A Study to Evaluate RIST4721 in Palmoplantar Pustulosis (PPP)

Inclusion Criteria: * At least a 6-month history of PPP as defined by the presence of pustules on palms and/or soles, but without evidence of infection on palms and soles * Moderate or severe PPP, as defined by Palmoplantar Pustulosis Psoriasis Area and Severity Index (PPPASI) ≥8 and Palmoplantar Pustulosis Physician Global Assessment (PPPGA) ≥3 at Day -1, and a minimum of 8 fresh pustules at screening (fresh pustule count on both right/left palms and soles) and 20 fresh pustules at Day -1 (fresh pustule count on both right/left palms and soles) * Males and females must be willing to use birth control as indicated Exclusion Criteria: * Moderate to severe psoriasis, as defined by plaque psoriasis covering ≥10% of total Body Surface Area (BSA) at Day -1 * Subject is known to have an immune deficiency or is immunocompromised * Positive test for hepatitis, human immunodeficiency virus (HIV) or tuberculosis * Use of topical therapies for PPP within 2 weeks of Day -1 and/or systemic therapies for PPP within 4 weeks