CD80, a costimulatory molecule that isa member of the immunoglobulinsuperfamily, is crucial to the activation of T lymphocytes and acts as the main auxiliary signal that enhancesthe MHC/TCR signal in T cells constitutively expressing the CD28 receptoron their surfaces. Patients taking tisagenlecleucelfor relapsed/refractory diffuse large B-cell lymphoma have increasedlevels of CD80 and/or CD86 in their tumor tissue. The gene discussed is CD80; the disease is diffuse large B-cell lymphoma.