OBJECTIVES: To determine factors associated with CD4 responses to maraviroc (MVC)-containing regimens in treatment-experienced patients. METHODS: Forty-eight-week data from MOTIVATE 1 and 2 was used to assess MVC once or twice daily versus placebo (PBO), each with optimized background therapy (N = 1047). A repeated measures model evaluated longitudinal CD4 changes, multivariate linear regression evaluated predictors of week 48 increases, and Cox proportional hazard modeling evaluated time to category C events. RESULTS: Median CD4 increases were greater on MVC once or twice daily than PBO (92, 103, and 24 cells/mm3, respectively; P < 0.05), and the difference remained significant among patients achieving less than 50 HIV-1 RNA copies/mL (126, 125, and 96 cells/mm3; P < 0.05) or when adjusted for other predictors of CD4 increase including change in HIV-1 RNA. Time to a category C event was longer on MVC; in multivariate models, higher on-treatment CD4 count, but not MVC treatment, was protective against new events (hazard ratio 0.8 per +25 cells/mm3; 95% confidence interval 0.78-0.87). CONCLUSIONS: MOTIVATE patients receiving MVC had larger CD4+ T-cell increases than those receiving PBO, even after adjusting for the greater virologic potency of MVC-containing regimens. This additional CD4 response was associated with a longer time to the development of AIDS-defining events on MVC.