Immune response to pneumococcal polysaccharide vaccine in adults with chronic plaque psoriasis treated with alefacept

Background Alefacept is a T cell–modulating biologic therapy for psoriasis that could affect patients' ability to mount immune responses. Objective This open-label, phase IV, multicenter study assessed the ability of adults with chronic plaque psoriasis receiving alefacept to generate antibodies to a pneumococcal polysaccharide vaccine (PPV). Methods Patients were treated with a standard 12-week course of alefacept and administered the 23-valent PPV at week 6. Antipneumococcal antibodies were measured at baseline and weeks 6, 9, 12, and 33. The primary end point was the percentage of patients with a 2-fold or greater increase from prevaccination (week 6) to 6 weeks postvaccination (week 12) in antibody titers to 2 or more of 5 designated PPV antigens. Results Of 43 patients enrolled, 42 were included in the full analysis set, with 86% of patients exhibiting a 2-fold or greater increase and 57% of patients exhibiting a 4-fold or greater increase in antibody titers to 2 or more of 5 designated antigens from prevaccination to 6 weeks postvaccination. At 6 months postvaccination, 78% of patients had a 2-fold or greater increase and 47% of patients had a 4-fold or greater increase in antibody titers to 2 or more of the 5 designated antigens. There were statistically significant increases in mean antibody titers to all 23 antigens in PPV from prevaccination to 6 weeks postvaccination. Limitations This was an open-label study with no comparator. Conclusions Most patients mounted immune responses to PPV; increases in antibody titers in these patients were consistent with those seen in healthy individuals.