**3.2 Abatacept**

Abatacept is a fusion protein composed of an Fc fragment of IgG1 and the extracellular domain of CTLA-4 (cytotoxic lymphocyte antigen-4) that inhibits T-cell costimulation. Abatacept is currently approved for the treatment of rheumatoid arthritis (Bristol-Myers Squibb, 2009). A phase II study has been terminated for psoriatic arthritis and it showed that 10 mg/kg may be an effective treatment (Mease et al, 2011).

#### **3.3 Rituximab**

Rituximab is a chimeric monoclonal antibody that selectively binds the CD20 antigen of B cells. Rituximab is currently used in the treatment of non Hodgkin's lymphoma and rheumatoid arthritis (Genentech USA, Inc., 2011). A phase I trial is ongoing to assess the efficacy and safety of rituximab in patients with psoriatic arthritis (Swedish Medical Center, 2009).
