Antigen presentation, a prerequisite for T-cell activation, is also compromised in tumor-bearing hosts via the loss of major histocompatibility complex (MHC) I in tumor cells, the downregulation of MHC II in antigen-presenting cells (dendritic cells or macrophages), and the downregulation of costimulatory molecules, such as CD80, CD86, CD40, and OX40L [15,16,17,18]. The gene discussed is CD80; the disease is neoplasm.