CD4 and hemorrhagic fever with renal syndrome: RNA-dependent RNA polymerase (L) is encoded by the L segment [11] In humans CD4+ and CD8 T+ cell epitopes on hantavirus proteins were identified by analyzing peripheral blood mononuclear cells (PBMCs) obtained either from donors who had immune memory to the virus [65–69] or from HCPS or HFRS patients in the acute phase [60,70–72].