CD19 and hematologic disorder: The ever-expanding clinical application of these treatments, along with CD19-targeted chimeric antigen receptor T cell (CAR T) employment in hematological malignancies [252], led to an increase in patients with SID showing susceptibility to encapsulated bacteria and recommended as candidates for prophylactic immunoglobulin replacement therapy (IgRT), at a dose of 400 up to 600 mg/kg every 3–4 weeks, with recommended trough IgG levels ranging from 750 to 850 mg/dL [239,253].