Protalex Inc. announced that following completion of its U.S.-based, multicenter Phase 1b randomized, multiple-dose, dose-escalation study of PRTX-100 (the 104 Study) in combination with methotrexate or leflunomide in adults with active rheumatoid arthritis (RA), the company has initiated enrollment of a Phase I/II open-label, multiple, fixed-dose study (the 105 Study) that is open only to 104 Study patients who indicated their desire for additional treatment. Protalex's lead drug PRTX-100 is a highly purified form of Staphylococcal Protein A. The PRTX-100-105 Study is an open-label, single group study with up to 12 former participants from the 104 Study who will receive a fixed dose of PRTX-100 over a 6-month period at a single site in the U.S. The primary study endpoint of the 105 Study is the safety and tolerability of a fixed dose of PRTX-100 administered over an extended period. The secondary endpoints include immunogenicity, effects on measures of RA disease activity, evaluation of anti-PRTX-100 antibody presence, and feasibility of joint evaluations with ultrasound and biomarkers as disease markers.