In the SCD HU+ subgroup, treated in a dosage range of 15–30 mg/kg/day, we observed immunophenotypical assets similar to those detected in the control group, with the exception of the CD4+ naïve T-cell% and CD19+ switched-memory B-cell%, being, on average, significantly lower in patients on HU therapy. Here, CD4 is linked to Schnyder corneal dystrophy.