Elevated expression of the voltage-gated channel Kv1.3 in effector memory T (TEM) lymphocytes is implicated in the pathology of a range of autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus and type 1 diabetes2, as well as non-autoimmune conditions such as asthma, chronic obstructive pulmonary disease and graft-versus-host disease, and therefore Kv1.3 channels are a highly promising therapeutic target for the treatment of such diseases3, 4. Here, KCNA3 is linked to graft versus host disease.