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Structured Treatment Interruptions Workshop Summary

January 31, 2001

Designing Trials to Demonstrate Immune Benefit from STI

The aggregate of experience from many small studies, anecdotal reports and observational databases provides what we know so far about the safety of STI. Despite this experience, reproducible HIV-1-specific immune control has not yet been demonstrated.

The number of variables that must be considered when designing trials to evaluate potential immune benefits are daunting: The duration of a scheduled interruption may be determined by:

  • HIV RNA copy number trigger

  • CD4 cell count trigger

  • A hybrid of RNA and CD4 count


  • By regularly scheduled clinic visits

(CD4+ or RNA triggers can be defined as absolute numbers or as relative changes from a setpoint.)

The choice of number and duration of subsequent interruptions multiplies the variables:

  • Fixed periods of equal duration

  • Fixed periods of progressive duration

  • Individualized periods - CD4+ decline

  • Individualized periods - VL increase

  • Individualized periods - VL plateau

The duration of treatment after interruption is another consideration:

  • Treat until suppressed (<400; <200; <50, or <20 copies/mL)

  • Treat until CD4+ counts have recovered

  • Treat for a fixed period

Hypotheses exist to support each of these approaches, and evidence from animal models can be used to argue for one or another. Short of hitting on a lucky combination in another round of small trials, much basic science and animal research may be needed before interruption schedules for large Phase III trials can be confidently selected. Appendix 2

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