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Session 72 Poster Session Treatment Interruption Session Time: 4:30-6:30 pm Room 4E-F

528-M. SSITT: A Prospective Trial of Treatment Interruptions in HIV Infection B. Hirschel*1, C. Fagard1, A. Oxenius2, H. Gunthard3, and F. Garcia4 for the Swiss HIV Cohort Study 1Geneva, Switzerland; 2Oxford, UK; 3Zürich, Switzerland; and 4Barcelona, Spain Background: Re-exposure to HIV during planned treatment interruptions may stimulate anti-HIV immunity (the autovaccination hypothesis). Methods: Patients recruited for SSITT had been on HAART, with viral suppression to < 50 copies/mL, for at least 6 months. Treatment was suspended for 2 weeks, and restarted during 8 weeks. After 4 such cycles, treatment was definitely suspended at week 40, unless pre-determined limits of VL and CD4 counts were exceeded. The proportion of patients without treatment, and the proportion of responders (defined as those with a VL < 5000 copies/mL), was measured after 12-56 weeks without treatment. HIV-specific immune responses were evaluated by gamma interferon CD8 ELISPOT. Results: 133 patients were recruited, with a mean CD4 count of 740. 96% had started HAART during chronic HIV infection. Their VL had been BLD for a median of 22 months before SSITT. 24 of 133 or 18% (CI 12-26) were responders at week 52, and 11% at week 96. Low pre-HAART VL, a low level of HIV pro-virus at the start of SSITT, and lack of rebound during week 0-40 predicted response, but the nadir of the CD4 count before HAART did not. 49 patients remain without treatment after a median 44 weeks. The CD4 count decreased by 175 cells/mm3 during the first 12 weeks without treatment (medians 755 to 600, p < 0.001), but stabilized thereafter (medians of 600 at week 52 and 583 at week 84, p > 0.1). HIV-specific immune responses increased between week 0 and week 52 (from a mean of 600 to a mean of 1900 SFCs per million, p < 0.001), but there was no correlation between response and the number of SFCs. 1 of 133 patients showed evidence of virologic escape, with need for salvage therapy. Genotypic evidence or resistance was not found, except for the 184V substitution Conclusions: SSITT shows that a substantial minority of patients currently on HAART can safely be managed without drugs for at least several months, potentially diminishing side effects and costs of therapy. However, SSITT strongly suggests that iterative treatment interruptions will rarely be sufficient to attain the goal of low viremia without antiretroviral therapy, and does not favor the autovaccination hypothesis.

©2002 9th Conference on Retroviruses and Opportunistic Infections