Background
The United Kingdom (U.K.) has a relatively small HIV-1 epidemic, with just over 100,000 people living with HIV-1 and an adult prevalence of 0.16%, despite the recent increase in the annual number of new diagnoses, particularly in people born in the country [
1]. Nonetheless, the U.K. is a clear example of how access to combination antiretroviral therapy (cART) can transform a national HIV-1 epidemic: 98% of the people living with HIV-1 were receiving cART in 2017 with 97% achieving virus suppression [
1,
2]. The prevalence of resistance to any antiretroviral drug among ART-experienced patients in the country seems to have remained stable -around 30%- since 2011, while transmitted HIV-1 drug resistance (prevalence in ART-naïve individuals) is approximately 7% [
3‐
6]. These results highlight the fact that monitoring HIV-1 drug resistance is not only crucial to controlling plasma viremia in patients receiving antiretroviral drugs but also in the surveillance of transmitted drug resistance, a critical public health issue in the fight against HIV/AIDS.
HIV-1 genotyping assays, based on population (Sanger) sequencing, have been the most common method to manage patients infected with HIV-1 for almost 20 years [
7‐
11]. Our current understanding of HIV-1 drug resistance, and the great success controlling HIV-1 disease during the last decade, have been the result of a myriad of HIV-1 studies using this standard methodology [
7,
12,
13]. Nevertheless, HIV-1 genotypes based on Sanger sequencing can only detect HIV-1 variants present at frequencies above approximately 20% of the viral quasispecies [
14‐
18], failing to quantify low-levels of HIV-1 drug resistant variants [
10,
19]. These variants, usually present as minority members of the virus population, can be selected and become predominant under the appropriate pressure by antiretroviral drugs [
20‐
22]. With the advent of deep (next-generation) sequencing, several new HIV-1 genotyping approaches based on this ultrasensitive methodology have been developed with the goal of detecting drug resistant HIV-1 variants at low frequencies, i.e., below 20% of the viral population [
19,
23‐
26], with only a few assays being used in the clinical setting [
19,
27,
28]. Although the clinical significance of these minority drug resistant HIV-1 variants is still on discussion [
29‐
33], numerous groups are now using these assays not only to monitor HIV-1 drug resistance but also to better understand the role of low-level HIV-1 variants on transmission, disease progression, and HIV-1 cure strategies [reviewed on [
10,
11]].
Several groups in the U.K. have used deep sequencing to investigate minority HIV-1 variants associated with transmitted drug resistance [
3,
6,
34], selection and prevalence of low-abundance drug resistant HIV-1 variants [
35], genetic diversity in full-length HIV-1 genomes [
36], HIV-1 coreceptor tropism [
37‐
39], and their potential contribution to virologic failure [
40]; however, in-house HIV-1 genotyping based on deep sequencing is only available in reference laboratories in the United Kingdom. In this verification study, we implemented DEEPGEN™, a validated deep sequencing-based HIV-1 genotyping assay used in a CLIA/CAP-accredited laboratory in the United States since 2013 [
19] and in Uganda since January 2017 [
41], in two clinical laboratories in the U.K. i.e., St. George’s University Hospitals Healthcare NHS Foundation Trust (London) and at NHS Lothian (Edinburgh). A comprehensive list of comparative studies first verified the feasibility of using DEEPGEN™ to monitor HIV-infected individuals in the U.K., while we characterized majority and minority drug resistant HIV-1 variants in these cohorts of patients and their correlation with virological and immunological parameters.
Discussion
Widespread HIV-1 drug resistance, usually associated with suboptimal virological suppression and poor clinical outcomes [
52,
53], is the natural byproduct of years of treating HIV-infected individuals with cART. Monitoring and detecting HIV-1 drug resistance, as soon as possible, does not only help control the infection and preserve the immunologic response in the individual but also limits the transmission of HIV-1 drug resistant variants, restricting the increasing prevalence of pretreatment resistance [
53,
54]. Deep sequencing-based HIV-1 genotyping assays have the intrinsic capability of detecting minority HIV-1 drug resistant variants before they become majority members of the HIV-1 quasispecies, which may lead to virologic failure [
11,
19,
39,
55,
56]. Thus, the use of these highly sensitive assays should help controlling HIV-1 drug resistance both at the individual (patient) and population (epidemic) levels. In this study, we evaluated the use of DEEPGEN™, a deep sequencing-based HIV-1 genotyping and coreceptor tropism assay implemented in the clinical setting in the United States since 2013 [
19] and in Uganda since 2017 [
41], in two clinical laboratories in the U.K. i.e., St. George’s University Hospitals Healthcare NHS Foundation Trust (London) and at NHS Lothian (Edinburgh). As expected, DEEPGEN™ was able to accurately detect a series of drug resistance-associated mutations not identified using standard Sanger sequencing-based tests, correlating significantly with the patient’s cART history and providing a more accurate characterization of drug resistant HIV-1 infections in these clinical institutions.
Adapting and implementing deep sequencing-based methodologies has become much easier and accessible since its inception in the early 2000s [
11]. A multitude of deep sequencing-based tests have been developed and are being offered in clinical laboratories aimed to asses genomic, cancer, or infectious diseases related conditions [
11,
57‐
59] and HIV/AIDS is not the exception. Still, while numerous groups have used these methodologies in research studies, only a few deep sequencing-based HIV-1 tests have been developed to be used in nationally accredited (to ISO 15189 standards) and CLIA/CAP-accredited laboratories [
19,
27,
28]. Several studies have compared the performance of deep versus Sanger sequencing for HIV-1 genotypic resistance testing [
10,
19,
25,
28,
39]; however, this is the first study evaluating the implementation of DEEPGEN™, a clinically validated deep sequencing-based HIV-1 genotyping assay, in two clinical laboratories in the U.K. A previous study had described a limited evaluation of the now obsolete Roche 454 HIV-1 ultradeep sequencing drug resistance assay at Royal Free London NHS Foundation Trust [
60]. Here, both clinical laboratories (St. George’s and NHS Lothian) were already equipped with the proper instrumentation to perform deep sequencing (i.e., Ion Torrent’s PGMs) and were able to successfully perform DEEPGEN™ in their own facilities by following the Standard Operating Procedures developed at the UHTL (Cleveland, OH). The quality of all PGM runs in the U.K. were comparable, if not better, to those performed in the U.S., generating excellent deep sequencing run metrics (e.g., coverage, quality reads, median read lengths, etc.) confirming the established quality assurance of the system. This led to a perfect correlation during the verification studies, where a series of plasma samples from HIV-infected individuals were evaluated in parallel in the U.K. (St. George’s and NHS Lothian) and U.S. (UHTL) laboratories, i.e., the number of drug resistance associated mutations, drug resistance profiles (HIVdb scores) and HIV-1 coreceptor tropism determinations matched 100%, underscoring the capability of both U.K. clinical laboratories to perform the assay on site.
Similar to previous studies [
19,
41,
49,
61], DEEPGEN™ detected all the drug resistance mutations, in all 109 patients, originally identified in each laboratory using Sanger sequencing. More importantly, a total of 280 additional drug resistance mutations were identified in both cohorts of HIV-infected individuals, i.e., mutations below the limit of detection of Sanger sequencing (~ 20%) [
14‐
18] and only detectable using deep sequencing, therefore modifying the Sanger-based HIVdb scores and overall resistance interpretation. The kind, number, and frequency of the minority drug resistance mutations identified matched the cART history of the patients, the most common being M46I/L and I50 V (PIs), K65R, D67 N, L74I, M184 V/I, and K219Q (NRTIs), and L100I (NNRTIs). A few minority INSTI-resistance mutations were observed in the 109 HIV-infected individuals, reflecting the limited number of patients being treated with INSTIs at the time of the study (23/109). Most of these mutations have also been detected as minority variants in cohorts of patients failing first- or second-line cART [
10,
40,
41,
49,
55,
61‐
64] or in antiretroviral-naïve patients [
10,
65‐
69], including a study from the U.K. [
3]. As expected, drug resistance profiles based on Sanger sequencing correlated significantly with cART history; however, the correlation was stronger when minority mutations were included in the analysis, suggesting that the presence of drug resistant minority variants as part of the HIV-1 quasispecies is a direct consequence of the antiretroviral drug pressure. Interestingly, minority drug resistant variants were observed in both antiretroviral-experienced and antiretroviral-naïve individuals, some of them associated with the current cART of each patient but others not related nor conferring cross-resistance to any particular drug in the respective regimens. These minority variants may be lurking in the population, waiting for the proper conditions to be selected [
20,
22]. However, based on our cross-sectional analysis, it is difficult to discern whether the increase in drug resistance (mutations, HIVdb scores, resistance profiles) due to the detection of minority variants at the time the plasma samples were obtained will result in an increase in plasma viremia and subsequent immunologic decline.
It is important to highlight that DEEPGEN™, in addition to determining HIV-1 drug resistance and coreceptor tropism, was also designed to evaluate subtyping, inter-patient and intra-patient HIV-1 diversity based on
pol and
env genes [
19]. Here we were able to assess all these viral parameters for all 109 HIV-infected individuals. Interestingly, while 44% (48/109) of the patients in this study were infected with subtype B HIV-1 strains (66% in NHS Lothian’s patients), several non-B HIV-1 strains were detected in these individuals, including A1, A2, C, D, F1, G, CRF02_AG, and CRF01_AE. Most of these non-B HIV-1 subtypes have been previously reported in the U.K. [
4,
70‐
72]; however, it is important to highlight the presence of three individuals infected with subtype F1 HIV-1 strains. Prevalence of subtype F1 viruses has been increasing in North East Spain, particularly among men who have sex with men [
73,
74]. Since response to cART seems to be impaired in patients infected with F1 viruses [
74,
75], it will be important to monitor the circulation of this HIV-1 subtype in the U.K., particularly with the recent increase in chemsex among MSM living with HIV-1 in the country [
76].
As described above, a number of studies -including some from the U.K.—have shown that deep sequencing assays are excellent tools to increase the detection of drug resistance mutations [
19,
34,
40,
41,
62,
63,
65,
67], monitor transmission of HIV-1 drug resistance [
3,
19,
33,
41,
49,
61,
63,
65,
68,
69,
77‐
82], and potentially determine the relevance of detecting minority drug resistance mutations in the clinical setting [
10,
11,
31,
40,
55,
83,
84]. Are these minority drug resistant HIV-1 variants going to be selected as majority members of the quasispecies, eventually contributing to elevated plasma viremia and leading to virologic failure? What is the real importance and/or clinical significance of these minority variants? A multitude of studies have attempted to address these questions, adding to the controversy [
29‐
33,
40,
41]. Although it may seem logical that, under the right (drug) pressure, these drug resistant minority variants will become majority members of the HIV-1 population, only a few studies have been able to clearly demonstrate that pre-existent minority variants contribute to a negative clinical outcome [
33,
41,
62,
69,
85]. It is clear that further studies based on larger and well-characterized cohorts of patients, and using clinically validated deep sequencing-based HIV-1 genotyping assays such as DEEPGEN™, will be needed to determine whether drug resistant minority variants contribute to virologic failure.
In summary, to our knowledge, this is the first study evaluating the transition, training, and implementation of DEEPGEN™, a deep sequencing-based HIV-1 genotyping assay, between three clinical laboratories in two different countries (we are in the process of publishing the establishment of DEEPGEN™ in Uganda). More importantly, we were able to characterize the HIV-1 drug resistance profile (including minority variants), coreceptor tropism, subtyping, and intra-patient viral diversity in 109 individuals from the United Kingdom, providing valuable information to help control the HIV/AIDS epidemic in the country. This study provides a rigorous basis for basing clinical decisions on highly sensitive and cost-effective deep sequencing-based HIV-1 genotyping assays. Moreover, our work is an example of a verification study of a fully validated deep sequencing-based HIV-1 genotyping assay, which can replace Sanger sequencing assays and improve the HIV-1 drug resistant profiles of HIV-infected patients. DEEPGEN™ can be effectively implemented into nationally accredited clinical and molecular pathology laboratories in the U.K., supporting local HIV-1 treatment services and contributing to public health programs that monitor the emergence and transmission of HIV-1 drug resistance quasispecies in the country.
Authors’ contributions
MEQ-M, KT, and DC designed the study. NS, GM, MP, MA, CS, JS, and DW performed molecular and sequencing experiments. FSH and KB provided most needed logistics for the implementation of the DEEPGEN™ assay in the United Kingdom. DJA and MEQ-M contributed to the overall analysis of the data. MEQ-M collected and assembled the data, wrote and drafted the manuscript. All authors read and approved the final manuscript.