Continuous quality evaluation of the Asanté rapid test for recent infection for robust kit lot quality verification

The Sedia Biosciences Asanté rapid test for recent infection (RTRI) can identify HIV infections and characterize HIV-1 as recent or long-term infection via the positive verification (V) line and long-term line (LT) line, respectively. Tracking with Recency Assays to Control the Epidemic (TRACE) program uses RTRI assays. Successful implementation of TRACE requires high-quality test performance. The goal of this study is to evaluate the additional quality practices established for new kit lots prior to field use. Asanté lot quality control data from the manufacturer is reviewed by the Centers for Disease Control and Prevention International Laboratory Branch (CDC-ILB) in the Division of Global HIV and TB using. If a lot passes manufacturer quality control and CDC-ILB review, test kits are sent to CDC-ILB for further evaluation. Evaluation by CDC includes inter-rater reliability and linear regressions comparing the V and LT lines against reference data as well as V and LT line data between testers. A Bland-Altman analysis was conducted to assess bias and systematic error. Overall, CDC-ILB passed 29 (91%) out of 32 Sedia Biosciences Asanté kit lots that initially passed manufacturing quality control from July 2017 to May 2020. Regression analyses demonstrate that test kits are performing as expected with consistent R2≥0.92 for both V and LT lines. On average, inter-rater reliability kappa was 0.9, indicating a strong level of agreement. Bland-Altman analyses demonstrate high agreement with little to no systematic error and bias. Ongoing evaluation of new RTRI kit lots is important to ensure high quality test performance. Rejecting 9% of kit lots highlight the importance of continuing to work with manufacturers to ensure consistent kit production and quality assurance (QA) activities. Investing in effective QA measures, conducting both pre- and post-market performance data reviews, could help improve RTRI accuracy and outcomes in similar testing programs.

Comparison of HIV prevalence, incidence, and viral load suppression in Zambia population-based HIV impact assessments from 2016 and 2021

BACKGROUND

The Zambian government has implemented a public health response to control the HIV epidemic in the country. Zambia conducted a population-based HIV impact assessment (ZAMPHIA) survey in 2021 to assess the status of the HIV epidemic to guide its public health programs.

METHODS

ZAMPHIA 2021 was a cross-sectional two-stage cluster sample household survey among persons aged ≥15 years conducted in Zambia across all 10 provinces. Consenting participants were administered a standardized questionnaire and whole blood was tested for HIV according to national guidelines. HIV-1 viral load (VL), recent HIV infection, and antiretroviral medications were tested for in HIV-seropositive samples. Viral load suppression (VLS) was defined as <1000 copies/ml. ZAMPHIA 2021 results were compared to ZAMPHIA 2016 for persons aged 15-59 years (i.e., the overlapping age ranges). All estimates were weighted to account for nonresponse and survey design.

RESULTS

During ZAMPHIA 2021, of 25 483 eligible persons aged ≥15 years, 18 804 (73.8%) were interviewed and tested for HIV. HIV prevalence was 11.0% and VLS prevalence was 86.2% overall, but was <80% among people living with HIV aged 15-24 years and in certain provinces. Among persons aged 15-59 years, from 2016 to 2021, HIV incidence declined from 0.6% to 0.3% ( P -value: 0.07) and VLS prevalence increased from 59.2% to 85.7% ( P -value: <0.01).

DISCUSSION

Zambia has made substantial progress toward controlling the HIV epidemic from 2016 to 2021. Continued implementation of a test-and-treat strategy, with attention to groups with lower VLS in the ZAMPHIA 2021, could support reductions in HIV incidence and improve overall VLS in Zambia.

Correction: Performance evaluation of the Asante Rapid Recency Assay for verification of HIV diagnosis and detection of recent HIV-1 infections: Implications for epidemic control

[This corrects the article DOI: 10.1371/journal.pgph.0000316.].

Performance evaluation of the Asante Rapid Recency Assay for verification of HIV diagnosis and detection of recent HIV-1 infections: Implications for epidemic control

We previously described development of a rapid test for recent infection (RTRI) that can diagnose HIV infection and detect HIV-1 recent infections in a single device. This technology was transferred to a commercial partner as Asante Rapid Recency Assay (ARRA). We evaluated performance of the ARRA kits in the laboratory using a well-characterized panel of specimens. The plasma specimen panel (N = 1500) included HIV-1 (N = 570), HIV-2 (N = 10), and HIV-negatives (N = 920) representing multiple subtypes and geographic locations. Reference diagnostic data were generated using the Bio-Rad HIV-1-2-O EIA/Western blot algorithm with further serotyping performed using the Multispot HIV-1/2 assay. The LAg-Avidity EIA was used to generate reference data on recent and long-term infection for HIV-1 positive specimens at a normalized optical density (ODn) cutoff of 2.0 corresponding to a mean duration of about 6 months. All specimens were tested with ARRA according to the manufacturer's recommendations. Test strips were also read for line intensities using a reader and results were correlated with visual interpretation. ARRA's positive verification line (PVL) correctly classified 575 of 580 HIV-positive and 910 of 920 negative specimens resulting in a sensitivity of 99.1% (95% CI: 98.0-99.6) and specificity of 98.9% (95% CI: 98.1-99.4), respectively. The reader-based classification was similar for PVL with sensitivity of 99.3% (576/580) and specificity of 98.8% (909/920). ARRA's long-term line (LTL) classified 109 of 565 HIV-1 specimens as recent and 456 as long-term compared to 98 as recent and 467 as long-term (LT) by LAg-Avidity EIA (cutoff ODn = 2.0), suggesting a mean duration of recent infection (MDRI) close to 6 months. Agreement of ARRA with LAg recent cases was 81.6% (80/98) and LT cases was 93.8% (438/467), with an overall agreement of 91.7% (kappa = 0.72). The reader (cutoff 2.9) classified 109/566 specimens as recent infections compared to 99 by the LAg-Avidity EIA for recency agreement of 81.8% (81/99), LT agreement of 9% (439/467) with overall agreement of 91.9% (kappa = 0.72). The agreement between visual interpretation and strip reader was 99.9% (95% CI: 99.6-99.9) for the PVL and 98.1% (95% CI: 96.6-98.9) for the LTL. ARRA performed well with HIV diagnostic sensitivity >99% and specificity >98%. Its ability to identify recent infections is comparable to the LA-Avidity EIA corresponding to an MDRI of about 6 months. This point-of-care assay has implications for real-time surveillance of new infections among newly diagnosed individuals for targeted prevention and interrupting ongoing transmission thus accelerating epidemic control.

Performance of HIV rapid testing algorithm in Nigeria: Findings from a household-based Nigeria HIV/AIDS Indicator and Impact Survey (NAIIS)

BACKGROUND

The Nigeria AIDS Indicator and Impact Survey (NAIIS), a cross-sectional household survey, was conducted in 2018 with primary objectives to estimate HIV prevalence, HIV-1 incidence, and status of UNAIDS 90-90-90 cascade. We conducted retrospective analysis of the performance of HIV rapid tests and the national HIV testing algorithm used in Nigeria.

METHODS

The national algorithm included Determine HIV-1/2 as test 1 (T1), Unigold HIV-1/2 as test 2 (T2), and StatPak HIV-1/2 as the tie-breaker test (T3). Individuals reactive with T1 and either T2 or T3 were considered HIV-positive. HIV-positive specimens from the algorithm were further confirmed for the survey using supplemental test Geenius HIV-1/2. If Geenius did not confirm HIV-positive status, HIV-1 Western blot was performed. We calculated the concordance between tests and positive predictive value (PPV) of the algorithm on unweighted data.

RESULTS

Of 204,930 participants (ages ≥18 months) 5,103 (2.5%) were reactive on T1. Serial testing of T1 reactive specimens with T2 or if needed by tiebreaker T3 identified 2958 (1.44%) persons as HIV-positive. Supplemental testing confirmed 2,800 (95%) as HIV-positive (HIV-1 = 2,767 [98.8%]; HIV-2 = 5 [0.2%]; dual infections = 22 [0.8%]). Concordance between T1 and T2 was 56.6% while PPV of the national algorithm was 94.5%.

CONCLUSIONS

Our results show high discordant rates and poor PPV of the national algorithm with a false-positive rate of about 5.5% in the NAIIS survey. Considering our findings have major implications for HIV diagnosis in routine HIV testing services, additional evaluation of testing algorithm is warranted in Nigeria.

A Comprehensive Approach to Assuring Quality of Laboratory Testing in HIV Surveys: Lessons Learned From the Population-Based HIV Impact Assessment Project

BACKGROUND

Conducting HIV surveys in resource-limited settings is challenging because of logistics, limited availability of trained personnel, and complexity of testing. We described the procedures and systems deemed critical to ensure high-quality laboratory data in the population-based HIV impact assessments and large-scale household surveys.

METHODS

Laboratory professionals were engaged in every stage of the surveys, including protocol development, site assessments, procurement, training, quality assurance, monitoring, analysis, and reporting writing. A tiered network of household, satellite laboratories, and central laboratories, accompanied with trainings, optimized process for blood specimen collection, storage, transport, and real-time monitoring of specimen quality, and test results at each level proved critical in maintaining specimen integrity and high-quality testing. A plausibility review of aggregate merged data was conducted to confirm associations between key variables as a final quality check for quality of laboratory results.

RESULTS

Overall, we conducted a hands-on training for 3355 survey staff across 13 surveys, with 160-387 personnel trained per survey on biomarker processes. Extensive training and monitoring demonstrated that overall, 99% of specimens had adequate volume and 99.8% had no hemolysis, indicating high quality. We implemented quality control and proficiency testing for testing, resolved discrepancies, verified >300 Pima CD4 instruments, and monitored user errors. Aggregate data review for plausibility further confirmed the high quality of testing.

CONCLUSIONS

Ongoing engagement of laboratory personnel to oversee processes at all levels of the surveys is critical for successful national surveys. High-quality population-based HIV impact assessments laboratory data ensured reliable results and demonstrated the impact of HIV programs in 13 countries.

HIV-1 Recent Infection Testing Algorithm With Antiretroviral Drug Detection to Improve Accuracy of Incidence Estimates

BACKGROUND

HIV-1 incidence calculation currently includes recency classification by HIV-1 incidence assay and unsuppressed viral load (VL ≥ 1000 copies/mL) in a recent infection testing algorithm (RITA). However, persons with recent classification not virally suppressed and taking antiretroviral (ARV) medication may be misclassified.

SETTING

We used data from 13 African household surveys to describe the impact of an ARV-adjusted RITA on HIV-1 incidence estimates.

METHODS

HIV-seropositive samples were tested for recency using the HIV-1 Limiting Antigen (LAg)-Avidity enzyme immunoassay, HIV-1 viral load, ARVs used in each country, and ARV drug resistance. LAg-recent result was defined as normalized optical density values ≤1.5. We compared HIV-1 incidence estimates using 2 RITA: RITA1: LAg-recent + VL ≥ 1000 copies/mL and RITA2: RITA1 + undetectable ARV. We explored RITA2 with self-reported ARV use and with clinical history.

RESULTS

Overall, 357 adult HIV-positive participants were classified as having recent infection with RITA1. RITA2 reclassified 55 (15.4%) persons with detectable ARV as having long-term infection. Those with detectable ARV were significantly more likely to be aware of their HIV-positive status (84% vs. 10%) and had higher levels of drug resistance (74% vs. 26%) than those without detectable ARV. RITA2 incidence was lower than RITA1 incidence (range, 0%-30% decrease), resulting in decreased estimated new infections from 390,000 to 341,000 across the 13 countries. Incidence estimates were similar using detectable or self-reported ARV (R2 > 0.995).

CONCLUSIONS

Including ARV in RITA2 improved the accuracy of HIV-1 incidence estimates by removing participants with likely long-term HIV infection.

Discovery, characterization, and lead optimization of 7-azaindole non-nucleoside HIV-1 reverse transcriptase inhibitors

A library of 585 compounds built off a 7-azaindole core was evaluated for anti-HIV-1 activity, and ten hits emerged with submicromolar potency and therapeutic index >100. Of these, three were identified as non-nucleoside reverse transcriptase (RT) inhibitors and were assayed against relevant resistant mutants. Lead compound 8 inhibited RT with submicromolar potency (IC50=0.73μM) and also maintained some activity against the clinically important RT mutants K103N and Y181C (IC50=9.2, 3.5μM) in cell-free assays. Free energy perturbation guided lead optimization resulted in the development of a compound with a two-fold increase in potency against RT (IC50=0.36μM). These data highlight the discovery of a unique scaffold with the potential to move forward as next-generation anti-HIV-1 agents.

Anti-HIV activity of new pyrazolobenzothiazine 5,5-dioxide-based acetohydrazides

A series of fifteen new 2-[3-(3-chlorophenyl)-5,5-dioxidobenzo[e]pyrazolo[4,3-c][1,2]thiazin-4(2H)-yl]-N'-arylmethyleneacetohydrazides (5a-o) were synthesized and screened for their anti-HIV-1 and cytotoxicity activity. Out of fifteen pyrazolobenzothiazine-based hydrazones, thirteen were found to be active inhibitors of HIV with EC50 values <20 μM. Moreover, the cytotoxicity results showed that most of the compounds were toxic to PBM, CEM and Vero cell lines. This information could be used for structural modifications to acquire good candidates of HIV drugs.

β-D-2'-C-Methyl-2,6-diaminopurine Ribonucleoside Phosphoramidates are Potent and Selective Inhibitors of Hepatitis C Virus (HCV) and Are Bioconverted Intracellularly to Bioactive 2,6-Diaminopurine and Guanosine 5'-Triphosphate Forms

The conversion of selected β-D-2,6-diaminopurine nucleosides (DAPNs) to their phosphoramidate prodrug (PD) substantially blocks the conversion to the G-analog allowing for the generation of two bioactive nucleoside triphosphates (NTPs) in human hepatocytes. A variety of 2'-C-methyl DAPN-PDs were prepared and evaluated for inhibition of HCV viral replication in Huh-7 cells, cytotoxicity in various cell lines, and cellular pharmacology in both Huh-7 and primary human liver cells. The DAPN-PDs were pan-genotypic, effective against various HCV resistant mutants, and resistant variants could not be selected. 2'-C-Me-DAPN-TP and 2'-C-Me-GTP were chain terminators for genotype 1b HCV-pol, and single nucleotide incorporation assays revealed that 2'-C-Me-DAPN-TP was incorporated opposite U. No cytotoxicity was observed with our DAPN-PD when tested up to 50 μM. A novel, DAPN-PD, 15c, has been selected for further evaluation because of its good virologic and toxicologic profile and its ability to deliver two active metabolites, potentially simplifying HCV treatment.

Molecular docking and antiviral activity of N-substituted benzyl/phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acetamides

Two series of fifteen N-substituted benzyl/phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acetamides were screened for anti-HIV-1 activity and cytotoxicity. The compounds 6a, 6d, 6e, 6g and 6i from the series 6a-i of benzylamides and 7a, 7b, 7c, 7d and 7e from the series 7a-f of anilides were identified as effective anti-HIV-1 agents with EC50 values <20μM. Among these compounds that displayed anti-HIV-1 activity, 6a, 6e, 6g and 6i showed no toxicity in human PBM, CEM and Vero cells, with the exception of 6a which displayed toxicity in Vero cells. Molecular docking of these compounds provided insight into the molecular mechanism and it was found that 6e, 6g and 6i bound deeply in the NNRTI binding pocket of the HIV-1 reverse transcriptase, using RT-bound nevirapine X-ray data and molecular docking for validation, showing the potential of these new structures as inhibitors of this viral enzyme.

Ruxolitinib and tofacitinib are potent and selective inhibitors of HIV-1 replication and virus reactivation in vitro

The JAK-STAT pathway is activated in both macrophages and lymphocytes upon human immunodeficiency virus type 1 (HIV-1) infection and thus represents an attractive cellular target to achieve HIV suppression and reduced inflammation, which may impact virus sanctuaries. Ruxolitinib and tofacitinib are JAK1/2 inhibitors that are FDA approved for rheumatoid arthritis and myelofibrosis, respectively, but their therapeutic application for treatment of HIV infection was unexplored. Both drugs demonstrated submicromolar inhibition of infection with HIV-1, HIV-2, and a simian-human immunodeficiency virus, RT-SHIV, across primary human or rhesus macaque lymphocytes and macrophages, with no apparent significant cytotoxicity at 2 to 3 logs above the median effective antiviral concentration. Combination of tofacitinib and ruxolitinib increased the efficacy by 53- to 161-fold versus that observed for monotherapy, respectively, and each drug applied alone to primary human lymphocytes displayed similar efficacy against HIV-1 containing various polymerase substitutions. Both drugs inhibited virus replication in lymphocytes stimulated with phytohemagglutinin (PHA) plus interleukin-2 (IL-2), but not PHA alone, and inhibited reactivation of latent HIV-1 at low-micromolar concentrations across the J-Lat T cell latency model and in primary human central memory lymphocytes. Thus, targeted inhibition of JAK provided a selective, potent, and novel mechanism to inhibit HIV-1 replication in lymphocytes and macrophages, replication of drug-resistant HIV-1, and reactivation of latent HIV-1 and has the potential to reset the immunologic milieu in HIV-infected individuals.

Synthesis, docking, and biological studies of phenanthrene β-diketo acids as novel HIV-1 integrase inhibitors

In the present study we report the synthesis of halogen-substituted phenanthrene β-diketo acids as new HIV-1 integrase inhibitors. The target phenanthrenes were obtained using both standard thermal- and microwave-assisted synthesis. 4-(6-Chlorophenanthren-2-yl)-2,4-dioxobutanoic acid (18) was the most active compound of the series, inhibiting both 3'-end processing (3'-P) and strand transfer (ST) with IC50 values of 5 and 1.3 μM, respectively. Docking studies revealed two predominant binding modes that were distinct from the binding modes of raltegravir and elvitegravir, and suggest a novel binding region in the IN active site. Moreover, these compounds are predicted not to interact significantly with some of the key amino acids (Q148 and N155) implicated in viral resistance. Therefore, this series of compounds can further be investigated for a possible chemotype to circumvent resistance to clinical HIV-1 IN inhibitors.

Adenosine Dioxolane Nucleoside Phosphoramidates as Antiviral Agents for Human Immunodeficiency and Hepatitis B Viruses

There are currently six nucleoside reverse transcriptase inhibitors (NRTI) that are FDA approved for human clinical use and these remain the backbone of current HIV therapy. In order for these NRTIs to be effective they need to be phosphorylated consecutively by cellular kinases to their triphosphate forms. Herein, we report the synthesis of C-6 modified (-)-β-D-(2R,4R)-1,3-dioxolane adenosine nucleosides and their nucleotides including our novel phosphoramidate prodrug technology. We have introduced a side chain moiety on the phenol portion of the phosphoramidate to reduce the toxicity potential. The synthesized phosphoramidates displayed up to a 3,600-fold greater potency versus HIV-1 when compared to their corresponding parent nucleoside and were up to 300-fold more potent versus HBV. No cytotoxicity was observed up to 100 μM in the various cell systems tested, except for compound 17 and 18 which displayed a CC₅₀ of 7.3 and 12 μM respectively in Huh-7 cells. The improved and significant dual antiviral activity of these novel phosphoramidate nucleosides was partially explained by the increased intracellular formation of the adenosine dioxolane triphosphate.

Synthesis and anti-HIV-1 screening of novel N'-(1-(aryl)ethylidene)-2-(5,5-dioxido-3-phenylbenzo[e]pyrazolo[4,3-c][1,2]thiazin-4(1H)-yl)acetohydrazides

A novel series of N'-(1-(aryl)ethylidene)-2-(5,5-dioxido-3-phenylbenzo[e]pyrazolo[4,3-c][1,2]thiazin-4(1H)-yl)acetohydrazides was synthesized. The synthesis was carried out by thermal method as well as ultrasonic bath to reduce reaction time and to enhance product yields. The synthesized compounds were characterized by spectroscopic techniques like NMR, infrared and EIMS. The structure of compound 5w was elucidated by X-ray crystallography. The titled compounds were evaluated for anti-human immunodeficiency virus type 1 (anti-HIV-1) and cytotoxic activities. Biological studies indicated that amongst these compounds, 5a, b, j, h and i showed the activity with median effective concentration (EC50) values less than 20 μM. Compound 5i exhibited the most potent anti-HIV-1 activity (EC50 = 3.2 μM) while 5h showed anti-HIV-1 activity (EC50 = 3.8 μM) with no toxicity at all in primary human lymphocytes, CEM and VERO cells.

Universal profiling of HIV-1 pol for genotypic study and resistance analysis across subtypes

BACKGROUND

The increased use of anti-HIV-1 treatments in developing countries primarily infected by non-B subtypes necessitates development of novel tools to assess susceptibility and resistance. HIV-1 genomes are highly polymorphic and present challenges for the development of universal protocols capable of screening across subtypes. Currently available viral genotyping methods are useful for viral quantification, but are inadequate for sequence profiling or comprehensive mutation detection in the variable regions of HIV polymerase (pol).

METHODS

A novel set of universal primers within pol, with consensus among a variety of HIV-1 subtypes, was developed. One-round amplification was performed by one-step reverse transcription PCR on 79 samples from HIV-1 subtypes. Using a second set of primers, the amplified fragment was sequenced and assembled to produce a profile database per sample.

RESULTS

First-round amplification using universal primers generated a unique amplicon encompassing the major pol regions in all tested HIV-1 subtype samples. Sequence analysis of the amplified fragment not only confirmed the subtype of each HIV-1 isolate but also identified resistance mutations in the pol genes of HIV-1, including protease, reverse transcriptase, connection, RNase H, and integrase. Last, some of these primers were used to develop a viral load test using quantitative real time-PCR.

CONCLUSIONS

A novel protocol was produced to effectively identify and simultaneously generate extensive sequence profiles of pol genes across HIV-1 subtypes. This protocol allows for expeditious and cost-effective mutation detection, genotypic evaluation and viral load determination in multiple HIV-1 subtypes.

Synthesis and Biological Evaluation of 4'-C,3'-O-Propylene-Linked Bicyclic Nucleosides

A set of pyrimidine nucleosides fused with a 4'-C,3'-O-propylene bridge was successfully synthesised in 12 steps from 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose, an inexpensive starting material, based on a ring-closing metathesis (RCM) reaction followed by Vorbrüggen-type nucleobase coupling. Antiviral and cytotoxicity activities of the targeted modified nucleosides, as well as their phosphoramidate prodrugs, are described.

Food insufficiency and medication adherence among people living with HIV/AIDS in urban and peri-urban settings

Food insufficiency is associated with medication non-adherence among people living with HIV/AIDS. The current study examines the relationship between hunger and medication adherence in a US urban and peri-urban sample of people living with HIV/AIDS. Men (N=133) and women (N=46) living with HIV/AIDS were recruited using snowball sampling and small media in Atlanta, Georgia. Participants completed computerized behavioral interviews that included measures of demographics, food insufficiency, social support, depression, and substance use, and provided blood specimens to determine HIV viral load. Participants also completed monthly unannounced pill counts to prospectively monitor medication adherence over 8 months. Results indicated that 45% of participants were less than 85% adherent to their medications and that food insufficiency was related to non-adherence; nearly half of non-adherent participants reported recent hunger. Geocoding of participant residences showed that 40% lived more than 5 miles from the city center. Multivariable logistic regression controlling for demographics and common factors associated with adherence showed that the interaction between distance from downtown and experiencing hunger significantly predicted non-adherence over and above all other factors. Medication adherence interventions should address access to food, particularly for people living outside of urban centers.

Synthesis of purine modified 2'-C-methyl nucleosides as potential anti-HCV agents

Based on the anti-hepatitis C activity of 2'-C-methyl-adenosine and 2'-C-methyl-guanosine, a series of new modified purine 2'-C-methyl nucleosides was prepared as potential anti-hepatitis C virus agents. Herein, we report the synthesis of both 6-modified and 2-modified purine 2'-C-methyl-nucleosides along with their anti-HCV replication activity and cytotoxicity in different cells.

Substrate mimicry: HIV-1 reverse transcriptase recognizes 6-modified-3'-azido-2',3'-dideoxyguanosine-5'-triphosphates as adenosine analogs

β-D-3′-Azido-2′,3′-dideoxyguanosine (3′-azido-ddG) is a potent inhibitor of HIV-1 replication with a superior resistance profile to zidovudine. Recently, we identified five novel 6-modified-3′-azido-ddG analogs that exhibit similar or superior anti-HIV-1 activity compared to 3′-azido-ddG in primary cells. To gain insight into their structure–activity–resistance relationships, we synthesized their triphosphate (TP) forms and assessed their ability to inhibit HIV-1 reverse transcriptase (RT). Steady-state and pre-steady-state kinetic experiments show that the 6-modified-3′-azido-ddGTP analogs act as adenosine rather than guanosine mimetics in DNA synthesis reactions. The order of potency of the TP analogs against wild-type RT was: 3′-azido-2,6-diaminopurine >3′-azido-6-chloropurine; 3′-azido-6-N-allylaminopurine > 2-amino-6-N,N-dimethylaminopurine; 2-amino-6-methoxypurine. Molecular modeling studies reveal unique hydrogen-bonding interactions between the nucleotide analogs and the template thymine base in the active site of RT. Surprisingly, the structure–activity relationship of the analogs differed in HIV-1 RT ATP-mediated excision assays of their monophosphate forms, suggesting that it may be possible to rationally design a modified base analog that is efficiently incorporated by RT but serves as a poor substrate for ATP-mediated excision reactions. Overall, these studies identify a promising strategy to design novel nucleoside analogs that exert profound antiviral activity against both WT and drug-resistant HIV-1.

Synthesis, antiviral activity, cytotoxicity and cellular pharmacology of l-3'-azido-2',3'-dideoxypurine nucleosides

Microwave-assisted optimized transglycosylation reactions were used to prepare eleven modified l-3'-azido-2',3'-dideoxypurine nucleosides. These l-nucleoside analogs were evaluated against HIV and hepatitis B virus. The l-3'-azido-2',3'-dideoxypurines nucleosides were metabolized to nucleoside 5'-triphosphates in primary human lymphocytes, but exhibited weak or no antiviral activity against HIV-1. The nucleosides were also inactive against HBV in HepG2 cells. Pre-steady state kinetic experiments demonstrated that the l-3'-azido-2',3'-dideoxypurine triphosphates could be incorporated by purified HIV-1 reverse transcriptase, although their catalytic efficiency (k(pol)/K(d)) of incorporation was low. Interestingly, a phosphoramidate prodrug of l-3'-azido-2',3'-dideoxyadenosine exhibited anti-HIV-1 activity without significant toxicity.

Monthly unannounced pill counts for monitoring HIV treatment adherence: tests for self-monitoring and reactivity effects

BACKGROUND

Unannounced home-based pill counts conducted in person or on the telephone are reliable and valid for monitoring medication adherence. However, expecting to have one's pills counted, organizing medications for pill counts, and increased attention from the person conducting the pill counts may have reactive effects and inadvertently improve adherence. The current study determined whether monthly unannounced pill counts conducted by telephone influence adherence over time.

METHODS

Two prospective cohorts, one drawn from a social support condition in a behavioral intervention trial (n=186) and the other an observational study (n=187), were followed for 12 months and 8 months, respectively. Medication adherence was monitored using monthly unannounced pill counts conducted by telephone. In addition, blood plasma viral load was collected at the final pill count for the observational cohort.

RESULTS

Analyses did not indicate increases in medication adherence over time for antiretroviral or psychiatric medications among men, women, people with detectable and undetectable viral loads, and various medication regimens.

CONCLUSIONS

Unannounced pill counts conducted by telephone do not demonstrate reactivity effects and remain a viable, unobtrusive, objective method of monitoring medication adherence.

Chemoenzymatic syntheses and anti-HIV-1 activity of glucose-nucleoside conjugates as prodrugs

Phosphodiester linked conjugates of various nucleosides such as d4U, d4T, IdUrd, ddI, ddA, virazole, ara-A, and ara-C containing a glucosyl moiety have been described. These compounds were designed to act as prodrugs, where the corresponding 5'-monophosphates may be generated intracellularly. The synthesis of the glycoconjugates was achieved in good yields by condensation of a glucosyl phosphoramidite 7 with nucleosides in the presence of an activating agent. It was demonstrated that the glucose conjugates improve the water solubility of the nucleoside analogues, for example, up to 31-fold for the ara-A conjugate compared to that of ara-A alone. The new conjugates were tested for their anti-HIV-1 activity in human lymphocytes. These derivatives offer a convenient design for potential prodrug candidates with the possibility of improving the physicochemical properties and therapeutic activity of nucleoside analogues.

Synthesis and evaluation of 3'-azido-2',3'-dideoxypurine nucleosides as inhibitors of human immunodeficiency virus

Based on the promising drug resistance profile and potent anti-HIV activity of beta-d-3'-azido-2',3'-dideoxyguanosine, a series of purine modified nucleosides were synthesized by a chemical transglycosylation reaction and evaluated for their antiviral activity, cytotoxicity, and intracellular metabolism. Among the synthesized compounds, several show potent and selective anti-HIV activity in primary lymphocytes.

Synthesis, antiviral activity, and stability of nucleoside analogs containing tricyclic bases

A series of 3,9-dihydro-9-oxo-5H-imidazo[1,2-A]purine nucleosides (tricylic nucleosides) were synthesized from 9-[4-alpha-(hydroxymethyl)cyclopent-2-ene-1-alpha-yl]guanine (CBV) 5, (-)-beta-D-(2R,4R)-1,3-dioxolane-guanosine (DXG) 6, 3'-azido-3'-deoxy-guanosine (AZG) 7, and 2'-C-methylguanosine 8. Their in vitro activity against HIV and HCV was evaluated and correlated to their ability to degrade to their purine counterpart.

Monitoring medication adherence by unannounced pill counts conducted by telephone: reliability and criterion-related validity

BACKGROUND

Although demonstrated valid for monitoring medication adherence, unannounced pill counts conducted in patients' homes are costly and logistically challenging. Telephone-based unannounced pill counts offer a promising adaptation that resolves most of the limitations of home-based pill counting.

PURPOSE

We tested the reliability and criterion-related validity of a telephone-based unannounced pill count assessment of antiretroviral adherence.

METHOD

HIV-positive men and women (N = 89) in Atlanta, Georgia, completed a telephone-based unannounced pill count and provided contemporaneous blood specimens to obtain viral loads; 68 participants also received an immediate second pill count conducted during an unannounced home visit.

RESULTS

A high degree of concordance was observed between the number of pills counted on the telephone and in the home (intraclass correlation [ICC] = .981, p < .001) and percent of pills taken (ICC = .987, p < .001). Adherence obtained by the telephone count and home count reached 92% agreement (Kappa coefficient = .94). Adherence determined by telephone-based pill counts also corresponded with patient viral load, providing evidence for criterion-related validity.

CONCLUSION

Unannounced telephone-based pill counts offer a feasible objective method for monitoring medication adherence.

Pre-steady-state kinetic studies establish entecavir 5'-triphosphate as a substrate for HIV-1 reverse transcriptase

The novel 2'-deoxyguanosine analog Entecavir (ETV) is a potent inhibitor of hepatitis B virus (HBV) replication and is recommended for treatment in human immunodeficiency virus type 1 (HIV-1) and HBV-co-infected patients because it had been reported that ETV is HBV-specific. Recent clinical observations, however, have suggested that ETV may indeed demonstrate anti-HIV-1 activity. To investigate this question at a molecular level, kinetic studies were used to examine the interaction of 5'-triphosphate form of ETV with wild type (WT) HIV-1 reverse transcriptase (RT) and the nucleoside reverse transcriptase inhibitor-resistant mutation M184V. Using single turnover kinetic assays, we found that HIV-1 WT RT and M184V RT could use the activated ETV triphosphate metabolite as a substrate for incorporation. The mutant displayed a slower incorporation rate, a lower binding affinity, and a lower incorporation efficiency with the 5'-triphosphate form of ETV compared with WT RT, suggesting a kinetic basis for resistance. Our results are supported by cell-based assays in primary human lymphocytes that show inhibition of WT HIV-1 replication by ETV and decreased susceptibility of the HIV-1 containing the M184V mutation. This study has important therapeutic implications as it establishes ETV as an inhibitor for HIV-1 RT and illustrates the mechanism of resistance by the M184V mutant.

Synthesis, cytotoxicity, and antiviral activities of new neolignans related to honokiol and magnolol

A series of new bisphenol derivatives bearing allylic moieties were synthesized as potential analogs of honokiol and/or magnolol. Certain compounds exhibited specific anti-proliferation activity against SVR cells and moderate anti-HIV-1 activity in primary human lymphocytes. Compound 5h was the most potent compound and its anti-tumor activity was evaluated in vivo.

Differential maintenance of the M184V substitution in the reverse transcriptase of human immunodeficiency virus type 1 by various nucleoside antiretroviral agents in tissue culture

The M184V substitution in human immunodeficiency virus type 1 reverse transcriptase (RT) is rapidly selected in tissue culture following serial passage of wild-type virus in the presence of increasing concentrations of lamivudine (3TC). M184V is also associated with several alterations of RT enzymatic function in vitro that may adversely affect viral fitness or replication capacity, which creates a potential rationale for its maintenance once it has been selected by antiviral chemotherapy. However, the relative effectiveness of nucleoside RT inhibitors that are structurally unrelated to 3TC in selecting and/or maintaining M184V has not been investigated. In the present study, we have studied the abilities of a variety of drugs, i.e., zalcitabine (ddC), didanosine (ddI), abacavir (ABC), and the novel nucleoside SPD754, in addition to 3TC, to maintain the presence of M184V in tissue culture and have shown that SPD754, ABC, and 3TC are able to preserve M184V in mixed dual infections consisting of wild-type viruses and clinical isolates which contained the M184V mutation. Moreover, M184V could also be maintained in these cultures when a subtherapeutic concentration of 3TC (i.e., 0.05 microM) was used. In contrast, neither ddI nor ddC was able to maintain M184V to the same extent as the other drugs after 10 weeks of tissue culture in mixtures of wild-type viruses and isolates containing M184V in different proportions.

Nucleotide and amino acid polymorphisms at drug resistance sites in non-B-subtype variants of human immunodeficiency virus type 1

We have compared nucleotide substitutions and polymorphisms at codons known to confer drug resistance in subtype B strains of human immunodeficiency virus type 1 (HIV-1) with similar substitutions in viruses of other subtypes. Genotypic analysis was performed on viruses from untreated individuals. Nucleotide and amino acid diversity at resistance sites was compared with a consensus subtype B reference virus. Among patients with non-subtype B infections, polymorphisms relative to subtype B were observed at codon 10 in protease (PR). These included silent substitutions (CTC-->CTT, CTA, TTA) and an amino acid mutation, L10I. Subtype A viruses possessed a V179I substitution in reverse transcriptase (RT). Subtype G viruses were identified by silent substitutions at codon 181 in RT (TAT-->TAC). Similarly, subtype A/G viruses were identified by a substitution at position 67 in RT (GAC-->GAT). Subtype C was distinguished by silent substitutions at codons 106 (GTA-->GTG) and 219 (AAA-->AAG) in RT and codon 48 (GGG-->GGA) in PR. Variations relative to subtype B were seen at RT position 215 (ACC-->ACT) for subtypes A and A/E. These substitutions and polymorphisms reflect different patterns of codon usage among viruses of different subtypes. However, the existence of different subtypes may only rarely affect patterns of drug resistance-associated mutations.

Effects of a single amino acid substitution within the p2 region of human immunodeficiency virus type 1 on packaging of spliced viral RNA

Human immunodeficiency virus type 1 encapsidates two copies of viral genomic RNA in the form of a dimer. The dimerization process initiates via a 6-nucleotide palindrome that constitutes the loop of a viral RNA stem-loop structure (i.e., stem loop 1 [SL1], also termed the dimerization initiation site [DIS]) located within the 5' untranslated region of the viral genome. We have now shown that deletion of the entire DIS sequence virtually eliminated viral replication but that this impairment was overcome by four second-site mutations located within the matrix (MA), capsid (CA), p2, and nucleocapsid (NC) regions of Gag. Interestingly, defective viral RNA dimerization caused by the DeltaDIS deletion was not significantly corrected by these compensatory mutations, which did, however, allow the mutated viruses to package wild-type levels of this DIS-deleted viral RNA while excluding spliced viral RNA from encapsidation. Further studies demonstrated that the compensatory mutation T12I located within p2, termed MP2, sufficed to prevent spliced viral RNA from being packaged into the DeltaDIS virus. Consistently, the DeltaDIS-MP2 virus displayed significantly higher levels of infectiousness than did the DeltaDIS virus. The importance of position T12 in p2 was further demonstrated by the identification of four point mutations,T12D, T12E, T12G, and T12P, that resulted in encapsidation of spliced viral RNA at significant levels. Taken together, our data demonstrate that selective packaging of viral genomic RNA is influenced by the MP2 mutation and that this represents a major mechanism for rescue of viruses containing the DeltaDIS deletion.

The M184V substitution in human immunodeficiency virus type 1 reverse transcriptase delays the development of resistance to amprenavir and efavirenz in subtype B and C clinical isolates

The M184V substitution in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), encoding high-level resistance to lamivudine (3TC), results in decreased HIV-1 replicative capacity, diminished RT processivity, and increased RT fidelity in biochemical assays. We assessed the effect of M184V on the development of resistance to the nonnucleoside RT inhibitors efavirenz (EFV) and nevirapine, and to the protease inhibitor amprenavir (APV) in tissue culture. Genotypic analysis revealed differences in EFV resistance-conferring mutations in subtype B (K103N) versus subtype C (V106 M), and the appearance of both was significantly delayed in the M184V-containing variants compared with the wild type (WT). Similarly, there was a marked delay in the emergence of mutations associated with APV resistance (I54 M/L/V) in subtype B viruses harboring M184V compared with paired WT viral isolates.

A V106M mutation in HIV-1 clade C viruses exposed to efavirenz confers cross-resistance to non-nucleoside reverse transcriptase inhibitors

OBJECTIVE

We have shown that HIV-1 clade C variants contain a valine codon 106 polymorphism (GTG) that facilitates a V106M transition (GTG<--ATG) after selection with efavirenz (EFV). This study evaluates the prevalence of V106 (GTG) and 106M (ATG) codons in clinical isolates as well as the effects of V106M on resistance to non-nucleoside reverse transcriptase inhibitors (NNRTI).

METHODS

Genotypic analysis ascertained sequence diversity at codon 106, including both valine polymorphisms (GTA and GTG) and the V106A (GCA) and V106M (ATG) resistance-conferring mutations in B (n = 440) and non-B (n = 84) clinical isolates. Cell-based phenotypic assays were performed to determine the effects of V106M and V106A on levels of resistance to EFV, nevirapine and delavirdine.

RESULTS

Most subtype B isolates harbored GTA (valine) at codon 106 (97% of cases) while the GTG (valine) polymorphism was generally present in clade C viruses (94% of cases). Under conditions of EFV but not nevirapine or delavirdine pressure (n = 8) in tissue culture, clade C isolates developed the V106M mutation (GTG<--ATG), conferring high-level (100-1000-fold) cross-resistance to all NNRTI. Generation of V106M recombinant viruses by site-directed mutagenesis confirmed the ability of V106M to confer NNRTI cross-resistance. This mutation also developed in three of six EFV-treated patients harboring clade C infections. In current genotypic interpretative reports (including 15 algorithmic databases), V106A is listed as an nevirapine-specific mutation while V106M is not recognized.

CONCLUSIONS

V106M may be a signature mutation in clade C patients treated with EFV and may have the potential to confer high-level multi-NNRTI resistance.

Polymorphisms of cytotoxic T-lymphocyte (CTL) and T-helper epitopes within reverse transcriptase (RT) of HIV-1 subtype C from Ethiopia and Botswana following selection of antiretroviral drug resistance

Drug resistance is the major limiting factor in the effective therapeutic management of HIV infection with antiretroviral drugs (ARVs). In developing countries, where access to ARVs may be limited, therapeutic vaccine protocols designed to restrict the advent of drug resistance may be of interest. Whereas the immunodominant regions of HIV-1 clade B RT peptides have been well characterized, little is known about potential divergence among RTs of other HIV-1 subtypes. In this study, RT sequence polymorphisms were ascertained in phylogenetically classified subtype C isolates from treatment-nai;ve Ethiopian (n = 5) and Botswanian persons (n = 9). There were clusters of variability in some RT epitopes associated with cytotoxic T lymphocyte (CTL) and helper T cell function within subtype C viruses, although other epitopes remained conserved among subtype C and B viruses. Subtype C mutations associated with drug resistance were identified in vitro, using increasing concentrations of non-nucleoside RT inhibitors (NNRTIs) and nucleoside RT inhibitors (NRTIs). Mutations within immunogenic regions of clade C RT were noted during drug selection of subtype C isolates with nevirapine (S98I, Y181C, V108I and K103N), delavirdine, (A62V, V75E, L100I, K103T, V108I, Y181C), efavirenz (K103E, V106M, V179D, Y188C/H, G190A), lamivudine (M184I, M184V), and zidovudine (K70R), respectively. Further characterization of predicted CTL and T-helper anchor motifs and ARV-induced mutations in HIV-1 non-B subtype RTs is warranted.

The M184V mutation in reverse transcriptase can delay reversion of attenuated variants of simian immunodeficiency virus

We previously constructed a series of simian immunodeficiency virus (SIV) mutants containing deletions within a 97-nucleotide region of the SIVmac239 untranslated region or leader sequence. However, as is common with live attenuated viruses, several of the mutants exhibited a moderate propensity for reversion. Since the M184V mutation in human immunodeficiency virus type 1 reverse transcriptase is associated with diminished fitness as well as lamivudine resistance, we introduced this substitution into several of our deletion mutants to determine its effects on viral replication and compensatory reversion. Our results indicate that M184V impaired viral fitness in pair-wise comparisons of mutants that contained or lacked this substitution. We also observed that M184V significantly impaired the potential for both compensatory mutagenesis and reversion in these mutants both in cell lines and in peripheral blood mononuclear cells.

Genetic divergence of human immunodeficiency virus type 1 Ethiopian clade C reverse transcriptase (RT) and rapid development of resistance against nonnucleoside inhibitors of RT

We sequenced and phylogenetically analyzed the reverse transcriptase (RT) region of five human immunodeficiency virus type 1 isolates from treatment-naive Ethiopian émigrés to Israel. Heteroduplex mobility assays were performed to confirm the clade C status of env genomic regions. The RT sequences showed that the strains clustered phylogenetically with clade C viruses, and a KVEQ-specific motif of silent mutations (amino acids 65, 106, 138, and 161, respectively) at resistance sites was present in the polymerase region of all studied Ethiopian isolates and subtype C reference strains. In addition, many other silent mutations were observed in the clade C viruses at various resistance sites. In general, the Ethiopian isolates were more closely related genotypically to a clade C reference strain from Botswana (southern Africa) than to previously sequenced Ethiopian reference strains. Genotypic analysis showed that two Ethiopian isolates naturally harbored the mutations K70R and G190A associated with resistance to ZDV and nonnucleoside reverse transcriptase inhibitors, respectively. Phenotypic assays revealed that the K70R substitution in this context did not reduce susceptibility to ZDV, whereas the G190A substitution resulted in high-level resistance to nevirapine (NVP). Moreover, variants resistant to NVP, delavirdine (DLV), and efavirenz (EFV) were more rapidly selected at lower drug doses culture with clade C than with clade B wild-type isolates. In the case of subtype C, selection with NVP and/or EFV led to the appearance of several previously unseen mutations in RT, i.e., V106M and S98I, as well as other mutations that have been previously reported (e.g., K103N, V106A, V108I, and Y181C). After selection with DLV, a polymorphism, A62A, initially observed in the Ethiopian isolate 4762, mutated to A62V; the latter is a secondary substitution associated with multidrug resistance against nucleoside RT inhibitors. Phenotypic analysis of clade C mutants selected against NVP, DLV, and EFV revealed broad cross-resistance, particularly in regard to NVP and DLV. These findings suggest that RT genotypic diversity may influence the emergence of drug resistance.

Co-receptor usage and HIV-1 intra-clade C polymorphisms in the protease and reverse transcriptase genes of HIV-1 isolates from Ethiopia and Botswana

Knowledge of baseline amino acid substitutions arising at certain critical positions in the HIV-1 non-clade-B protease (PR) and reverse transcriptase (RT) enzymes may yield important information with regard to anticipation of responses to antiretroviral treatment and development of drug resistance. We have compared RT and PR sequences within HIV-1 clade C strains isolated from 14 treatment-naive patients originating from Ethiopia and Botswana with those of PR and RT consensus subtype B RT and PR sequences. Variations in the frequency of natural polymorphisms were observed in clade C isolates at drug-resistance sites. Intra-clade C divergence among mutations within PR was statistically significant while that within RT was not. Only a M361 substitution in PR was shared among almost all isolates from Ethiopia and Botswana. Analysis of the co-receptor usage of clade C isolates from Ethiopia and Botswana supports the known preferential usage of the CCR5 co-receptor by HIV-1 clade C strains. No Ethiopian or Botswanian isolates exclusively used the CXCR4 co-receptor, which is consistent with most data obtained with HIV-1 clade B isolates.

Persistence and fitness of multidrug-resistant human immunodeficiency virus type 1 acquired in primary infection

This study examines the persistence and fitness of multidrug-resistant (MDR) viruses acquired during primary human immunodeficiency virus infection (PHI). In four individuals, MDR infections persisted over the entire study period, ranging from 36 weeks to 5 years, in the absence of antiretroviral therapy. In stark contrast, identified source partners in two cases showed expected outgrowth of wild-type (WT) virus within 12 weeks of treatment interruption. In the first PHI case, triple-class MDR resulted in low plasma viremia (1.6 to 3 log copies/ml) over time compared with mean values obtained for an untreated PHI group harboring WT infections (4.1 to 4.3 log copies/ml). Increasing viremia in PHI patient 1 at week 52 was associated with the de novo emergence of a protease inhibitor-resistant variant through a recombination event involving the original MDR virus. MDR infections in two other untreated PHI patients yielded viremia levels typical of the untreated WT group. A fourth patient's MDR infection yielded low viremia (<50 to 500 copies/ml) for 5 years despite his having phenotypic resistance to all antiretroviral drugs in his treatment regimen. In two of these PHI cases, a rebound to higher levels of plasma viremia only occurred when the M184V mutation in reverse transcriptase could no longer be detected and, in a third case, nondetection of M184V was associated with an inability to isolate virus. To further evaluate the fitness of MDR variants acquired in PHI, MDR and corresponding WT viruses were isolated from index and source partners, respectively. Although MDR viral infectivity (50% tissue culture infective dose) was comparable to that observed for WT viruses, MDR infections in each case demonstrated 2-fold and 13- to 23-fold reductions in p24 antigen and reverse transcriptase enzymatic activity, respectively. In dual-infection competition assays, MDR viruses consistently demonstrated a marked replicative disadvantage compared with WT virus. These results indicate that MDR viruses that are generated following PHI can establish persistent infections as dominant quasispecies despite their impaired replicative competence.

Partial restoration of replication of simian immunodeficiency virus by point mutations in either the dimerization initiation site (DIS) or Gag region after deletion mutagenesis within the DIS

We used the simian immunodeficiency virus (SIV) molecular clone SIVmac239 to generate a deletion construct, termed SD2, in which we eliminated 22 nucleotides at positions +398 to +418 within the putative dimerization initiation site (DIS) stem. This SD2 deletion severely impaired viral replication, due to adverse effects on the packaging of viral genomic RNA, the processing of Gag proteins, and viral protein patterns. However, long-term culture of SD2 in either C8166 or CEMx174 cells resulted in restoration of replication capacity, due to two different sets of three compensatory point mutations, located within both the DIS and Gag regions. In the case of C8166 cells, both a K197R and a E49K mutation were identified within the capsid (CA) protein and the p6 protein of Gag, respectively, while the other point mutation (A423G) was found within the putative DIS loop. In the case of CEMx174 cells, two compensatory mutations were present within the viral nucleocapsid (NC) protein, E18G and Q31K, in addition to the same A423G substitution as observed with C8166 cells. A set of all three mutations was required in each case for restoration of replication capacity, and either set of mutations could be substituted for the other in both the C8166 and CEMx174 cell lines.

Construction and in vitro properties of a series of attenuated simian immunodeficiency viruses with all accessory genes deleted

We have generated simplified simian immunodeficiency virus (SIV) constructs lacking the nef, vpr, vpx, vif, tat, and rev genes (Delta6 viruses). To accomplish this, we began with an infectious molecular clone of SIV, i.e. SIVmac239, and replaced the deleted segments with three alternate elements: (i) a constitutive transport element (CTE) derived from simian retrovirus type 1 to replace the Rev/Rev-responsive element (RRE) posttranscriptional regulation system, (ii) a chimeric SIV long terminal repeat (LTR) containing a cytomegalovirus (CMV) promoter to augment transcription and virus production, and (iii) an internal ribosome entry site (IRES) upstream of the env gene to ensure expression of envelope proteins. This simplified construct (Delta6CCI) efficiently produced all viral structural proteins, and mature virions possessed morphology typical of wild-type virus. It was also observed that deletion of the six accessory genes dramatically affected both the specificity and efficiency of packaging of SIV genomic RNA into virions. However, the presence of both the CTE and the chimeric CMV promoter increased the specificity of viral genomic RNA packaging, while the presence of the IRES augmented packaging efficiency. The Delta6CCI virus was extremely attenuated in replication capacity yet retained infectiousness for CEMx174 and MT4 cells. We also generated constructs that retained either the rev gene or both the rev and vif genes and showed that these viruses, when complemented by the CMV promoter, i.e., Delta5-CMV and Delta4-CMV, were able to replicate in MT4 cells with moderate and high-level efficiency, respectively. Long-term culture of each of these constructs over 6 months revealed no potential for reversion. We hope to shortly evaluate these simplified constructs in rhesus macaques to determine their long-term safety as well as ability to induce protective immune responsiveness as proviral DNA vaccines.