CD40LG and common variable immunodeficiency: Although different immune cell types can be affected in PIDs, more than half of the diagnosed patients present with antibody deficiencies (Bousfiha et al., 2018; Picard et al., 2018) and, in the clinic, almost 90% of the patients suffer from defects in B-cell differentiation (Liadaki et al., 2013), with disorders like hyper-IgM (HIGM), common variable immunodeficiency (CVID), selective IgA deficiency (IgAD), or IgG subclass deficiency.