Attachment Inhibitor Comparison in Heavily Treatment Experienced Patients

Inclusion Criteria: * Men and non-pregnant women with chronic HIV-1 infection * Antiretroviral-experienced with documented historical or baseline resistance, intolerability, and/or contraindications to antiretrovirals in at least three classes * Failing current antiretroviral regimen with a confirmed plasma HIV-1 RNA ≥ 400 c/mL (first value from Investigator, second from Screening labs) * Must have ≤ 2 classes with at least 1 but no more than 2 fully-active antiretrovirals remaining which can be effectively combined to form a viable new regimen, based on current and/or documented historical resistance testing and tolerability and safety * Able to receive ≥ 1 fully active approved antiretroviral as part of the OBT from Day 9 onwards in the Randomized Cohort * Subjects without any remaining fully active approved antiretroviral may be enrolled in the Non-Randomized Cohort Exclusion Criteria: * Chronic untreated Hepatitis B virus (HBV) (however, patients with chronic treated HBV are eligible) * HIV-2 infection * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 7 x ULN * Alkaline Phosphatase \> 5 x ULN * Bilirubin ≥ 1.5 x Upper limit of normal (ULN) (unless subject is currently on atazanavir and has predominantly unconjugated hyperbilirubinemia)