Ustekinumab is a fully human monoclonal antibody directed against the p40 
subunit shared by interleukin 12 and interleukin 23, two naturally occurring 
protein regulators that play an important role in immune-mediated inflammatory 
diseases, including psoriatic arthritis (PsA). In September of 2009, the US FDA 
approved ustekinumab for the treatment of adult patients with moderate to severe 
plaque psoriasis. Beginning in November of 2009, Janssen Biotech (formerly 
Centocor Biotech), the developer of ustekinumab, initiated clinical trials to 
investigate the efficacy of ustekinumab in the treatment of other inflammatory 
disorders, including PsA. Phase II and Phase III studies showed both a good 
safety profile and significant efficacy for ustekinumab in the treatment of PsA, 
leading to the drug's approval in both Europe and the USA. In an immunotherapy 
market currently dominated by anti-TNF-α drugs for the treatment of PsA, 
ustekinumab offers an alternative option for patients with PsA, including those 
unresponsive to methotrexate and the TNF-α inhibitory agents currently approved 
for this potentially debilitating disease.