 Cohorts 2, 3, and 4 will be on a boosted protease inhibitor PI or any other 3rd ARV agent and will switch their current 2-NRTI-containing regimen to open-label FTAF while continuing their boosted PI or 3rd agent through 48 weeks. A minimum of 10 participants each in Groups 1 and 2 of Cohort 2, and Cohorts 3 and 4, who are on boosted-ATV as their 3rd ARV agent will be enrolled. Participants in Cohort 2, Group 1 receive boosted PI agents only. Cohorts 2, 3, and 4 will be enrolled by cohort into a two-part study Parts A and B. 