Thesis (MScMedSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Background: The conventional sequence analysis is the most common method used for the detection of drug-resistant mutants. Due to its sensitivity limitations, it is unable to detect these mutants when comprising less than 20% (minor populations) of the total virus population in a sample. However, real-time PCR-based assays offer a rapid, sensitive, specific and easy detection and quantification of such mutants. The HIV-1 variants harbouring the K103N mutation are associated with resistance to nevirapine (NVP) and efavirenz (EFV). The persisting drug-resistant mutants decay slowly to low levels, and therefore they are called minor drug-resistant mutants. Consequently, they affect subsequent treatment with the drugs of the relevant class.
Objectives: The objective of this study was to design two TaqMan real-time PCR-based assays called selective-polymerase chain reaction (SPCR), namely the total viral copy SPCR assay and the K103N-SPCR assay. The former detects HIV-1 of subtype C reverse transcriptase sequences, whereas the latter detects K103N drug-resistant variants in these sequences.
Design and Methods: In developing the SPCR assays, sets of appropriate primers and probes for the HIV-1 subtype C reverse transcriptase (RT) were developed to use in the K103N-specific reaction and the total copy reaction. Twelve DNA plasmid standards with sequence diversity were constructed for the assay from two HIV-1subtype C samples known to harbour the K103N mutation (AAC or AAT) in our Department‟s Resistance Databank. Their RT regions were amplified, cloned and verified with sequencing. Site-directed mutagenesis was used to induce mutations at 103 amino acid position in some of these clones to generate more standards with either one of the three codons (AAA, AAC and AAT). The two assays were optimized and validated, and a standard curve was generated for each assay using 10-fold serial dilution (5x107-5x100 DNA copy/μL) of a K103N-mutant plasmid standard. The optimized and validated SPCR assays were used to screen 40 nested PCR products of previously genotyped patient samples for minor K103N variants.
Results: Two sensitive and reproducible selective real-time PCR (SPCR) assays, with cut-offs of 8.23 and 10.33 and a detection limit of 0.01% for the K103N resistance variants, were successfully developed. The assays detected a prevalence of 25.64-46.15% for the K103N resistance mutation in 39 patient samples. The genotyping (population sequencing) missed 40-53.85% of these variants.
Conclusion: In conclusion, sensitive and reliable selective real-time PCR assays to detect and quantify minor K103N variants of HIV-1 in nested PCR products were successfully developed. The assay had a lower detection limit of 0.01%. / AFRIKAANSE OPSOMMING: Agtergrond: Konvensionele volgorde bepaling analise is die mees algemeenste metode wat gebruik word vir die opsporing van middel-weerstandige mutasies, maar weens beperkte sensitiwiteit is dit nie moontlik om hierdie mutante op te spoor wanneer dit minder as 20% (minderheids populasie) van die totale viruspopulasie in `n monster uitmaak nie. Nietemin, kwalitatiewe PKR-gebaseerd toetse bied vinnige, sensitiewe, spesifieke en makliker opsporings en kwantifisering van sulke mutante aan. MIV-1 variante wat die K103N mutasie bevat word geassosieer met weerstand teen nevirapine (NVP) and efavirenz (EFV). Volhoudende middel-weerstandige mutasies vergaan stadig na laer vlakke en word daarom na minderheids middel weerstandige mutasies verwys. Gevolglik affekteer dit opvolgende behandeling met die middel van die relevante klas.
Doelwitte: Die doel van die studie was om twee TaqMan kwantifiserende PKR gebaseerde selektiewe polymerase ketting reaksies (SPKR), naamlik totale virale kopie SPKR en K103N-SPKR te ontwikkel. Die voormalige toets het die MIV-1 subtipe C omgekeerde transkriptase volgorde bepaal, waar K103N die middel-weerstand variante in hierdie volgorde opspoor.
Ontwerp en Metodes: `n Geskikte stel inleiers en peiler was ontwikkel vir die MIV-1 subtipe C omgekeerde transkriptase (OT) vir gebruik in die K103N-spesifieke en die totaal kopie reaksie. Twaalf DNS plasmied standaarde met volgorde diversiteit was saamgestel vir die toets vanaf twee MIV-1 subtipe C monsters wat volgens ons Departement se weerstand databasis geklassifeer is vir die besit van die K103N mutasie (AAC of AAT). Die OT streke was geamplifiseer, gekloneer en geverifieer deur volgorde bepaling. Punt-gerigte mutagenese is gebruik om `n mutasie by die amino suur posisie 103 van sekere klone te induseer om meer standaarde te genereer wat een van die drie kodons (AAA, AAC en AAT) bevat. Die twee toetse is geoptimiseer en gevalideer en `n standard kurwe is genereer vir elk van die toetse deur die gebruik van tienvoud serie verdunnings (107-1 DNS kopie/μL) van `n algemene K103N-mutante plasmied standard. Die geoptimiseerde en gevalideerde SPKR toets was gebruik om vir die minderheids K103N variante in 40 “nested” PKR produkte van voorheen gegenotipeerde pasiënt te soek.
Resultate: Twee sensitiewe en herproduseerbare selektiewe kwantitiewe PKR toetse met `n ΔCt afsnypunt van 8.23 en `n deteksie limiet van 0.006% was ontwikkel vir die K103N weerstand variant. Die toets het `n voorkomsyfer van 25.6 % vir die K103N weerstand mutasie in 40 pasiënt monsters bepaal, waar genotipering (populasie volgorde ) 40% van hierdie variante nie opgespoor het nie.
Gevolgtrekking: `n Sensitiewe en betroubare selektiewe kwantitatiewe PKR toets vir die opspoor en kwantifisering van die minderheids K103N variante van MIV-1 in PKR produkte was ontwikkel. Hierdie toets het `n laer opsporings limiet van 0.01%. / Poliomyelitis Research Foundation (PRF) / National Research Fund (NRF) / National Health Laboratory Service Research Trust (NHLS RT)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18028 |
| Date | 12 1900 |
| Creators | Seleka, Mpho Maria |
| Contributors | Engelbrecht, Susan, Van Zyl, Gert, Stellenbosch University. Faculty of Health Sciences. Dept. of Pathology. Medical Virology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 137 p. : col. ill. |
| Rights | Stellenbosch University |
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