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In 2019, an outbreak of HIV infection predominantly affecting children occurred in Larkana district, Pakistan. This is the largest outbreak ever reported in this age group in Pakistan. In this study, we report two HIV-1 unique recombinant forms identified during the outbreak. Blood samples were collected from HIV-positive children as part of a case-control study to investigate the outbreak. The pol gene was sequenced and used to detect HIV subtype/recombinant forms using subtype, recombination, and phylogenetic analyses. Drug resistance mutation (DRM) analysis was performed to characterize the DRMs in each sequence. We observed the emergence of two unassigned unique recombinant forms related to CRF36_cpx in 15 individuals of the 344 samples collected. Genotype analysis revealed the presence of multiple DRMs associated with resistance to reverse transcriptase inhibitors. The discovery of these unassigned unique recombinant forms in our population highlights the need for comprehensive molecular epidemiological studies to fully understand the distribution and drug resistance patterns to aid control efforts.

This study aimed to monitor the prevalence of HIV-1 drug resistance and risk factors associated with drug resistance in antiretroviral therapy (ART)-failure individuals in Liaoning Province, China. Plasma samples were collected from HIV-1-positive individuals who experienced ART failure in Liaoning Province between April 2018 and September 2019. Genotype resistance test was performed using an in-house assay on these collected samples. Factors associated with drug resistance were identified by logistic regression analysis. We collected a total of 468 ART-failure individuals, of which 256 were successfully included in the final study. Of these, the most predominant genotype was CRF01_AE, accounting for 77.73%. The resistance rate to any of the three classes of antiretroviral drugs (non-nucleoside reverse transcriptase inhibitors [NNRTIs], nucleoside reverse transcriptase inhibitors [NRTIs], and protease inhibitors [PIs]) was 64.84%. Among 256 ART-failure patients, 62.89% showed drug resistance to NNRTIs, 50.39% to NRTIs, and 3.13% to PIs. G190S (31.25%) and Y181C (25.78%) mutations were the most common NNRTIs resistance mutations. K65R (29.69%), M184V (28.52%) were the most common NRTIs resistance mutations. Factors associated with drug resistance included current ART regimen and viral load. The high drug resistance rate among ART-failure individuals in Liaoning Province needs more attention. Corresponding strategies for the risk factors associated with HIV drug resistance can better control and prevent the prevalence of resistance.

South Africa introduced the "diagnose and treat" universal HIV treatment program in September 2016. This program enables all identified HIV-positive patients to immediately start first-line antiretroviral therapy (ART). However, the presence of drug-resistant (DR) viruses in the drug-naive population complicates the choice of ART. We used next-generation sequencing (NGS) to determine the prevalence and diversity of HIV DR mutations in patients entering HIV treatment programs in northern South Africa. RNA was isolated from plasma of drug-naive HIV-1-infected patients. Using reverse transcriptase polymerase chain reaction, the HIV-1

Justice-involved (JI) populations bear a disproportionate burden of HIV infection and are at risk of poor treatment outcomes. Drug resistance prevalence and emergence, and phylogenetic inference of transmission networks, understudied in vulnerable JI populations, can inform care and prevention interventions, particularly around the critical community reentry period. We analyzed banked blood specimens from CARE+ Corrections study participants in Washington, D.C. (DC) across three time points and conducted HIV drug resistance testing using next-generation sequencing (NGS) at 20% and 5% thresholds to identify prevalent and evolving resistance during community reentry. Phylogenetic analysis was used to identify molecular clusters within participants, and in an extended analysis between participants and publicly available DC sequences. HIV sequence data from 54 participants (99 specimens) were analyzed. The prevalence of transmitted drug resistance was 14% at both thresholds, and acquired drug resistance was 47% at 20%, and 57% at 5% NGS thresholds, respectively. The overall prevalence of drug resistance was 43% at 20%, and 52% at 5% NGS thresholds, respectively. Among 34 participants sampled longitudinally, 21%-35% accumulated 10-17 new resistance mutations during a mean 4.3 months. In phylogenetic analysis within the JI population, 11% were found in three molecular clusters. The extended phylogenetic analysis identified 46% of participants in 22 clusters, of which 21 also included publicly-available DC sequences, and one JI-only unique dyad. This is the first study to identify a high prevalence of HIV drug resistance and its accumulation in a JI population during community reentry and suggests phylogenetic integration of this population into the non-JI DC HIV community. These data support the need for new, effective, and timely interventions to improve HIV treatment during this vulnerable period, and for JI populations to be included in broader surveillance and prevention efforts.

New South Wales has the greatest burden of HIV in Australia, with 2012 and 2013 recording the highest rates of new diagnoses in 20 years. Concurrently, there has been significant changes in antiretroviral treatments and testing paradigms. We compiled a statewide resistance database to characterize changes in HIV-1 resistance mutations over time. Genotypic antiretroviral resistance testing (GART) was performed on request at three reference laboratories using commercial and in-house methods. In total, 7629 HIV-1 polymerase sequences obtained from GART from 2004 to 2013 were retrospectively collated, reformatted, de-identified, and analyzed using Stanford HIVdb program 7.0 and the 2009 World Health Organization (WHO) surveillance drug resistance mutations (SDRMs). Analyses were performed on subgroups of known treatment naives, treatment experienced, and seroconverters. There has been a decrease in overall rates of prevalent drug resistance mutations from 57.8% in 2004 to 21% in 2013. Dual and triple class resistance mutations have decreased from 32.7% in 2004 to 5.8% in 2013 and 16.4% to 1.2%, respectively. In treatment-naive individuals (

We aim to characterize the drug resistance mutations in reverse transcriptase gene of HIV-1 subtype C-infected North Indian population in those who are failing first-line antiretroviral therapy (ART) and if these mutations are associated with mortality. We also attempted the assessment of switch over to second-line antiretroviral therapy in these patients. Based on the immunological marker CD4 count (

There has been no systematic review of the prevalence of transmitted integrase strand transfer inhibitor (INSTI) resistance. We systematically searched the English-language PubMed database and GenBank to identify studies published since 2010 reporting 50 or more INSTI-naive HIV-1-infected adults undergoing integrase genotyping. We extracted data related to country, sample year, specimen type, sequencing method, and subtype. For studies with sequences in GenBank, we determined the prevalence of three categories of INSTI-associated resistance mutations: (1) nonpolymorphic INSTI-selected drug resistance mutations (DRMs) that we refer to as surveillance DRMs; (2) rarely selected nonpolymorphic INSTI-associated DRMs; and (3) common polymorphic accessory INSTI-selected DRMs. A total of 103 studies met inclusion criteria including 75 studies in GenBank containing integrase sequences from 16,481 INSTI-naive persons. The median sample year was 2013 (interquartile range: 2008-2014). The prevalence of INSTI surveillance DRMs, rarely selected DRMs, and common polymorphic accessory INSTI-selected DRMs were 0.5%, 0.8%, and 6.2%, respectively. There was no association between the presence of nonpolymorphic surveillance DRM and region, sample year, or subtype. Two surveillance DRMs, E138K and R263K occurred in 0.15% and 0.10% of naive sequences, respectively. Several lines of evidence suggested that the 0.5% prevalence of surveillance DRMs partly reflects the cumulative natural occurrence of these mutations in the absence of selective drug pressure. There was an unexplained temporal increase in the proportion of sequences with polymorphic accessory mutations. The prevalence of INSTI-associated surveillance DRMs is low even in regions where INSTIs have been a major component of antiretroviral therapy for several years. The presence of INSTI-associated surveillance DRMs in INSTI-naive persons likely results from actual cases of transmitted INSTI resistance and from a low background level reflecting the cumulative rare natural occurrence of several nonpolymorphic mutations.

The analysis of a pol gene fragment encoding protease and part of reverse transcriptase was carried out for 55 sera collected in 2016 and 2018 from HIV-1-infected patients diagnosed in 2014–2018 li...

Prevalence of drug resistance (DR) challenges the epidemic control of human immunodeficiency virus (HIV)-1. However, little is known about DR among patients with antiretroviral therapy (ART) failure in Guangxi province, China. This cross-sectional study was aimed to investigate the prevalence of DR and the characteristics of DR sequences in the genetic transmission network among HIV-1 patients with ART failure in Guangxi. We enrolled 358 eligible patients between 2012 and 2018. Blood samples were subjected to reverse transcription polymerase chain reaction, followed by sequencing of the HIV-1 polymerase (

To identify genotype distribution and drug resistance in people infected by HIV-1 in Wuhan, China, 105 infected people diagnosed with HIV-1 from January to December in 2019 were involved in this study. Ninety-eight gag genes, 101 PR genes, and 98 RT genes were successfully amplified. The phylogenetic analysis results showed that CRF01_AE (38.2%) and CRF07_BC (35.3%) were the two dominant genotypes, followed by CRF55_01B (6.9%), CRF59_01B (2.0%), B (2.0%), B' (2.0%), CRF08_BC (1.0%), CRF80_0107 (1.0%), and unique recombinant form (URF) (11.8%). Most URFs were the recombinants between CRF01_AE and CRF07_BC or CRF07_BC and CRF55_01B. Among the 93 subjects of antiretroviral therapy (ART)-naive, transmitted drug resistance against non-nucleoside reverse transcriptase inhibitors (NNRTIs) was 23.9%, of which V179D/E was the most frequent mutation, accounting for 18.2%. Among the 12 subjects of ART-experienced, drug resistance to first-line regimens developed severely.

HIV variants carry natural polymorphisms related to drug resistance (R-markers) fixed during viral evolution in the absence of antiretroviral therapy (ART) that may impact on drug susceptibility and resistance pathways. We aimed to identify the HIV type 2 (HIV-2) variant-specific R-markers at Pol in all available sequences from ART-naive subjects deposited in Los Alamos database according to reported HIV-2 drug resistance-associated mutations (DRMs) and report the performance of two online HIV-2 resistance interpretation tools (HIV2EU Tool and Stanford HIVdb Program for HIV-2) to detect them. From a total of 587 sequences, we found 23 R-markers in low frequency, in groups A, B, and G. Four were present in10% of the sequences with no direct impact on antiretroviral susceptibility. HIV2EU Tool detected one, whereas Stanford program all four. Stanford new tool, although still under development, seems effective in detecting HIV-2 DRMs and may prove a useful tool for HIV-2 resistance interpretation when fully developed.

The prevalence of transmitted non-nucleoside reverse transcriptase inhibitor (NNRTI) resistance around the world has been estimated up to 2010. Treatment recommendations have since evolved from NNRTIs to integrase strand inhibitors (INSTIs). This analysis estimates more recent trends in transmitted NNRTI resistance given emerging INSTI use. Studies reporting prevalence of transmitted NNRTI resistance in Europe, the United States, and Canada were meta-analyzed to generate yearly estimates in four regions. Overall prevalence of transmitted resistance continued to rise in the United States to10% in 2015. Prevalence in European countries with larger surveillance networks was consistent at ∼4% from 2000 through 2012, increasing to 7% in 2016. Prevalence in European countries with fewer available data was generally5%. Two publications with Canadian data were identified, reporting 0%-3% resistance. This analysis showed increasing prevalence of transmitted NNRTI resistance up to 2016, despite the availability of newer classes of treatments.

Multiple HIV-1 genotypes were found circulating in Guangdong Province, China, as this province is located in South China and has a high frequency of international trade. In this study, we report the near full-length genome (NFLG) of CRF12_BF that was identified from a male patient in Guangzhou city, Guangdong Province; this is the first time CRF12_BF has been reported in mainland China. The NFLG was amplified, and then PCR products were sequenced by Sanger sequencing. The CRF12_BF strain was confirmed by the Basic Local Alignment Search Tool and a neighbor-joining phylogenetic tree. In addition, this CRF12_BF strain was confirmed to contain the non-nucleoside reverse transcriptase inhibitor mutation E138A associated with potential low-level resistance against efavirenz and low-level resistance against rilpivirine by the Stanford University HIV Drug Resistance Database program. The analyzed sequence data in this study will provide more information on the HIV epidemic in China.

The HIV type 1 (HIV-1) epidemic has continued to grow in Indonesia; however, continuous updates on the epidemiology of HIV-1 in Indonesia remain challenging because it is the biggest archipelago in the world. Furthermore, the emergence of HIV drug resistance (HIVDR) has had a negative impact on the treatment of infected individuals. In this study, we performed HIV-1 subtyping and the detection of HIVDR in 105 HIV-1-infected individuals residing in various cities in Indonesia during 2018-2019. The results obtained identified CRF01_AE as the major epidemic HIV-1 strain, responsible for 81.9% of infection cases, followed by subtype B (12.4%), CRF02_AG (3.8%), CRF52_01B (1%), and a recombinant between CRF01_AE and CRF02_AG (1.0%). Major drug resistance-associated mutations against reverse transcriptase inhibitors were detected in 20% of samples. These results suggest that CRF01_AE is a major HIV-1 strain in Indonesia, while CRF02_AG is emerging. The prevalence of HIVDR in Indonesia needs to be monitored.

The prevalence of HIV-1 drug resistance is increasing worldwide and monitoring its emergence is important for the successful management of populations receiving combination antiretroviral therapy. It is likely that pre-existing drug resistance mutations linked on the same viral genomes are predictive of treatment failure. Because of the large number of sequences generated by ultrasensitive single-genome sequencing (uSGS) and other similar next-generation sequencing methods, it is difficult to assess each sequence individually for linked drug resistance mutations. Several software/programs exist to report the frequencies of individual mutations in large data sets, but they provide no information on linkage of resistance mutations. In this study, we report the HIV-DRLink program, a research tool that provides resistance mutation frequencies as well as their genetic linkage by parsing and summarizing the Sierra output from the Stanford HIV Database. The HIV-DRLink program should only be used on data sets generated by methods that eliminate artifacts due to polymerase chain reaction recombination, for example, standard single-genome sequencing or uSGS. HIV-DRLink is exclusively a research tool and is not intended to inform clinical decisions.

Diversity of genotypes and prevalence of pretreatment drug resistance (PDR) are challenges for the epidemic control and vaccine development of HIV-1. However, little is known about the situation in Tianjin. Blood samples were collected from newly diagnosed, antiretroviral treatment (ART)-naive HIV/AIDS patients from January 2016 to November 2019. The target fragment in the

HIV drug resistance (HIVDR) is of increasing health concern, especially among key populations. We investigated the prevalence of virological suppression (VS), prevalence and correlates of HIVDR in HIV-infected women, enrolled in a high-risk cohort. We enrolled 267 women initiated on first-line antiretroviral therapy (ART) between 2015 and 2018. Participants' plasma samples were analyzed for HIV RNA viral load (VL) and genotypic resistance testing was performed on those with VL nonsuppression (defined as VL ≥1,000 copies/mL). We used the Stanford HIVDR database-algorithm to assess HIVDR mutations and logistic regression to assess risk factors for VL nonsuppression and HIVDR. We observed an overall VS prevalence of 76.0% (203/267) and detected respective acquired drug resistance prevalence to non-nucleoside reverse transcriptase inhibitors (NNRTIs) and nucleoside reverse transcriptase inhibitors (NRTIs) of 81.3% [confidence interval (CI) 67.4-91.1] and 45.8% (CI 31.4-60.8) among the 48 successfully genotyped VL nonsuppressors. NNRTI mutations were observed in 81.3% (39/48) of the genotyped participants and 45.8% (22/48) had both NRTI and NNRTI mutations. The mutation K103N was detected in 62.5% (30/48) of participants, 41.7% (20/48) had M184V/I, 14.6% had K65R, and 12.5% (6/48) had thymidine analog mutations (TAMs). None of the analyzed potential risk factors, including age and duration on ART, was significantly correlated with VL nonsuppression or HIVDR. Although high levels of NNRTI mutations support the transition to dolutegravir, the presence of NRTI mutations, especially TAMs, may compromise dolutegravir-based regimens or other second-line ART options. The moderate VS prevalence and high HIVDR prevalence therefore call for timely ART switching and intensive adherence counseling.

Barriers to sustainable virologic suppression (VS) of HIV-infected adolescents and young adults include drug resistance mutations (DRMs) and limited treatment options, which may impact the outcome of second-line antiretroviral therapy (ART). We sequenced plasma viral RNA from 74 adolescents and young adults (16-24 years) failing first-line ART at Newlands Clinic, Zimbabwe between October 2015 and December 2016. We evaluated first-line nucleoside reverse transcriptase inhibitor (NRTI) susceptibility scores to first- and second-line regimens. Boosted protease inhibitor (bPI)-based ART was provided and viral load (VL) monitored for ≥48 weeks. Fisher's exact test was used to evaluate factors associated with VS on second-line regimens, defined as VL

Tanzania has recently adapted World Health Organization antiretroviral guidelines that include integrase strand transfer inhibitors (INSTIs) in the first-line regimen. However, there is lack of evidence on integrase (IN) gene polymorphisms in viral strains circulating in Tanzania. In this study, we characterize IN gene polymorphisms in viral strains circulating in Dar es Salaam, Tanzania, before introduction of INSTIs. Plasma viral RNAs were prepared from 158 HIV-1-infected subjects, including 111 treated, but viremic (INSTI-naive), subjects. A part of the pol gene encompassing the IN-coding region was amplified and directly sequenced by the Sanger sequencing method. Subtype analysis revealed that subtypes A1, C, and D and intersubtype recombinants were 42%, 38%, 11%, and 9%, respectively. Although multiple subtypes cocirculate, the IN gene exhibited a relatively conserved amino acid sequence pattern with an average Shannon entropy score of 0.16. No major INSTI resistance mutations were found; however, accessory resistance mutations at positions T97A, E157Q, G163E/K, and 128A/T were detected in 5% of subjects.

The World Health Organization (WHO) has put forth recommendations for the use of integrase (IN) strand transfer inhibitors (INSTIs) to be part of the first-line combination antiretroviral therapy regimen to treat HIV infections. The knowledge of pretreatment drug resistance against INSTIs is still scarce in resource-limited settings (RLS). We characterized the

To investigate the prevalence and characteristics of drug-resistance genotypes among unique recombinant forms (URFs) in HIV-1 infected people under long-term antiretroviral treatment failure from Yunnan Province. The plasma samples were collected from antiretroviral therapy (ART)-failure experienced individuals from 2016 to 2017 in Yunnan Province, China. The genotyping drug resistance of HIV-1 pol gene fragments was implemented using in-house assay. According to the analysis of RIP and MEGA 7.0, the HIV-1 strains related to URFs were screened for recombinant identification and drug resistance analysis. A total of 130 pol sequences of HIV-1 URF strains were obtained from 1,121 samples. The proportion of HIV-1 URF strains was 11.6% among the ART-failure individuals from 2016 to 2017 in Yunnan. The overall drug-resistance rate of HIV-1 URF strains was 56.9%. Meanwhile, the percentage of protease inhibitors, nucleoside reverse transcriptase inhibitors (NRTIs), and non-nucleoside reverse transcriptase inhibitors (NNRTIs) resistance was 3.8% (5/130), 36.2% (47/130), and 53.8% (70/130), respectively. Mutations such as M184V/I (35.4%) in NRTIs and K103N/R/S/T (25.4%), V179D/E/T/Y (18.9%), G190A/E/R/S (13.8%), and Y181C (9.2%) in NNRTIs were common among the HIV-1 URF strains relative to other mutations. Factors such as male, sexual transmission pathway, and source of the year 2017 were significantly correlated with the development of HIV-1 URF drug resistance. The emergence of the multiple recombinant forms identified in Yunnan indicates active transmission networks of HIV-1 of different HIV-1 subtype/circulating recombinant forms cross-infection in this region. Therefore, it is necessary to further monitor the molecular epidemiology and drug resistance of HIV-1 in Yunnan.

Drug resistance mutations (DRMs) can affect the success of the therapy and compromise new prevention strategies. Increasing rates of resistance to antiretroviral (ARV) drugs have been reported in some areas. This study evaluated the DRMs prevalence among patients at Hospital das Clínicas (São Paulo). Among treatment-naive patients, the prevalence of transmitted DRMs (Stanford Calibrated Population Resistance) was 8.4% (21/249), with 69% (75/109) of acquired resistance among treatment-experienced patients. Rates of transmitted DRM showed an increase (6.6% in 2002-2009 vs. 15.1% in 2010-2015

New recombinant variants are a predominant challenge for preventing the spread of the HIV-1 epidemic. In this study, we confirmed a novel HIV-1 CRF07_BC/CRF55_01B recombinant form for the first time, which was isolated from a male patient in Jiangmen, China. The genomic sequence of the variant with four CRF55_01B segments inserted into the CRF07_BC backbone is 8,510 bp in length, extending from nucleotides 669 to 9,293 according to the HXB2 genome. Specifically, the recombinant strain contains site mutations associated with drug resistance.

Transgenders (TGs) are highly affected by HIV with high prevalence of 3.14% in India. Since 2017, targeted preventive efforts have been initiated by the government and HIV-infected TGs are being provided the antiretroviral (ART) treatment. Information on the primary HIV drug resistance is crucial for appropriate treatment selection to curb further spread of HIV in this population. In this study, we analyzed HIV-1 pol gene sequences from 36 TGs for presence of drug resistance mutations. To our knowledge, this first study from India reports high-level primary drug resistance (13.8%) among the TG population. Mutations M184V, A98G, K103N, G190A, and Y318F associated with resistance to nucleoside reverse transcriptase inhibitor and non-nucleoside reverse transcriptase inhibitors were observed. All pol gene sequences revealed HIV-1 subtype C in all study TG. High-level HIV-1 drug resistance warrant nationwide larger studies on TGs to understand the level of primary ART drug resistance among this population.

There are about 2.1 million children infected with HIV globally and about 120,000 deaths annually. Nigeria has one of the highest rates of pediatric HIV infection globally. Pretreatment HIV drug resistance data inform the choice of first- and second-line antiretroviral therapy (ART) regimens. This study investigated the prevalence of HIV drug-resistant strains among ART-naive children in Ibadan, Nigeria. A total of 20 children aged15 years were enrolled. Demographic, clinical, and laboratory data were documented. Total nucleic acid was extracted from blood samples after which amplification of HIV-1 pol gene was done using polymerase chain reaction. Amplified gene was sequenced using big dye sequencing method. The sequenced HIV-1 pol gene was typed and analyzed for identification of mutations indicative of drug resistance across the different classes of ART. HIV-1 RNA pol gene was successfully amplified in 12/20 (60%) children. All were identified as HIV-1 and the subtypes were G and CRF 02AG, recombinant of 02_AG/G and recombinant of 02_AG/A1. Drug-resistant mutations (DRMs) were identified in 4/12 (33%). Three out of the four mutations were identified as non-nucleoside reverse transcriptase inhibitors DRM (K103N), whereas the fourth had nucleoside reverse transcriptase inhibitors DRM (M184V). Results from this preliminary study show that drug resistance among ART-naive children is a problem in Ibadan. Pretreatment drug resistance testing is desirable in children before initiation of ART to guide effective treatment.

All people living with HIV should receive antiretroviral therapy (ART), but those with CD4 counts >500 cells/mm(3) at ART initiation (“early initiators”) may be less motivated to adhere to treatment, compared with those with CD4 counts 1,000 copies/mL. We used Poisson regression models with robust variance to evaluate associations between early ART initiation and viral suppression 500 cells/mm(3). In multivariable analysis, early initiators were more likely to be virally suppressed compared with late initiators (adjusted risk ratio: 1.29, 95% confidence interval: 1.13–1.46). All 18 participants with viral load >1,000 copies/mL had successful genotyping, which identified drug resistance in 14/18 (77.8%). Among early initiators, drug resistance was detected in only 1/117 (0.9%), compared with 11/93 (11.8%) among late initiators. In conclusion, among people receiving ART in a South African public clinic, early initiators had better viral suppression after 6 months and less drug resistance than late initiators, which further supports universal treatment. Clinical trials registration: NCT03066128.

Trends in resistance to antiretroviral drugs for HIV-1 may inform clinical support and drug development. We evaluated drug resistance mutation (DRM) trends for nucleoside reverse transcriptase inhibitor (NRTI), non-nucleoside reverse transcriptase inhibitor (NNRTI), protease inhibitor (PI), and integrase strand transfer inhibitor (INSTI) in a large U.S. reference laboratory database. DRMs with a Stanford HIV Drug Resistance Database mutation score ≥10 from deidentified subtype B NRTI/NNRTI/PI specimens (2006-2017;10,000/year) and INSTI specimens (2010-2017;1,000/year) were evaluated. Sequences with NRTI, NNRTI, or PI single- or multiclass DRMs declined from 48.9% to 39.3%. High-level dual- and triple-class resistance declined from 43.3% (2006) to 17.1% (2017), while sequences with only single-class DRMs increased from 40.0% to 52.9%. The prevalence of DRMs associated with earlier treatment regimens declined, while prevalence of some DRMs associated with newer regimens increased. M184V/I decreased from 48.3% to 29.4%. K103N/S/T declined from 42.5% in 2012 to 36.4% in 2017. Rilpivirine and etravirine DRMs E138A/Q/R and E138K increased from 4.9% and 0.4% to 9.7% and 1.7%, respectively. Sequences with ≥1 darunavir DRM declined from 18.1% to 4.8% by 2017. INSTI DRM Q148H/K/R declined from 39.3% (2010) to 13.8% (2017). Prevalence of elvitegravir-associated DRMs T66A/I/K, E92Q, S147G, and the dolutegravir-associated DRM R263K increased. For a subset of patients with serial testing, 50% (2,646/5,290) of those who initially had no reportable DRM subsequently developed ≥1 DRM for NRTI/NNRTI/PI and 49.7% (159/320) for INSTI. These trends may inform the need for baseline genotypic resistance testing. The detection of treatment-emergent DRMs in serially tested patients confirms the value of genotypic testing following virologic failure.

A cross-sectional study was undertaken to examine the prevalence and pattern of HIV drug resistance mutations (DRMs) among recently HIV-1-infected and antiretroviral therapy (ART)-naive individuals from Chennai, South India. The HIV-1 pol gene encompassing the protease and reverse transcriptase (RT) regions were analyzed from 53 ART-naive HIV-1-infected individuals using an in-house method for identifying DRMs by genotyping. The overall prevalence of transmitted drug resistance (TDR) was found to be 11.3% (6/53), which is categorized as moderate level (5.0%-15.0%) of TDR according to the World Health Organization (WHO) survey guidelines. Surveillance drug resistance mutations to non-nucleoside reverse transcriptase inhibitors (NNRTI) were observed in 8.3% (

Jiangsu province has severe HIV-1 epidemic in China. Suqian which is located in north of the province has limited HIV epidemic information. Therefore, this study aimed to characterize the epidemic details in the area. A total of 196 plasma samples were collected from treated HIV-1-positive cases and viral RNA was extracted. Then HIV partial

The Indian national AIDS control program heavily relies on low cost nucleoside reverse transcriptase inhibitor (NRTI) and non-nucleoside reverse transcriptase inhibitor (NNRTI). With global increase in resistance to these, alternative antiretroviral combinations need to be explored. Owing to higher potency, better efficacy and tolerability, recently WHO recommended integrase strand transfer inhibitor (INSTI) based first-line antiretroviral therapy (ART). There is lack of INSTI resistance surveillance data from India. Thus, there is a need to analyze integrase (IN) gene from primarily HIV-1 subtype C infected Indian population, before widespread introduction of INSTI in first-line ART. Plasma samples were collected from INSTI naïve individuals reporting to ART centre of Pune, India. RNA was extracted and IN gene was amplified by nested polymerase chain reaction (PCR) using prior published primers. PCR product of 867 bp was bi-directionally sequenced and resistance associated mutation were analyzed using Stanford University HIV drug resistance algorithm. A total of 58 HIV-1 sequences from 62 INSTI naïve individuals were successfully genotyped. Of these 58, 40 were ART naïve, newly diagnosed and remaining individuals were on NRTI, NNRTI, or protease inhibitors based failing regimen. The commonest subtype identified in the study was C (93%) followed by A1 (3.5%). A total of 191 (66.31%) fully conserved amino acid (aa) positions were observed in IN gene. Overall there was absence of major INSTI resistance mutation, however, E157Q (13.79%) emerged as common polymorphic mutation. Other accessory mutations were L74IM (34.48%), Q95K (1.72%), and T97A (1.72%). To conclude, this first Indian study on primarily HIV-1 subtype C sequences characterized aa variations in IN gene and indicated absence of major INSTI resistance associated mutations.

High level of HIV prevalence was found in some specific areas or populations in China. Shijingshan district was one of the areas with rapid increase of newly reported HIV cases in Beijing, China. Comprehensive investigation on HIV genetic characteristics is necessary in the district. In this study, we enrolled 223 newly identified HIV-1 sero-positive drug-naive patients from Shijingshan district. The full-length gag, pol, and partial env gene sequences were amplified and sequenced. Genetic characterization and transmission of drug resistance of HIV-1 were further investigated. Many stains, including CRF01_AE (48.25%), CRF07_BC (31.47%), subtype B (4.9%), 55_01B (1.40%), 59_01B (0.70%), 65_cpx (2.10%), 79_0107 (0.70%), and A (0.70%) and unique recombinant forms (URF) of 0107 (6.29%), 01B (1.40%), and 01BC (2.10%), were identified. Among 106 strains that harbor full-length PR gene, 10 (9.43%) strains contain mutations associated with drug resistance to protease inhibitors. Among 59 strains that harbor full-length reverse transcriptase (RT) gene, no strains contained mutations conferred to nucleoside reverse transcriptase inhibitors resistance and 4 strains (6.78%) contained drug-resistant mutations to non-nucleoside reverse transcriptase inhibitors. Among 58 sequences harboring full-length IN gene, 1 stain (1.72%) contained a mutation causing drug resistance to integrase strand transfer inhibitors. Our results provided detailed genetic data on HIV prevalent in Shijingshan district of Beijing, which would be helpful for understanding HIV-1 transmission among local populations.

Updated guidelines for the treatment of antiretroviral therapy (ART)-negative patients with HIV recommend integrase strand transfer inhibitor (INSTI)-based regimens. HIV patients are tested for resistance to antiretrovirals, and the reported prevalence of transmitted INSTI resistance remains rare worldwide. However, no data related to INSTI resistance in Korean HIV patients have been reported. We aimed to determine the prevalence of INSTI resistance-related mutations in South Korea. We subjected both ART-naive (n = 58) and ART-experienced Korean HIV patients (n = 41) to genotypic resistance analysis and determined a prevalence of INSTI major resistance mutations of 3.4% (n = 2) among ART-naive patients and 22.0% (n = 9) among ART-experienced patients. In the former group, both major INSTI resistance cases involved the nonpolymorphic E92Q mutation in the integrase strand. Our findings suggest that INSTI resistance testing should be included in the standard resistance screening protocols for Korean HIV patients.

The emergence and transmission of antiretroviral drug resistance have been and remain a concern among people living with human immunodeficiency virus (HIV)-1 infection. The protease inhibitor (PI) darunavir has been approved for use in the United States for more than 10 years and has demonstrated a high barrier to resistance. Previous analyses identified significant reductions in the prevalence of samples with darunavir resistance-associated mutations (RAMs) and with phenotypic resistance to darunavir and other PIs between 2006 and 2012. This analysis extends those findings by evaluating darunavir and PI resistance among clinical samples submitted for routine drug resistance testing (combined genotyping and phenotyping) in the United States from 2010 to 2017. Frequencies of 11 darunavir and 23 primary PI RAMs, and phenotypic susceptibility, were assessed yearly among all samples and in a subset of samples with distinct phenotypic resistance to one or more PIs. Among all samples (N = 60,760), the proportion with 0 darunavir RAMs was 91.7% in 2010 and 95.8% in 2017. The proportions of all samples with phenotypic susceptibility to darunavir, atazanavir, and lopinavir were, respectively, 97.4%, 94.2%, and 94.7% in 2010 and 98.6%, 97.7%, and 97.5% in 2017. Among the 4,799 samples with phenotypic resistance to one or more PIs, the proportions with phenotypic susceptibility to darunavir, atazanavir, and lopinavir were, respectively, 73.3%, 41.5%, and 46.0% in 2010 and 70.7%, 53.7%, and 48.8% in 2017. The prevalence of darunavir RAMs among commercially tested HIV-1 samples remained low and generally stable from 2010 to 2017, and high proportions showed phenotypic darunavir susceptibility.

The efficacy of antiretroviral (ARV) therapy can be compromised by the emergence and transmission of HIV-1 drug-resistant strains. HIV-1 drug-resistance (DR) genotypic testing thus plays an important role in the selection of optimal treatment regimens for HIV-infected individuals. Given the complexities of the testing procedures and the variety of approaches used, there is considerable potential for results to vary between laboratories. In Thailand, the national External Quality Assessment (EQA) scheme assesses the DR genotype testing performance of laboratories. Here, we evaluated the performance of laboratories in nucleotide sequencing and compared drug-resistance-associated mutations (DRMs) in the HIV-1 protease (PR) and reverse transcriptase (RT) genes during 2010-2015. The EQA samples in the 12 panels showed predominance for the CRF01_AE (85%) and subtype B (15%). Fourteen laboratory datasets were generated: eight using TruGene (TG), two using ViroSeq (VS), and four using in-house (IH) assays. All IH and VS laboratories had penalty scores7, whereas five of the eight TG laboratories had fluctuating penalty scores. Moreover, seven and six TG laboratories could not amplify the two identical samples, 10B and 10E samples, or the CRF01_AE. Our findings demonstrate the requirement for laboratory participation in the ongoing EQA program and the optimization of kit assays using CRF01_AE samples. Our results also indicate that one advantage of participation is that the laboratories can monitor and investigate the source of laboratory errors.

Pretreatment drug resistance (PDR) can compromise antiretroviral therapy (ART) efficacy and undermine the WHO targets to end the AIDS epidemic as a public health threat by 2030. Thus, we examined the level of PDR in Harare, Zimbabwe. Eligible study participants were adults who were ART naive or individuals with previous ART exposure reinitiating treatment, recruited between October 2018 and February 2020 in a HIV ART treatment clinic, in Harare. HIV drug resistance tests were performed for all specimens with viral load ≥400 copies/mL and interpreted using the Stanford HIVDB Algorithm. Chi-square test or Fisher's exact test was used for comparison of proportions of PDR across ART-naive or prior ART-exposed participants. All statistical analyses were performed using Stata version 14. Overall, 120 samples were genotyped of whom 104 were ART naive and 16 reported previous ART exposure. The overall PDR frequency among all participants was 31% [95% confidence interval (CI): 22.5-39.6]. PDR to any non-nucleotide reverse transcriptase inhibitor (NNRTI) was reported in 29% (95% CI: 21.0-37.9). PDR to nucleotide reverse transcriptase inhibitors (NRTIs) and protease inhibitors were low, found in 3% (95% CI: 0.9-8.2) and 1% (95% CI: 0.02-4.52), respectively. PDR to NNRTIs [efavirenz/nevirapine (EFV/NVP)] was found in 17% (95% CI: 10.5-24.6) and was more than six times higher among people with previous ART exposure than ART-naive people: 63% versus 10%

The wide variety of new HIV-1 recombinant variants are a predominant challenge for understanding the molecular epidemiology and preventing the spread of the HIV-1 epidemic. In this study, we confirmed a novel HIV-1 unique B/C recombinant (ZLQ01186) isolated from a male patient infected with HIV-1 through injection drug use in Foshan city, Guangdong Province. The near full-length genome was amplified, and then the polymerase chain reaction products were sequenced by Sanger sequencing. The genomic sequence of the strain, with two subtype B segments inserted into the subtype C backbone, was 8,953 bp in length, extending from 647 to 9,599 bp according to the HXB2 genome. In addition, this B/C recombinant strain contained the non-nucleoside reverse transcriptase inhibitor resistance mutation K103N and the integrase strand transfer inhibitor other resistance mutation L74I according to the Stanford University HIV Drug Resistance Database program. The drug resistance profile indicates high-level resistance against efavirenz and rilpivirine. This study identified a recombinant between the main circulating strains, indicating a more complicated trend of the HIV-1 epidemic in Guangdong, China.

HIV drug resistance testing is fundamental in clinical patient management, but data on HIV-1 drug-resistant mutations (DRMs) is scarce in the Caribbean and in Suriname limited to one survey on transmitted resistance. The aim of this study was to address this gap, to gain insight in acquired HIV drug resistance (ADR) prevalence and mutation patterns, and to improve HIV-1 treatment outcome of people living with HIV (PLHIV) in Suriname. A prospective cross-sectional study was conducted from July 2018 through January 2019 among treatment-experienced PLHIV (

To evaluate the national prevalence of antiretroviral therapy (ART)-resistant HIV-1 viruses among both ART-initiators (pretreatment drug resistance, PDR) and ART-failure HIV patients in Uzbekistan. A nation-wide, cross-sectional active HIV-1 PDR surveillance was conducted in Uzbekistan from 2015 to 2016. In total, 713 blood plasma samples from adults were collected, including samples from ART-naive patients initiating ART and ART-failure HIV patients. HIV-1 genome polregion viral sequences were obtained from 309 patients, of those 106 on ART and 203 on ART-initiators. Analysis of HIV-1 subtypes and drug resistance mutations (DRMs) to HIV protease and reverse transcriptase inhibitors was performed. Among all the viruses studied, HIV-1 CRF 02_AG recombinant was the most common-57% (176/309). The second major group was represented by A1-40.5% (125/309). Two viruses were found to be recombinants formed by subtypes A1 and CRF02_AG sequences. ART-naive cohort I (PDR) included six samples that contained at least one surveillance drug resistance mutation (SDRM) (2.96%), with the most common being K103N mutation (4/6). In ART-experienced patients, cohort II, 77.4% (82/106) of viruses contained at least one mutation against PIs, NRTIs, or NNRTIs, with the most common mutations of M184V/I (49.1%; 52/106), K65R (18.9%; 20/106), K103N (23.6%; 25/106), and G190S (22.6%; 24/106). The significant difference in frequency of mutations was found between two dominant subtypes, A1 and CRF02_AG. The molecular epidemiological profile of HIV infection in Uzbekistan has changed toward a predominance of CRF02_AG viruses. In the first national-scale study of the PDR prevalence, it was found to be relatively low (2.96%). The DR mutations in failure patients correspond to the main therapy regimens (NRTI/NNRTI) adopted in the country. The observations provide new evidence for differences in ART efficacy and resistance profiles for different subtypes.

Transmitted drug resistance (TDR) in treatment-naive HIV patients can contribute to failure of initial antiretroviral therapy. In Korea, there has been a gradual increase in TDR, but the recent increase in the use of integrase strand transfer inhibitors (INSTIs) could affect TDR trends and INSTI resistance mutations. We evaluated the patterns of TDR in newly diagnosed HIV patients over time from 2011 to 2019. We analyzed the genotypic resistance of strains in 336 patients and sequenced the integrase gene in 71 among 336 subjects. The overall prevalence of TDR was 5.9% (20 of 336 patients), and it showed a tendency to increase over time (5.1% in 2011-2013, 6.1% in 2014-2016, and 7.2% in 2017-2019

HIV-1 integrase (IN) is a primary target for combination antiretroviral therapy. Only a limited number of studies report on the emergence of resistance-associated mutations (RAMs) in Cameroon. We observed that 1.4% of sequence from treatment-naive patients had IN strand transfer inhibitor (INSTI) RAMs. These mutations confer resistance to raltegravir and elvitegravir. We also observed that 10.1% of the sequences have INSTI accessory RAMs. HIV-1 CRF02_AG was the predominant subtype (44.7%) in this study analyses. The occurrence of INSTI RAMs among the sequences at baseline needs to be monitored carefully.

In this study, we identified a novel circulating recombinant form (CRF) of HIV (CRF105_0108) in a total of five patients with no obvious epidemiological linkage in Sichuan, China. Four strains were found in this study, and another strain (XC2014EU01) was reported in a previous study. The phylogenetic analysis of the five near full-length genomes showed that a CRF08_BC segment was inserted into the CRF01_AE backbone with one recombinant breakpoint in the pol region, which is the first HIV-1 CRF of CRF01_AE and CRF08_BC. Three genetic sequences had drug-resistant mutations, E138Q and V179D, indicating that there were low resistance levels to efavirenz (EFV) and nevirapine (NVP) in Liangshan Yi Autonomous Prefecture. CRF105_0108 increases the diversity and complexity of the prevalent HIV-1 CRFs in Sichuan. Simultaneously, drug-resistant mutations in this CRF may influence the efficacy of highly active antiretroviral treatments (ARTs) in Liangshan Yi Autonomous Prefecture.

College students are disproportionately affected by HIV-1 in China. However, little is known about the genetic characteristics of HIV-1 among this population. A molecular epidemiological investigation was conducted among the newly diagnosed antiretroviral therapy-naïve HIV-1-infected individuals during 2015-2019 in Nanjing city, China. The

Rilpivirine (RPV) and Etravirine (ETR) are approved second-generation non-nucleoside reverse transcriptase inhibitors (NNRTIs) for HIV treatment. There is a cross-resistance HIV mutation profile between first- and second-generation NNRTI drugs. We determined the prevalence of HIV-1 drug resistance mutations (DRMs) to RPV and ETR in Botswana. A total of 168 HIV-1 polymerase gene sequences from participants failing nevirapine (NVP)- or efavirenz (EFV)-containing regimens were analyzed for DRMs using the Stanford University HIV drug resistance database. Forty-one sequences were from an adult antiretroviral therapy (ART) study, the Tshepo study, and 127 from a prevention of mother-to-child transmission (PMTCT) study, the Mashi study, all conducted in Botswana. Prevalence of RPV and ETR highest DRM in the adult ART study (n = 41) were K101E (26.2%), E138A (23.8%), and Y181C (26.2%). The PMTCT cohort's (n = 127) high prevalence mutations were Y181C (15.7%), E138A (15%), and K101E (11%). A total of 42.9% and 3.2% of patients in the adult ART study and PMTCT study, respectively, had three or more NNRTI mutations at virologic failure. We identified HIV-1 mutations conferring resistance to RPV and ETR even though they have not been used in Botswana. Of concern was the high proportion of sequences from the adult ART study that displayed multiple DRMs; as the number of NNRTI mutations increases, the level of cross-resistance increases. It is plausible that patients displaying such profiles maybe at increased risk of failing second-generation NNRTI drugs, hence, calls for genotyping in patients with prior NVP or efavirenz exposure before prescription of RPV- or ETR-containing cART.

Pre-existing HIV drug resistance can jeopardize first-line antiretroviral therapy (ART) success. Changes in the prevalence of drug resistance-associated mutations (DRMs) were analyzed from HIV-infected, ART-naive, U.S. individuals seeking ART treatment from 2000 to 2009. HIV DRM data from 3,829 ART-naive subjects were analyzed by year of sample collection using International Antiviral Society-United States (IAS-USA) and World Health Organization (WHO) “surveillance” DRM definitions; minor IAS-USA-defined DRMs were excluded. IAS-USA DRM prevalence between 2000 and 2009 was 14%, beginning with 8% in 2000 and 13% in 2009. The greatest incidence was observed in 2007 (17%). Overall, IAS-USA-defined non-nucleoside reverse transcriptase inhibitor (NNRTI) DRMs were 9.5%; nucleoside reverse transcriptase inhibitor (NRTI): 4%, and major protease inhibitor (PI): 3%. The most frequently detected IAS-USA-defined DRMs by class were NNRTI: K103N/S (4%), NRTI: M41L (1.5%), and PI: L90M (1%). Overall, WHO-defined DRM prevalence was 13% (5% in 2000; 13% in 2009). By class, NNRTI prevalence was 6%, NRTI: 6%, and PI: 3.2%. The most frequent WHO-defined DRMs were NRTI: codon T215 (3.0%), NNRTI: K103N/S (4%), and PI: L90 (1%). WHO-defined NNRTI DRMs declined significantly (p = .0412) from 2007 to 2009. The overall prevalence of HIV-1 containing major IAS-USA or WHO-defined DRMs to ≥2 or ≥3 classes was 2% and

Integrase strand transfer inhibitor (InSTI) resistance rates are low. However, genotypic resistance test (GRT) is not routinely performed in many centers. The aim of this study is to evaluate the prevalence of InSTI-related mutations in our large cohort. We examined all integrase GRTs performed as part of routine clinical practice at Spedali Civili General Hospital, University of Brescia from 2011 to 2016. Analysis was performed through the Stanford HIV Drug Resistance Database. A total of 341 patients were included. Genotypic resistance assays were performed in naive (48), ART-experienced but InSTI-naive (114), and both ART-experienced/InSTI-experienced (179) patients. No major resistance-associated mutations (RAMs) were detected in patients never exposed to InSTIs. Of 179 samples from patients exposed to InSTIs (mostly to raltegravir [RAL]), the overall prevalence of major RAMs was 11.7%. Among them, 10 harbored N155H, 4 Q148H, 2 Q148R, 2 Y143C/S, and 2 T66A/I/T, respectively. A novel mutation at a recognized resistance site (E92K) was identified in one RAL-experienced patient. The overall prevalence of InSTI mutations in our cohort was low, particularly in naive patients indicating no transmitted RAMs, although in InSTIs-experienced patients the rate of RAMs was high (11.7%). We support an implementation of surveillance of InSTI resistance.

HIV-1 subtype B virus is the most prevalent subtype in Puerto Rico (PR), accounting for about 90% of infection in the island. Recently, other subtypes and circulating recombinant forms (CRFs), including F(12_BF), A (01_BF), and CRF-39 BF-like, have been identified. The purpose of this study is to assess the distribution of drug resistance mutations and subtypes in PR. A total of 846 nucleotide sequences from the period comprising 2013 through 2017 were obtained from our “HIV Genotyping” test file. Phylogenetic and molecular epidemiology analyses were performed to evaluate the evolutionary dynamics and prevalence of drug resistance mutations. According to our results, we detected a decrease in the prevalence of protease inhibitor, nucleoside reverse transcriptase inhibitor (NRTI), and non-NRTI (NNRTI) resistance mutations over time. In addition, we also detected recombinant forms and, for the first time, identified subtypes C, D, and CRF-24BG in PR. Recent studies suggest that non-subtypes B are associated with a high risk of treatment failure and disease progression. The constant monitoring of viral evolution and drug resistance mutation dynamics is important to establish appropriate efforts for controlling viral expansion.

Historically, in HIV patients, the K65R mutation and thymidine analogue mutations (TAMs) have been reported to rarely coexist. We retrospectively reviewed genotype data from paired samples in a cohort of HIV-1-infected Nigerian patients failing first-line antiretroviral therapies containing zidovudine (AZT) or tenofovir (TDF). Samples for each patient were taken at initial confirmed virological failure ≥1000 copies/ml (S1) and then at the latest available sample with viral load ≥1000 copies/ml before switch to second line (S2). Among 103 patients failing AZT, 19 (18.4%) had TAM-1s, 29 (28.2%) TAM-2s, and 21 (20.4%) mixed TAMs by S2. In contrast, in the 87 patients failing TDF, drug resistance mutations at S2 included K65R in 56 (64.4%), TAM-1s in 1 (1.1%), and TAM-2s in 25 patients (28.7%). Interestingly, 30.4% of patients with K65R in our study developed TAMs. These were exclusively K219E ± D67N and were not predicted to confer a resistance cost to future AZT-containing regimens.

To screen for drug resistance and possible treatment with Dolutegravir (DTG) in treatment-naive patients and those experiencing virologic failure during first-, second-, and third-line combined antiretroviral therapy (cART) in Uganda. Samples from 417 patients in Uganda were analyzed for predicted drug resistance upon failing a first- (N = 158), second- (N = 121), or third-line [all 51 involving Raltegravir (RAL)] treatment regimen. HIV-1 pol gene was amplified and sequenced from plasma samples. Drug susceptibility was interpreted using the Stanford HIV database algorithm and SCUEAL was used for HIV-1 subtyping. Frequency of resistance to nucleoside reverse transcriptase inhibitors (NRTIs) (95%) and non-NRTI (NNRTI, 96%) was high in first-line treatment failures. Despite lack of NNRTI-based treatment for years, NNRTI resistance remained stable in 55% of patients failing second-line or third-line treatment, and was also at 10% in treatment-naive Ugandans. DTG resistance (n = 366) was not observed in treatment-naive individuals or individuals failing first- and second-line cART, and only found in two patients failing third-line cART, while 47% of the latter had RAL- and Elvitegravir-resistant HIV-1. Secondary mutations associated with DTG resistance were found in 2%–10% of patients failing third-line cART. Of 14 drugs currently available for cART in Uganda, resistance was readily observed to all antiretroviral drugs (except for DTG) in Ugandan patients failing first-, second-, or even third-line treatment regimens. The high NNRTI resistance in first-line treatment in Uganda even among treatment-naive patients calls for the use of DTG to reach the UNAIDS 90:90:90 goals.

Maraviroc (MVC) is an allosteric inhibitor of human immunodeficiency virus type 1 (HIV-1) entry, and is the only CCR5 antagonist licensed for use as an anti-HIV-1 therapeutic. It acts by altering the conformation of the CCR5 extracellular loops, rendering CCR5 unrecognizable by the HIV-1 envelope (Env) glycoproteins. This study aimed to understand the mechanisms underlying the development of MVC resistance in HIV-1-infected patients. To do this, we obtained longitudinal plasma samples from eight subjects who experienced treatment failure with phenotypically verified, CCR5-tropic MVC resistance. We then cloned and characterized HIV-1 Envs (n = 77) from plasma of pretreatment (n = 36) and treatment failure (n = 41) samples. Our results showed variation in the magnitude of MVC resistance as measured by reductions in maximal percent inhibition of Env-pseudotyped viruses, which was more pronounced in 293-Affinofile cells compared to other cells with similar levels of CCR5 expression. Amino acid determinants of MVC resistance localized to the V3 Env region and were strain specific. We also observed minimal cross-resistance to other CCR5 antagonists by MVC-resistant strains. We conclude that 293-Affinofile cells are highly sensitive for detecting and measuring MVC resistance through a mechanism that is CCR5-dependent yet independent of CCR5 expression levels. The strain-specific nature of resistance mutations suggests that sequence-based diagnostics and prognostics will need to be more sophisticated than simple position scoring to be useful for managing resistance in subjects taking MVC. Finally, the minimal levels of cross-resistance suggests that recognition of the MVC-modified form of CCR5 does not necessarily lead to recognition of other antagonist-modified forms of CCR5.