YM-58483/BTP2 is a blocker of store-operated Ca²⁺ entry (SOCE), which regulates the activation of non-excitable cells such as lymphocytes. YM-58483 has been reported to inhibit cytokine production and proliferation in T cells, and to be useful as a probable medicinal candidate for treatment of bronchial asthma. The present study investigated the pharmacological profile and therapeutic potential of YM-58483 in relation to cell-mediated immune responses. In the mouse graft-versus-host disease (GVHD) model, YM-58483 (1–30 mg/kg, p.o.) and cyclosporine A (1–30 mg/kg, p.o.) inhibited donor anti-host cytotoxic T lymphocyte (CTL) activity and IFN-γ production, and also reduced the number of donor T cells, especially donor CD8⁺ T cells, in the spleen. YM-58483 and cyclosporine A inhibited T cell proliferation in a one-way mixed lymphocyte reaction (MLR) with IC₅₀ values of 330 and 12.7 nM, respectively. Additionally, YM-58483 (1–10 mg/kg, p.o.) and cyclosporine A (2, 10 mg/kg, p.o.) inhibited the sheep red blood cell (SRBC)-induced delayed type hypersensitivity (DTH) response. These results suggest that the inhibition of SOCE leads to the prevention of antigen-induced T cell responses, which participate in autoimmune diseases such as autoimmune hepatitis and rheumatoid arthritis.