Among those without GBV-C viremia, CD4 cell responses were significantly greater among those assigned to receive IV IL-2 when compared with those assigned to receive subcutaneous IL-2 at both week 60 and week 84 (Table 1, P < 10−6 and P < 10−7, respectively). In contrast, individuals with GBV-C viremia assigned to IV IL-2 did not demonstrate a significant increase over those assigned subcutaneous (P = 0.50 at week 60, P = 0.89 at week 84, respectively). The comparison of CD4 cell response in the IV versus subcutaneous comparison for those with GBV-C viremia to those nonviremic was significant (interaction P = 0.002 at week 60 and P < 10−4 at week 84).
There were no differences in HIV RNA levels between GBV-C viremic and nonviremic patients, irrespective of IL-2 treatment group, and GBV-C viral load did not correlate with change in CD4 cell counts (data not shown). IL-2 administration was not associated with significant differences in GBV-C viral load at any time point, nor did CD4 cell count changes correlate with GBV-C viral load (data not shown).
In this substudy of ACTG 328, the GBV-C viremia status was characterized at the time individuals were randomly assigned to IL-2 or no IL-2 in combination with ART. Among individuals with GBV-C viremia, there was no significant difference in CD4 cell count increases in subjects assigned to receive IL-2 compared with individuals who were not assigned IL-2. Thus, IL-2 failed to stimulate CD4 cell expansion in people with GBV-C viremia. In contrast, CD4 cell counts increased significantly among those without GBV-C viremia assigned to IL-2 (437 cells/μl greater than those not assigned IL-2 at week 60). Treatment interaction was significant based on GBV-C viremia status at week 60 (P = 0.01) and week 84 (P = 0.02), providing strong statistical credibility to the interaction of GBV-C viremia with IL-2 [26,27].
Limitations of this analysis include the fact that samples were not available for GBV-C testing in 42% of the randomized individuals in ACTG 328, and that this study was designed retrospectively. Despite these limitations, significant differences in CD4 cell count responses were observed between GBV-C positive and GBV-C negative individuals following both 60 and 84 weeks of therapy. In addition, individuals with samples studied for GBV-C were not significantly different from the entire ACTG 328 cohort either at baseline or in CD4 cell change and HIV change following IL-2 within the treatment groups (data not shown). Thus, further investigations of GBV-C status in randomized studies of IL-2 administration in HIV-infected people are warranted. If the results observed in this study were validated, the measurement of GBV-C viremia status would be important prior to administration of IL-2 therapy, particularly if the goal is to increase CD4 cell number.
In this study GBV-C viremia was associated with a block in IL-2-related T-cell proliferation. This, in combination with the in vitro evidence that IL-2 decreases GBV-C replication suggests that there is an interaction between GBV-C and IL-2 signaling pathways. Further study of mechanisms by which GBV-C influences IL-2 response is warranted.
This work was supported in part by Merit Review Grants from the Veterans Administration (J.T.S. and J.X.), and by an NIH RO1 grant (AI-58740, J.T.S.), ACTU grants, (AI-69424, AI-27660, R.M. and J.F.). We are grateful to Rebecca Gelman PhD and Deborah Wang Cheng MS for providing the ACTG data and to Suhong Zhang PhD for an analysis of an earlier data set, and Jennifer Nowack for assistance with specimens. Supported in part by the AIDS Clinical Trials Group funded by the National Institute of Allergy and Infectious Diseases.
J.S. proposed the idea to the ACTG, and oversaw all aspects of the protocol design, testing, data evaluation, and writing of the manuscript. K.C. assisted in preparing the proposal, in study design, data analysis and interpretation, and in writing the manuscript. J.Z. assisted in the data analysis, interpretation, and writing the manuscript. D.K. and I.S. oversaw GBV-C testing, data analysis and interpretation, and writing the manuscript. J.X. developed and validated the real-time PCR method for GBV-C quantification used in these studies, and assisted in testing samples, interpreting results and writing the manuscript. A.L., J.F., R.P., and R.M. served as co-chairs for the ACTG protocols, coordinated sample shipping, data transferal, study interpretation and writing the manuscript.
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