Replicative fitness of wild-type and mutated viruses in monkey PBMCs. Viral replication was assessed in PHA-activated rhesus PBMCs using 10ng of viral inocula normalized on the basis of p27-CA Ag. All replication experiments were conducted in triplicate. Viral replication was monitored by RT assay of culture supernatants at multiple time points. All RT activity results are the average of duplicates. Mock infection denotes exposure of cells to heat-inactivated wild-type virus as a negative control. A. Growth curves of SD2-variants harboring mutations in the DIS (A423G) and NC (E18G and G31K) regions. B. Growth curves of variants harboring compensatory mutations in the DIS (A423G), CA (K197R) and p6 (G49K) regions. C. Viral replication analysis of mutated viruses by TCID50 analysis of viral infectivity as described in Materials and Methods. Results shown are representative of three independent endpoint dilution assay experiments. The scale of the ordinate is logarithmic. Mock infection represents a negative control in which cells were exposed to heat-inactivated wild-type virus.