Background: Psoriasis is characterized by infiltration with mononuclear cells. Especially activated memory CD4+ T cells are critical in the pathogenesis. Interaction between the CD4 receptor and the major histocompatibility complex class II molecule is important for T-cell activation.

Objective: To test safety and efficacy of a fully human monoclonal anti-CD4 antibody (HuMax-CD4) in the treatment of psoriasis.

Design: Multicenter, double-blind, placebo-controlled, randomized clinical trial. Patients Eighty-five patients with moderate to severe psoriasis.

Interventions: Subcutaneous infusions of placebo or HuMax-CD4 at doses of 20, 80, 160, or 280 mg once weekly for 4 weeks.

Main outcome measures: Psoriasis Area and Severity Index (PASI), investigators' and patients' overall response assessment, adverse events, laboratory assessment including total T-cell and subtype counts, CD4 receptor occupancy, and interleukin 2 receptor levels.

Results: At week 7, mean PASI was reduced in all treatment groups (95% confidence intervals are in parentheses): placebo, 8% (-3% to 19%); 20 mg, 12% (-6% to 27%); 80 mg, 14% (-14% to 35%); 160 mg, 16% (-4% to 33%); and 280 mg, 24% (-10% to 48%). At the highest dose level, 6 (38%) of 16 patients obtained more than 25% reduction of PASI and 3 (19%) obtained more than 50% reduction of PASI. A dose-dependent decrease in total lymphocyte count was seen and was parallel to a dose-dependent decrease in CD4+ T cells. This decrease was due to a decrease in the memory subset, whereas the naive subset was affected to a minor degree. Four weeks of treatment with HuMax-CD4 was safe and well tolerated.

Conclusions: Treatment with HuMax-CD4 led to a moderate, not statistically significant reduction in PASI. The efficacy results obtained after only 4 weeks of treatment suggest that longer treatment would lead to even further reduction of PASI.