Experimental outline and proof-of-principle. (A) Based on the use of multi-colour LeGO vectors, drug-sensitivity of several (here: four) RT variants can be assessed simultaneously. (B + C) For proof of principle, two established antiviral drugs (B: AZT, C: Nevirapine) were tested in independent assays against four RT variants (wild-type, two double mutants [D67N/K70R = NR, T215F/K219Q = FQ] and one quadruple mutant [D67N/K70R/T215F/K219Q = NRFQ]) pseudotyped with VSV-G protein in two different cell lines (Left panels: SC1 cells, right panels: Jurkat cells). As expected, RT mutants, but not wild-type RT were highly resistant towards AZT (B). In contrast, all RT variants showed comparable sensitivity against Nevirapine (C). Data points represent mean values from three independent measurements. P-values that were significantly different between all other data groups, or only for those connected by lines, are denoted with *, for values < 0.05 or **, for values < 0.01.