Consistent with this finding, transfer of cell-free supernatants from HIV-1R7/3 YU-2 Env GFP-infected double-tg rat T-cells onto naïve rat cultures did not initiate an infection, while transfer of infected hCD4/hCCR5-tg T-cells again led to a steady increase of GFP-positive rat CD4 T-cells in the recipient culture (data not shown). The gene discussed is CD4; the disease is infection.