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CD4 Cell Count--Guided Treatment Interruption: Be Smart and Wait for More Evidence
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EDITORIAL COMMENTARY
Clinical Infectious Diseases March 1, 2005;40:000
Roberto Arduino
Division of Infectious Diseases, The University of Texas Health Science Center at Houston, Houston
(See the article by Nuesch et al. after Editorial below)
The striking improvement of HIV infection--related morbidity and mortality after the introduction of HAART in the mid 1990s [1] was followed by the daunting realization that eradication of HIV infection is not possible with current antiretrovirals and that prolonged HAART leads to substantial abnormalities in the metabolism of glucose and lipids, which may accelerate the progression of atherosclerosis. Indeed, several reports have linked the use of combination antiretroviral therapy to an increased risk of cardiovascular disease [2, 3]. In addition, changes in body appearance, such as lipoaccumulation and lipoatrophy, as a result of HAART may negatively impact quality of life and long-term adherence to anti-HIV therapy.
These findings have driven the exploration of 2 major strategies of structured treatment interruptions (STIs) for chronically HIV-infected individuals receiving prolonged suppressive HAART: (1) discontinuation of all antiretroviral drugs for a defined period of time, and (2) discontinuation of all antiretroviral drugs until the CD4 cell count drops below a predetermined level. By decreasing the duration of exposure to antiretroviral drugs, these strategies seek to prevent long-term toxicities, to improve quality of life, and to reduce the cost associated with continuous HAART. Achievement of these goals depends on the length of time of the HAART interruption while the integrity of the immune system is preserved. Lower CD4 cell count nadir [4], greater CD4 cell count increase after HAART is commenced, and older age [5] have been associated with a more rapid decline in CD4 cell count after interruption of therapy. Patients with these characteristics might expect planned CD4 cell count--guided interruptions to be shorter.
Risks associated with the rebound in viremia after discontinuation of HAART include the progression of HIV disease as a result of an abrupt decline in the CD4 cell count, the emergence of antiretroviral drug resistance that may hinder future treatment options, the reseeding of viral reservoirs, the occurrence of acute retroviral syndrome, the increased transmission of HIV, and decreased quality of life. HIV-1 resistance mutations may be archived in the latent reservoirs of resistant viruses and reemerge after antiretroviral drugs are discontinued or may emerge under the selective pressure of repeated cycles of intermittent therapy. Simultaneous discontinuation of all components of a regimen containing antiretrovirals with different half-lives may select for resistant viruses during periods of exposure to "monotherapy" in patients without detectable plasma viremia. The nonnucleoside reverse-transcriptase inhibitors (NNRTIs) efavirenz and nevirapine and the nucleoside reverse-transcriptase inhibitor (NRTI) lamivudine have prolonged plasma and intracellular half-lives, respectively. In addition, these drugs have a low genetic barrier, since even a single mutation confers a high level of resistance to them. These properties might explain, in part, the emergence of resistance mutations that has been reported after repeated STIs in patients receiving these antiretrovirals [6, 7].
The article by Nuesch and colleagues [8] in this issue reports the risk of virologic failure and emergence of resistance mutations during CD4 cell count--guided STIs in chronically HIV-infected individuals after 3 years of continuous suppressive HAART. This study enrolled individuals at high risk for development of HIV with major resistance mutations. Participants had been previously treated with dual-NRTI therapy—either standard or half-dose zidovudine plus zalcitabine—and the majority had experienced virologic failure before commencing ritonavir-boosted, saquinavir-based HAART. Almost half of the individuals were receiving a lamivudine-containing HAART regimen, but no one was receiving an NNRTI-containing regimen. Data were analyzed from 20 individuals with well-preserved immune systems whose antiretroviral treatment was interrupted and then reinitiated when the CD4 cell count dropped to <350 cells/mm3 or to 30% of the preinterruption count. After 96 weeks, continuous HAART was commenced for all participants, and follow-up continued for 12 additional weeks.
After 1--3 cycles of treatment interruption, a major resistance mutation was detected in only 1 of 17 amplifiable plasma samples. The identified reverse-transcriptase mutation—T215Y—was not present before the patient commenced the current zidovudine- and lamivudine-containing HAART regimen. Except for 1 patient with virologic failure attributed to nonadherence to antiretroviral therapy, all participants achieved complete viral suppression 12 weeks after the same antiretroviral regimen was resumed continuously. Of note, the M184V mutation was not detected in any of the 7 plasma samples from patients receiving a lamivudine-containing regimen. As the authors indicate, a limitation of this study relates to the performance of genotypic resistance testing 28--64 days after antiretroviral therapy was discontinued, which may have allowed either a shift of resistant viruses to wild type or the outgrowth of the wild-type virus, resulting in the low frequency of other major resistance mutations [9]. Low-frequency drug-resistant variants present in <25% of the HIV population may have not been reliably detected by the genotypic testing method used. Indeed, the emergence of minor populations of HIV-1 harboring the M184V and L90M mutations was detected in individuals undergoing repeated cycles of STI, after a very high sensitive quantitative real-time PCR assay and allele-specific oligonucleotides were used for detection of these mutant sequences [10].
Nuesch and colleagues [8] detected clinically significant resistance mutations in 4 of 11 plasma samples obtained from the participants before HAART was commenced, but these mutations were not detected in samples from the same patients obtained after treatment was stopped. The loss of resistance mutations may not represent a true genetic reversion of the resistant virus after therapy was discontinued, but rather the outgrowth or reemergence of wild-type virus probably archived in the latent reservoir in resting memory CD4 cells. In addition, these mutations may be present as low-frequency variants. These archived resistance mutations may reemerge after HAART is reinstituted.
As Nuesch and colleagues [8] indicate, other limitations of this study are the small sample size and the low number of treatment interruptions experienced by the individuals during the follow-up period. Indeed, for the 20 patients analyzed, only 11 plasma samples were available before HAART was commenced and 17 plasma samples were available during CD4 cell count--guided STIs. A unique aspect of this study is that it provides information on antiretroviral drug resistance for patients who have previously received dual-NRTI therapy and experienced virologic failure who initate CD4 cell count--guided STI.
The time-defined interruption strategy was initially reported to be safe and to decrease total serum cholesterol and triglyceride levels, when the time of exposure to antiretroviral drugs was halved, in a small pilot study of 10 chronically HIV-infected individuals [11]. Repeated short cycles of 1 week of HAART followed by 1 week without HAART did not promote the emergence of resistance mutations, despite the fact that most of the patients in the study received extensive suboptimal antiretroviral therapy before commencing HAART [11]. However, when the same group of investigators evaluated repeated, long-cycle, STI with 4 weeks without HAART followed by 8 weeks of HAART, the study was prematurely terminated because of the emergence of new resistance mutations [12]. Nuesch and colleagues [8] had to terminate early the study arm receiving 1 week of HAART followed by 1 week without HAART because of the unacceptable high frequency of emergence of antiretroviral drug resistance. Results from the Swiss-Spanish Intermittent Treatment Trial also suggest that repeated treatment interruptions for 2 weeks followed by 8 weeks of continuous therapy with the same regimen may select for resistance to antiretroviral drugs with a low genetic barrier [13].
Recent data from observational cohorts identified the CD4 cell count as a strong predictor of progression to AIDS or death in individuals receiving HAART [14, 15]. The risk of disease progression markedly increases as CD4 cell count drops to <200 cells/mm3. These data suggest that a strategy of discontinuation of HAART until the CD4 cell count drops to 250 cells/mm3 may have merit. Although the study by Nuesch and colleagues [8] suggests that a CD4 cell count--guided STI strategy may be safe among patients previously treated with dual-NRTI therapy, the benefits and risks of strategic treatment interruptions for chronically HIV-infected individuals like those studied and others who initiate HAART can best be determined by a large, long-term, randomized, clinical end point trial that is adequately powered not only to evaluate risk of resistance for CD4 cell count--guided STI and continuous treatment strategies but also to compare clinical outcomes, including AIDS, major toxicities, and survival. The SMART Study (a large trial comparing 2 strategies for management of antiretroviral therapy) plans to randomize 6000 HIV-infected subjects with a CD4 cell count >350 cell/mm3 to receive 1 of 2 different strategies: (1) "drug conservation," aimed at minimizing patients' exposure to antiretroviral drugs by use of episodic antiretroviral treatment to maintain a CD4 cell count between 250 and 350 cell/mm3; or (2) "viral suppression," aimed at maintaining the viral burden as low a level as possible by use of continuous antiretroviral treatment. Given the established benefits of continuous HAART, we need much more definitive data on CD4 cell count--guided strategies before they should be recommended in clinical practice.
Potential conflicts of interest. R.A. receives research funding from the National Institute of Allergy and Infectious Diseases (grants UO1 AI46957, UO1 AI46360, and UO1 AI46362), has received recent research funding from Merck, Chiron, and Trimeris; and has served as a consultant for GlaxoSmithKline, Gilead Sciences, Pfizer Global Pharmaceuticals, Vertex Pharmaceuticals, and Abbott Laboratories.
References
1. Palella FJ Jr, Delaney KM, Moorman AC, et al. Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. HIV Outpatient Study Investigators. N Engl J Med 1998; 338:853--60. First citation in article | PubMed | CrossRef
2. The Data Collection on Adverse Events of Anti-HIV Drugs Study Group. Combination antiretroviral therapy and the risk of myocardial infarction. N Engl J Med 2003; 349:1993--2003. First citation in article | PubMed | CrossRef
3. Klein D, Hurley LB, Quesenberry CP Jr, Sidney S. Do protease inhibitors increase the risk for coronary heart disease in patients with HIV-1 infection? J Acquir Immune Defic Syndr 2002; 30:471--7. First citation in article | PubMed
4. 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--46. First citation in article | PubMed | CrossRef
5. Tebas P, Henry K, Mondy K, et al. Effect of prolonged discontinuation of successful antiretroviral therapy on CD4+ T cell decline in human immunodeficiency virus--infected patients: implications for intermittent therapeutic strategies. J Infect Dis 2002; 186:851--4. First citation in article | Full Text | PubMed
6. Schweighardt B, Ortiz GM, Grant RM, et al. Emergence of drug-resistant HIV-1 variants in patients undergoing structured treatment interruptions. AIDS 2002; 16:2342--4. First citation in article | PubMed | CrossRef
7. Martinez-Picado J, Morales-Lopetegi K, Wrin T, et al. Selection of drug-resistant HIV-1 mutants in response to repeated structured treatment interruptions. AIDS 2002; 16:895--9. First citation in article | PubMed | CrossRef
8. Nuesch R, Ananworanich J, Sirivichayakul S, et al. Development of resistance after CD4-guided structured treatment interruptions in HIV-infected patients treated with highly active antiretroviral therapy after dual-nucleoside treatment. Clin Infect Dis 2005; 40:XXX--XX (in this issue). First citation in article
9. Lawrence J, Mayers DL, Hullsiek KH, et al. Structured treatment interruption in patients with multidrug-resistant human immunodeficiency virus. N Engl J Med 2003; 349:837--46. First citation in article | PubMed | CrossRef
10. Metzner KJ, Bonhoeffer S, Fischer M, et al. Emergence of minor populations of human immunodeficiency virus type 1 carrying the M184V and L90M mutations in subjects undergoing structured treatment interruptions. J Infect Dis 2003; 188:1433--43. First citation in article | Full Text | PubMed
11. Dybul M, Chun TW, Yoder C, et al. Short-cycle structured intermittent treatment of chronic HIV infection with highly active antiretroviral therapy: effects on virologic, immunologic, and toxicity parameters. Proc Natl Acad Sci USA 2001; 98:15161--6. First citation in article | PubMed | CrossRef
12. Dybul M, Nies-Kraske E, Daucher M, et al. Long-cycle structured intermittent versus continuous highly active antiretroviral therapy for the treatment of chronic infection with human immunodeficiency virus: effects on drug toxicity and on immunologic and virologic parameters. J Infect Dis 2003; 188:388--96. First citation in article | Full Text | PubMed
13. Yerly S, Fagard C, Gunthard HF, Hirschel B, Perrin L; Swiss HIV Cohort Study. Drug resistance mutations during structured treatment interruptions. Antivir Ther 2003; 8:411--5. First citation in article | PubMed
14. Mocroft A, Katlama C, Johnson AM, et al. AIDS across Europe, 1994--98: the EuroSIDA study. Lancet 2000; 356:291--6. First citation in article | PubMed | CrossRef
15. The PLATO Collaboration. Predictors of trend in CD4-positive T-cell count and mortality among HIV-1--infected individuals with virological failure to all three antiretroviral-drug classes. Lancet 2004; 364:51--62. First citation in article | PubMed | CrossRef
ARTICLE
Development of HIV with Drug Resistance after CD4 Cell Count--Guided Structured Treatment Interruptions in Patients Treated with Highly Active Antiretroviral Therapy after Dual--Nucleoside Analogue Treatment
Reto Nuesch,1,2,3 Jintanat Ananworanich,1 Sunee Sirivichayakul,4 Sasiwimol Ubolyam,1 Umaporn Siangphoe,1 Andrew Hill,5 David Cooper,1,6 Joep Lange,1,7 Praphan Phanuphak,1,4 and Kiat Ruxrungtham1,4
1HIV Netherlands, Australia, Thailand Research Collaboration (HIV-NAT), Thai Red Cross AIDS Research Centre, Bangkok, Thailand; 2Outpatient Department of Internal Medicine and 3Division of Infectious Diseases, University Hospital Basel, Basel, Switzerland; 4Department of Medicine, Chulalongkorn University, Bangkok, Thailand; 5University of Liverpool, Liverpool, United Kingdom; 6National Centre in HIV Epidemiology and Clinical Research, Sydney, Australia; and 7International Antiviral Therapy Evaluation Center, Amsterdam, The Netherlands
(See the editorial commentary by Arduino above)
ABSTRACT
Background. For patients with human immunodeficiency virus (HIV) infection, structured treatment interruption (STI) is an attractive alternative strategy to continuous treatment, particularly in resource-restrained settings, because it reduces both side effects and costs. One major concern, however, is the development of resistance to antiretroviral drugs that can occur during multiple cycles of starting and stopping therapy. Methods. HIV genotypic drug resistance was investigated in 20 HIV-infected Thai patients treated with highly active antiretroviral therapy (HAART) and CD4 cell count--guided STI after dual nucleoside reverse-transcriptase inhibitor (NRTI) treatment. Resistance was tested at the time of the switch from dual-NRTI treatment to HAART and when HAART was stopped during the last interruption. Results. After STI, one major drug-resistance mutation occurred (T215Y), and, in the 4 samples with preexisting major mutations (D67N [n = 2], K70R [n = 2], T215Y [n = 2], and T215I [n = 1]), the mutations disappeared. All mutations in the HIV protease gene were minor mutations already present, in most cases, before STI was started, and their frequency was not increased through STI, whereas the frequency of reverse-transcriptase gene mutations significantly decreased after the interruptions. After the 48-week study period, no patients had virological failure. Long-term follow-up (108 weeks) showed 1 case of virological failure in the STI arm and 1 in the continuous arm. No virological failure was seen in patients with major mutations. Conclusions. Major HIV drug-resistance mutations were not induced through CD4 cell count--guided treatment interruptions in HIV-infected patients successfully treated with HAART after dual-NRTI therapy.
AUTHOR DISCUSSION
CD4 cell count--guided STI was tested in 23 HIV-infected Thai patients who had previously been treated with dual-NRTI therapy. Samples from 20 patients were available for HIV genotypic resistance testing. The patients were switched to HAART for 3 years and had a viral load of <50 copies/mL before enrollment. Before HAART, antiretroviral--associated major HIV reverse-transcriptase mutations were found in 4 (36%) of 11 samples, and minor mutations were found in 5 (45%) of 11 samples. After CD4 cell count--guided treatment, only 1 (6%) of 17 had major mutations, and minor mutations were found in 8 (47%) of 17 samples. No virological failure was seen in patients with major HIV mutations after 108 weeks of follow-up.
HIV with drug resistance is a major concern in STI and has been shown to occur in clinical trials investigating structured interruptions of HAART [13, 15, 16, 23]. On the other hand, it also has been shown that interruption of HAART can convert a resistant virus population to wild-type virus [24--27]. Although this strategy has been harmful in the patients receiving salvage therapy [28], the situation may be different in immunologically intact patients infected with HIV resistant to NRTIs but treated successfully with HAART. Indeed, major HIV mutations present after dual-NRTI therapy and before HAART had disappeared after STI. Seventy percent of our patients had a detectable viral load of > 400 copies/mL after dual-NRTI therapy. Despite having undetectable viral load after HAART, they can be considered a population at risk for resistance development after STI. However, a major HIV mutation was found in only 1 patient after STI, and this did not lead to virological failure during a follow-up period of 108 weeks. To our knowledge, this study is the first investigation of STI done exclusively in HIV-infected patients with viral supression who are treated with HAART after dual-NRTI therapy.
In this CD4 cell count--guided treatment-interruption trial, HIV mutations were frequently observed after STI in patients previously treated with dual-NRTI therapy before HAART. However, only 1 of these mutations (T215Y) was a major mutation. HIV from 8 patients displayed 1 or 2 secondary mutations, which alone do not result in resistance to antiretrovirals. They probably represent naturally occurring polymorphisms rather than drug-selected mutations. Indeed, the minor HIV protease gene mutations seen after STI were nearly all present before initiation of HAART. Major mutations seen after STI involved the reverse-transcriptase gene, whereas minor mutations involved polymorphic positions coding for the protease gene. In our study, positions 10, 20, 63, and 77 were involved. Although these mutations do not cause significant drug resistance by themselves, some of them contribute to drug resistance when present together with other protease mutations [29, 30]. Whether further HIV mutations will be acquired and thus lead to clinical drug resistance after additional cycles of STI cannot be determined from the data available at present. But none of the patients, except for the one who did not adhere to HAART, developed virological failure by week 108 of follow-up. One other case of virological failure occurred in the continuous treatment arm [22]. Deeks et al. [31] have shown that durable suppression of the HIV virus population may be achieved with a combination regimen containing only 1 fully active agent. Patients infected with HIV that developed major mutations still had at least 1, and usually 2, drugs that were still active against the strain, which could explain why even patients with resistant HIV responded well to reinitiation of HAART after treatment interruption. How sustainable viral suppression will be remains to be seen. Nevertheless, after 108 weeks of follow-up and with only 1 treatment failure, CD4 cell count-guided STI appears to be safe in this patient population. Accordingly, all patients with major HIV mutations in the "week-on, week-off" arm whose treatment failed had a viral load of <50 copies/mL after reinitiation of HAART. Using a univariate model, we found no factors predicting the development of HIV mutations. In accordance with a study performed in a very similar group of patients, multidrug resistance against NRTIs was frequently seen in patients predominantly infected with HIV subtype A/E for whom NRTI treatment failed [20]. In our study, presence of preexisting mutations was not associated with development of resistance after STI. However, when mutations were present before initiation of HAART, we observed either reversion to wild-type virus or substitution of these mutations with minor mutations during STI. Interestingly, the frequency of reverse-transcriptase gene mutations significantly decreased after STI, and there was a trend toward a reduction in the number of preexisting major mutations in the HIV reverse-transcriptase gene after STI. Whether these mutations truly disappeared or whether we just measured overgrowth of wild-type virus is difficult to determine. The time from the stopping HAART to the performance of genotyping was 32 days, and a previous study has shown that, within the first 30 days, most reverse-transcriptase mutations remain [25]. Although we cannot conclude from our data that CD4 cell count--guided STI is beneficial for such patients, we did not find any harmful effects of STI on the virological outcome.
The study has some limitations. The strength of the results and conclusions is somewhat diminished by the limited sample size. Because of RNA degradation, 6 samples could not be amplified. Another 3 samples could not be amplified due to probable mutations at the primer site. During the last treatment-interruption cycle, half of our patients had genotyping performed >30 days after stopping HAART (median, 32 days). It is possible that mutated viruses were not detected because of the relative increase in the number of wild-type viruses. However, Miller et al. [25] showed that mutations in the reverse-transcriptase gene remain largely unchanged 30 days after treatment interruption. Moreover, all major HIV mutations in our study population were mutations in the reverse-transcriptase gene. The observed decrease in major mutations may also have been due to random effects caused by small sample size and nonamplification of samples, rather than STI.
Nevertheless, the study offers an interesting insight into the effect of STI on patients who have received suboptimal antiretroviral therapy before HAART, and it is the first investigation that exclusively studied patients previously treated with dual-NRTI therapy. The long clinical follow-up of 108 weeks strengthens many of the conclusions and also supports the further use of CD4 cell count--guided STI in controlled conditions for patients with preexisting major HIV mutations. This is relevant, since STI may become an important treatment strategy in resource-limited places like Thailand, where many patients have previously been treated with dual-NRTI therapy and thus harbor HIV with major mutations in the reverse-transcriptase gene [20].
In conclusion, major HIV mutations were not induced through CD4 cell count--guided treatment interruptions in HIV-infected patients successfully treated with HAART after dual-NRTI therapy. However, the power of this trial is limited, and a cautious follow-up is necessary. The prevalence of infection with HIV with major mutations conferring drug resistance by themselves decreased from 36% of patients before CD4 cell count--guided STI to 6% after STI. Also, the mutations did not correlate with virological response to HAART so far, and the presence of preexisting mutations after dual-NRTI therapy did not negatively influence the virological outcome of STI. These findings only apply for the chosen CD4 cell count--guided treatment interruption strategy and cannot be extrapolated to other interruption strategies.
INTRODUCTION
The introduction of HAART has dramatically improved the course of HIV infections [1, 2]. However, with HAART being widely used, long-term toxicity occurs [3, 4]. Although the therapy is cost-effective in some developed countries [5, 6], the costs of antiretroviral drugs impose a major economic burden on countries with limited resources like Thailand [7]. Structured treatment interruption (STI) is, therefore, an attractive alternative to continuous treatment, reducing both side effects and costs. One major concern, however, is the emergence of HIV with resistance to antiretroviral drugs that can occur during multiple cycles of starting and stopping therapy. Previous clinical trials investigating STI in the treatment of well-controlled chronic HIV infection did not demonstrate an increased occurrence of resistance [8--12]. However, new data demonstrate the appearance of resistance during STI. A trial with long-cycle STI, which is more similar to CD4 cell count--guided treatment interruptions, and the use of efavirenz-based HAART was stopped because of the occurrence of resistance in 3 of 8 patients [13]. In another similar study with various HAART regimens, resistance developed in 21.3% of patients who receive STI [14]. In a trial with repeated cycles of STI, M184V and L90M mutations could be detected in minor virus populations at different times during the trial [15]. Furthermore, the week-on, week-off arm of a large treatment-interruption trial had to be discontinued because of virological failure [16]. Thus, the risk of emergence of resistance might have been underestimated so far. In addition, these trials were performed with patients who had no history of previous failure to respond to antiretroviral therapy or in a mixed population, restricting the population of patients who might profit from STI. Previous results had shown that the week-on, week-off strategy had to be stopped because of virological failure also in patients previously treated with a dual nucleoside reverse-transcriptase inhibitor (NRTI) regimen [17]. We therefore investigated genotyping resistance in patients previously treated with dual-NRTI therapy who were being successfully treated with HAART and were undergoing CD4 cell count--guided STI, probably the most-promising interruption strategy for such patients.
RESULTS
Results for the primary end points of this study have been presented elsewhere [17]. In summary, 74 NRTI-pretreated patients were included in the study, and continuous HAART was compared with CD4 cell count--guided STI. "Week-on, week-off" STI treatment was discontinued ahead of schedule, because failures were unacceptably frequent (occuring in 12 [46%] of 26 patients) [17, 22]. At the time of virological failure, no HIV with drug resistance was found in plasma samples from 3 patients, samples from 2 patients were not amplifiable, and, for 1 patient, no testing was done. Mutations in the HIV reverse-transcriptase gene were found in samples from 3 patients (at position 215 [n = 3] and positions 219, 210, 67, and 41 [n = 1 for each]). Mutations in the HIV protease gene were detected in samples from 4 patients (at position 63 [n = 3] and 82 [n = 1]). Of note, all patients had a viral load of <50 copies/mL after reinitiating continuous HAART. The "week-on, week-off" strategy was unreliable and thus not investigated further. Twenty-three patients were treated with CD4-guided STI, and 25 patients were treated with continuous HAART. The observational period was 48 weeks, and follow-up continued for 108 weeks. After 108 weeks (96 weeks of STI and 12 weeks of continuous treatment), 1 case of virological failure, defined as a viral load >500 copies/mL, occured after 3 months of continuous treatment, in a patient with nonadherence in the STI group [22]. Another failure occurred in the continuous treatment group at week 96; no results of resistance testing were available for this patient.
Frozen plasma samples obtained before HAART were available from 20 (87%) of the patients, and samples obtained after STI were available from 20 (87%) of the patients. Baseline characteristics of these patients are shown in table 1. Of note, only 30% of patients had a VL < 400 copies/mL before switching from dual-NRTI (zidovudine/zalcitabine) treatment to HAART. The NRTI regimen was changed from zidovudine/zalcitabine to zidovudine/lamivudine for 9 patients and to stavudine/didanosine for 11 patients. The female-to-male sex ratio was balanced, and the mean age (±SD) was 35.4 ±6.4 years. Most patients (55%) were asymptomatic before starting antiretroviral therapy. Depending on their reaction to STI, the patients underwent 1--3 (mean, 1.65) treatment interruptions during the 48-week observation period. Resistance testing was performed at a median of 32 days (IQR, 28--63.5 days) after treatment was stopped during the last treatment interruption within the 48-week observation period.
Table 2 shows the results of HIV genotyping before HAART and after CD4 cell count--guided STI. Genotyping could be done on 11 samples obtained before HAART, and 9 samples could not be amplified. Three of these 9 samples had a viral load of <400 copies/mL, and, in 6 other samples, RNA degradation had occurred. In 11 samples obtained before the switch from dual-NRTI treatement to HAART, mutations were found in 4 (36%), and no mutation was present in 7 (64%). In 17 samples obtained after CD4 cell count--guided STI, resistance mutations were found 9 (53%). Three of these 17 samples could not be amplified, possibly because of mutations at the primer site. HIV mutations present before the start of protease inhibitor--based HAART and detected after STI are shown in figure 1 and table 2. Major mutations were found in 4 (36%) of 11 samples obtained before HAART and in 1 (6%) of 17 samples obtained after STI (P = .062, by Fisher's exact test). The matched pair comparison showed that minor mutations in the HIV protease gene that were present before HAART were also found after STI. Minor mutations emerged in HIV from 4 samples, and, in HIV from 1 sample, 1 mutation was lost. New mutations were acquired by HIV in 2 samples, and 2 samples obtained before HAART could not be amplified. Preexisting mutations in the HIV reverse-transcriptase gene disappeared after STI. In 2 patients with this HIV mutation pattern, the virus reverted to wild type, whereas, in 2 others, secondary mutations which do not lead to drug resistance were present after the treatment interruption. Only 1 major mutation (T215Y) occurred after STI, in a patient with HIV that did not have genotoypic resistance before HAART. As shown in figure 2, the frequency of mutations in the HIV reverse-transcriptase gene was significantly reduced, from 72% before HAART to 12% after STI (P < .01, by Fisher's exact test). The frequency of mutations in the protease gene did not significantly change (72% vs. 65% after STI).
During the 48-week observation period, the same HAART regimen remained effective in suppressing the viral load in all patients who had to restart therapy for at least 3 months, in accordance with the protocol criteria. Eighteen patients who reinitiated HAART achieved a viral load of <500 copies/mL after 3 months of continuous therapy. The median viral load rebound after STI was 4.6 log10 copies/mL (IQR, 3.9--4.9) in patients with drug-resistant HIV and 4.3 log10 copies/mL (IQR, 3.9--4.3) in patients without drug-resistant HIV. After posttrial follow-up of 108 weeks, 1 patient had a viral load of >500 copies/mL 3 months after reinitiating HAART, which qualified as virological failure. This failure occurred at week 72 because the patient did not adhere to reinitiated HAART. The patient demonstrated no major HIV mutations after STI and was discontinued from the study. At week 108, all patients had received 3 months of continuous HAART. All but the patient mentioned above had a viral load of <400 copies/mL [22]. The factors believed to predict the occurrence of HIV drug-resistance mutations after STI—presence of resistance before HAART, viral load rebound, CD4 cell count at the time of initiation of STI, number of STI cycles, CD4 cell count before antiretroviral therapy, CD4 cell count before HAART, viral load before HAART, sex, and the NRTIs included in the HAART—were investigated without significant results.
PATIENTS AND METHODS
STI for patients previously treated with dual-NRTI therapy followed by HAART was investigated by the HIV Netherlands, Australia, Thailand Research Collaboration (HIV-NAT) of the Thai Red Cross AIDS Research Centre. An open-label, randomized 3-arm study was conducted to evaluate and compare the efficacy, safety, and tolerability of the following regimens: (1) continuous treatment with saquinavir--soft gel capsule, 1600 mg once per day, plus ritonavir, 100 mg once a day, plus 2 NRTIs (either zidovudine and lamivudine or stavudine and didanosine; (2) STI with the same regimen that was suspended and restarted on alternating weeks of week on, week off; and (3) STI with the same regimen that was suspended and restarted on the basis of CD4 cell count--driven criteria (from study HIV-NAT 001.4 [17]), in which therapy was stopped if the CD4 cell count decreased to <350 cells/μL or to 30% of preinterruption level, depending on the patient's choice. Patients qualified for the study if their last CD4 cell count was >350 cells/μL and their viral load had been <50 copies/mL for at least 6 months prior to enrollment. The "week-on, week-off" arm had to be discontinued because of virological failures at week 72 [17]. This strategy was not investigated further.
Ethics. The study was performed in accordance with the approval of the ethics committee of Chulalongkorn University, which conforms to the Helsinki Declaration of 1975, as revised in 1983.
Participants. The participants were HIV-infected Thai patients who had participated in the HIV-NAT 001 trial series that started in 1997, when they were treated with dual-NRTI therapy that consisted of zidovudine and zalcitabine at either the standard or half the standard dosage for 48 weeks, as described in a previous publication [18]. Initial treatment was followed by 3 years of saquinavir-based HAART [19]. If the viral load remained undetectable (<50 copies/mL) and the CD4 cell count was >350 cells/μL, a patient was enrolled in the study after written informed consent had been obtained.
Procedures. During the 48-week observation period, patients randomized to either of the STI arms had an evaluation every 2 months, and frozen plasma samples were obtained for further analysis. To assess whether resistance was acquired during multiple cycles of CD4 cell count--guided treatment interruptions, HIV genotyping resistance testing was performed on the first plasma sample with a viral load of >1000 copies/mL that was obtained after treatment was stopped during the last cycle of treatment interruption, for the CD4-guided arm. The "week-on, week-off" arm was not investigated further, as this strategy showed too many virological failures. To differentiate preexisting resistance from acquired resistance, viral genotypic resistance testing was done on the last plasma sample obtained before patients were switched from dual-NRTI therapy to protease inhibitor--based HAART. The methodology for HIV reverse-transcriptase genotyping has been described elsewhere [20]. For the protease genotypic resistance assay, the same methodology was used but with the following primers: PI-1685 (5′-GGAATTTTCCTCAGAGCAGACCAG-3′), PI-2209 (5′-TCTTCTGTCAATGGCCACTGTTTAAC-3′), and PI-2172 (5′-CCATTCCTGGCTTTAATGTTACTGGTAC-3′). We categorized major and minor mutations in accordance with guidelines set by the International AIDS Society--US Drug Resistance Mutations Group [21].
Poststudy follow-up during STI totaled 108 weeks. For the final 12 weeks, all patients were treated with continuous HAART. Virological failure was defined as a viral load of >500 copies/mL at any time, for the continuous-treatment arm, and after 3 months of continuous HAART, for the STI arm.
Statistical analysis. Descriptive results are presented as means ±SD, medians with interquartile range (IQR), and percentages. Inferential statistics using either parametric or nonparametric tests were used, as appropriate for the data type. The overall level of significance was set at α = 0.05. To compare means, medians, and proportions of investigated factors between groups with and groups without resistance, the Student's t test, Mann-Whitney U test, and χ2 test were used. Fisher's exact test was used for small values for which the χ2 test was not applicable. Statistics were done using the SPSS software, version 9.0 (SPSS).
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