CD80 and neoplasm: In this study, its absence was shown to result in an ineffective effector response and a lack of viral control.83 In addition, adoptive transfer of CD80-transfectant tumor cells into mice produced a strong CD28-responsive CTL-mediated immune responses and tumor rejection.84 As CD28 and CTLA-4 share the same ligands of CD80 and CD86,56 these two receptors heavily compete for the same ligand recognition and therefore can affect and define the overall activatory or inhibitory outcome of T-cell activities.