CSF3 and agammaglobulinemia: For rituximab, which is known to be associated with the development of secondary antibody deficiency, the risks for an individual are increased with low baseline IgG prior to rituximab initiation; exposure to prior therapies, such as cyclophosphamide, steroids, and purine analogs, purine synthesis inhibitors (mycophenolate mofetil), or the use of combination therapy or granulocyte-colony stimulating factor (166).