Multiple Drug Resistance Genotype Causing Failure of Antiretroviral Treatment in an HIV-Infected Patient Heavily Exposed to Nucleoside Analogues

 A 37-year-old homosexual man began antiretroviral combination therapy with didanosine (ddI), lamivudine (3TC) and indinavir (IDV) after being exposed previously to zidovudine (ZDV), ddI and 3TC in different sequential regimens. The patient's viral load did not fall below a detectable level despite his adherence to drug therapy, which was considered optimal. Stavudine (d4T) was prescribed in the third month of treatment instead of ddI without any evident improvement in the treatment response. A point mutation nested PCR assay showed that the patient carried a virus with a codon Q151M mutation, which confers multiple drug resistance to nucleoside analogues. Genetic sequence analysis showed that, despite none of the classically associated mutations to Q151M being present at the beginning of treatment, continuous genetic evolution under selective drug pressure allowed the virus to accumulate mutations at codons 62, 74 and 116 over time. As expected, the CD4+ cell count declined during the study period, and the viral load remained detectable.     

Emergence of dual resistance to zidovudine and lamivudine in HIV-1-infected patients treated with zidovudine plus lamivudine as initial therapy

Presence of mutations associated with resistance to zidovudine or lamivudine was determined in isolates of HIV-1 obtained after long-term follow-up of 64 infected individuals who received zidovudine, lamivudine, or both drugs as initial antiretroviral therapy. Zidovudine resistance mutations were less frequent in isolates from patients treated with combination lamivudine plus zidovudine compared with zidovudine alone, but these mutations accumulated over time. Phenotypic resistance to both drugs was found in isolates from 3 of 23 patients. In 3 other patients, lamivudine-resistant virus detected at week 12 was replaced by wild-type virus after longer follow-up, which correlated with a return to baseline levels of plasma HIV-1 RNA. These results show that dual resistance to zidovudine and lamivudine develops over time despite the delayed emergence of zidovudine-resistant mutations. These results also suggest a selective advantage in vivo for HIV-1 species that are wild-type at RT codon 184.     

Generation of multiple drug resistance by sequential in vitro passage of the human immunodeficiency virus type 1

Summary We have sequentially passaged both laboratory and clinical isolates of the human immunodeficiency virus type 1 (HIV-1) in MT-4 cells in the presence of increasing concentrations of different drugs to derive viral variants that are multiply resistant to various combinations of ddC, ddI, d4T and AZT. The EC₅₀ values obtained for the viruses thus generated varied between 50–100 times above those of parental wild-type strains in the case of AZT, 20–30 times for d4T, but only 10–15 times for ddI and ddC. Cultivation of AZT-resistant viruses in the presence of increasing concentrations of ddI yielded viruses that were resistant to the latter compound, with no apparent decrease in susceptibility to AZT. Sometimes, viruses selected for resistance against ddI were cross-resistant as well against ddC, although most viruses selected for resistance to ddC were not cross-resistant to ddI. Combinations of two or three of these compounds inhibited replication of HIV variants that displayed resistance to the same drugs when tested individually. No emergence of drug resistance was demonstrable when combinations of drugs were employed simultaneously in these selection protocols or when single drugs were used in concert with interferon-2 or high dilutions of virus-neutralizing antisera. Cloning and sequencing of some viruses resistant to each of AZT, ddI, and ddC revealed the simultaneous presence of mutations at sites 41, 74, 184 and 215 within the HIV pol gene open reading frame.