ICOS and common variable immunodeficiency: Other PID have leaky B cell development with alterations of the B cell diversity autoimmunity and B cell malignancies, jointly termed common variable immunodeficiency (CVID) and include PID with mutations in BAFF and the BAFF receptor TACI (64), BLNK/SLP65 (mouse) (65) and ICOS (expressed on Tfh cells) (66) (Figure 1).