hTFR1 knock-out Hs578T cells are susceptible to MMTV infection. (A & B) Target cells were transduced with MMTV-based vectors carrying wild-type MMTV(C3H) Env, G42E MMTV(C3H) Env, JUNV GP or TCRV GP. Neutralization, heat inactivation and AZT treatment were performed as described in materials and methods. Transduction of target cells was detected by FCM 3 days post infection The number of eGFP-expressing cells was counted using forward scatter vs. fluorescence intensity in the FL1 channel (eGFP) plots. (A) Transduction levels were made relative to the value obtained for the infected cells expressing detectable levels of hTfR1 and expressed as percentage of that control. (B) Transduction levels were made relative to the value obtained for the infected cells and expressed as percentage of that control. The values shown are mean ± standard errors from three independent experiments.