In Amyotrophic Lateral Sclerosis (ALS), the reduction of regulatory T-lymphocyte (Treg) numbers and suppressive function correlates with rapid disease progression. The investigator completed a phase 1 study of infusions of expanded autologous Tregs in combination with subcutaneous IL-2 injections in ALS patients, which showed enhancement of Treg numbers and suppressive function in vivo. The enhanced Treg suppressive function correlated strongly with slowing and stabilization of disease progression. Drugs that enhance endogenous Treg numbers and suppressive function may also stabilize disease in ALS. This phase 1 study aims to determine whether the combination therapy of subcutaneous IL-2 and abatacept (Orencia®) is safe and well-tolerated in 6 patients with ALS, and whether the therapy enhances Treg numbers and suppressive function in vivo.