Alefacept-induced decreases in circulating blood lymphocyte counts correlate with clinical response in patients with chronic plaque psoriasis.

This international, double-blind study examined the effects of alefacept on circulating lymphocytes in 507 patients with chronic plaque psoriasis, and determined whether these effects were related to clinical improvement. Patients were randomized to intramuscular placebo, alefacept 10 mg, or alefacept 15 mg once weekly for 12 weeks followed by 12 weeks of observation. Alefacept dose-dependently reduced CD4+ and CD8+ memory T cells, while sparing the na ve population. The greatest reductions in disease activity occurred in patients with the largest decreases in memory T cells. For example, a 50 % reduction from baseline Psoriasis Area Severity Index at any time during treatment or follow-up was observed in 66 % of patients who had the greatest reductions in CD4+ memory T cells versus in 40 % of patients who had the smallest reductions in this T-cell subset. These results provide further support for the deleterious roles of CD4+ and CD8+ memory T-cell subpopulations in psoriasis pathogenesis.