NCT07455578 Study of S-4321 in Participants With an Autoimmune or Immune-mediated Disease

Eligibility & Interventions

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What to Expect as a Participant

You will actively receive the study intervention — which may be a drug, biologic, device, or procedure.

Phase 1 is the earliest stage of human testing — safety and dosage are the primary focus. Visits are frequent and medical supervision is intensive. You will be among the first people to receive this treatment.

This trial targets 24 participants in total. It began in 2026-06 with a primary completion date of 2027-09.

Brief Summary

This is a multi-center, open-label Ph 1b basket study to assess safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, biomarker response, and preliminary efficacy of multiple doses of S-4321 in adults with autoimmune or immune-mediated disease including rheumatoid arthritis (RA), psoriatic arthritis (PsA), psoriasis (PsO), cutaneous lupus erythematosus (CLE) with or without systemic manifestations, or atopic dermatitis (AD).

Eligibility Criteria

All Participants Major Inclusion Criteria: 1. Adult males and females, 18 to 75 years of age (inclusive) 2. Body mass index (BMI) ≥18.0 and \<40.0 kg/m2 with a minimum body weight of 45 kg 3. Use of adequate contraception for both males and females. Female volunteers must be of nonchildbearing potential or if of childbearing potential, must have a negative pregnancy test. All Participants Major Exclusion Criteria: 1. Have received a PD-1 agonist, immune checkpoint agonist, immune checkpoint inhibitor, anti-CD19 or anti-CD20 agents, cell therapy, B cell modulating agents, alkylating agents, or any other immune cell depleting therapy. 2. Have received azathioprine, cyclosporine, mycophenolate mofetil, or tacrolimus within 4 weeks 3. Unable or unwilling to discontinue a prohibited medication 4. Presence of clinically relevant immunosuppression 5. Current infection or history of severe infection 6. Any history of malignant disease, with some exceptions Major inclusion/exclusion for each autoimmune or immune-mediated disease: For RA: 1. Confirmed diagnosis of moderate to severe active RA by the American College of Rheumatology (ACR) 2010/European League Against Rheumatism (EULAR) criteria for at least 3 months prior to the Screening 1 visit, and: 1. ≥6 swollen joint count based on 66 joint count 2. ≥6 tender joint count based on 68 joint count 3. Seropositive for RF and/or ACPA 4. Elevated hsCRP ≥1.2 times greater than the ULN 5. Does not have Class IV RA according to ACR revised criteria 2. Inadequate response to, or loss of response, or intolerance to: 1. \>1 conventional synthetic DMARD after 3 months of therapy OR 2. \>1 biologic DMARD/targeted synthetic DMARD after 3 months of therapy 3. Has not failed 3 or more bDMARDs and/or tsDMARDs For PsA: 1. Confirmed diagnosis of adult-onset PsA classified by the Classification Criteria for Psoriatic Arthritis (CASPAR) for at least 3 months prior to the Screening 1 visit, with all of the following: 1. Active PsO defined by at least 1 psoriasis lesion 2. Active disease defined by \>3 swollen joints and \>3 tender joints using the 76/78 swollen and tender joint count 2. Received standard doses of NSAIDs for \>4 weeks or csDMARDs for \>3 months and has been on a stable dose for \>8 weeks, or participant has intolerance to NSAIDs or DMARDs 3. Participants may be TNF inhibitor therapy naïve or may have received 1 prior TNF inhibitor 4. Has not had inadequate response or intolerance to 2 or more bDMARDs or csDMARDs For PsO: 1. Confirmed diagnosis of moderate to severe plaque PsO for at least 6 months, with all of the following: 1. Psoriasis Area and Severity Index (PASI) \>12 points 2. Static Physician's Global Assessment (sPGA) \>3 points 3. Body surface area (BSA) of PsO involvement \>10% 2. Cannot have a clinically significant flare within 12 weeks 3. Does not have history of erythrodermic psoriasis, generalized or localized pustular psoriasis, predominantly guttate psoriasis, or medication-induced or medication-exacerbated psoriasis 4. Has not had inadequate response to more than 2 prior bDMARDs For CLE (with or without systemic manifestations): 1. Histologically confirmed diagnosis of CLE with or without systemic manifestations for at least 6 months 2. Has active skin manifestations as measured by CLASI-A \>10 or CLASI-A \>8, if there is no alopecia or mucous membrane lesions 3. Participant must have an active CLE lesion despite an adequate trial of antimalarial treatment for at least 6 months. 4. Cannot have active lupus nephritis or moderate-to-severe or chronic kidney disease with eGFR \<45 mL/min/1.73m2 5. Cannot have active neuropsychiatric SLE For AD: 1. Confirmed diagnosis of AD as defined by the American Academy of Dermatology: Guidelines of Care for the Management of Atopic Dermatitis for at least 12 months 1. Eczema Area and Severity Index (EASI) \>16 2. Validated Investigator Global Assessment (vIGA-AD) \>3 3. BSA of AD involvement \>10% 4. PP-NRS) \>4 (average of daily scores) during the 7 days prior to dosing 2. Inadequate response to existing topical medications within 6 months or has a history of intolerance to topical therapy as defined by at least 1 of the following: 1. Inability to achieve good disease control after use TCS for at least 4 weeks 2. Documented history of clinically significant AEs with the use of TCS 3. Failed systemic therapies intended to treat AD within 6 months Additional inclusion/exclusion criteria will apply.

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