We will conduct an open label pilot study of 15 patients with moderate to severe Alopecia Areata treated with SC abatacept 125mg once per week for 6 months. A few subjects with alopecia totalis or universalis will also be included. Subjects will be followed for another 6 months to evaluate durability of response following the treatment phase. The primary efficacy outcome will be the proportion of responders after 6 months of treatment compared to the historically known rate of response in untreated/placebo-treated subjects of 8 to 10%. Punch biopsies and peripheral blood will be obtained at baseline prior to treatment and then after 4, 12 and 24 weeks for immunomonitoring and molecular studies.