Suppression of viremia and evolution of human immunodeficiency virus type 1 drug resistance in a macaque model for antiretroviral therapy

Abstract

Antiretroviral therapy (ART) in human immunodeficiency virus type 1 (HIV-1)-infected patients does not clear the infection and can select for drug resistance over time. Not only is drug-resistant HIV-1 a concern for infected individuals on continual therapy, but it is an emerging problem in resource-limited settings where, in efforts to stem mother-to-child-transmission of HIV-1, transient nonnucleoside reverse transcriptase inhibitor (NNRTI) therapy given during labor can select for NNRTI resistance in both mother and child. Questions of HIV-1 persistence and drug resistance are highly amenable to exploration within animals models, where therapy manipulation is less constrained. We examined a pigtail macaque infection model responsive to anti-HIV-1 therapy to study the development of resistance. Pigtail macaques were infected with a pathogenic simian immunodeficiency virus encoding HIV-1 reverse transcriptase (RT-SHIV) to examine the impact of prior exposure to a NNRTI on subsequent ART comprised of a NNRTI and two nucleoside RT inhibitors. K103N resistance-conferring mutations in RT rapidly accumulated in 2/3 infected animals after NNRTI monotherapy and contributed to virologic failure during ART in 1/3 animals. By contrast, ART effectively suppressed RT-SHIV in 5/6 animals. These data indicate that suboptimal therapy facilitates HIV-1 drug resistance and suggest that this model can be used to investigate persisting viral reservoirs.

FIG. 1.

Plasma viral loads versus CD4 counts for each animal in the pilot study. Four animals were challenged with RT-SHIV_mne from cell culture supernatant at week 0, and plasma vRNA levels (filled symbols) and CD4⁺ cell numbers (open symbols) were measured for animals 96P071 (A), 97P015 (B), 97P029 (C), and 96P084 (D).

FIG. 2.

Plasma viral loads and CD4 counts of animals receiving ART. Animals were challenged intravenously with 1 × 10⁵ infectious units of RT-SHIV_mne at week 0. (A) Three animals were given EFV monotherapy for 3 days during week 13. Daily ART was administered for 20 weeks (17 to 37 weeks postinfection). Animal M03250 was euthanized after virologic failure at week 26. ART was discontinued for the other two animals and reinitiated at week 40 or 41, continuing until week 45. (B) Three animals were given daily ART for 20 weeks (17 to 37 weeks postinfection). ART was discontinued and reinitiated at week 39, 40, or 41, continuing until week 45. (C) Absolute CD4 counts of the ART group animals were measured in the blood at multiple time points. Gray shading represents the time when animals received therapy. Arrows denote when ART was reinitiated for each animal after treatment interruption. The plasma virus decay kinetics are shown for the animals during the week of EFV monotherapy (week 13-14) (D) and the first week of combination therapy (week 17-18) (E). The viral loads are plotted relative to the last pretherapy value. Regression lines for all animals combined are shown for EFV monotherapy and combination therapy, along with the inferred half-lives (r² values are 0.83 and 0.91, respectively).

FIG. 3.

Frequency of drug resistance-conferring mutations for animal M03250 prior to and during therapy. Bars indicate frequencies of K103N (AAC, open; AAT, striped) (A), M184I/V (M184I, striped; M184V, open) (B), and K65R (C), as determined by ASP. The plasma viral load is shown as solid triangles. Gray shading represents therapy administration. The thin line represents the background for each ASP assay.

FIG. 4.

Diversity of the RT coding region of viral genomes at multiple time points from animal M03250. The average pairwise difference per site for 35 genomes at each time point is represented by open bars, and diversity with drug resistance-conferring mutations removed from analysis is represented by striped bars. Plasma viral load is represented by solid triangles. Gray shading represents therapy administration.

FIG. 5.

Frequency of drug resistance-conferring mutations for animal M04008 prior to, during, and after therapy, as determined by ASP. The frequencies of K103N AAC (open) or AAT (solid) are plotted as bars. Solid circles indicate the plasma viral load. Gray shading represents therapy administration. K103N AAC and AAT were not detected in plasma prior to week 13. The background level for the ASP K103N assay is 0.02%. Gray shading represents therapy administration.