Primary antiretroviral resistance in newly diagnosed patients with established heterosexually acquired HIV-1

Published guidelines [1,2] have indicated that resistance testing should be considered for drug-naive patients with established HIV-1 infection before the initiation of therapy. These recommendations follow reports suggesting that the transmission of drug-resistant HIV-1 is increasing in Europe and North America [3,4]. However, the prevalence of primary resistance appears to vary widely among different cohorts [3–6]. Furthermore, most studies have targeted recently infected patients, and there are limited data on patients with established infection [7,8]. The aim of this study was to determine the prevalence of primary resistance among newly diagnosed patients with heterosexually acquired HIV-1, who represent a growing number of new HIV-1 diagnoses in the UK [9]. Seventy-two consecutive patients were identified between 1999 and 2001. These included 47 black African patients (43 born in Africa, four in UK/western Europe), 14 black Caribbean patients (11 born in the Caribbean, three in the UK), nine white patients (seven born in UK/western Europe, two in South America) and two Indian patients. All presented with established infection. The median CD4 cell count was 304 cells/μl (range 4–1095). Genotypic resistance was determined in plasma RNA using the TruGene assay (Visible Genetics, France). Reverse transcriptase and protease sequences were obtained in 68 out of 72 and 71 out of 72 patients, respectively. Sequences were analysed for the presence of resistance mutations at reverse transcriptase codons 41–236. D30N, M46I/L, G48V, I50V, V82A/F/T/S, I84V, and L90M were regarded as primary protease mutations [1]. Genotypes were analysed using the Stanford software (http://hiv-4.stanford.edu). Non-B subtypes were detected in 38 out of 42 patients (90%) born in Africa, seven out of 14 patients (50%) born in UK/western Europe, and two out of 11 patients (18%) born in the Caribbean, and in 42 out of 46 black African (91%), three out of nine white (33%), and two out of 14 black Caribbean patients (14%). Subtype prevalence was 38% C, 34% B, 8.5% CRF_AG, 7% A, 5.5% CRF_AE, 4% D, and 3% G. The majority of newly diagnosed patients with heterosexually acquired HIV-1 were thus black Africans from sub-Saharan Africa infected with non-B subtypes. The high prevalence of subtype C was consistent with the large number of patients from eastern African countries where subtype C predominates, suggesting that the infection was either acquired in Africa or transmitted in the UK within a closed ethnic group. Four patients had resistance mutations, including three out of 68 (4.4%) with reverse transcriptase and three out of 71 (4%) with primary protease mutations (Table 1). M184V, which confers high-level resistance to lamivudine, was detected in one patient whose estimated date of infection was 2 years previously. As M184V affects virus fitness, it would be expected to revert to minority quasispecies in the absence of drug pressure [10]. Its detection supports the hypothesis that resistant mutants may persist for longer when transmitted as dominant quasispecies [11]. The same patient showed low-to-intermediate resistance to available protease inhibitors (PI) associated with L10I, L63P, A71T, V77I, and L90M. V108I and V179E, detected in one CRF_AG patient, confer low-level non- nucleoside reverse transcriptase inhibitor resistance, of uncertain clinical significance. L100I, detected in one subtype A patient, confers low-to-intermediate non-nucleoside reverse transcriptase inhibitor resistance. The same patient showed low-level resistance to saquinavir and lopinavir and intermediate-to-high level resistance to other PI (M36I, M46I/L, V82F). Another subtype A patient showed low-to-intermediate PI resistance (M36I, M46M/L, I54T/I). A fifth patient, also with subtype A, had the unusual mutations D30D/E, V32Q, M36I, I54N/I, and L63V, with unknown effects on PI susceptibility. The prevalence of resistance was thus less than 5%, and only two patients had evidence of high-level resistance. This may reflect a low level of use of antiretroviral drugs both in the region of infection and within the risk group. Furthermore, as all patients had established infection, transmitted mutants may have reverted over time to minority quasispecies, escaping detection [10]. It is also uncertain to what extent some of the mutations detected in non-B subtypes were the product of drug pressure, rather than natural polymorphisms [12].Table 1: Reverse transcriptase and protease mutations of 66 drug-naive patients.It has been proposed that secondary protease mutations may facilitate the emergence of PI resistance [13]. In the absence of primary protease mutations, secondary mutations occurred in 63 out of 68 patients (93%), with 22% showing three or more mutations. The most frequent mutations involved codons 36 (77%), 63 (32%), 20 (24%), and 93 (21%). Mutations at codons 20, 36, 63 and 77 were prevalent in subtype B, and those at codons 36, 63 and 93 in subtype C. M36I was more common in subtype C than B (96 and 42%, P < 0.001), and occurred in all A, CRF_AE and CRF_AG sequences. K20I occurred in all CRF_AG sequences, but was uncommon in subtype C (P = 0.009). Further studies are planned to determine the clinical impact of the distinct mutation patterns observed in different subtypes. Acknowledgements The authors would like to thank Shahed Murad for help with the statistical analysis.