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Immunological and Virological Impact of Highly Active Antiretroviral Therapy Initiated during Acute HIV-1 Infection
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The Journal of Infectious Diseases Sept 15, 2006;194:734-739
Hendrik Streeck,1,2,5 Heiko Jessen,a Galit Alter,1 Nickolas Teigen,1 Mike T. Waring,1 Arne Jessen,a Ingrid Stahmer,4 Jan van Lunzen,4 Mathias Lichterfeld,1 Xiaojiang Gao,3 Todd M. Allen,1 Mary Carrington,3 Bruce D. Walker,1,2 Juergen K. Rockstroh,5 and Marcus Altfeld1
1Partners AIDS Research Center, Infectious Disease Unit, and 2Howard Hughes Medical Institute, Massachusetts General Hospital and Division of AIDS, Harvard Medical School, Boston, Massachusetts; 3Basic Research Program, Science Applications International Corporation-Frederick, Laboratory of Genomic Diversity, National Cancer Institute, Frederick, Maryland; 4Infectious Diseases Unit, University Medical Center Hamburg-Eppendorf, Hamburg, and 5Department of Internal Medicine, University of Bonn, Bonn, Germany
(See the article by Hecht et al., and the editorial commentary by Kinloch-de Loes.)
Abstract
The immunological and virological impact of short-term treatment initiated during acute human immunodeficiency virus type 1 (HIV-1) infection was assessed prospectively in 20 subjects, 12 of whom initiated highly active antiretroviral therapy (HAART) for 24 weeks and then terminated treatment. Treatment resulted in suppression of viremia, an increase in the CD4+ T cell count, enhanced differentiation of HIV-1-specific CD8+ T cells from effector memory to effector cells at week 24 of HAART, and significantly higher virus-specific interferon-y+ CD8+ T cell responses after viral rebound (at week 48). However, despite these immunological changes, no differences in viremia or in the CD4+ T cell count were found 6 months after HAART was stopped, when treated subjects were compared with untreated subjects.
The majority of cases of acute HIV-1 infection present as a transient symptomatic illness associated with high-level HIV-1 replication and an expanding virus-specific immune response. It is during this initial phase of infection that important pathogenic events are thought to occur, including the seeding of virus within a range of tissue reservoirs and the depletion of HIV-1-specific CD4+ T lymphocytes. As a consequence, it has been proposed that therapeutic intervention initiated during acute HIV-1 infection may represent a unique opportunity to reduce the pathogenic effect of HIV-1 replication and to modulate the immune response of the host to HIV-1, allowing for subsequent immune control of disease [1-4].
The current study was designed to test the hypothesis that early antiretroviral therapy (ART) given for 24 weeks during acute HIV-1 infection would allow for the maturation and preservation of HIV-1-specific immune responses, ultimately resulting in enhanced immune control of HIV-1 viremia. Here, we demonstrate that the differences in interferon (IFN)-y+ HIV-1-specific CD8+ T cell responses between treated and untreated individuals, including the differentiation of IFN-y+ HIV-1-specific CD8+ T cells toward effector T cells in treated subjects, did not translate into improved control of viremia or increased CD4+ T cell counts 6 months after termination of HAART that had been initiated at the time of infection and given for 24 weeks. These data suggest the absence of a durable virological benefit of short-term HAART initiated during acute HIV infection.
Methods. Twenty individuals with acute HIV-1 infection were recruited in Berlin, Germany, from October 2002 through November 2003 (table 1). Acute HIV-1 infection was defined by symptomatic disease, high-risk exposure to HIV-1, a detectable plasma HIV-1 RNA level, and either a negative result of HIV-1 ELISA or a positive result of ELISA with an indeterminate result of HIV-1 Western blot analysis (i.e., <3 bands). The study was approved by local institutional review boards, and all individuals provided written, informed consent for participation in this study.
At diagnosis of acute HIV-1 infection, subjects were given the choice to either initiate HAART or remain without therapy while under close clinical observation (table 1). All study subjects presented with an acute viral syndrome, and the estimated median interval between HIV-1 infection and initiation of HAART was 25 days. Individuals who chose to initiate HAART did not differ from those who elected not to initiate HAART, in terms of viral load, CD4+ T cell counts, clinical presentation, and known host factors (table 1). After receiving HAART for 24 weeks, all 12 treated subjects terminated HAART and remained without therapy for the following 6 months. A final evaluation of viral loads, CD4+ T cell counts, and HIV-1-specific T cell responses was performed at week 48. The plasma HIV-1 level was quantified using the Roche Amplicor test, and CD4+ T cell counts were determined using flow cytometry.
An IFN-y ELISPOT assay was used to quantify HIV-1-specific CD8+ T cell responses by use of cryopreserved peripheral blood mononuclear cells (PBMCs) and peptides corresponding to HLA-matched optimal epitopes, as described elsewhere [5]. PBMCs were stimulated with pools of overlapping peptides spanning the clade B consensus sequences of HIV-1 Gag, Pol, Nef, and Env, as well as Vpr, Vpu, Vif, Tat, and Rev, as described elsewhere [6]. The cells were then stained with surface antibodies against CD3, CD8, CD45RA, and CCR7, to determine the differentiation status of CD8+ T cells [7]. Intracellular interleukin (IL)-2 and IFN-y staining was performed as described elsewhere [6], to characterize the functional capacity of antigen-specific CD8+ T cells, and CD107a expression was evaluated as a surrogate for T cell degranulation [8]. A response was considered to be positive if it consisted of at least 10 acquired events, if the staining was at least 2-fold higher than the background levels, and if the staining involved >0.03% of CD8+ T cells.
Statistical significance was determined using the Mann-Whitney 2-tailed t test, a multivariate analysis of variance test, or the Friedman procedure tests, as indicated. P < .05 was considered to be statistically significant.
Results. Twenty consecutive subjects were enrolled in the present study (table 1). Untreated and treated individuals did not differ significantly in terms of their viral loads and CD4+ T cell counts at baseline (table 1). All treated subjects had full suppression of viremia (<50 HIV-1 RNA copies/mL) after receiving HAART for 24 weeks, and the 2 groups of subjects had significantly different viral loads and CD4+ T cell counts at that time (figure 1). However, after termination of treatment, the viral load rebounded in all treated subjects, and viral loads and CD4+ T cell counts did not differ between the 2 groups at the end of the 48-week study (figure 1). Taken together, these data demonstrate that early short-term treatment initiated during acute HIV-1 infection had no sustained influence on viral loads or CD4+ T cell counts after 1 year of infection.
To assess the association of HIV-1 viremia with evolution of HIV-1-specific CD8+ T cells, we performed a longitudinal analysis of HIV-1-specific CD8+ T cell responses by means of intracellular cytokine staining and evaluation of CD107a expression with the use of multiparameter flow-cytometric analysis. At baseline, no difference was observed between the 2 study groups, with regard to the magnitude of the HIV-1-specific IFN-y+ or CD107a+ CD8+ T cell responses against the full HIV-1 proteome (P = .7 and P = .3, respectively) (figure 2). At 8 and 24 weeks after infection, the proportion of HIV-1-specific CD8+ T cells secreting IFN-y and expressing CD107a was higher in the untreated group than in the treated group; however, this difference did not reach statistical significance (figure 2).
In contrast to the higher HIV-1-specific CD8+ T cell responses noted in the untreated individuals during the first 24 weeks of the study, responses were higher in the treated individuals at week 48, when both groups were not receiving therapy. In line with the findings of previous reports, the immunodominant targets for HIV-1-specific CD8+ T cells in both groups of infected study subjects were HIV-1 Nef and Gag.
Overall, we observed a significant increase in the IFN-y+ and CD107a+ HIV-1-specific CD8+ T cell responses in both groups during the 12-month study period, and this increase was more prominent in the subjects who received treatment at baseline. In line with this increase in overall responses to the pools of peptides, HIV-1-specific CD8+ T cell responses to individual HIV-1 CD8+ T cell epitopes increased over the study period when quantified using an IFN-y ELISPOT assay (mean values [± SD]: 883 ± 969 to 3258 ± 3294 spot-forming cells [sfc]/million PBMCs, for untreated subjects; 696 ± 979 to 4756 ± 5417 sfc/million PBMCs, for treated subjects). In contrast to strong IFN-y+ and CD107a+ HIV-1-specific CD8+ T cell responses, IL-2 production by the same cells was low at all time points and was below the cutoff level for a positive response (data not shown). Taken together, these data indicate that short-term HAART for 24 weeks during acute HIV-1 infection, followed by treatment discontinuation, results in a stronger increase in IFN-y+ and CD107a+ HIV-1-specific CD8+ T cell responses than does continuous exposure to virus. However, the viral set point at 48 weeks after infection was not modulated by these differences in HIV-1-specific CD8+ T cell responses.
Recent studies have suggested that functional impairment of HIV-1-specific T cells is associated with a block in T cell differentiation from effector memory cells to effector cells [7]. To evaluate whether the use of short-term therapy during acute infection could overcome this maturation defect, we monitored the differentiation status of IFN-y+ HIV-1-specific CD8+ cells. Study subjects exhibited an accumulation of HIV-1-specific CCR7-CD45RA- effector memory CD8+ T cells during acute infection (figure 2), and the maturation status of HIV-1-specific CD8+ T cells in the 2 groups did not differ at baseline. Interestingly, this block of maturation from effector memory cells to effector cells was resolved after 24 weeks of therapy; however, it reemerged with viremia after treatment discontinuation, and the degree of HIV-1-specific CD8+ T cell differentiation was again identical in both groups at week 48 (figure 2). These data suggest that the use of ART for individuals with acute HIV-1 infection may have at least transiently overcome the defective maturation of CD8+ T effector cells but that this increased differentiation was not associated with better control of viremia after treatment discontinuation and was rapidly lost in the presence of rebounding viral replication.
Discussion. In the present study, we evaluated the influence of HAART that was initiated at the time of diagnosis of acute HIV-1 infection and was given for 24 weeks, followed by simple termination of treatment, on HIV-1-specific CD8+ T cell responses and viral control at 1 year after infection in a cohort of 20 subjects. Our data demonstrate that, despite an increase in the percentage of fully differentiated HIV-1-specific CD8+ T cells in treated subjects and a more pronounced increase in IFN-y+ HIV-1-specific CD8+ T cells after reexposure to virus, no enhanced control of HIV-1 replication was observed 24 weeks after treatment termination in the treated subjects, compared with that in the untreated subjects. This pilot study suggests that short-term HAART initiated during acute HIV-1 infection may not, in itself, be sufficient to enhance the immune control of HIV-1 replication.
In line with data reported elsewhere [9-11], our study demonstrated that HIV-1-specific CD8+ T cell responses during acute HIV-1 infection were of low magnitude. Although these responses increased in the presence of ongoing viral replication in subjects who were not receiving treatment, initiation of HAART during acute HIV-1 infection led to a blunting of IFN-y+ HIV-1-specific CD8+ T cell responses in the treated subjects, compared with those in the untreated subjects. However, control of viremia through ART allowed for the maturation of HIV-1-specific CD8+ T cells to fully differentiated (CCR7-CD45RA+) effector cells at week 24. After treatment termination, HIV-1-specific CD8+ T cell responses increased dramatically in the treated subjects, resulting in IFN-y+ and CD107a+ HIV-1-specific CD8+ T cell responses that were stronger at 48 weeks than those noted in the untreated subjects. However, the population of CCR7-CD45RA+ HIV-1-specific CD8+ effector T cells observed in the treated group before termination of treatment decreased in the presence of rebounding viremia. These data suggest that the differentiation status of HIV-1-specific CD8+ T cells is largely determined by the level of viremia, and the data are consistent with recent studies that have demonstrated that the phenotypic and functional heterogeneity of antigen-specific CD4+ T cells is largely dictated by antigenemia [12]. Furthermore, receipt of treatment for 24 weeks during acute infection did not result in a reconstitution of IL-2+ HIV-1-specific CD8+ T cell responses, and longer treatment periods may be needed to reconstitute this potentially important T cell population [12, 13]. Finally, despite these changes in IFN-y+ HIV-1-specific CD8+ T cell counts and differentiation that occur as a result of early treatment, no impact on viral load was observed in the treated subjects after discontinuation of HAART, compared with study subjects who remained untreated during the entire study period.
The present study shows that short-term HAART initiated during acute HIV-1 infection has no major impact on the control of HIV-1 viremia 6 months after HAART is discontinued and that several immunological markers that are currently used to characterize HIV-1-specific CD8+ T cell responses fail to predict the ability of the immune system to control viral replication. No gut-tissue biopsy specimens from these study subjects were available, and we therefore were not able to assess the influence of early use of HAART on the gut-associated lymphoid tissue, a compartment that is heavily affected during acute HIV-1 infection [14]. Although this study does not allow direct conclusions to be drawn regarding the potential long-term benefit of short-term treatment initiated during acute infection, the finding of an identical viral set point at 48 weeks, representing a strong predictor of the overall speed of disease progression, makes such a long-term benefit unlikely. The recently published results of the QUEST study [15] have shown that the addition of therapeutic immunizations has no benefit in terms of the virological control noted 6 months after discontinuation of HAART initiated during the acute phase of HIV-1 infection. However, it is important to continue to investigate in larger cohorts the immunotherapeutic interventions that involve newer and more powerful agents at this early stage of the infection, to provide an alternative to the currently limited choice of receiving no treatment or continuing to receive HAART.
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