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Dolutegravir monotherapy of simian immunodeficiency virus-infected macaques selects for several patterns of resistance mutations with variable virological outcomes.

Van Rompay KK, et al. J Virol. 2018.


Drug resistance remains a major concern for 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 either during 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 10-50 weeks of treatment was highly variable, and ranged from viral rebound to near pre-treatment levels, to sustained suppression, with viremia 0.5 to 5 log lower than expected based on pre-treatment viremia. A variety of mutations previously described to confer low-level resistance of HIV-1 to DTG or other INSTI were detected, sometimes followed by mutations believed to be compensatory. Some mutations, such as G118R, previously shown to severely impair replication capacity in vitro, were associated with more sustained virologic and immunologic benefits of continued DTG therapy, while other mutations such as E92Q and G140A/Q148K were associated with more variable outcomes. The observed variability of outcomes in macaques warrants avoidance of DTG monotherapy in HIV-infected people.IMPORTANCE A growing number of 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 either during 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.


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