 This is a nonrandomized, open-label, multicenter study to investigate the HIV antiviral response in CSF when vicriviroc is added for 2 weeks to the subjects failing antiretroviral background regimen. The primary efficacy endpoint of this study is the mean change in log10 CSF HIV RNA from baseline at Week 2. The secondary efficacy endpoint is the proportion of subjects achieving CSF HIV RNA 50 copiesmL at Week 2. At Week 2, the subjects background regimen will be optimized and vicriviroc continued up to Week 24. After completing Week 24 of the study, subjects will be offered the option to continue on open-label VCV 30 mg once daily, if appropriate, until commercially available or until the sponsor terminates the clinical development of VCV. Subjects who discontinue vicriviroc for any reason will be requested to participate in long-term follow up. 