The MASTER study is a phase IV, randomized, open label, cross-over, intervention study. Study subjects who are on stable abacavir-containing regimen will be randomized into two arms. In arm A maraviroc will be added to their regimen at baseline, while study subjects in arm B will continue their abacavir-containing regimen. After 8 weeks, cross-over of the study arms will be performed. Subjects in arm A will then stop maraviroc, while in subjects in arm B maraviroc will be added to their regimen (for 8 weeks again). The total duration of the study will be 16 weeks.