ICOS costimulation plays an important role in effector T cell responses and in maintaining B cell responses through T follicular helper cell generation, and ICOS/ICOSL inhibition ameliorates several autoimmune conditions, such as acute graft-versus-host disease, rheumatoid arthritis, and systemic lupus erythematosus (50). The gene discussed is ICOS; the disease is systemic lupus erythematosus.