Detection of drug resistance associated mutations in HIV primary infection within the UK (2000)

Resistance has developed to all antiretroviral drugs to date. An increasing number of mutations within the reverse transcriptase (RT) and protease genes are associated with variable reductions in drug susceptibility, and the transmission of variants with these mutations has been documented [1]. The potential spread of drug-resistant viruses within the population is of major public health consequence because it may compromise the response to initial therapy, and it may therefore be appropriate to undertake resistance assays before initiating therapy. The potential benefits of such an approach depend on the prevalence of drug resistance within the population, the likelihood of transmission and the impact on clinical response [2]. In view of the continual evolution of HIV after transmission and the potential reversion of drug resistance mutations to wild type in the absence of drug selective pressure, the best estimates of the rate of transmission of resistant virus are derived from individuals with recent infection. Recent studies [3–5] from elsewhere in Europe and the USA suggest that the prevalence of resistance in primary infection ranges from 10 to 25%; however, few data on this patient group are available for the UK. We report HIV drug resistance genotypic data on 20 infected patients from the UK, all with specimens available for sequencing work within 15 months of a negative test date (maximum time 446 days), during the period 1995–1999. These individuals had been enrolled into the UK Register of HIV Seroconverters [6], and were drug naïve at the time of resistance testing. HIV RNA was extracted from serum samples previously stored at −70°C. RT–polymerase chain reaction was used to amplify the entire protease gene and codons 1–220 of RT. Sequencing of polymerase chain reaction products was undertaken using an ABI automated sequencer. Sequences were analysed using the HRP-ASAPv1.0 program [7], which also provided subtype designations. The codon changes in protease and RT relative to the subtype B consensus previously associated with drug resistance are summarized in Table 1. Only one patient had evidence of RT mutations associated with drug resistance, namely M41L and T215L. The former amino acid change is a well-recognized zidovudine resistance mutation, associated with high level resistance when present with other mutations. These include two mutations at position 215, namely T215 F and T215Y. Of interest is the fact that a leucine at this position has only been described once before, also in the context of primary infection [8]. This variant probably represents a single codon change from the transmitted strain with the resistance-associated mutation 215 F (phenylalanine) (i.e. codons TTC–CTC). The rapidity of this evolution in the absence of zidovudine selective pressure (sequencing on sample taken within 17 days of antibody-negative test) suggests that the T215F mutant within this context confers a reduced fitness on the virus. By contrast, reversion to wild type at this position (phenylalanine to threonine, TTC–ACC) requires two base changes, and would presumably be less likely to occur rapidly. Of note is the fact that other unusual switches of amino acids at position 215 in primary infection, such as 215D and 215C, even in the context of M41L, D67N and K70R, leads to a zidovudine-sensitive virus [8]. Zidovudine resistance may, however, rapidly emerge after the initiation of treatment in patients with these single nucleotide revertant mutations.Table 1: Mutations observed in codon positions associated with drug resistance. Mutations were also observed at RT codon 98 (A98S) in three patients; which is considered a common polymorphism not associated with resistance [7]. Patient 11 showed an E44D mutation and patient 5, V118I. These mutations are observed more commonly in treated patients but do not confer resistance in isolation. We did not detect any primary protease inhibitor (PI) resistance mutations (key mutations essential for reduced drug susceptibility) but identified numerous secondary mutations in this group of patients (Table 1). Secondary mutations, in the presence of primary mutations, may further decrease drug susceptibility or compensate for reduced viral fitness. However, the protease gene is remarkably polymorphic [9], and it is unlikely that these variants represent the transmission of PI-resistant virus from a treated individual. Indeed, both the non-clade B viruses identified in our study had the M36I mutation, a common polymorphism in these HIV-1 subtypes [7]. There is no evidence that these changes alone confer an increased risk of PI failure. Therefore, care should be taken in the interpretation of such genotypic information. In conclusion, we described the presence of RT inhibitor resistance-associated mutations in one out of 20 (5%) primary HIV-1 infections on which analysis was undertaken within the UK between 1995 and 1999. These samples were taken 1–15 months after infection, and it is possible that drug resistance mutations may have reverted to wild type during this time. Our results may thus underestimate the prevalence of the transmission of drug resistance. The one patient with zidovudine resistance-related mutations was tested very soon after infection (patient 18; within 17 days). Although we observed many secondary mutations in the protease gene, we did not detect any key, primary PI resistance mutations. During the period that these samples were collected, the use of highly active antiretroviral therapy became much more widespread with consequent increases in the levels of resistance. The monitoring of primary infections should be undertaken in order to document a potential increase in the transmission of drug-resistant variants. These data will inform decisions on the routine resistance testing of drug-naïve patients. Deenan Pillaya Pat A. Canea Jane Shirleya Kholoud Porterb