Eric H. Sasso

OBJECTIVE: To evaluate the efficacy and safety of treatment with adalimumab, a fully human anti-tumor necrosis factor (anti-TNF) monoclonal antibody, over 48 weeks in patients with moderate to severe psoriatic arthritis (PsA). METHODS: Patients who completed the Adalimumab Effectiveness in Psoriatic Arthritis Trial (ADEPT), a 24-week, double-blind study of adalimumab versus placebo in PsA, could elect to receive open-label adalimumab, 40 mg subcutaneously every other week after week 24. Radiographs were obtained at week 48 and were read with radiographs obtained previously. Clinical and radiographic efficacy data were analyzed overall and in patient subsets. Safety data were collected over 48 weeks. RESULTS: At week 48, patients from the adalimumab arm of ADEPT (n = 151) had achieved American College of Rheumatology 20% improvement (ACR20), ACR50, and ACR70 response rates of 56%, 44%, and 30%, respectively. Among those evaluated with the Psoriasis Area and Severity Index (PASI) (n = 69), PASI50, PASI75, PASI90, and PASI100 response rates (> or =50%, > or =75%, > or =90%, and 100% reduction in PASI scores, respectively) were 67%, 58%, 46%, and 33%, respectively (ACR and PASI response rates were analyzed using nonresponder imputation). Improvements in disability, as measured by the Disability Index of the Health Assessment Questionnaire (mean change in score -0.4) were sustained from week 24 to week 48. At week 24 and week 48, the mean changes from baseline in the modified total Sharp score were -0.1 and 0.1, respectively, for patients who received adalimumab for 48 weeks (n = 133), and 0.9 and 1.0, respectively, for patients who received placebo for 24 weeks followed by adalimumab for 24 weeks (n = 141). Adalimumab demonstrated clinical and radiographic efficacy regardless of whether patients were receiving methotrexate (MTX) at baseline. Adalimumab was generally safe and well tolerated through week 48. CONCLUSION: Adalimumab improved joint and skin manifestations, reduced disability, and inhibited radiographic progression over 48 weeks in patients with PsA who were participants in ADEPT. MTX use at baseline was not required for clinical or radiographic efficacy. Adalimumab had a good safety profile through week 48.

Staphylococcal protein A (SPA) is a bacterial membrane protein that possesses, in addition to its Fc gamma-binding activity, a distinct specificity for the Fab region of some IgM, IgA, IgG, and IgE. The Fab site that binds to SPA has been localized to the V region of the Ig H chain. In a previous study of human monoclonal and polyclonal IgM, we demonstrated that binding to SPA was highly restricted to molecules of the VHIII subgroup, and that nearly all VHIII IgM were able to bind SPA. The present study examines the VH composition of SPA-binding and SPA-nonbinding fractions of purified human polyclonal IgA, and IgG F(ab')2 fragments. We found that 22% of the IgA and 15% of the IgG F(ab')2 bound to SPA-agarose. Analysis with VH subgroup-specific antisera indicated that the SPA-binding fraction of IgA was dominated by the VHIII subgroup, and the SPA-binding fraction of IgG F(ab')2 contained only VHIII molecules. Furthermore, substantial portions of the total VHIII protein in IgA and in IgG F(ab')2 bound to SPA. We conclude that Fab binding to SPA is both restricted to and highly prevalent among human VHIII molecules, regardless of Ig class. These results suggest that protein A is an Ig superantigen.

Staphylococcal protein A (SPA) is a bacterial membrane protein which has distinct binding sites for Fc gamma and for the Fab region of some IgM, IgG, IgA, and IgE molecules. This study establishes a structure-function correlation responsible for the binding of Ig Fab regions to SPA. Binding of 24 isolated human monoclonal IgM proteins to SPA was measured in a solid phase RIA. VH and V kappa subgroups of each IgM were determined by SDS-PAGE, transfer blotting, and detection with antisera prepared against specific first framework region peptides. Binding to SPA was seen with 10 of 11 VHIII IgM, but none of the 7 VHI or 6 VHII. Similarly, polyclonal IgM fractionated on a SPA-Sepharose CL4B column showed nearly complete partition of VHIII molecules into the SPA-binding fraction, and VHI and VHII subgroup proteins into the fall-through. We conclude that SPA binding is a functional marker for VHIII H chains in human IgM molecules.