Background: Alefacept, human LFA-3/IgG1 fusion protein, selectively reduces memory-effector (CD45RO+) T cells, a source of the pathogenic mediators of psoriasis. Objective: To evaluate the effect of alefacept on immune function, T-cell-dependent humoral responses to a neoantigen (φX174) and recall antigen (tetanus toxoid) were assessed. Methods: Patients with psoriasis were randomized to the control group or to receive alefacept (7.5 mg intravenously weekly for 12 weeks). The alefacept group received φX174 immunizations at weeks 6, 12, 20, and 26 and tetanus toxoid at week 21; control subjects received φX174 at weeks 6 and 12 and tetanus at week 10. Results: Mean anti-φX174 titers were comparable in both groups. There was no difference in the percentage of responders (anti-φX174 IgG ≥30% of the total anti-φX174) between the alefacept group and the control group (86% and 82%, respectively; P = .73). The percentage of patients with anti-tetanus toxoid titer increases ≥2 times baseline also was similar (alefacept, 89%; control 91%). Conclusion: A single 12-week course of alefacept did not impair primary or secondary antibody responses to a neoantigen or memory responses to a recall antigen. The selective immunomodulatory effect of alefacept against a potentially pathogenic T-cell subset is associated with maintenance of a significant aspect of immune function (antibody response) to fight infection and respond to vaccinations.
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