Currently, there is no cure for HIV-1, but thanks to antiretroviral therapy, viral loads can be kept low enough to prevent transmission. While patients generally cannot suppress HIV-1 replication without antiretroviral therapy, about 10-20% of people who start treatment early after HIV diagnosis can keep their viral numbers low even after a temporary pause in therapy. Studies suggest that this ability to control virus numbers could be linked to the gut microbiome. To explore that relationship, scientists compared the gut microbiome between three “viremic controllers” and nine “viremic non-controllers." After receiving an HIV vaccine, all patients were monitored over a 32-week period during which they paused antiretroviral therapy. Patients were predominantly Caucasian (92%) and men who have sex with men (92%). Viremic controllers showed significantly higher levels of bacteria of the order Bacteroidales and lower levels of bacteria of the order Clostridiales, which exhibit anti-inflammatory properties. These high ratios correlated with small sizes of HIV-1 viral reservoirs—pools of viruses that stay hidden from the immune system. Accordingly, viremic controllers showed increased expression of genes related to immune system activation and inflammatory response. Although small, this exploratory study supports the predictive role played by gut microbes in controlling HIV-1 infection and opens new avenues toward finding a cure.