HAART Interruption: risks-benefits

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HAART Treatment Interruptions: potential risks/benefits

Below are two recently published studies discussing potential risks & benefits.

“Prolonged treatment interruption in chronic HIV infection: a new strategy?â€

Research Letter

AIDS: Volume 19(2) 28 January 2005

Giuntini, Riccardoa; elli, Canioa; Ambu, Silviaa; Bartolozzi, Darioa; Farese, Albertoa; Boddi, Vierib; Leoncini, Francescoa

aInfectious Diseases Unit, AOU Careggi, Florence, Italy

bDepartment of Public Health, University of Florence, Italy

Abstract

The introduction of highly active antiretroviral therapy in 1995 dramatically decreased AIDS-related events and deaths rates; however, the enthusiasm among the medical and social community was soon limited by the growing incidence of various side-effects that often greatly limited patients' quality of life. The second problem caused by such a complex treatment consisted of sub-optimal adherence, with a consequent higher risk of the development of drug resistance.

In the past few years, several approaches to treatment interruption have been tried [1-4]. One involves patients with a successful immunological response to highly active antiretroviral therapy (HAART) who interrupt treatment as long as the CD4 cell count does not decrease to levels that necessitate re-starting therapy [5,6].

In this study we evaluated the safety and duration of prolonged antiretroviral treatment interruption in patients with a good response to antiretroviral therapy, with regard to clinical and laboratory parameters.

The duration of treatment interruption was evaluated using the Kaplan-Meier curve, and was studied among the total population and among groups with different ranges of CD4 cell count before starting antiretroviral therapy (CD4 nadir), which were less than 200, 200-350, and greater than 350 cells/mm3.

The rate of change in the CD4 cell count during treatment interruption was measured using the linear regression method. The rates of change in CD4 cell counts at first control after resuming therapy were calculated using the Wilcoxon signed-rank test; the Kruskal-Wallis test evaluated the statistical significance of CD4 cell increases among the three groups after treatment resumption.

Seventy-four patients were enrolled in the cohort (58 men and 16 women), with a median age at treatment interruption of 40 years (range 28-63), they had been diagnosed as HIV positive between 1985 and 2000; the risk behaviors were: homo/bisexual contact (20), heterosexual contact (13), a history of drug injection (10), and unknown (31). Two patients were hepatitis B surface antigen positive, 16 were hepatitis C virus IgG positive and one was positive for both markers.

Antiretroviral therapy was started at a median distance of one year (0-10) from serological diagnosis, with a median CD4 cell count of 391 cells/mm3 (21-952); HIV viral load pre-therapy was available for 16 patients only, with a median value of 27 000 copies/ml (1000-500 000).

The first regimen consisted of zidovudine (27 patients), didanosine (three patients), two nucleoside reverse transcriptase inhibitors (NRTI; 24 patients), two NRTI and one non-nucleoside reverse transcriptase inhibitor (NNRTI; one patient), and two NRTI and one protease inhibitor (19 patients).

The duration of therapy was 4 years (1-10), with two median regimen switches (0-8).

At treatment interruption, 39 patients presented with genotypic drug resistances: one or more NRTI (21), one or more NNRTI (two), one or more NRTI/NNRTI (11), one or more NRTI/protease inhibitor (two), and one or more of all classes of drugs (three).

At treatment interruption, patients had been treated for a median time of 20 months (1-62) with a HAART regimen (62), with two NRTI (11), and with three NRTI (one). The median CD4 cell count was 816.5 cells/mm3 (380-2226), the HIV viral load had been undetectable (<50 copies/ml) for a median time of 10 months (1-72) in 52 patients, whereas in 22 patients it was 2239 copies/ml (median; 80-34 000).

The criteria for treatment resumption were patients' decision, the presence of AIDS-defining events, a decrease in the CD4 cell count to 350 cells/mm3 and an increase in HIV RNA to 100 000 copies/ml.

The median treatment interruption was 14 months (4-46); 51 patients resumed antiretroviral therapy, with median treatment interruption duration of 9 months. The motivations for treatment resumption were a CD4 cell count decrease to 350 cells/mm3 (17), HIV-RNA increase to 100 000 copies/ml (15) and both events (four); 15 patients resumed antiretroviral therapy by their own decision. The median CD4 cell count after treatment resumption (median 3 months) was 477.5 cells/mm3, with a percentage increase of 49.2% (P < 0.00005). No statistical differences in CD4 cell increases were noted among the three groups of patients with different CD4 cell nadirs.

On January 2004, 23 patients were still on treatment interruption, with a median duration of 23 months (9-46), a median CD4 cell count of 513 cells/mm3 (331-892), and a median HIV-RNA level of 30 000 copies/ml (470-355 000). One patient with a CD4 cell count of less than 350 cells/mm3 and two patients with HIV-RNA levels greater than 100 000 copies/ml refused to resume therapy.

Statistically significant differences in treatment interruption duration were noted on the basis of the CD4 cell nadir. The median duration of treatment interruption in patients with a CD4 cell nadir under 200 cells/mm3 was 7 months (5-40), in those with a CD4 cell nadir between 200 and 350 cells/mm3 it was 9 months (4-35), and in those with a CD4 cell nadir up to 350 cells/mm3 it was 22 months (6-46) (P < 0.002). The median CD4 cell count during treatment interruption decreased to 471 cells/mm3 (92-671) (-42.1%, P < 0.0005).

For most patients, the HIV viral load pre-therapy was not available. At the first month of treatment interruption, a median viral load rebound of 4.65 log 10 copies/ml was observed; however, no differences were noted between patients with undetectable and detectable pre-treatment interruption viremia. The median HIV viral load before resumption of therapy was 113 000 copies/ml; after 3 median months (1-7) of treatment resumption it decreased to 325 copies/ml (50-163 000; <50 copies in eight patients).

In 25 patients who presented with hyperlipidaemia at treatment interruption, lipid values decreased to the normal range during treatment interruption; in 10 out of 15 patients who presented with lipodystrophy a clinical improvement was observed.

No AIDS-defining events or HIV-related deaths were observed during treatment interruption. One patient died from cerebral aneurism rupture; one patient experienced generalized lymphoadenopathy after one month of treatment interruption and did not want to resume therapy before 6 months; one patient experienced multimethameric thoracic herpes zoster, which was successfully treated with valaciclovir.

The main predictor factor of treatment interruption duration seems to be the CD4 cell nadir. Patients with a CD4 cell nadir greater than 350 were much less likely to resume therapy than those with a lower CD4 cell nadir. It was noted that all patients with a CD4 cell nadir greater than 350 who were under HAART during the late 1990s would not have started treatment according to the 2001 Department of Health and Human Services guidelines.

The security of this strategy was proved by the absence of AIDS-defining events and by the significant CD4 cell increases and HIV viral load decreases in most patients who resumed antiretroviral therapy.

Finally, the study results may suggest a critical approach towards the right antiretroviral therapy starting time. It is strongly questionable whether patients who start therapy with CD4 cell counts of approximately 200 cells/mm3 can afford a future durable and safe treatment interruption, while starting therapy with a higher immunological assessment may guarantee a better immune reconstitution, allowing clinicians to manage these patients in a simpler way.

References

1 Gallant JE. Current status of antiretroviral treatment interruption and intermittent therapy strategies. Med Gen Med 2002; 4:19.

2 Hirschel B, Fagaard C, Oxenius A, Gunthard H, F. SSITT: a prospective trial of treatment interruption in HIV infection. Presented at the 9th Conference on Retroviruses and Opportunistic Infections. Seattle, 24-28 February 2002 [Abstract 528].

3 Deeks SG, Wrin T, Liegler T, Hoh R, Hayden M, Barbour JD, et al. Virologic and immunologic consequences of discontinuing combination antiretroviral-drug therapy in HIV-infected patients with detectable viremia. N Engl J Med 2001; 344:472-480.

4 Krolewiecki AJ, Bouzas MB, Cahn P, Ochoa C, H, Bouzas MB, et al. Treatment discontinuation in patients who started antiretroviral therapy following the 1996 IAS - USA recommendations. A prospective randomized trial. Presented at the XIVth International AIDS Conference. Barcelona, 7-12 July 2002 [Abstract ThOrB1440].

5 Tarwater PM, Parish M, Gallant JE. Prolonged treatment interruption after immunologic response to highly active antiretroviral therapy. Clin Infect Dis 2003; 37:1541-1548.

6 Maggiolo F, Ripamonti D, Gregis G, Quinzan G, Callegaro A, Suter F. Effect of prolonged discontinuation of successful antiretroviral therapy on CD4 T cells: a controlled, prospective trial. AIDS 2004; 18:439-446.

Treatment Interruptions in Chronic HIV Infection

December 28, 2004

PLoS Medicine 1(3): e70.

“…..trials…..do not support short-term clinical benefits of treatment interruptions….additional trials of STIs are warranted….it remains undetermined to what extent resistant mutations are a signal for future therapy failure…..viral replication and rebound-which eventually occurred in all participants-is seen by some researchers as inherently detrimental, and these experts argue that treatment interruptions are unsafe and their use should be discontinued……..STIs have no place outside controlled clinical trials and that questions regarding long-term safety remain unanswered.â€

Patient Summary

Why Was This Study Done? Highly active antiretroviral therapy has revolutionized HIV treatment for patients who have access to the medications. But the drugs are expensive, have side effects, and can become ineffective when the virus develops resistance. Structured treatment interruptions (STIs), also known as “drug holidays†(because patients take a holiday from their drugs), have been suggested as possible alternatives to continuous therapy. Initially, there was fear that patients who went back on therapy after an interruption would not be able to control the virus again, but there was also hope that STIs might actually strengthen the immune system. In addition, STIs might alleviate some side effects, and they would certainly reduce costs. This study uses a particular design to examine the risks and benefits of STIs.

What Did the Researchers Do? The researchers studied 42 patients who received either continuous therapy for 40 weeks or three successive treatment interruptions of two, four, and six weeks, followed by a final open-ended interruption for both groups. The researchers then recorded how long patients were able to control the virus before their viral load reached a certain threshold and they had to restart therapy. They also examined CD4 counts and therapy failure, and looked for resistant viruses on and off therapy.

What Did They Find? In terms of being able to control the virus, it made no difference whether patients were on continuous therapy or had three STIs. In other words, when both groups stopped treatment at 40 weeks, the length of time that the patients could control the virus was the same in both groups. Eventually, all patients (except two who elected to stay off antiretroviral therapy) re-initiated therapy because of a rising viral load, and the patients once on therapy all regained control over the virus. Resistant viruses were found in patients from both groups, but during the final interruption they were more common in the group that had received the three STIs.

What Does This Mean? The study confirms that STIs do not help with viral control, consistent with other studies that found that STIs had no clinical benefit. On the other hand, no short-term adverse events were present, as all patients were able to regain control over the virus after they went back on treatment (without a drop in CD4 count), even after several rounds of interruptions and tests to detect of resistant viruses. There remains concern about whether recurrent cycles of viral replication and suppression might in themselves be harmful, and whether the presence of resistant virus is a signal for future treatment failure. Given these unanswered questions, STIs should only be undertaken within clinical trials.

What Next? Possible risks and benefits of STIs in the management of therapy remain an active area of research. Evidence so far has not shown clinical benefits. Ongoing studies need to clarify whether there are long-term risks (and what they are), so that we can weigh these against the benefits of reducing costs and side effects.

TEXT OF STUDY ARTICLE

Adverse side effects, viral resistance, and the high cost of antiretroviral therapies remain obstacles in the way of turning HIV/AIDS into a manageable chronic disease. Structured treatment interruptions (STIs) in individuals who have good viral control on therapy have been proposed as a strategy for overcoming these obstacles. The initial hope that STIs would help patients achieve greater viral control has so far not been supported by data from clinical trials, but interrupting treatment has also been proposed as a strategy to reduce the cost of long-term therapy and drug-associated toxicity.

Montaner and colleagues now report results from a randomized trial of 42 participants (75% on their second to fourth regimen, 66% on regimens containing non-nucleoside reverse-transcriptase inhibitors) who received either continuous therapy for 40 weeks or three successive treatment interruptions of two, four, and six weeks, followed by a final open-ended interruption for both groups.

The study was designed to be able to detect a difference of four weeks or greater between the two groups for the time to viral rebound during the open-ended interruption-the primary outcome. No difference between the two groups was seen (median time for the group on continuous treatment was four weeks, and for the STI group was five weeks).

Secondary outcomes included serious adverse events (disease progression, acute retroviral syndrome, therapy failure, or opportunistic infections at any point in the study), changes in CD4 count on therapy, immune reconstitution changes (CD4 recall responses and CD4 naïve/memory T cell distribution), and detection of viral mutations There were no study-related serious adverse events in either group and no increase of therapy failure in the STI arm. CD4 counts fluctuated between the start and end of each monitored treatment interruption, but levels recovered after resuppression of virus, with retention of recall responses throughout. Viral resistance was detected in both groups (in seven of 21 patients in the continuous treatment group and ten of 21 patients in the STI group), but it was more commonly detected (50% versus 18%) in the STI group during the open-ended final interruption, even though all subjects suppressed virus upon reinitiating the same therapy.

Possible risks and benefits of STIs remain controversial, but data from this and other published trials do not support short-term clinical benefits of treatment interruptions. However, because they do not see increased therapy failure and find preservation of immune function in the STI group, the authors conclude that, in light of the possibility of reducing costs and drug-related toxicity, additional trials of STIs are warranted.

Particularly important in the debate over the safety of STIs is whether the detection of resistant mutants should be of concern. The authors point out that all participants were able to resuppress the mutant virus when they resumed their previous drug regimens but state that it remains undetermined to what extent resistant mutations are a signal for future therapy failure. Moreover, viral replication and rebound-which eventually occurred in all participants-is seen by some researchers as inherently detrimental, and these experts argue that treatment interruptions are unsafe and their use should be discontinued.

What seems clear is that STIs have no place outside controlled clinical trials and that questions regarding long-term safety remain unanswered. At least a dozen additional trials that examine STIs are currently recruiting patients and will help answer these questions.

“Randomized, Controlled Trial of Therapy Interruption in Chronic HIV-1 Infectionâ€

READ THE AUTHOR DISCUSSION BELOW, PARTICULARLY THE CONCERNS ABOUT DRUG RESISTANCE

Emmanouil Papasavvas1, Jay R. Kostman2, Karam Mounzer3, M. Grant4, Gross5, Cele Gallo3, Livio Azzoni1, Foulkes6, Thiel1, Maxwell Pistilli1, Agnieszka Mackiewicz1, Jane Shull3, J. Montaner1*

1 The Wistar Institute, Philadelphia, Pennsylvania, United States of America, 2 Philadelphia Field Initiating Group for HIV-1 Trials and the Division of Infectious Diseases, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 3 Philadelphia Field Initiating Group for HIV-1 Trials, Philadelphia, Pennsylvania, United States of America, 4 The Gladstone Institute of Virology and Immunology, University of California, San Francisco, California, United States of America, 5 Center for Clinical Epidemiology and Biostatistics and the Division of Infectious Diseases, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 6 Department of Biostatistics, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America

INTRODUCTION

Antiretroviral therapy (ART) has been a milestone in the treatment of HIV infection. Current treatment guidelines for HIV-1 infection in the United States recommend the initiation of ART in patients with CD4 T cell counts of less than 350 cells/μl [1]. In implementing these guidelines, health-care providers face the ongoing challenge of developing treatment strategies that minimize drug-related toxicity and adverse effects while retaining effective control of viral replication. Furthermore, treatment-associated costs (particularly in resource-poor areas), difficulty in maintaining long-term optimal adherence [2], and the emergence of viral resistance [3,4,5] have limited the feasibility of life-long ART-mediated viral suppression, increasing the need for alternative treatment strategies. Intermittent therapy strategies, consisting of alternating cycles on and off ART, have increasingly emerged as a potential intervention to address limitations of continuous ART [6,7,8,9]. Therapy interruption (TI) studies in ART-treated patients with suppressed HIV infection [10] have addressed the general questions as to whether such strategies can achieve greater viral control through increased antiviral responses (autoimmunization hypothesis) or simply serve as a strategy to reduce cost of long-term therapy and drug-associated toxicity. While pilot studies and uncontrolled (or incomplete) trials in patients with chronic HIV infection have addressed viral and immune outcomes of fixed-length TI and fixed on-drug cycles [11,12,13,14,15,16], no completed randomized, controlled trial has yet addressed by intent-to-treat analysis the outcome during an open-ended TI of sequential TIs versus continuous treatment in patients with confirmed suppression. The largest study to date in this area is the prospective single-arm Swiss-Spanish Intermittent Trial (SSITT) conducted in 133 recruited patients undergoing sequential 2-wk TIs and showing a lack of impact of this strategy on achieving sustained viral loads of less than 5,000 copies/ml off therapy in those that completed the study [11]. However, the lack of a control arm in this study has left unanswered questions about the impact of multiple TIs on time to rebound, immune reconstitution, therapy failure, and viral resistance when analyzed against a randomized control arm of continuous treatment followed for equal time before a single open-ended interruption.

We completed a randomized, controlled trial on the outcome of repeated 2- to 6-wk TIs in patients with chronic infection in which the comparator group maintained continuous therapy and then an open-ended interruption period was applied in both treatment groups. The study addressed the potential for repeated interruptions of therapy to delay time to viral rebound as a primary outcome and analyzed secondary outcomes regarding study-defined safety criteria, viral suppression and resistance, and retention of immune reconstitution.

ABSTRACT

Background-

Approaches to limiting exposure to antiretroviral therapy (ART) drugs are an active area of HIV therapy research. Here we present longitudinal follow-up of a randomized, open-label, single-center study of the immune, viral, and safety outcomes of structured therapy interruptions (TIs) in patients with chronically suppressed HIV-1 infection as compared to equal follow-up of patients on continuous therapy and including a final therapy interruption in both arms.

Methods and Findings-

Forty-two chronically HIV-infected patients on suppressive ART with CD4 counts higher than 400 were randomized 1:1 to either (1) three successive fixed TIs of 2, 4, and 6 wk, with intervening resumption of therapy with resuppression for 4 wk before subsequent interruption, or (2) 40 wk of continuous therapy, with a final open-ended TI in both treatment groups. Main outcome was analysis of the time to viral rebound (>5,000 copies/ml) during the open-ended TI. Secondary outcomes included study-defined safety criteria, viral resistance, therapy failure, and retention of immune reconstitution.

There was no difference between the groups in time to viral rebound during the open-ended TI (continuous therapy/single TI, median [interquartile range] = 4 [1-8] wk, n = 21; repeated TI, median [interquartile range] = 5 [4-8] wk, n = 21; p = 0.36). No differences in study-related adverse events, viral set point at 12 or 20 wk of open-ended interruption, viral resistance or therapy failure, retention of CD4 T cell numbers on ART, or retention of lymphoproliferative recall antigen responses were noted between groups. Importantly, resistance detected shortly after initial viremia following the open-ended TI did not result in a lack of resuppression to less than 50 copies/ml after reinitiation of the same drug regimen.

Conclusion-

Cycles of 2- to 6-wk time-fixed TIs in patients with suppressed HIV infection failed to confer a clinically significant benefit with regard to viral suppression off ART. Also, secondary analysis showed no difference between the two strategies in terms of safety, retention of immune reconstitution, and clinical therapy failure. Based on these findings, we suggest that further clinical research on the long-term consequences of TI strategies to decrease drug exposure is warranted.

AUTHOR DISCUSSION

Earlier reports on TI strategies in patients with chronic HIV infection include multiple pilot or single-arm study designs centered on the effects on viral control by comparison with pre-therapy periods, detection of resistance mutations without parallel follow-up of a continuously treated arm, and inclusion of variable criteria regarding viral resuppression before proceeding with repeated TIs [11,12,14,16]. In contrast, our strategy mandated resuppression of viral replication to less than 50 copies/ml before each TI and presents the first comparison of viral replication during a final open-ended interruption of therapy between patients randomized to complete three sequential TIs or stay under continuous therapy. Our data, based on intent-to-treat analysis, did not show that repeated TIs resulted in a clinically significant virological benefit as measured by the time to viral rebound to more than 5,000 copies/ml. Secondary as-treated analysis on viral replication magnitude also indicated a lack of difference between arms. Consistent with the findings of SSITT [11], analysis of our data by the categorical classification of a “responder†as a patient with viral load less than 5,000 copies/ml at week 12 off therapy showed no significant difference in this frequency between arms (single TI, 5/18; repeated TI, 5/16), suggesting the presence of “responders†irrespective of previous protocol-mandated TIs.

Based on secondary outcome measures, the incidence of adverse events (SAEs, therapy failure, and patient discontinuation) or clinical disease progression (as indicated by CD4 count on therapy or opportunistic infections) was not observed to be different between arms. Prospective safety outcomes in our study are in accordance with reports from a retrospective analysis of 1,290 patients who interrupted treatment at least once (< 3 mo) without an increased risk of HIV-associated morbidity or mortality (with the exception of patients in Center for Disease Control and Prevention stage C during first interruption only) [21]. In regards to immunological outcomes, a concern associated with interruption of suppressive therapy is the potential for irreversible, viral-mediated CD4 T cell loss leading to disease progression [6,22]. We did not observe a decrease in CD4 cell numbers or lymphoproliferative responses against C. albicans when measured between arms before the open-ended TI (see Figure 4), nor following resuppression after monitored TI reinitiation cycles in the repeated interruptions arm (see Figure 5). The latter is consistent with observations by others and does not support an immediate immunological “cost†to short-term TIs [12,14,15,16,23]. However, we do show that monitoring CD4 cell numbers by percentage could lead to misinterpreting a significant loss of CD4 cells as a result of a significant increase in CD8 count following TIs, even though absolute CD4 count numbers remained unchanged. Interestingly, the increase in CD8 T cell number also corresponded with an increase in HIV-specific responses as measured by interferon-gamma expression (data not shown), which in light of an absence of effect on viral load between arms further supports that TI strategies alone may not significantly alter the pre-existing balance between viral replication and host antiviral responses [14,16,23,24].

Importantly, no evidence for an increase of viral resistance in association with therapy failure was present in the repeated interruptions arm (See Table 2). We did not observe a greater clinical failure of NNRTI-based regimens in the repeated interruption arm due to “single drug†periods as predicted by recently redefined drug half-life estimates and the presence of viral replication during each interruption [25,26,27]. However, the percentage of patients with resistance mutations detected in this study in the repeated interruption arm (47%) is higher than the 17% observed in the SSITT cohort [11], in which patients with prior treatment failures were excluded [28]. We interpret this difference to mean that the resistance detected off drug in both our and their cohorts is likely associated with the greater number of drug-experienced patients in our cohort (75%) and the detection of prior archived resistance mutations as supported by Metzner et al. [29], who documented in 14/25 (56%) SSITT patients the presence of minor populations of M184V occurring at least once off drug during interruption of therapy.

In spite of the lack of difference in the total number of patients with resistant mutations detected on therapy during phase I and off therapy in phase II (7/21 [33%] versus 10/21 [47%], respectively) in both arms, we do report in similarity to others a greater detection of resistance mutations in the TI arm when restricting analysis to the last off-drug period only [29,30] as three of 16 (18%) had mutations detected off drug in the continuous therapy/single interruption arm compared to nine of 18 (50%) in the repeated interruption arm. However, based on the lack of association between viral resistance detected off-drug shortly after TI and resuppression by the same regimen in all patients, it remains undetermined to what extent TIs favor the detection of archived mutations in chronically suppressed patients and to what extent these mutations are a signal for a future therapy failure. The latter is best exemplified by the data we collected on patients on NNRTI-based regimens in the repeated interruptions arm where two patients (S19 and S43) showed K103N detection (only during the off-drug periods) in the absence of therapy failure while maintaining the same regimen after each TI, including post-study follow-up (Table S1). On the other hand, virological failure in the continued presence of an NNRTI-based regimen in phase I was associated with detection of K103N, as observed in one patient (S56) in the repeated interruption arm and three patients (S37, S52, and S59) in the continuous therapy arm with self-reported non-adherence.

Drug resistance that occurs during virological drug failure predicts virological responses to salvage treatment [31,32,33]. In contrast, the clinical implications of drug resistance mutations that appear shortly after TI in chronically suppressed patients are not clear. Case reports in this cohort of patients have demonstrated that drug-resistant variants that appeared during TIs may not persist in subsequent time points even after repeated use of the same antiretroviral regimen [19,34]. We now observe that drug resistance appearing during TIs can be transient since 50% and 33% of patients listed in Table 3 showed complete and partial reversion to wild type, respectively, when comparing to resistance at the last available viremic time point in phase II. Further, we observed durable resuppression of plasma viral RNA level in many patients who had drug-resistance mutations off therapy that would otherwise be expected to affect part of their treatment regimen when reinitiated. Virus populations that expand shortly after TI may lack all of the adaptations required to achieve high levels of plasma viremia in the presence of drug during continuous treatment. These adaptations may include the resistance-associated mutations, which were detected, as well as secondary mutations that may increase the viral replication capacity [35,36] or envelope adaptations required to escape concurrent humoral immune responses [37,38]. It is of interest to note that despite the large amount of research activity on TIs in patients with suppressed chronic infection and the hundreds of monitored interruptions studied to date, only limited cases of development of clinical resistance (as evidenced by a lack of viral resuppression following therapy reinitiation) have emerged, in contrast to the multiple reports of detection of viral sequences off ART associated with resistance as shown in this study and others [11,19,29,30,39,40].

Taken together, while our data show no clinically significant benefit for repeated TIs of less than 1.5 mo in patients with CD4 counts greater than 400 on therapy with regard to viral control as defined by time to rebound, secondary outcomes document no significant difference in levels of retention of immune reconstitution between arms and no increased incidence of virological failure as a consequence of TIs. While our data indicate that this TI strategy should not be pursued outside of a clinical trial setting, we argue that it will be important to collect additional data on the potential benefits of drug-sparing regimens (such as reduced long-term toxicity and reduced cost) and to define long-term outcomes in comparison with continuous therapy.

Methods

Participants

Between August 2000 and December 2003, we enrolled 42 patients infected with HIV who were older than 18 y and on ART; eligibility criteria included CD4 counts of greater than 400 cells/μl on ART with a nadir of no less than 100 cells/μl, ART-mediated suppression (< 500 copies/ml) for more than 6 mo and less than 50 copies/ml at recruitment on any antiretroviral regimen. Approval of the study protocol was obtained from the institutional review board (IRB) of the Philadelphia Field Initiating Group for HIV Trials (Philadelphia, Pennsylvania, United States). Written informed consent was obtained from all patients. Human experimentation guidelines of the United States Department of Health and Human Services and of the authors' institutions were followed. The study protocol, including the patient consent form, the CONSORT form, and the IRB approval, can be found in Protocols S1-S4.

Randomization and Study Design

Forty-two eligible patients from the Lax Immune Disorder Clinic in Philadelphia, Pennsylvania, were randomized via sealed envelopes in a 1:1 fashion to a first phase (phase I) of either (1) three successive TIs of 2, 4, and 6 wk, respectively, or (2) maintenance of ART for 40 wk before a final interruption of therapy in both arms (phase II) subject to therapy reinitiation criteria as described below. Phase II consisted of an open-ended interruption to allow for virological and immunological comparisons between the groups off therapy. Study visits were every 2 wk for the repeated interruptions group and every 4 wk for the continuous ART group during phase I. Both groups were followed every 2 wk during phase II. We followed a study design with step-wise increases in the length of TI cycles to address potential safety concerns (resuppression was confirmed after shorter TIs before longer interruptions were initiated) and the hypothesis that sequential viral replication intervals would stimulate viral control and a delay in time to viral rebound.

Phase I procedures for the repeated interruptions group included the following. (1) Interruption of therapy was individually timed to occur after two HIV RNA measurements of less than 50 copies/ml without any viral load measurements greater than 400 copies/ml in between; these interruptions increased from 2 to 4 to 6 wk sequentially. (2) If a 0.5-log or greater reduction in viral load did not occur by 6 wk of reinitiated therapy or less than 50 copies/ml was not achieved within 20 wk of reinitiated therapy, patients were withdrawn as therapy failures and a resistance test was performed. (3) Patients were also withdrawn as therapy failures if (a) the CD4 cell number declined by more than 45% of the baseline CD4 count, ( participants developed an opportunistic infection, even if retaining required CD4 count levels, or © a viral load of greater than 500,000 copies/ml occurred once, with or without development of acute retroviral syndrome as defined by fever, skin lesions, and pharyngitis.

Phase I procedures for the continuous therapy arm included the following: (1) patient monitoring if detected viremia was between 50 and 999 copies/ml, with the patient withdrawn if their viral load did not return to less than 50 copies/ml immediately prior to phase II, and (2) patient study withdrawal as therapy failure if during the 40-wk ART period viral load rebounded to more than 1,000 copies/ml at two consecutive time points.

Phase II procedures for both arms included the following: (1) monitoring for patient study withdrawal criteria as described in phase I, (2) determining time to primary end point of a viral load greater than 5,000 copies/ml, (3) monitoring until the time of therapy reinitiation at a viral load greater than 30,000 copies/ml for three consecutive time points, and (4) after reinitiation of therapy, follow-up on therapy to confirm resuppression to less than 50 copies/ml at 6, 10, and 14 wk on therapy. Clinical and laboratory parameters (CD4 count and viral load) were monitored at each visit, and venous blood was collected for additional secondary outcomes during selected study visits.

In both phase I and II, participants taking non-nucleoside reverse-transcriptase inhibitors (NNRTIs) were instructed to stop them a day earlier than the remaining drugs in the regimen.

Primary and Secondary Outcomes

The primary outcome was time to confirmed virological rebound during phase II. Rebound was defined as first time point with greater than 5,000 copies/ml. Viral replication magnitude as defined by mean HIV-1 plasma RNA area under the curve (AUCHIV RNA) was measured as a secondary outcome at weeks 12 and 20 of phase II based on reinitiation-of-therapy criteria outlined above.

Additional secondary outcomes included (1) safety outcomes (serious adverse events [sAEs] and patient withdrawal based on criteria defined above), (2) retention of ART-mediated immune reconstitution, and (3) detection of viral resistance. Retention of immune reconstitution was analyzed by (1) same-day whole blood flow-cytometry-based analysis of CD4 and CD8 T cells, including total and naïve (CD62 l/CD45RA) and memory (CD45RO) subsets as described [17], and (2) same-day recall response analysis of peripheral blood mononuclear cell lymphoproliferative responses to Candida albicans as described [17]. Viral resistance mutations were retrospectively analyzed on cryopreserved plasma samples by genotyping of first available sample with viral load greater than 100 copies/ml following each interruption using the TruGene Assay (Visible Genetics, Toronto, Canada) at the Gladstone Institute of Virology and Immunology (San Francisco, California, United States) as previously described [18,19].

Sample Size

The sample size required was calculated using PS [20] software, and based on a type I error of 0.05, with 90% power, to detect a difference of 4 wk or more in time to viral rebound between arms. Eighteen patients per group resulted in sufficient power (18 for 90%, 13 for 80%) to determine a difference of 4 wk or greater between groups in time to rebound of virus during the open-ended interruption. Assuming a loss to follow-up of 15%, we targeted 21 patients per group, or 42 total.

Results

Patient Flow and Discontinuations

Trial patient flow is summarized in Figure 1. Between August 2000 and December 2003, 42 patients at the Lax Immune Disorder Clinic at the Philadelphia Field Initiating Group for HIV Trials were enrolled, randomized, and followed as shown in Figure 2. In the continuous therapy/single interruption arm, 16 of 21 patients reached the open-ended interruption. Reasons for study discontinuation in this arm were loss to follow-up (n = 1; patient moved away) and virological failure during continuous therapy (n = 4; further discussed below). In the repeated interruptions arm, 18 of 21 patients reached the open-ended interruption following three TIs of 2, 4, and 6 wk duration, with median peak rises in viral loads of 136 (50-2,590), 13,651 (180-222,589), and 18,887 (3,893-96,101) copies/ml, respectively. Median time to less than 50 copies/ml after resumption of therapy was 2 (0-4), 3 (1.8-12), and 9.5 (2-12) wk, respectively, with 9, 18, and 20 wk as the maximum time needed to achieve suppression in 100% of patients before reaching the open-ended interruption. Study discontinuation in the repeated interruptions arm was due to protocol violation (n = 1; patient restarted therapy during interruption out of protocol), loss to follow-up (n = 1; patient imprisoned), and virological failure during on-therapy period (n = 1; further discussed below).

Baseline Criteria and Follow-Up

The demographic and clinical characteristics of the two groups at baseline are summarized in Table 1. Seventy-five percent of participants were on their second to fourth regimen while 25% were in their first regimen. No significant difference was found in baseline parameters between arms, with 33%-47% of patients on protease-inhibitor-containing and 61%-71% on NNRTI-containing regimens. Owing to the high participation of patients on NNRTI-based regimens and concerns about TI and safety in general, patient outcomes and treatment failure were reviewed monthly by the IRB of this study during the first 8 mo of study, quarterly for the following 4 mo, and semi-annually thereafter. Figure 2 shows study design for both arms, with a median follow-up of 41 (41-42) wk during phase I for the continuous therapy/single interruption arm and 42 (30-51) wk for the repeated interruptions arm. Follow-up during phase II had a median duration of 27 wk in both arms (continuous therapy/single interruption arm, 27 [8.75-47]; repeated interruptions arm, 27 [16.5-35]). Following reinitiation of therapy after phase II, patients suppressed viral replication to less than 50 copies/ml by a median time of 10 (6-12) wk in both arms, excluding for two patients in the continuous therapy/single interruption arm who elected to stay off ART indefinitely and one patient from the repeated interruptions arm who reported nonadherence following regimen reinitiation yet reached 52 copies/ml before withdrawing from additional follow-up.

Primary Outcome

An intent-to-treat analysis of the time to viral rebound (>5,000 copies/ml) in the open-ended interruption showed no difference between groups (continuous therapy/single TI, median = 4 [1-8] wk, n = 21; repeated TI, median = 5 [4-8] wk, n = 21; p = 0.36). Figure 3 (top panel) shows the probability of plasma HIV-1 RNA remaining less than 5,000 copies/ml for the two groups (n = 21 per group). Exclusion of drop-outs in an as-treated analysis did not alter conclusions (single TI, median = 5 [4-9] wk, n = 18; repeated TI, median = 6 [4-8] wk, n = 16; p > 0.05). Additional secondary analysis of the magnitude of viral load as shown in Figure 3 (second panel) showed similar viral replication as determined by mean AUCHIV RNA analysis at week 12 (single TI, median = 124,621 [23,326-262,348] AUCHIV RNA; repeated TI, median = 100,400 [47,221-365,731] AUCHIV RNA; p > 0.05) or week 20 (single TI, median = 114,550 [31,829-362,628] AUCHIV RNA; repeated TI, median = 153,097 [67,427-515,421] AUCHIV RNA; p > 0.05)