Antiretroviral therapy (ART) is extremely effective in the prevention of mother-to-child transmission (pMTCT) of HIV1 and is frequently given during pregnancy to women who otherwise would not qualify for treatment.2 Stopping ART after immune reconstitution has been linked with increased morbidity and mortality.3,4 Nevertheless, pregnant women who do not qualify for ART based on treatment guidelines2 often choose to discontinue ART after the birth of their infant.5
A few studies5,6 have evaluated the selection of drug resistance mutations when women stop ART postpartum. These studies suggest that cessation of ART postpartum may select drug-resistant mutants. To further investigate the risk of stopping ART postpartum, we assessed and compared the frequency of HIV drug resistance in women randomized between nelfinavir (NFV)-based and Nevirapine (NVP)-based regimens for pMTCT and who discontinued ART postpartum.
MATERIALS AND METHODS
Study Design and Participant Specimens
Pregnant women with plasma HIV RNA loads >1000 copies/mL were enrolled into Pediatric AIDS Clinical Trials Group protocol 1022 (P1022).7 The study aimed to determine whether a protease inhibitor (PI)- or nonnucleoside reverse transcriptase inhibitor (NNRTI)-based regimen would be more effective or better tolerated in women initiating therapy during pregnancy. HIV-infected antiretroviral (ARV)-naive pregnant women who consented to enrollment were randomized to NFV or NVP in combination with Zidovudine (ZDV) and Lamivudine (3TC) for pMTCT. Women randomized to NVP (supplied as Viramune by Boehringer Ingelheim Pharmaceuticals, Inc., Ingelham am Rhein, Germany) were administered 200 mg by mouth once daily for 14 days, then the frequency was increased to 200 mg twice daily as tablets or suspension. Those randomized to NFV (supplied as Viracept by Agouron Pharmaceuticals, Inc., San Diego, CA) were given 1250 mg orally twice daily, given as five 250-mg tablets (“older” formulation). In addition, women in both study arms were given ZDV 300 mg and 3TC 150 mg orally twice a day, which could be administered as Combivir. NFV and NVP were considered to be the safest PI and NNRTI, respectively, for pregnant women at the time. Enrollment into P1022 was discontinued early due to greater than expected toxicity in the NVP group.7
Participants eligible for this ART resistance substudy were ART naive at enrollment into P1022, had HIV replication suppressed to <400 copies/mL during study ART, and discontinued ART postpartum. Women continued with study visits until 2 years postpartum, even if study ART was discontinued. Specimens were collected between September 2002 and October 2005, with women discontinuing ART an average of 43 weeks (range, 12–101 weeks) after delivery. The first available specimen with plasma virus rebound >1000 copies/mL after documented suppression of plasma HIV RNA <400 copies/mL was evaluated for drug resistance by oligonucleotide ligation assay (OLA) of both plasma and peripheral blood mononuclear cells (PBMCs). In addition, plasma viral genotype was determined by consensus sequencing. If drug resistance was detected by either method, then specimens from study entry and intermediate visits were also evaluated for resistance.
Genotypic Testing of Plasma
RNA extracted from the plasma was reverse transcribed and HIV pol was polymerase chain reaction (PCR) amplified and sequenced using the ViroSeq HIV-1 Genotyping System (Abbott Molecular, Des Plaines, IL) per manufacturer's instructions. Consensus sequences spanned from protease codon 1 through at least reverse transcriptase (RT) codon 225. Our laboratory was certified to perform ViroSeq Genotyping continuously from 2001 to 2009 by the Viral Quality Assurance Program of the National Institutes of Health. Mutations in HIV-1 group M subtype were identified using the Stanford HIV Drug Resistance Database.8 The nucleic acid sequence was reported to GenBank (JN191665-JN191705, JN202340; submission in process).
PCR products from ViroSeq plasma preparations were submitted to a second round of PCR, as described below, before OLA.
HIV DNA Quantification and Amplification
DNA was extracted from cryopreserved PBMCs using the Puregene Cell and Tissue Kit (Gentra Systems, Minneapolis, MN). DNA concentrations were measured by optical density (OD) at 260 nm and stored at −20°C. Specimens with sufficient DNA had the HIV DNA concentrations assessed by real-time PCR of the gag region.9
To prepare specimens for OLA testing, PCR was carried out on DNA as previously described10 with approximately 100 HIV DNA copies per reaction, using PRA and RTA first-round primers.11 The first-round PCR amplicon from DNA and the ViroSeq amplicon were separately submitted to a second-round PCR using primers PRB and RT3.11 The amplicons from the second-round PCR, an 1193-base pair DNA fragment encoding most of pol, were visualized in a 1.2% agarose gel with ethidium bromide staining.
OLA Testing of Plasma and PBMCs
An OLA was performed on all amplicons derived from plasma and PBMCs using probes that detect mutations associated with high-level drug resistance to NFV, codons D30N (AAT) and L90M (ATG), nucleoside RT inhibitors at codons K70R (AGA), M184V (GTG), and T215F/Y (TTC, TAC), and NNRTIs at codons K103N (AAC), Y181C (TGT), and G190A (GCA) as described.9 The relative concentration of resistant virus was estimated using a standard curve of mutant mixed with wild-type virus at the following concentrations: 0%, 2%, 5%, and 100%. Specimens were classified as mutant at the specific codon if the OD exceeded the 2% mutant standard for RT codons 103, 181, 190, and 184 and PR codon 90 and the 5% mutant standard for RT codons 70 and 215 and PR codon 30. Reactions with a mutant OD below the mutant cutoff and a wild-type OD less than half the OD of the wild-type control were considered indeterminate. All participant's specimens and OLA controls were analyzed in duplicate. Control plasmids are described in the OLA manual.11
Pharmacokinetics and Adherence
Intensive blood sampling of women to evaluate the pharmacokinetics of NFV and NVP during pregnancy was conducted in both study arms. Blood sampling occurred at 34 ± 2 weeks gestation and 8 ± 4 weeks postpartum and was collected predose, 0.5, 1, 1.5, 2, and 4 hours postdose. Additional samples were collected at 6 and 8 hours postdose and at 20 ± 4 weeks from women receiving NVP. The maximum plasma concentration (C max) and predose concentration (C predose) were analyzed, and the differences between the third trimester and postpartum concentrations were compared. Adherence data were collected by self-report questionnaire at ante- and postpartum visits.
Plasma HIV RNA concentrations, CD4 counts, and time on ART were compared in a Wilcoxon nonparametric test. The 95% confidence interval (CI) estimates were calculated by the modified Wald method. Proportions within ARV arms were compared by Fisher exact test. P values of ≤0.05 were considered statistically significant.
Sixteen of 38 women enrolled into Pediatric AIDS Clinical Trials Group 1022 were eligible and evaluated in this substudy (Fig. 1); 8 women had been randomized to NFV and 8 to NVP. The pre-ART plasma HIV RNA and CD4+ cell concentrations were similar between the 2 arms (mean 402 log10 copies/mL and 322 cells/μL, respectively). Women randomized to NFV received ART an average of 88 days before delivery and 236 days postpartum (range, 7–145 and 121–514 days, respectively), which was similar to women randomized to NVP (mean days ART antepartum 125, range, 94–159, P = 0.07; and mean days postpartum 372, range, 85–708 days, P = 0.33). The substudy participants were infected with HIV-1 subtype B, except 1 infected with subtype CRF02_AG.
By design, all substudy women were ART naive and had ART-associated suppression of viral replication. Subsequently, each woman had HIV RNA rebound to >400 copies/mL, which in 8 women occurred postpartum in association with discontinuing ART. Importantly, rebound to >400 copies/mL was detected during gestation and before discontinuation of ART in 8 women, suggestive of inadequate ARV concentrations due to suboptimal pharmacokinetics, poor adherence, or resistance in the woman's virus population pre-ART. The median pre-ART plasma HIV RNA concentrations (3.85 versus 3.80 log10 copies/mL, P = 0.39) and median CD4 counts (241 versus 414 cells/μL, P = 0.09) did not differ between women with viral rebound during versus after stopping ART postpartum.
HIV Drug Resistance Detected During Pregnancy or With Discontinuation of ART
A high rate of drug resistance mutations (11 of 16, 69%; 95% CI: 41 to 89) was detected by OLA (Fig. 2). Consensus sequencing of plasma HIV detected resistance in fewer, 8 of 16 (50%; 95% CI: 25 to 75), consistent with its lower sensitivity.10 Although study records show that the women did not report receiving ARV before study entry, 2 had HIV resistance detected in the enrollment specimen, 1 in each study arm. The woman assigned to NFV (participant #10, Fig. 2) had mutations conferring resistance to 2 classes of ARV at enrollment (L90M and K70R) and selected M184V during study ART. The L90M mutation was estimated at 100% in both her pre-ART plasma and PBMCs, highly suggestive of transmitted drug resistance. She had ART-associated suppression of viral replication, but subsequently her virus rebounded with the L90M and K70R mutations and M184V was newly detected. The woman assigned to NVP (participant #12, Fig. 2) had T215Y by OLA at low concentrations in her enrollment PBMCs. The T215 codon was indeterminate in plasma virus by OLA, suggestive of a transitional mutation, which by consensus sequencing was T215D. No additional mutations were detected in her virus during study ART. Excluding the mutations in the pre-ART specimens of these 2 women, new resistance mutations were detected at the time of virus rebound either during gestation or postpartum in 10 of 16 women (63%; 95% CI: 35 to 85).
The rate of selection of new ARV resistance mutations did not differ by treatment arm, occurring in 6 of 8 (75%) randomized to NFV and in 4 of 8 (50%) randomized to NVP (Fig. 2). However, new nucleoside RT inhibitor mutations were more common in women randomized to NFV compared with NVP: 6 of 8 (75%) versus 1 of 8 (13%), P = 0.04 (Fig. 2). The new nucleoside RT inhibitor mutations included M184V associated with resistance to 3TC/FTC, and K70R and T215Y associated with resistance to thymidine analogs. M184V was detected in 6 of 8 women randomized to NFV (75%, 95% CI: 35 to 97) compared with only 1 of 8 women (13%, 95% CI: 0 to 53) given NVP, P = 0.04.
New NNRTI resistance mutations were detected in (4 of 8) women randomized to NVP-ART and in none assigned to NFV-ART, P = 0.08 (Fig. 2). K103N was detected in 3 of 8 (38%), 1 also had Y181C, and G190A was detected in a fourth participant. New mutations conferring resistance to PI were detected in 2 of 8 (25%) participants in the NFV arm (Fig. 2). Selection of ≥2 new resistance mutations to 2 classes of ART was detected in 4 of 8 women; of these, 3 were assigned to NFV-ART and 1 was assigned to NVP-ART.
Time to Detection of New Drug Resistance Mutations
During receipt of study ART, the plasma HIV RNA loads rebounded to >400 copies/mL in 8 of the 16 women. New resistance mutations were detected in specimens from 4 of these (3 of 5 NFV and 1 of 3 NVP), including participant #10 with L90M and K70R present at entry and newly detected M184V (Fig. 2). New resistance mutations were detectable only after study ART was discontinued in 6 of the 11 participants (3 NFV and 3 NVP). The median interval between stopping study ART and resistance testing was 88 days: median 77 days (range, 0–140 days) and 88 days (range, 49–133 days) for the NFV and NVP arms, respectively. No resistance mutations were detected at any time point in 5 of the 16 women in the substudy, including 3 from the NVP and 2 from the NFV.
Detection of Resistance by Consensus Sequencing and OLA
Testing to detect drug resistance by consensus sequencing (plasma) and OLA (plasma or PBMCs) were compared across a total of 42 specimen dates, including ≥2 time points from 15 of the 16 participants. The detection of mutations at codons 30 and 90 in protease and 70, 103, 181, 184, 190, and 215 in RT were tallied for both consensus sequencing and OLA. The mutations identified in consensus sequences were also detected by OLA. In addition, OLA detected 4 resistance mutations in 4 women that were not detected by sequencing, including the mutations encoding K103N, Y181C, M184V, and K70R. Several mutations associated with drug resistance that were not evaluated by OLA were detected by consensus sequencing, including M41L, V118I, E138A, and L210W.
Detection of Resistance in Plasma Versus PBMCs by OLA
Resistance mutations were not consistently detected by OLA in both the PBMCs and plasma (Fig. 2). Across all specimens tested, detection of resistance at specific codons by OLA was greater in the NFV compared with NVP arm when testing plasma (n = 15/151 in NFV arm versus 4/126 in NVP arm; P = 0.03), but rates were similar in PBMCs [n = 15/148 versus 7/109, respectively; P = 0.37 (Fisher exact test)].
NFV and NVP Pharmacokinetics and Adherence
Ten of the 16 participants had intensive pharmacokinetic data available: 3 receiving NFV (participants 3, 4, and 5) and 7 receiving NVP (all participants except 13). The NFV “trough” concentration (C predose) was 0.2 μg/mL (range, 0.0–0.5 μg/mL) in the third trimester and the “peak” (C max) was 2.1 μg/mL (range, 0.9–3.7 μg/mL). The 4-hour postdose value is missing for 1 of these women, which may artificially lower the C max average. The corresponding postpartum values are as follows: C predose and C max were 2.0 μg/mL (range, 0.4–3.6 μg/mL) and 3.8 μg/mL (range, 2.4–5.2 μg/mL), respectively, but were only available for 2 of the 3 women. No second trimester values were available from the women given NFV.
The C predose for the NVP participants in the second trimester was 2.3 μg/mL (range, 1.6–3.1 μg/mL) and C max was 4.4 μg/mL (range, 3.9–5.3 μg/mL). Third trimester values were available for only 1 woman with C predose and C max of 4.8 μg/mL and 6.9 μg/mL, respectively. Five NVP participants had postpartum values with C predose of 5.7 μg/mL (range, 3.7–9.0 μg/mL) and C max of 6.7 μg/mL (range, 6.0–8.9 μg/mL).
Ante- and postpartum adherence data for 11 of the 16 participants indicated missed doses within 30 days of completing the questionnaire. Of the 5 women in the NFV group and 6 women in the NVP group who reported missing doses, only 3 women from each group developed new drug resistance mutations. Three women on NFV and 2 on NVP who reported never missing a dose still developed new resistance mutations.
In our study of HIV-infected women who took ART for pMTCT, we observed relatively high rates of new HIV drug resistance mutations. Although these women all had ART-induced suppression of viral replication, resistance was detected when plasma HIV RNA was >400 copies/mL during gestation or in viral rebound specimens when ART was stopped between 2 and 24 months postpartum. In this small study, resistance rates did not differ in women randomized to NVP-ART versus NFV-ART. However, the pattern of resistance differed, with significantly greater selection of resistance to 3TC (M184V) in women randomly assigned to NFV and selection of NVP resistance (K103N, Y181C, and/or G190A) in women randomized to NVP.
The high rate of resistance in our study is consistent with rates reported in a larger observational study of NFV-ART, which detected M184V in 29% by consensus sequencing and 52% by allele-specific PCR.5 Mutations encoding M184I/V have been reported across studies of pregnant and postpartum women.5,12,13 However, the clinical significance of M184V on later ART has not been evaluated.
When ART is discontinued, unequal drug pressure can occur due to variation in the pharmacokinetics of each ARV. The longer half-life of NVP14 compared with 3TC15 likely protected participants randomized to NVP-ART from selection of M184V. Instead, when NVP pressure was unopposed, NNRTI mutations were preferentially selected. Resistance to NVP and 3TC can occur rapidly because the single base changes that confer high-level resistance likely exist in the viral population due to the permissive nature of HIV polymerase, and when ARV concentrations are low or not complemented by other ARV, these mutants are rapidly selected. In contrast, ≥2 mutations are required for high-level resistance to ZDV and to most PI, except NFV, and the likelihood for ≥2 specific mutations occurring randomly in the same virus is exceedingly low,8 providing a greater genetic barrier to the selection of drug-resistant virus.
Several factors, in addition to stopping ART postpartum, could have contributed to the high rates of ARV resistance detected in this study. First, women who stopped ART postpartum may not have been committed to treatment and may have had poorer adherence during gestation.16 Our adherence data showed that half the women in the study reported decreased adherence during gestation, but resistant viruses were selected in women who reportedly adhered to ART during gestation. Second, variable pharmacokinetics of NFV in pregnant women were evident in the women we studied, consistent with previously published studies of both the “older” and “newer” NFV formulations that observed lower and variable third trimester NFV concentrations17–22 compared with postpartum values. Low NFV concentrations17 along with diminished concentrations of the active form of ZDV in a subset of infected cells23 would allow selection of 3TC resistance (ie, low NFV trough concentrations plus low triphosphorylation of ZDV in cells would result in unopposed 3TC pressure and favor the selection of M184V).
The more frequent detection of resistance mutations by OLA compared with consensus sequencing indicates that mutants were at low concentrations in the population.10 Cell-free virions in the plasma are known to turn over rapidly, with resistance fading from the plasma within weeks of stopping therapy.24,25 The detection of mutants at high concentration in the PBMCs and plasma of 1 participant at the time of study enrollment is consistent with transmitted drug resistance.26
Our study has several important limitations. The study population was small, and although a significant difference was detected in the selection of M184V, the small group sizes precluded an analysis of differences in the selection of resistance to other ARV. The increased detection of resistance in the NFV compared with the NVP arm when testing plasma by OLA may be biased by the lack of paired specimens for all time points tested. The absence of ARV concentrations and information concerning ART adherence practices did not allow us to evaluate the potential mechanisms leading to viral rebound and selection of resistance during pregnancy. Importantly, we were not able to determine whether the resistance first detected in the postpartum specimens of certain women was due to stopping ART or if these women had low ARV concentration throughout gestation due to suboptimal pharmacokinetics or nonadherence. In addition, our study did not evaluate the clinical significance of the resistance on the efficacy of future ART.
Many HIV-infected pregnant women do not qualify for ART based on symptoms or CD4 cell counts. Recently, the World Health Organization revised its pMTCT guidelines to favor ART regardless of maternal CD4.27 This may increase episodic use of ART during gestation. Comparative studies are needed to select the safest ART regimen for episodic use in pregnancy. Ideally, these studies would compare various gestational ART regimens on the efficacy of subsequent ART. As drug-resistant viruses are rarely detected at “virologic failure” of Ritonavir-boosted PI regimens,28 either PI-based regimens or ARV “tails”29,30 may diminish the selection of drug-resistant mutants. Given that the detection of mutants in association with ARV given to pMTCT ARV diminish the efficacy of later ART,31–33 pre-ART resistance testing could help guide health care workers select ARV with a high likelihood of suppressing viral replication.
In summary, a high rate of drug-resistant HIV was detected in women taking NFV- or NVP-based ART for pMTCT who stopped ART within 2 years postpartum. 3TC resistance was selected at a higher rate in women randomized to NFV-ART, which suggests suboptimal NFV pharmacokinetics in pregnancy. As more programs utilize ART for pMTCT, studies such as the National Institutes of Health–sponsored Promoting Maternal and Infant Survival Everywhere (PROMISE) trial are important to inform us on the risks of stopping compared with continuing ART postpartum. Additionally, studies are needed to define the risks of discontinuing various gestational ART regimens on the clinical outcome of ART subsequently administered to treat the mother's HIV-associated immunodeficiency.
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