Schematic representation of the viral vectors.

(A) The lentiviral vector pHR'NTP expresses NTP under the transcriptional control of the CMV promoter and/or the HIV LTR. The MLV-vector, MPSV-NTP, contains a chimeric MPSV/MLV-LTR in which the U3 region of MLV was replaced by the U3 region of the myeloproliferative sarcoma.27 (B) In the bicistronic vector HFIG, the Flu peptide and the eGFP reporter gene are linked by the IRES of the encephalomyocarditis virus. In the vector HIG, the Flu peptide has been deleted. Ψ indicates packaging signal of HIV-1; Ψ⁺, extended packaging signal of MLV; Δgag, truncated gag gene containing an out-of-frame mutation; RRE, Rev-responsive element.