 - Change in the ART regimen in the 12 weeks prior to study entry or intended modification of ART during the study. NOTE: Modifications of ART doses during the 12 weeks prior to study entry are permitted. In addition, the change in formulation e.g., from standard formulation to fixed-dose combination is allowed within 12 weeks prior to study entry. A within class single drug substitution e.g., switch from nevirapine to efavirenz or from atazanavir to darunavir is allowed within 12 weeks prior to study entry, with the exception of a switch from any other nucleoside reverse transcriptase inhibitor NRTI to abacavir. No other changes in ART in the 12 weeks prior to study entry are permitted. 