<qa>  What is the name of the study that has been investigated by the U.S. CentersAntiretroviral prophylaxis with the combination of tenofovir and emtricitabine has recently been investigated by the U.S. Centers for Disease Control and Prevention in a series of studies with rhesus macaques. Researchers developed a rectal inoculation model using concentrations of Simian HIV SIV that were representative of HIV exposure in humans. With this model, researchers demonstrated that standard doses of tenofovir disoproxil fumarate delayed, or partially protected, animals from the acquisition of Simian HIV during a 14-week time period. In this same model, high dose tenofovir was fully protective from infection.2 However, it is unknown how concentrations in the macaque mucosal surfaces compare to that in humans. Notwithstanding, a number of clinical studies are currently investigating daily dosing of tenofovir or tenofovir with emtricitabine for pre-exposure prophylaxis.3 