CD4 and COVID-19: The results depicted in Figure 5 indicate that cTfh and Tmem from CVID patients showed significantly reduced levels of activation marker expression in response to SEB stimulation as compared to healthy controls (HC) or oPAD patients, indicating that defective antigen-specific recall activation of cTfh and Tmem following COVID-19 vaccination was associated with a more general defect in TCR-mediated CD4+ T cell activation in CVID patients.