To the Editor:
Recent studies have not detected accumulation of resistance mutations in highly active antiretroviral therapy (HAART)-treated patients whose plasma viral load (VL) persists at less than 50 copies/mL.1 In contrast, at viremia levels of 50 to 1000 copies/mL, low-grade viral replication may lead to an accumulation of resistance mutations that endanger the effectiveness of current and even posterior treatments.2,3 Although these patients ideally should undergo resistance testing before deciding on treatment change or intensification, current clinical assays for resistance often fail to yield results when VL is lower than 1000 copies/mL.
Treatment interruption (TI) is usually followed by VL rebound within days or weeks.4,5 Therefore, TI followed by resistance testing when VL reaches 1000 copies/mL, in theory, may be used to advantage to perform conventional resistance tests in these patients. The problem is that some of these mutations may go undetected in the resistance test a few days after TI due to replacement of the mutating virus by wild-type virus,6-8 which could reduce the utility of this strategy.
We performed TI in 9 clinically and immunologically stable patients with persistent viremia of 50 to 1000 copies/mL (using Amplicor HIV-1 Monitor test, version 1.5, Roche Molecular System, Branchburg, NJ; lower limit of detection = 50 copies/mL) on at least 3 consecutive occasions separated by intervals of at least 1 month.
All were on continuous HAART for at least 1 year, with good compliance. None had previously undergone resistance testing.
One week after total TI, blood samples were obtained to determine VL, and 4 mL was frozen for later use in the resistance test. When VL was less than 1000 copies/mL, the frozen sample was discarded; this process was repeated weekly until a VL of at least 1000 copies/mL was detected. Then the corresponding frozen sample was thawed and used to perform the genotypic resistance test (Trugene, Bayer HealthCare LLC, Tarrytown, NY). Patients received no antiretroviral treatment until the results of the test were obtained and evaluated to guide the new treatment regimen. Informed consent was obtained from all patients.
All patients were male with a mean age of 46 years (range, 39-61 years). By Centers for Disease Control classification (1993), 1 patient was at stage A-1, 3 at A-2, 3 at B-2, 1 at B-3, and 1 at stage C-2.
Mean time receiving continuous HAART before TI was 57 months (range, 31-84 months); 5 patients had changed their HAART plan at least once due to adverse effects (1 patient) or previous virologic failure (4 patients). Thus when low-level viremia was detected, mean time on the last HAART regimen was 22.7 months (range, 3-60 months).
Only 2 patients had started antiretroviral treatment with a HAART-type regimen, whereas the remaining 7 had started with non-HAART regimens.
Table 1 shows all the antiretroviral drugs that each patient had received previously, those being taken at the time this study began, and the mutations found in each patient.
All patients had stable viremia of 50 to 1000 copies/mL, with a mean 6.5 determinations of VL (range, 3-14) as from the 1st determination of more than 50 copies/mL, and a median time of 11 months (interquartile range [IQR] 5-20).
At the time of initiating TI, median VL was 428 copies/mL (IQR 162-727) and median CD4 lymphocytes was 598/mm3 (IQR 383-740).
Mean time between TI and resistance testing was 2.4 weeks (median 2, IQR 1-3.5). Median VL at the time of resistance testing was 8105 copies/mL (IQR 2132-23,275). Two patients presented significant decline of 115 and 228 lymphocytes CD4/mm3, respectively, during TI, whereas the other patients' CD4 values remained stable. No clinical events were recorded during TI.
We found a mean of 5.3 resistance mutations per patient (range 3-7), and in all patients we detected resistance mutations that compromised the effectiveness of at least 1 of the drugs used in their current treatment (range, 1-4). Furthermore, 3 patients presented with resistance mutations related to drugs previously taken.
In 8 patients, salvage therapy began 2 to 8 weeks after TI, except in 1 patient in whom this was 32 weeks by personal decision.
After evaluating resistance test results, treatment changes were as follows: 1 patient, 1 drug; 5 patients, 2 drugs; 2 patients, 3 drugs; and 1 patient, 4 drugs. In only 4 patients, all the drugs were changed.
On initiating the new regimen, median VL was 48,200 copies/mL (IQR 2135-84,800) and median CD4 count was 487/mm3 (IQR 201-761).
After treatment change, mean follow-up was 13 months (range 3-21 months). All patients presented with a VL of less than 50 copies/mL as from 3 months until the last follow-up analysis.
CD4 lymphocyte evolution after treatment change was: no change in 4 patients, significant increase (mean 276/mm3; range, 93-364) in 4 patients, and decrease (−292/mm3) in 1 patient.
No HIV-related clinical event was recorded during follow-up.
The strategy we employed to be able to perform conventional resistance testing in our 9 patients with persistently detectable low-level viremia proved safe and effective. After treatment changes based on this procedure, all patients achieved a VL of less than 50 copies/mL. Despite the small sample size, our results suggest that this strategy merits further study and meanwhile should be considered when planning changes in antiretroviral therapy for such patients.
In this series we found what we consider a high number of resistance mutations, probably attributable to the fact that 7 of the 9 patients had started with non-HAART therapy. All patients presented with resistance mutations compromising the effectiveness of at least 1 of the drugs in their current treatment, and 7 of the 9 patients presented mutations compromising the effectiveness of at least 2 of these drugs. This highlights the need for resistance testing in this type of patient and justifies the strategy of TI used in this study. Had we waited for the VL to reach 1000 copies/mL without TI, the risk of further mutation accumulation would have increased and could have complicated the new salvage antiretroviral regimen.
Reversibility of resistance mutations has been demonstrated as soon as 15 days after TI in some patients, whereas in others these persisted for years.7-9 An important aspect of our strategy was performing the resistance test as soon as the viremia rose over 1000 copies/mL, which makes it theoretically improbable that current treatment-related mutations reverted after TI, because viral replication at that time was still low and thus extensive replacement of mutant virus by wild-type virus was improbable.
In our study, resistance mutations were found to drugs taken in the past, but not currently, in 3 patients. The possibility of our not having detected other such mutations exists, but the favorable response of all our patients to the new regimen indicates that, had they existed, they were not determinant.
All drugs were withdrawn simultaneously, which could favor the appearance of resistance mutations to nevirapine or efavirenz as from TI in those patients taking them, due to their long half-life and low genetic threshold. In fact, we detected resistance mutations to nonnucleoside reverse transcriptase inhibitors in all patients taking them. Although it would seem more logical that these mutations developed during the months when viremia was detectable, we cannot rule out the possibility that they were produced by TI in some cases. Currently, there is controversy as to the frequency and clinical significance of this occurring after TI, and about the most appropriate strategy to prevent it.10-13
In our study, because all our patients presented with sufficiently high CD4 values, treatment was suspended until the results of resistance testing became available. Two patients presented with significant decline in CD4 values during the period of no treatment. One made a clear recovery after salvage therapy was initiated; at 6-months follow-up, he had gained 304 CD4 cells with respect to his immediate post-TI values. In contrast, the other patient presented with a continual decline in CD4 values, from 1102/mm3 before TI to 469/mm3 at 17 months on the new salvage treatment with VL of less than 50 copies/mL. It is noteworthy that his salvage treatment included tenofovir-didanosine, and this particular combination has recently been associated with a decline in CD4 lymphocytes despite viremia control.14
To minimize the decline in CD4 lymphocytes during TI, current antiretroviral treatment could be resumed while waiting for resistance test results, thus reducing nontreatment time (<15 days for 50% of our study patients); this would keep basal VL low at initiation of salvage treatment, thus favoring the virologic success of the new therapy15 as well as minimizing the decline in CD4 lymphocyte count-which is especially important in heavily immunosuppressed patients.
Determining weekly VL is costly and time-consuming for both patients and staff. In our experience, the cost and effort was acceptable because TI was soon followed by VL greater than 1000 copies/mL in all patients (mean number of 2 determinations before resistance testing). It remains to be established whether a greater interval between VL determinations (2-3 weeks perhaps) is equally effective. However, important interpatient variations in progression of VL after TI have been reported4,5 and a greater interval might increase the risk of not detecting reverting resistance mutations.
In conclusion, in this small series, the strategy of interrupting antiretroviral therapy until patients reach a VL of 1000 copies/mL followed by conventional resistance testing proved safe and useful to establish more effective antiretroviral salvage therapy in patients with persistently detectable low-level viremia despite HAART.
Juan Luis Gomez Sirvent, MD, PhD
Maria Mar Alonso Socas, MD, PhD
Carlos Hernandez Calzadilla, MD, PhD*
Ana M. Lopez Lirola, MD, PhD
Maria Remedios Aleman Valls, MD, PhD
Infectious Diseases Section *Laboratory Service Hospital Universitario de Canarias Tenerife, Spain
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