Dolutegravir Monotherapy of Simian Immunodeficiency Virus-Infected Macaques Selects for Several Patterns of Resistance Mutations with Variable Virological Outcomes

Abstract

Drug resistance remains a major concern for human immunodeficiency virus (HIV) treatment. To date, very few resistance mutations have emerged in first-line combination therapy that includes the integrase strand transfer inhibitor (INSTI) dolutegravir (DTG). In vitro, DTG selects for several primary mutations that induce low-level DTG resistance; secondary mutations, while increasing the level of resistance, however, further impair replication fitness, which raised the idea that DTG monotherapy may be feasible. The simian immunodeficiency virus (SIV) rhesus macaque model of HIV infection can be useful to explore this concept. Nine macaques were infected with virulent SIVmac251 and started on DTG monotherapy during either acute (n = 2) or chronic infection (n = 7). Within 4 weeks of treatment, all animals demonstrated a reduction in viremia of 0.8 to 3.5 log RNA copies/ml plasma. Continued treatment led to overall sustained benefits, but the outcome after 10 to 50 weeks of treatment was highly variable and ranged from viral rebound to near pretreatment levels to sustained suppression, with viremia being 0.5 to 5 logs lower than expected based on pretreatment viremia. A variety of mutations previously described to confer low-level resistance of HIV-1 to DTG or other INSTI were detected, and these were sometimes followed by mutations believed to be compensatory. Some mutations, such as G118R, previously shown to severely impair the replication capacity in vitro, were associated with more sustained virological and immunological benefits of continued DTG therapy, while other mutations, such as E92Q and G140A/Q148K, were associated with more variable outcomes. The observed variability of the outcomes in macaques warrants avoidance of DTG monotherapy in HIV-infected people.IMPORTANCE A growing number of anti-HIV drug combinations are effective in suppressing virus replication in HIV-infected persons. However, to reduce their cost and risk for toxicity, there is considerable interest in simplifying drug regimens. A major concern with single-drug regimens is the emergence of drug-resistant viral mutants. It has been speculated that DTG monotherapy may be a feasible option, because DTG may have a higher genetic barrier for the development of drug resistance than other commonly used antiretrovirals. To explore treatment initiation with DTG monotherapy, we started SIV-infected macaques on DTG during either acute or chronic infection. Although DTG initially reduced virus replication, continued treatment led to the emergence of a variety of viral mutations previously described to confer low-level resistance of HIV-1 to DTG, and this was associated with variable clinical outcomes. This unpredictability of mutational pathways and outcomes warns against using DTG monotherapy as initial treatment for HIV-infected people.

Keywords: HIV; SIV; animal models; dolutegravir; resistance.

FIG 1

Experimental design. Two groups of SIVmac251-infected macaques were started on early (n = 2) or late (n = 7) DTG monotherapy. Therapy in group 1 was stopped after 50 weeks, while the animals of group 2 were maintained on treatment until the time of euthanasia.

FIG 2

DTG treatment of acute infection. Two male juvenile macaques were inoculated intravenously with SIVmac251 at time zero and started on chronic DTG therapy (yellow box) 2 weeks later. Plasma viremia (number of RNA copies per milliliter) (A) and the CD4⁺/CD8⁺ T cell ratio (B) were monitored regularly. The limit of detection of plasma viral RNA was 15 copies/ml. The dotted lines represent, for comparison, data on recent SIVmac251-infected historical control animals (juveniles and adolescents). In panel A, the main mutations observed in integrase (Tables 1 and 2) are listed after the animal numbers. Both animals were Mamu-A*01 negative but Mamu-B*01 positive. Animal 43921, which had additional testing, was Mamu-B*17 positive and Mamu-B*08 negative.

FIG 3

DTG monotherapy of chronic SIVmac251 infection. Seven SIVmac251-infected juvenile macaques with a high viral set point (>6 log RNA copies/ml plasma) were started on DTG monotherapy (yellow). Viral RNA levels in plasma and CD4⁺/CD8⁺ T cell ratios were monitored regularly. (A) Means for both markers; (B to H) individual values for all 7 animals. For each individual animal, the earliest detection of integrase mutations is indicated (arrow); the main mutations observed at the end of the study are summarized on the top right of each graph (Tables 1 and 2). The sex and presence of the Mamu-A*01 and Mamu-B*01 alleles are indicated after each animal number. F, female; M, male; A01+, Mamu-A*01 positive; A01−, Mamu-A*01 negative; B01+, Mamu-B*01 positive; B01−, Mamu-B*01 negative.

FIG 4

Effects of integrase mutations on SIV replicative capacity in PBMCs sand infectivity in TZM-bl cells. (A) Macaque PBMC cultures were infected with equivalent amounts (normalized on RT activity) of wild-type SIVmac239 or SIVmac239 engineered to have the indicated integrase mutations. Replicative capacity was measured over time using RT activity quantification. (B to D) TZM-bl reporter cells were infected with wild-type SIVmac239 or SIVmac239 engineered to have the indicated integrase mutations, and infectivity relative to that of the wild-type virus was measured. (E) Calculated half-effective infectious concentrations. Higher EC₅₀ values indicate lower infectiousness. RLU, relative light units; CI, confidence interval.