Curiously, evidence of a heightened cellular response to COVID-19 vaccination has also been detected in other congenital or acquired conditions characterized by strong B-cell aplasia, including patients with B-cell malignancies treated with CD19-targeting chimeric antigen receptor (CAR) T-cell therapy (81, 82), and individuals with X-linked agammaglobulinemia (XLA) who have an inherited inability to generate mature B-cells (83–85). This evidence concerns the gene CD19 and isolated agammaglobulinemia.