HIV enters hast cells by docking onto the CD4 receptor and one co-receptor (CCR5 or CXCR4) on the hast cells. CCR5-using variants are typically associated with HIV-1 transmission and primarily found in early stages of HIV infection, whereas CXCR4-tropic variants appear in advanced stages and are associated with accelerated progression towards AIDS. The aim of the project is to gain insights into molecular mechanisms that drive the dynamics of co-receptor switching in HIV-1 and to get insight in the community structure dynamics of viral quasi-species. We will analyze the quasi-species of HIVinfected patients with and without AIDS symptoms. Computational modelswill be developed and employed to unravel characteristic patterns in genetic and structural differences in the community structures of the quasi-species. By means of machine learning techniques, models will be developed to enable early predictions of co-receptor switches before the phenotypic appearance of CXCR4-tropic variants.