In contrast, Sauerwein et al. [39] reported a significantly decreased percentage of antigen-specific cTFH cells in CVID patients who made an antibody response to the vaccine and observed a defective function of cTFH cells following activation with the SARS-CoV-2 peptide; titers of spike protein-specific IgG three times the detection limit or more were associated with intact vaccine-specific activation of CXCR5-negative CD4+ memory T cells, despite defective activation of circulating T follicular helper cells (cTFH). Here, CD4 is linked to common variable immunodeficiency.