FIG. 6.

Efficient pseudotyping of MLV with S-protein variants. (A) C-terminal sequences of S-protein variants used in panel B are shown for comparison. The gray box indicates residues derived from a membrane-proximal region of the cytoplasmic domain of HIV-1 gp160 (S-H2). (B) A packaging cell line (GP2-293) stably expressing MLV gag and pol gene products was transfected with a vector containing the MLV packaging signal and engineered to express GFP and with either vector alone or a plasmid encoding S protein, S-H2, or an S-protein variant (S-TR) truncated, like S-H2, after residue 1228 but lacking the HIV-1-gp160-derived residues present in S-H2. Viruses were normalized for reverse transcriptase activity and incubated with ACE2-HEK293T cells. Numbers in parentheses indicate mean fluorescence as determined by flow cytometry. (C) MLV generated as for panel Band pseudotyped with S-H2 was incubated with ACE2-HEK293T cells and the indicated dilutions of convalescent-phase patient sera or the indicated concentrations of ACE2-NN-Ig or BSA. Infection is reported as mean fluorescence normalized to that observed in the absence of any inhibitor.