M. A. suffers from hypogammaglobulinemia that has been complicated by refractory Mycoplasma hominis septic arthritis. He has been receiving the antibiotic valnemulin under Emergency Investigational New Drug (eIND) 114686 following many prior treatments with standard antibiotics. M.A. has also been receiving intravenous immunoglobulin (IVIG) replacement. The antibiotic and IVIG have been helpful, but not sufficient for cure. Antibodies have been shown to be critical for defense against mycoplasma. Hyperimmune serum against mycoplasma isolated from rabbit or goat has been effective in cases of chronic erosive arthritis in the setting of immune deficiency, and in some cases resulted in cures. The investigators propose to use M. hominis isolated from M. A. to vaccinate one transgenic cow (developed by SAB Biotherapeutics), purify human antibody after vaccination, test the purified antibody in killing assays to confirm potency, and then administer the purified human IgG to M. A. after FDA compassionate use IND application and local Institutional Review Board (IRB) approval.