A pilot study evaluating time to CD4 T-cell count <350 cells/mm3 after treatment interruption following antiretroviral therapy ± interleukin 2:: Results of ACTG A5102

Background: Although an intermittent antiviral treatment (ART) strategy may limit long-term toxicity and cost, there is concern about the risk for virologic failure, selection of drug resistance mutations, and disease progression. By boosting CD4 T-cell counts, interleukin-2 (IL-2) could safely prolong the duration of treatment interruption (TI) in a CD4-driven strategy. Methods: The AIDS Clinical Trials Group (ACTG) study A5102 evaluated 3 cycles of IL-2 before TI, on clinical and immunologic outcomes, using a CD4 T-cell count of < 350 cells/mm(3) as the threshold for restarting ART. Forty-seven HIV-infected subjects on potent ART with CD4 T-cell counts of >= 500 cells/mm(3) or more and HIV RNA levels of less than 200 copies/mL were randomized to arm A (ART + three 5-day cycles of IL-2 at 4.5 million U, Sc, BID every 8 weeks, n = 23) or arm B (ART alone, n = 24) for 18 weeks (step 1). At the end of step 1, subjects with a CD4 T-cell count of >= 500 cells/mm(3) or more stopped ART until a CD4 count of < 350 cells/mm(3) (step 2). CD4 T-cell count, time to return of viremia, and the emergence of drug resistance mutations after TI were compared between study arms. Results: IL-2 recipients maintained higher CD4 counts during TI for 48 weeks with a waning of the CD4 effect by 72 weeks. A sustained CD4 T-cell count of more than 350 cells/mm(3) and more durable TI were associated with a higher nadir CD4 T-cell count before ART and higher naive CD4 T-cell count at entry. After TI, a higher viral set point and drug resistance mutations at virologic rebound were associated with a shorter time to CD4 T-cell count of less than 350 cells/mm(3). There were no differences in the magnitude of virologic rebound (at week 8 of step 2, median log(10) HIV RNA level was 4.23 for arm A and 4.21 for arm B) or the steady-state HIV-1 RNA level after week 8. Conclusions: IL-2 before TI did not prolong time to CD4 of less than 350 cells/mm(3). A TI strategy utilizing a CD4 T-cell threshold of less than 350 cells/mm(3) for restarting ART appears generally safe with most subjects in both arms remaining off ART for more than 1 year. Implications of our results for TI strategies include the potential advantage of starting ART at higher CD4 T-cell levels while avoiding any drug resistance and evaluating immunomodulators or drugs to reduce T-cell activation and HIV-1 RNA rebound during the TI.