Patients will be randomized in a ratio 1:1 to one of the two treatment arms Control group continuing the ongoing therapy STI group performing long term CD4 guided structured treatment interruptions In the STI arm patients will stay off therapy until their CD4 count will drop < 350 cells/mcL (one measurement will be considered sufficient). At that time point patients will resume the HAART regimen they were assuming before STI and will continue HAART until they CD4 count will raise > 600 cells/mcL (at least 2 consecutive measurements 2 months apart) and their HIV-RNA will drop below the detection limit of 50 copies/ml (one measurement will be considered sufficient). When both the CD4 count and the viral load will be within these pre-set values they will stop therapy again. There is no limit to the number of interruptions and re-start cycles during the study period