Intrinsic Replication Competences of HIV Strains After Zidovudine/Lamivudine/Nevirapine Treatment in the Philippines

Abstract

Although drug-resistant HIV variants are considered to be less fit than drug-susceptible viruses, replication competence of these variants harbored by patients has not yet been elucidated in detail. We herein assessed the replication competence of strains obtained from individuals receiving antiretroviral therapy. Among 11 306 participants in a drug resistance surveillance in the Philippines, 2629 plasma samples were obtained from individuals after a 12-month treatment with zidovudine (ZDV)/lamivudine (3TC)/nevirapine (NVP). The replication competence of HIV isolates was then assessed by reinoculation into seronegative peripheral blood mononuclear cells in the absence of drugs in vitro. The drug resistance rate was estimated to be 9.2%. Drug-resistant strains were still a minority of closely related strains in a phylogenetic cluster. Among the available 295 samples, 37 HIV strains were successfully isolated. Progeny viruses were produced at a wide range (5.1 × 10⁶ to 3.4 × 10⁹ copies/mL) in primary culture of peripheral blood mononuclear cells. The viral yields were higher than the corresponding plasma viral load (1300 to 3.4 × 10⁶ copies/mL) but correlated with those (r = 0.4). These results suggest that strains with higher intrinsic replication competence are one of the primary targets of newly selected drugs at the increasing phase of the plasma viral load during antiretroviral therapy.

Keywords: antiretroviral agents; drug resistance; human immunodeficiency virus; microbial cultures; virulence.

Figure 1.

A phylogenetic tree of the HIV-pol region of HIV isolated in the Philippines. The nucleotide sequences of the HIV-pol region (1306 bp, 2096-3401 of HXB2, accession no. K03455) were elucidated, and a phylogenetic tree was produced using the neighbor-joining method. Symbols denote drug-resistant (•) and drug-sensitive (ˆ) strains. In insets A and B, strains of interest are indicated with year and T/N. T and N denote strains collected from individuals with (T) or without (N) treatment history. Bootstrap values (88% and 80%) are indicated at the basal nodes of clusters A and B. The sequence of the simian immunodeficiency virus, isolate 239 (accession no. M33262), was used as an outgroup.

Figure 2.

Relationship between plasma HIV loads and replication potencies of HIV strains. A correlation analysis was performed between plasma HIV loads and the amounts of HIV produced from peripheral blood mononuclear cells inoculated with HIV (HIV-RNA: 10⁶ copies/1.5 × 10⁶ cells/mL) in 7 days (n = 37). Pearson correlation coefficient (r) was 0.375 (P < .05).

Figure 3.

HIV production and levels attained in peripheral blood mononuclear cell cultures. Peripheral blood mononuclear cells (1.5 × 10⁶/mL) were exposed to 5 representative strains (10⁶ copies) and cultured for 7 days. Drug resistance profiles are shown in Table 1, except for DR1509-397. This strain (DR1509-397) did not have a drug resistance-related amino acid variant, although it had a detectable plasma viral load (>1000 copies/mL). Symbols denote the mean values of HIV production; bars represent standard error.

Figure 4.

Relationship between inoculum sizes and production levels. Three different inoculum sizes were used for infections with 5 strains (A). The production levels attained for the strain (DR1606-505 with the lowest replication competence in this study) after its exposure to 10⁶, 10⁷, and 10⁸ (copies/mL) inoculum sizes to peripheral blood mononuclear cells in vitro (B). Bars (A) and symbols (B) denote the mean values of HIV production; error bars depict the standard error.