Your patient is a four-month-old boy with recurrent hospitalizations because of pneumonia, several episodes of acute otitis media with non-purulent drainage from the ear, and positive bacterial growth in laboratory cultures. His medical history included neonatal sepsis. Laboratory studies: CBC showed marked leukocytosis with a WBC count >40X103/microliter (normal:4-12X103/microliter), predominance of morphologically normal neutrophils and normal numbers of CD19+ and CD3+ cells in the peripheral blood that persisted during this hospitalization despite the antibiotic treatment. DHR and the NBT test is normal. Which of the following is the most likely underlying cause for his recurrent infections?
Select one of the following: