Prevalence of HIV-1 Azidothymidine(AZT) resistance in HIV-1 infected individuals at Chulalongkorn Hospital by codon 215 mutation of HIV-1 Reverse Transcriptase (RT) using selective Polymerase Chain Reaction (PCR)

Abstract

In Thailand, most of the individuals infected with Human Immunodefciency Virus type (HIV-1) are heterosexuals and the majority carries HIV-1 subtyple E. Much has been reported of azidothymidine (AZT) resistance of HIV-1 in North America and Europe where HIV-1 subtype B predominates. However little is known about the HIV-1 AZT resistance in other part of world, particulary in regards to other subtypes. The HIV reverse transcriptase (RT) gene of AZT-resistant viral isolates demonstrated a characteristic pattern of nucleotide changes. The most common mutation that associated with a significant reduction of sensitivity to AZT is at the codon 215. In the previously described (Mitsuya H., et al.) selective PCR for de-tection of codon 215 AZT resistant mutant failed to detect HIV-1 subtype E while detected subtype B. The des-cribed sense primer (L1M) of the outer pair was found mismatching with the target sequence of subtype E virus. A seminested RT-PCR was then developed by which ANMER B/AS 62 were used as outer primers and ANMER B/WT 215 or ANMER B/MT 215 were used as a second primer pair for the detection of either codon 215 wild type or mutant, respectively. This modified PCR assay was showed to detect the codon 215 genotypes of both HIV-1 subtype E and B. One hundred and fifty HIV-1 infected patients who attended the HIV Clinic at Chulalongkorn hospital, from December 1995 to August 1996 were enrolled into 3 groups (50 of each) according to the history of AZT-monotherapy as follows : AZT naive (group I), AZT experienced for less than 6 months (group II) and AZT experienced for more than 6 months (group III). Most of the subjects were male (75%) with the range of 18-67 years old (mean=34.12). The majority were heterosexuals (94%) and were symptomatic HIV patients (69 of ARC, and 56 of AIDS). There was no AZT resistant at 215 mutant in the AZT naive group, whereas, 22% of group II and 42% of group II showed the 215 mutant genotype (p<0.01,Chi-square test). Moreover, in 10 of the naive group who were followed-up in the prospective study, 7 subjects showed a switching from wild type to mutant virus within 12 months of AZT therapy. In conclusion, to study AZT-resistant at the codon 215 mutation in HIV-1 subtype E, the selective PCR needs a modification. There was no evidence of AZT-resistant HIV-1 transmission in the AZT-naive. The patients with CD4 cell count below 100, has a 22% risk of development of AZT-resistant mutant within 6 months after treated with AZT monotherapy. This finding supports the strategy of early trealment with combination therapy in the patients with a higher CD4 count which is below 350 cells/muL.