This is the first-in-human clinical study to see if a single dose of an investigational enema made from a modified plant protein called Q-Griffithsin is safe, tolerated, and acceptable for use by healthy adults 18-45 years of age who practice receptive anal intercourse. GRFT is one of the most powerful, broad-spectrum antivirals ever tested and its activity is under study for potential therapeutic applications against several viral pathogens including HIV, herpes simplex virus type-2, human papillomavirus (HPV), and hepatitis C. For the purposes of this study GRFT has been genetically modified to produce a more stable compound less prone to oxidation, Q-GRFT