Host factors seem to play a role in controlling the level of HIV-1 infection in some patients, according to research published in Nature Communications this week. The work describes that two patients, one with very low and another with undetectable levels of the virus, do not have defects in its replication. The researchers suggest this is not because of defects in the virus but factors in the patients themselves that control the circulating amounts of HIV-1. HIV-1 patients that maintain very low levels of virus are known as viremic controllers, other infected patients in whom the virus is undetectable are referred to as elite suppressors. How these two sets of patients maintain low levels of virus is unknown but has been suggested to occur due to a defective virus. Joel Blankson and colleagues studied an elite suppressor patient and a viremic controller patient and demonstrated that the virus found in these patients can multiply in cells in culture, discounting the theory that in these patients the virus was defective in replication. The two patients did not carry genetic variation in the CCR5 gene that is known to slow the progression of HIV disease. These findings suggest that unknown factors in the patients control the levels of virus.