The addition of an experimental amino acid to a standard HIV drug regimen may be all that’s necessary for people struggling to keep their viral loads undetectable, according to a study published in The Journal of Immunology and reported by EurekAlert.

Despite the potency of modern antiretroviral (ARV) treatment, it still fails to keep HIV completely under control in roughly 10 to 20 percent of people beginning treatment for the first time. Researchers have experimented with adding additional ARV drugs to typical regimens, but this strategy—called treatment intensification—comes with a good chance of additional side effects and without a guarantee of increased effectiveness.

Now, Adriano Boasso, PhD, from the Imperial College London, and his colleagues report that a modified amino acid called D-1mT increased the effectiveness of ARV treatment in monkeys infected with simian immunodeficiency virus (SIV)—the monkey version of HIV.

Boasso’s team originally theorized that D-1mT would help control SIV in monkeys regardless of whether they were given ARV treatment. This is because D-1mT is able to block an enzyme called IDO that HIV and SIV use to suppress the immune system’s attempts to control the viruses. Boasso’s team found that D-1mT had no effect at all in monkeys who were not on ARV therapy. To their surprise, however, D-1mT did help four of six monkeys who were on ARV therapy but had uncontrolled virus levels.

“The effect D-1mT seemed to have on viral load was really encouraging, but it was a surprise to us—we didn’t expect D-1mT to work only in [monkeys] that were already being treated with [ARVs],” Boasso said. “It seems that D-1mT synergizes with [ARVs], and we would really like to find out how this works.”

The authors intend to explore this effect further and to evaluate the safety of D-1mT, which is in a Phase I human study as a cancer treatment.