Exosomes are extracellular nanovesicles secreted by a variety of cells that contain cargo that can be delivered to recipient cells, leading to their physiological roles in regulating the host cell. Exosomes are found in many biological fluids such as semen. Previous research from our laboratory demonstrated that semen exosomes (SE) restrict HIV-1 replication and result in suppressed viral propagation, but the exact mechanism of this process is not currently known.  A key component of identifying the mechanism of action of SE is identifying the inhibitor in SE that mediates this effect. Using proteomic analysis of SE, through mass spectrometry, we identified the highly abundant protein “Y” in SE as a protein of interest for our identification of the HIV inhibitor in SE. Previous studies have shown that Protein “Y” reduces replication of viral protein R (Vpr) positive, but not Vpr-deficient HIV- 1. This suggests that protein “Y” may mediate SE’s inhibition of HIV through HIV Vpr. It is known that Vpr plays a role in the function of early events in the lifecycle including facilitation of reverse transcription, transcription of the viral genome, and nuclear transport of the HIV-1 pre-integration complex (PIC). Here we will investigate the hypothesis that proteins “Y” in SE may contribute to SE-mediated inhibition of HIV-1 potentially through interaction with HIV-1 Vpr. Investigation of this protein will aid in understanding the mechanism of SE mediated HIV-1 inhibitor.