Blisibimod (also known as A-623, formerly AMG 623) is a selective antagonist of B-cell activating factor (BAFF, also known as B-lymphocyte stimulator or BLyS), being developed by Anthera Pharmaceuticals as a treatment for systemic lupus erythematosus.

[2] Blisibimod is a fusion protein consisting of four BAFF binding domains fused to the N-terminus of the fragment crystallizable region (Fc) of a human antibody.

[3] Elevated levels of BAFF have been associated with several B-cell mediated autoimmune diseases, including systemic lupus erythematosus,[4][5][6] lupus nephritis,[7] rheumatoid arthritis,[5][6] multiple sclerosis,[8] Sjögren syndrome,[9] Graves' disease,[10] and Hashimoto's thyroiditis.

[1][3] Improvements in disease activity have been observed in patients with systemic lupus erythematosus[11] and rheumatoid arthritis[12] following treatment with BAFF inhibitors in clinical trials.

[1] It was subsequently acquired by Anthera Pharmaceuticals,[13] who in 2010 initiated a global Phase II study called PEARL-SC to investigate the efficacy, safety, and tolerability of blisibimod in subjects with systemic lupus erythematosus.