Peripheral Helper T-cells in Common Variable ImmunoDeficiency

Inclusion Criteria: * Male or female; * Age ≥ 18 years; * Standard criteria will be applied to diagnose CVID, specifically requiring: 1) low serum IgG level \<5 g/L, combined with low IgM- and/or IgA-isotype concentrations \<0.4 g/L or \<0.7 g/L, respectively; 2) poor antibody responses to immunization or infection; and 3) exclusion of other defined forms of secondary hypogammaglobulinemias. Patients meeting the definitional criteria for CVID will be included, regardless of the duration of the disease or the treatment received (gammaglobulins substitution or not); * Being affiliated to health insurance; * Willing to participate and to sign informed consent. Exclusion Criteria: * Patients on corticosteroids and/or immunosuppressants; * Patients with a primary immunodeficiency genetically characterized, such as Bruton disease our HyperIgM syndrome; * Patients with an active chronic infection; * Pregnant or breastfeeding women; * Persons deprived of their liberty by a judicial or administrative decision, minors, persons of legal age who are the object of a legal protection measure or unable to express their consent.