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Clinical Science

The Role of Hydroxyurea in Enhancing the Virologic Control Achieved Through Structured Treatment Interruption in Primary HIV Infection

Final Results From a Randomized Clinical Trial (Pulse)

Bloch, Mark T. MB BS, Dip FP, M Med; Smith, Don E. MB, ChB, MD; Quan, Dick MB BS; Kaldor, John M. PhD; Zaunders, John J. BSc(Hons), PhD; Petoumenos, Kathy BSc, MA, MPH(Hons), PhD; Irvine, Kathy BSc, MPsych, MBiostat; Law, Matthew MA, MSc, PhD; Grey, Pat RN, BA, DipEd, GradDipAppSci, DipCounselling; Finlayson, Robert J. MB BS, Dip Ven, FAChSHM; McFarlane, Robert MB BS; Kelleher, Anthony D. BSc(Hons), MB BS(Hons), PhD, FRACP, FRCPA; Carr, Andrew MMBS, MD, FRACP, FRCPA; Cooper, David A. AO, BSc(Med), MB BS, DSc, MD, FRACP, FRCPA, FRCP

Author Information
JAIDS Journal of Acquired Immune Deficiency Syndromes: June 2006 - Volume 42 - Issue 2 - p 192-202
doi: 10.1097/01.qai.0000219779.50668.e6
  • Free

Abstract

The goal of viral eradication in HIV disease has proven elusive.1,2 Long-term viral suppression is possible with antiretroviral (ARV) therapy but requires high levels of adherence from patients and is associated with complications.3-6 The level of plasma viremia-the "viral set-point"-following primary HIV infection (PHI) is known to be prognostic for long-term disease progression, making this stage of the illness an appealing target for short-term interventions.7 Therapy during PHI results in impressive suppression of high levels of viremia8-10 and may also reduce the size of viral reservoirs.11,12

Specific immune responses against HIV are impaired early in PHI if ART is not used, possibly due to preferential infection of those HIV-specific T lymphocytes expressing increased CD4 molecules on their surface.13,14 In addition, high levels of nonspecific immune activation, evidenced as CD38 expression on CD8+ T lymphocytes, are thought to result in accelerated senescence of the immune system15 and are a reliable indicator of poor prognostic outcome.16-18

Two therapeutic interventions have been postulated as possible means of either augmenting HIV-specific immune responses or reducing immune hyper-activation.19 Structured treatment interruptions (STIs) have been reported to augment specific responses and lead to off-therapy control of viremia.20-26 Durable virologic control may also be enhanced using hydroxyurea (HU), an immunomodulator that suppresses T-lymphocyte activation.27 HU augments the antiviral activity of didanosine, making it a potentially useful agent with immunologic and virologic effect.28-32

We therefore initiated a randomized clinical trial to determine whether the addition of HU in combination with ARV therapy including didanosine results in improved virologic control in the setting of STI in patients with PHI.

METHODS

Subject Population

Patients diagnosed with PHI were recruited from a network of primary care sites and St Vincent's Hospital, in Darlinghurst, Sydney, Australia, between January 2000 and February 2002.

Eligible patients had either HIV detected by p24 antigenemia or plasma viremia (Roche Amplicor kit 1.5, Roche Diagnostics, Pleasantown, CA) and a negative or indeterminate Western blot (by the Australian national definition, <4 bands is defined as indeterminate) (HIV Blot 2.2; Genelabs Diagnostics, Singapore) (acute PHI infection), or a fully positive Western blot and documented negative HIV antibody test (Axsym HIV-1/2; Abbott Diagnostics, Abbott Park, IL) within the previous 6 months (early PHI infection).

Consenting patients were given an ARV regimen consisting of a boosted protease inhibitor (PI) and 2 nucleoside analogues: indinavir 800 mg BID, ritonavir 100 mg BID, didanosine 400 mg, and either stavudine 40 mg BID or lamivudine 150 mg BID (the protocol was amended in September 2000 to replace stavudine with lamivudine once the cumulative toxicity of didanosine/stavudine was well reported33) with randomization, on a 1:1 basis, to the addition of HU, 500 mg BID. Patients were also stratified to ensure an even balance of acute or early PHI between each arm. Dose reduction of HU to 500 mg once daily was permitted because of intolerance. Substitution of individual medication within the same antiviral class was permitted because of drug intolerance.

Therapy was given as follows. Induction (phase A) which was administered for at least 6 and up to 12 months (to induce a plasma HIV RNA <50 copies/mL).

Patients who achieved a sustained undetectable viral load (<50 copies/mL within the first 6 months, without further detection of virus) were eligible to enter the interruption phases. This involved discontinuation of all ARVs for up to 6 months (patients randomized to HU were asked to continue this during the ARV treatment interruptions). If plasma viral loads exceeded 5000 copies/mL at any stage during a treatment interruption, therapy was reintroduced (phase C). Up to 3 STIs (phases B1, B2, and B3) and 2 reintroduction of ARV treatment phases (C1, and C2) were allowed.

Study visits were scheduled at screening, baseline, weeks 1, 2, 4, and 8, and monthly thereafter during induction (phase A). During STIs, visits were weekly for the first month, then monthly.

The primary study end point was defined as proportion of subjects who maintained plasma HIV RNA levels at less than 5000 copies/mL for 6 months after any treatment interruption. Secondary end points were mean time-weighted change in CD4 T lymphocyte count and HIV RNA changes in each group (±HU) during the interruption phases.

Adverse events were graded according to the ACTG grading system and grade 2 to 4 events were recorded at each study visit.

Research ethics approval was given by St Vincent's Hospital and the University of New South Wales Research Ethics Committees. All participants signed an informed consent form before study entry.

Statistical Analysis

Sample Size

The sample size was calculated to give 80% power to detect an increase in the proportion of patients with treatment success from 10% in treatment arm 1 (ARV-alone) to 50% in treatment arm 2 (ARV + HU).

Subject characteristics including demographics, clinical, immunologic, and virologic characteristics, were planned to be summarized at baseline and at the end of phase A. HIV infection was assumed to have occurred 2 weeks before the onset of acute retroviral symptoms for symptomatic patients34 or the midpoint between the last negative and first positive test for asymptomatic patients. The primary efficacy analysis compared the randomized treatment groups in terms of strategy success and immunologic and virologic markers at 6 months after cessation of therapy. Efficacy end points were analyzed according to intention to treat, including all randomized patients with data at baseline, who had at least 1 follow-up assessment and commenced treatment (regardless of treatments received during the study). Patients who did not interrupt treatment and patients who were permanently lost to follow-up were categorized as strategy failures. In secondary analyses, patients who did not commence treatment, patients without at least 1 follow-up assessment, patients who did not interrupt treatment, and patients who were lost to follow-up before completing the induction phase (Phase A) were excluded.

The primary end point, the proportion of patients with strategy success (maintaining viral load at <5000 copies/mL for at least 6 months off treatment), was summarized by treatment group. Secondary end points, time-weighted change from baseline to the end of each phase changes in CD4 T-cell count, CD8 T-cell count, and log viral load, were summarized by nominal study weeks using a time-window approach. Time windows for nominal study weeks were defined using the midpoint of the nominal study weeks, except for baseline and first visit. If there was more than 1 value in a time window, the average was used. Analysis was based on available data. Patients are excluded from any phase for which no measurements (CD4 T-cell count, CD8 T-cell count, and viral load) were made. The time-weighted approach was used to account for the variable duration of each phase as allowed by the protocol. Formal statistical comparisons of groups were based on the mean difference between treatment groups by treatment phase.

Treatment groups were compared using χ2 test or logistic regression for categorical end points (e.g. the proportion of patients with strategy success), and continuous end points were analyzed using t test or nonparametric alternatives.

An overall analysis of predictors of achieving a viral load of less than 5000 copies/mL at end point (success in any interruption phase) was also performed using logistic regression. The analysis was based on 59 patients and excluded those who did not commence treatment, patients without at least 1 follow-up assessment, patients who did not interrupt, and patients lost to follow-up before completing induction (phase A). Covariates considered for analysis were baseline patient demographic variables, randomized treatment group, time-weighted CD4 T-cell and CD8 T-cell change during induction, and length of induction phase.

RESULTS

Patients

Subject disposition is shown in Figure 1. Seventy-two patients consented to be randomized, but 4 failed to return for initiation of therapy and were excluded from further analysis.

FIGURE 1
FIGURE 1:
Patient disposition.

Sixty-eight homosexual or bisexual male patients were randomized (35 to ARV + HU, 33 to ARV-alone). Seven patients commenced therapy with a stavudine-containing regimen, and the remaining 61 with a lamivudine-containing regimen. Nine of the 68 patients were not eligible for interruption for the following reasons: 3 withdrew from the study (at weeks 16, 24 and 48), 3 stopped because of drug-related toxicities and were unwilling to use alternative medications (at weeks 16, 20 and 24), 1 was withdrawn for nonadherence at week 8, 1 was lost to follow-up at week 32, and 1 was not virologically suppressed after 52 weeks' therapy. Treatment groups were well matched for baseline characteristics (Table 1). Only 18 of the 29 ARV + HU patients elected to continue HU during their ARV treatment interruptions.

TABLE 1
TABLE 1:
Baseline Patient Characteristics

Viral Dynamics

No differences in viral load were found between treatment arms during any phase. All subjects showed rapid declines in plasma RNA levels during each treatment phase (Fig. 2), with a median time to less than 50 copies/mL of HIV RNA of 16 weeks for both the ARV + HU and ARV-alone groups. Overall, on an intent-to-treat analysis, 18 subjects were able to maintain virologic control (HIV RNA <5000 copies/mL) for 6 months after cessation of therapy (9 [26%] ARV + HU and 9 [27%] ARV-alone, P = 0.88), comprising 11 subjects after their first STI, 1 after a second STI, and 6 after a third STI. These results were not altered significantly if an as-treated analysis (excluding subjects lost to follow-up during phase A) was used with no difference detected between groups in the proportion controlling virus at 6 months off ARV treatment (31% ARV + HU and 30% ARV-alone, P = 0.93). Viral rebounds after each treatment cycle usually displayed a rapid reemergence of virus, with approximately a 2-log10 mean increase by 4 weeks, with no discernable delay in rebound kinetics between successive interruptions (Fig. 3).

FIGURE 2
FIGURE 2:
Viral decay during induction treatment phase. Similar decay patterns were noted during the second and third phases.
FIGURE 3
FIGURE 3:
Mean change in viral load during treatment interruptions.

Time-weighted changes in viral load during each phase are shown in Table 2. These also did not differ significantly between groups. In addition, there were no differences between groups in the duration patients remained off therapy during each interruption cycle: median time until reinitiation of therapy for ARV + HU and ARV-alone arms was 35 or 35 days during the first interruption, 41 or 40 days for the second interruption, and 34 or 43 days in the final interruption. Patients were able to resuppress virus with each reintroduction of therapy, and neither cases of virologic failure nor emergence of drug resistance were detected.

TABLE 2
TABLE 2:
Time-Weighted Changes* in log10 Viral Load and CD4 T-cell Count (cells/μL) by Phase

Lymphocyte Dynamics

Significant differences favoring ARV treatment alone were seen in time-weighted CD4 T-lymphocyte rebounds during phase A (Fig. 4). Patients randomized to ARV + HU exhibited a significantly blunted CD4 T-cell recovery during this initial treatment phase (+101 vs +196 CD4 cells in a time-weighted analysis between ARV + HU and ARV-alone groups, P = 0.006) with a trend toward a similar blunted recovery during the second treatment cycle (P = 0.079) (Table 2). Despite these differences in CD4 numbers, there were no apparent clinical sequelae, with no HIV-related infections detected in either treatment arm.

FIGURE 4
FIGURE 4:
CD4 lymphocyte cell increases with successive treatment cycles. Number of observations as per Figure 2.

There was no evidence that HU reduced CD8 numbers. Total CD8 cell numbers dropped during each treatment cycle and rose with interruptions, again to a similar degree within each treatment group (data not shown).

Predictors of Treatment Success

Predictors of achieving a viral load of less than 5000 copies/mL at end point (success in any interruption phase) were assessed using logistic regression. Multivariate analysis was not conducted as only 1 variable was significant at the 10% level (Table 3). Only a lower baseline viral load was associated with control of viremia during treatment interruptions. It is worth noting that the time interval from the onset of PHI symptoms to initiating therapy did not influence patients' ability to control viral replication later.

TABLE 3
TABLE 3:
Predictors of Treatment Success (Univariate Results)

Safety

Treatment was generally well tolerated, with only a small number of subjects discontinuing because of adverse reactions. Overall, 83 grade 2 or 3 laboratory and clinical adverse events were considered as possibly/probably related to study medication in the ARV + HU arm compared with 69 events in the ARV-alone arm (predominately, dry skin/cracked lips, diarrhea, renal colic or lipid elevations; 1 patient developed a grade 2 anemia, possibly related to HU use). Fifteen serious adverse events were recorded in 12 patients (Table 4). Nine of these were considered to be related to study medications by the investigators: 8 episodes of nephrolithiasis (7 in the ARV + HU arm and 1 in the ARV-alone arm), considered to be related to indinavir use; and 1 case of peripheral neuropathy (in the ARV-alone arm), considered to be related to stavudine/didanosine usage (P = 0.28). No patient was recorded as having acute retroviral syndrome symptoms during any interruption phase.

TABLE 4
TABLE 4:
Serious Adverse Events

CONCLUSIONS

In this randomized trial, the addition of HU to combination ARV therapy was not beneficial in improving virologic control off-therapy in patients treated during PHI. Eleven (16%) of the 68 patients were able to maintain an off-therapy viral load at less than 5000 copies/mL for 6 months. However, the majority of patients had rapid rebounds in viremia and required reinitiation of therapy. Only a lower baseline RNA was a significant factor in predicting which patients would successfully control their virus. In our study a threshold of 5000 copies was used to trigger reinitiation of therapy. This level of viremia was selected as one that has been used by others in STI studies and should be sufficient to stimulate any HIV-specific immune responses, but not allow an excessive viremia to impact on CD4 recovery.21,35 However this approach does not allow patients to have a large initial viral burst followed by subsequent control, as has been described in some interruption studies.36,37

Hydroxyurea use was associated with a significantly blunted CD4 T-cell increase during the treatment phases. There was no significant benefit in terms of reducing the elevated levels of circulating CD8 cell numbers. In addition, numerically, more adverse events were noted with HU use, although we did not see an increase in the prevalence of peripheral neuropathy, as has been reported by others.33

Primary HIV infection has been postulated as the most likely stage during HIV infection where a treatment interruption strategy could yield successfully virologic outcomes. Early initiation of ARV treatment in PHI has been shown to preserve specific HIV T-lymphocyte immunity.38,39 In addition, there is less likelihood of viral differentiation and theoretically less likelihood of viral escape with early immunologic control.40 Earlier studies showed promise in translating the biological plausibility into clinical outcome.20 However, longer follow-up revealed disappointing outcomes in terms of the strategy of treatment interruption and the sustainability of viral suppression.36 Other studies of transient continuous or interrupted therapy during PHI have similarly yielded disappointing results.41,42

The earliest report of virologic suppression following STI-type therapy in PHI came from the Berlin patient where didanosine was used in combination with indinavir and HU.26 Our study attempted to test and extend this finding in a prospectively recruited randomized trial.

Treatment interruption studies using HU have yielded mixed results. In studies where HU has been used in combination with suboptimal (<3) ARV agents, there has generally been a favorable response.27,43-45 However, where HU has been added to virologically suppressive regimens, only additional toxicity has been noted.33,46,47 Our study supports these findings. No additional virologic benefit was noted, but a blunted CD4 response and an increase in serious adverse events were seen. Unfortunately, the number of patients who continued their HU during the STIs were too small to determine if HU affected CD4 levels or adverse events during the off-therapy phases. In addition, although HU has been reported to interfere with T-cell activation, no detectable effect, in terms of stabilization of elevated total CD8 cell numbers, was seen in this study.48 This is in contrast to the inhibition of cellular activation seen with other agents (mycophenolate mofetil) where there was also associated control of viral rebound.49

In addition, the significantly lower CD4 rebound seen with HU is in contrast to other immunomodulatory agents. Cyclosporine or interleukin 2 both show marked increases in CD4 recovery, when added to ARV treatment in PHI patients in nonrandomized studies.50,51

The transient use of ARV therapy during the early stages of HIV infection, in an attempt to alter viral set points, has had mixed results. Some initial case series suggested that viral set points appeared to be altered.21,52 However, larger trials have failed to convincingly show any altered set-points when compared to untreated controls.37,42 STI studies in early chronically infected patients have also suggested enhanced HIV-specific responses, yet these responses do not appear to impact upon viremia.53

As with other STI studies, we did not see the emergence of drug resistance as all subjects successfully resuppresses the virus with each treatment reinitiation.24,54,55

Despite not detecting any antiviral effect from the addition of HU to a combination ARV regimen, we did note that a lower baseline viral load predicted better control of viremia during the off-treatment phase. Others have also noted that baseline viral load (as assessed by both HIV RNA and proviral DNA) and other factors-such as p24 proliferative responses or lower CD4 activation levels-are important variables in control of viremia.35,56,57 A low viral load before therapy is initiated suggests that other factors acting at very early stages of PHI, such as innate immune responses, or replication fitness of the virus may play an important role in influencing long-term viral set points. Importantly, the timing of PHI therapy did not influence subsequent viral control, suggesting that there is no urgency in commencing patients on therapy.

In summary, we were unable to detect a beneficial effect of adding HU to effective ARV therapy in PHI patients undertaking strategic treatment interruptions. Hydroxyurea blunted CD4 cell recovery and increased the number of serious adverse events associated with therapy.

ACKNOWLEDGMENTS

The National Centre in HIV Epidemiology and Clinical Research is funded by the Australian Government Department of Health and Ageing and is affiliated with the Faculty of Medicine, The University of New South Wales.

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APPENDIX

Members of the Pulse Study Team comprise

National Centre in HIV Epidemiology and Clinical Research, UNSW: D Smith, K Petoumenous, K Irvine, P Grey, R Munro, M Law, J Kaldor, and D Cooper.

St. Vincent's Hospital, Darlinghurst, Sydney: A Carr, R Feilden, M Lacey, S Pett and DA Cooper.

407 Doctors, Darlinghurst, Sydney: R Macfarlane, D Baker, W Genn, H McLeod, R Vale.

Holdsworth House General Practice, Darlinghurst, Sydney: M Bloch, D Quan, D Austin, S Miller.

Taylor Square Private Clinic, Darlinghurst, Sydney: R Finlayson, R Richardson, J Price.

Burwood Road Clinic, Burwood, Sydney: N Doong.

Centre for Immunology, St. Vincent's Hospital: A Kelleher, J Zaunders, P Cunningham, C Satchell, M-L Munier, K McGhie.

Prahan Market Clinic, Prahan, Melbourne: N Roth, H Wood.

Victorian Infectious Disease Reference Laboratory, Melbourne: C Birch, T Middleton.

Miami Sexual Health Clinic, Gold Coast: J Chuah.

Keywords:

primary HIV infection; therapy; treatment interruption; hydroxyurea; randomized clinical trial

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