title: Demonstration of helper activity with human leukemic tissue extracts.
mesh_terms: D001355:Alpharetrovirus; D000818:Animals; D046508:Culture Techniques; D005622:Friend murine leukemia virus; D006378:Helper Viruses; D006801:Humans; D007938:Leukemia / Q000382:microbiology; D009052:Leukemia Virus, Murine / Q000472:pathogenicity*; D051379:Mice; D012190:Retroviridae; D013154:Spleen / Q000382:microbiology*; D014020:Tissue Extracts
chemical_list: D014020:Tissue Extracts