The purpose of this study is to assess the safety/tolerability and efficacy of using ustekinumab in subjects with common variable immunodeficiency CVID or selective IgG subclass deficiency (functional agammaglobulinemia) who have associated symptomatic gastrointestinal inflammation (CVID enteropathy). Ustekinumab (a Food and Drug Administration [FDA] approved drug) is a monoclonal antibody to interleukin (IL)-12/23p40. CVID is a clinically heterogeneous disorder characterized by decreased serum immunoglobulin IgG and IgA levels. In addition to chronic or recurrent pyogenic sino-pulmonary infections, many patients develop non-infectious gastrointestinal manifestations that can be disabling or fatal. Currently there is no standard therapy for the associated gastrointestinal disease outside of empiric nutritional intervention for weight loss, anti-diarrheal agents, and non-specific anti-inflammatory agents.