Other findings on tumor cells lacking HLA class II antigen expression due to mutations of regulatory genes such as Regulatory Factor X5 (RFX5), Class II Major Histocompatibility Complex Transactivator (CIITA), and Regulatory Factor X Associated Protein (RFXAP), seem to be favored in an environment of dense CD4+ T cell infiltration [86]. The gene discussed is CIITA; the disease is neoplasm.