The purpose of the study is to evaluate whether mycophenolate mofetil (MMF) can treat the chronic hyperactivation of the immune system and (partly) prevent the decrease of the CD4+ T-cell count in chronically HIV-1 infected patients who are not treated with antiretroviral therapy (ART). The researchers also want to know what the effect is of treatment with MMF on plasma HIV-1 RNA; progression of disease (occurrence of AIDS defining events or reaching the indication to start ART); and the safety of treatment with MMF in this patient group.