CD267 / TACI (transmembrane activator calcium modulator and cyclophilin ligand interactor), a TNFR superfamily transmembrane protein, is expressed on B cells (predominantly on CD27+ memory cells), multiple myeloma cells and B cell chronic lymphocytic leukemia (B-CLL) . Its triggering leads to activation of the transcription factors NFAT, AP1, and NF-kappa-B. It plays a crucial role in humoral immunity. Mutations in CD267 are associated with common variable immunodeficiency and IgA deficiency.