Humoral Immunodeficiency With Rituximab and Therapy With Subcutaneous Ig

To study the use of subcutaneous (injected under the skin) immunoglobulin replacement therapy (replacement of antibodies, which are infection-fighting proteins) in patients with a type of blood cancer called lymphoma, who have been treated with rituximab (a type of chemotherapy) and have an abnormal immune system putting them at increased risk of infection.