Determinants of virologic and immunologic outcomes in chronically HIV-infected subjects undergoing repeated treatment interruptions: The Istituto Superiore di Sanità-Pulsed Antiretroviral Therapy (ISS-PART) study

BACKGROUND: Factors influencing the outcome of structured treatment interruptions (STIs) in HIV chronic infection are not fully elucidated. METHODS: In ISS-PART, 273 subjects were randomly assigned to arm A (137 assigned to continuous highly active antiretroviral therapy [HAART]) and arm B (136 assigned to 5 STIs of 1, 1, 2, 2, and 3 months' duration, each followed by 3 months of therapy). Main outcome measures were the proportion of subjects with a CD4 count >500 cells/mm, the rate of virologic failure, and the emergence of resistance at 24 months. RESULTS: The proportion of subjects with a CD4 count >500 cells/mm was higher in arm A than in arm B (86.5% vs. 69.1%; P = 0.0075). Pre-HAART CD4 cell count and male gender were independent predictors of a CD4 count >500 cells/mm in arm B. The overall risk of virologic failure was not increased in arm B; however, it was higher in the 38 subjects who had resistance mutations in the rebounding virus. Archived mutations at baseline and the use of a regimen that included an unboosted protease inhibitor (PI), compared with nonnucleoside reverse transcriptase inhibitor-based HAART, independently predicted the emergence of plasma mutations during STI (P = 0.002 for DNA mutations and P = 0.048 for PI-based HAART). CONCLUSIONS: Our results suggest that patients with preexisting mutations and treated with unboosted PI-based HAART should not be enrolled in studies of time-fixed treatment interruptions, being at higher risk of developing plasma mutations during STI and virologic failure at therapy reinstitution. © 2007 Lippincott Williams & Wilkins, Inc.