet Hy's Law criteria (ie, increased ALT and/or AST 3 fold or greater from upper limit of normal (ULN) combined with jaundice or weakness or hypochondrial pain/severity or increased Total Bilirubin (TBil) level 2 fold or greater from ULN, \[not explained by any other causative factors like virus\]).

The severity of SchS symptoms will be assessed daily from Day 0 through Day 28 using the PR SchS Scale, at clinic visits on Day 0, Day 14, and Day 28 using the Patient Global Impression of Severity (PGIS), at clinic visits on Day 14 and Day 28 using the Patient Global Impression of Change (PGIC), and at each clinic visit using the PGA, CRP, SAA, and SDAS. Subjects will be followed through Day 70 for safety (A Data Safety Monitoring Board (DSMB) will periodically review and evaluate the accumulated study data for subject safety).