A low CD4/CD8 ratio is considered a surrogate marker of immunosenescence and is an independent predictor of non-AIDS-related morbidity and mortality. Given the strong clinical implications the impact of different regimens on the CD4/CD8 ratio recovery needs to be analyzed. The MERIT study is a completed a randomized, double-blind, multicenter phase IIb/III study with an open-label extension phase (240-week follow-up) to assess the efficacy of zidovudine/lamivudine in combination with maraviroc (MVC) or efavirenz (EFV) in treatment-naïve patients. Anonymised patient level data of the MERIT trial to compare the trajectories of the CD4/CD8 ratio of participants treated with maraviroc vs. efavirenz will be used.