Maraviroc Switch Central Nervous System (CNS) Substudy: a Substudy of MARCH, a Randomised, Open-label Study to Evaluate the Efficacy and Safety of Maraviroc (MVC) as a Switch for Either Nucleoside or Nucleotide Analogue Reverse Transcriptase Inhibitors (N(t)RTI) or Boosted Protease Inhibitors (PI/r) in HIV-1 Infected Individuals With Stable, Well-controlled Plasma HIV-RNA While Taking Their First N(t)RTI + PI/r Regimen of Combination Antiretroviral Therapy (cART).

This substudy is a prospective, observational, open-label, randomised study within the MARCH study. The purpose of this substudy is to investigate the changes in cerebral function parameters at 5 timepoints over 96 weeks of the three different treatment arms within the MARCH study. The investigators hypothesise that there will be improvements in cerebral function in those patients randomised, as part of the parent study, into the maraviroc arms. the assessments in this CNS substudy will include: 1. Neurocognitive function as assessed by a computerised testing battery called CogState; 2. changes in cerebral metabolites as measured via 1H Magnetic Resonance Spectroscopy (1H-MRS) In those randomised to the maraviroc arms (arms 2 and 3) there is an optional Lumbar puncture at week 48. The cerebrospinal fluid will be used to measure maraviroc levels and an ultrasensitive CSF HIV-1 viral load. These results will be matched with levels in the plasma.