A 3-year-old boy presents with recurrent pneumonia, sinusitis, and otitis media. Physical examination is unremarkable. Laboratory findings reveal:

• Low IgG, IgA, and IgM levels
• Absent B cells (CD19+)
• Poor response to vaccinations

Which of the following is the most likely diagnosis?
A 5-year-old boy presents with recurrent abscesses caused by Staphylococcus aureus, Serratia, and Burkholderia. He also has a history of granuloma formation in his lungs. Diagnostic testing reveals an abnormal dihydrorhodamine (DHR) flow cytometry test. Which of the following is the most likely diagnosis?

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