Specifically, CD4 CTLs have been observed among human peripheral blood mononuclear cells (PBMCs) in chronic viral infections, such as infections with human cytomegalovirus (CMV) (29–31), human immunodeficiency virus 1 (HIV-1) (32, 33) and hepatitis viruses (HBV, HCV, and HDV) (34). The gene discussed is CD4; the disease is infection.