The average and standard deviation of the production rate ratio (PRR) is shown on the graph. reports of NNRTIs stimulating HIV-1 replication, although the M230L mutant was reported to display this property in presented but unpublished work (Huang W., Parkin N.T., Lie, Y.S., et al. 4th International Workshop on HIV Drug Resistance and Treatment Strategies, June 2000, Abstract #30; in Antiviral Therapy volume 5, supplement 3, pp. 24-25). Of interest is that at least one clinical isolate in that study also contained Agrimol B K101E and G190S. We confirmed that the M230L mutant in an NL4-3 backbone does replicate better in the presence of low concentrations of EFV than in the absence of drug; the magnitude of EFV-dependent stimulation is similar to that observed with Gipc1 K101E+G190S, although the peak of growth stimulation occurred at a much lower EFV concentration than K101E+G190S (10 nM vs. 400 nM, Fig. 2D). The peak p24 concentration for the K101E+G190S double mutant in 400 nM EFV was almost ten-fold greater than the p24 concentration of G190S in a similar concentration of EFV (Fig. 2A and B), consistent with the hypothesis that the property of EFV-dependent growth stimulation contributes to the improved fitness of K101E+G190S relative to G190S in 400 and 600 nM EFV (Fig. 1). Studies using PHA- and IL-2-stimulated primary human PBMCs confirmed that the properties of the K101E+G190S mutant are also observed in primary cells (data not shown). Identification of a clinical RT sequence containing K101E+G190S that has improved fitness compared to K101E+G190S in an NL4-3 backbone In order to determine the impact of RT backbone sequences on the properties of the K101E+G190S double mutant, we constructed a pNL4-3 clone containing an RT sequence derived from patient plasma (clone D10), which contained K101E+G190S. This clinical RT sequence also contained the nucleoside resistance mutations M41L+T215Y, in addition to 28 coding changes in RT compared to NL4-3 (Table 2). In the absence of EFV, NL4-3 virus containing the D10 RT sequence was somewhat more fit than K101E+G190S in an NL4-3 RT backbone (Fig. 3A), but still remained substantially less fit than G190S in an NL4-3 backbone (Fig. 3B). Open in a separate window Figure 3 Effects of the D10 RT sequence on HIV-1 replication in the absence and presence of EFVPanel A, Growth competition experiment Agrimol B with NL4-3 virus containing the D10 RT sequence (with the resistance mutations [K101E+G190S] + [M41L+T215Y]), versus the reference strain, (K101E+G190S) in an NL4-3 RT backbone. The average and standard deviation of the production rate ratio Agrimol B (PRR) is shown on the graph. Panel B, Growth competition experiment with NL4-3 virus containing the D10 RT sequence versus the reference strain, G190S in an NL4-3 RT backbone. The average and standard deviation of the production rate ratio (PRR) is shown on the graph. Panel C, drug susceptibility assay using virus with the D10 RT grown in the presence of varying concentrations of EFV. The peak fold increase in p24 concentration compared to the p24 concentration without drug is noted on the graph at 800 nM EFV. Table 2 Codon Agrimol B changes in the D10 RT compared to NL4-3 (Huang et al., 2003) who tested the resistance and fitness of patient RT sequences with various substitutions at the G190 position. They showed that the fitness of G190 mutations correlated with their prevalence in patients and that they were primarily responsible for the NNRTI resistance pattern. They also showed that the fitness of very poorly replicating mutants was better in the patient backbone where the mutation occurred and that L74V enhanced the replication of.