Specific Aim 2: To determine effects of the belimumab therapy on secondary endpoints (at the times detailed for Aim 1) that include levels of pneumococcal-binding antibodies (by ELISA), circulating B-cell numbers and phenotypes (by flow cytometry), and the rate and severity of adverse events (AE) at any time during treatment. The investigators hypothesize belimumab will have dose-related effects on B-cell numbers and their differentiation, while minimally reducing host defense antibodies, and will also have an acceptable AE profile.