363   Treatment Interruption (TI) Leads to a Rapid Recurrence of Immunological Changes and Viral Load in Chronic HIV-1 Infection.

J. Van Lunzen*¹, N. Frahm¹, J. E. Schmitz⁴, M. J. Kuroda⁴, C. Hoffmann³, B. Meyer¹, J. Lauer¹, O. Degen¹, K. Tenner-Racz², P. Racz², and H. J. Stellbrink¹for the COSMIC ARCHY Study Groups.
¹Univ. Hosp. Eppendorf, Hamburg, Germany;²Bernhard-Nocht-Inst., Hamburg, Germany;³Univ. of Kiel, Germany; and⁴Beth Israel Deaconess Med. Ctr., Harvard Med. Sch., Boston, MA.

Background:Our objective was to study the kinetics of viral rebound in correlation with parameters of T cell proliferation, activation and functionality after TI in aggressively pretreated asymptomatic patients in the chronic phase of infection.

Methods:Therapy was stopped in 15 patients from 2 randomized, controlled trials who discontinued HAART +/- IL-2 (n = 11) or hydroxyurea (n = 4) after having achieved plasma viremia <25 c/ml for 13—23 months. Patients showed T cell subsets in the normal range compared to age-matched normal controls and rare or no productive HIV replication in lymphoid tissue as well as VL < BLD in the CSF (n = 11) at the time of TI. Viral load was frequently measured by UltraSensitive Amplicor assay. T cell proliferation and activation were determined by 4-colour flow cytometry using a broad panel of mAb (e.g. Ki-67, HLA-DR, CD38, CD25, FAS). Functional assays using intracellular cytokine expression (e.g. IL-2, IFN-g, TNF-α;) were performed after stimulation with mitogens/SEB and recall antigens (e.g. CMV, TT). Tetramer staining (gag) was performed to detect HIV-specific CTL in 7 pts. bearing the A2 subtype. TREC analysis is performed in addition to CD103 staining to detect recent thymic emigrants (RTE).

Results:All patients showed a rapid rebound of viral load after 4 to 8 weeks to baseline levels with a slight overshoot at week four. This was paralleled by a reincrease of proliferation and expression of activation markers on CD4 and CD8 T cells (CD8 > CD4). The kinetics of viral rebound and increase of T cell proliferation and activation as well as the inversion of CD4/CD8 ratio were closely correlated. A slightly more rapid response in the CD8⁺T cell compartment was observed. Tetramer^L+CTL frequency decreased during therapy and is analysed after TI. T cells expressing CD103 as a marker for RTE and/or mucosal T cells reincreased during TI, indicating altered homeostatic mechanisms. T cell responses to mitogen/SEB and recall antigens in vitro decreased over time, indicating recurrence of functional defects. No influence of adjuvant IL-2 or HU therapy on the parameters studied was observed.

Conclusions:The rapid rebound of viral replication after discontinuation of therapy is associated with an inversion of the CD4/CD8 ratio due to increased T cell turnover and activation. Functional defects reappear in parallel despite previous sustained suppression of viral replication in chronic HIV infection. Neither adjuvant IL- 2 nor HU seemed to influence these parameters.