Antibody Secretion Capacity in CVID Patients: Immunoglobulin Isotypes and Antigen Specificities After T-Cell-Dependent In Vitro Stimulation.

Background

Common variable immunodeficiency (CVID), the most prevalent symptomatic inborn error of immunity, involves impaired B-cell differentiation and antibody production, causing recurrent infections and the need for life-long immunoglobulin replacement therapy.

Methods

This study evaluated the in vitro differentiation of memory B-cells (MBCs) into antibody-secreting cells (ASCs) in CVID patients. Peripheral blood mononuclear cells from 13 CVID patients and 10 healthy controls were stimulated using two protocols: (I) Staphylococcus aureus Cowan Strain I, Pokeweed mitogen, and CpG, or (II) a T-cell-dependent approach using CD40 ligand, interleukin-21, and CpG. B-cell subpopulations were analyzed by flow cytometry, ASC differentiation using ELISpot, and antibody levels in supernatants by ELISA.

Results

Despite severely restricted in vivo antibody production, MBCs from all 13 CVID patients differentiated into IgG and IgM ASCs under adequate in vitro stimulation. Protocol II, mimicking T-cell help, was more effective than protocol I. As expected, the patients exhibited reduced class-switched MBCs ex vivo, but the MBCs differentiated and proliferated to an extent similar to those in healthy controls. IgA secretion remained significantly impaired post-stimulation. Specific IgG antibodies against tetanus toxoid and Streptococcus pneumoniae were detected in the patient supernatants, while no double-stranded DNA autoantibodies emerged after in vitro stimulation.

Conclusions

These findings indicate that the MBCs of most patients retain functional B-cell differentiation and antigen-specific IgG secretion under T-cell dependent stimulation, though IgA secretion remains impaired. Tailored stimulation protocols could deepen our understanding of how to restore MBC formation in CVID patients in vivo. This methodology provides a platform to investigate antigen-specific functional memory responses like post-vaccination.