CD19 and common variable immunodeficiency: In contrast, condition II stimulation protocol led to significant in vitro B-cell expansion in the HCs and CVID patients (Figure 2A), indicating a superior stimulatory effect compared to condition I. However, absolute counts of CD19+ B-cells remained significantly lower in the CVID patients compared to HCs ex vivo at baseline and under both in vitro stimulation conditions (Figure 2A).