Specifically, when the T cell receptor (TCR) of a T cell recognizes foreign antigens in the context of the major histocompatibility complex, additional binding events modulate the ensuing response through co-stimulatory factors, such as CD28 (serving to amplify the signal by binding to CD80/CD86 on antigen-presenting cells) or immune checkpoint molecules, such as CTLA-4 or PD-1 (to suppress the signal by binding to CD80/CD86 on antigen-presenting cells or PD-L1 on tumor cells or activated macrophages). The gene discussed is CD80; the disease is neoplasm.