Improvement of HIV-1 coreceptor tropism prediction by employing selected nucleotide positions of the env gene in a Bayesian network classifier.

OBJECTIVES: This study aimed to develop a genotypic method to predict HIV-1 coreceptor usage by employing the nucleotide sequence of the env gene in a tree-augmented naive Bayes (TAN) classifier, and to evaluate its accuracy in prediction compared with other available tools. METHODS: A wrapper data-mining strategy interleaved with a TAN algorithm was employed to evaluate the predictor value of every single-nucleotide position throughout the HIV-1 env gene. Based on these results, different nucleotide positions were selected to develop a TAN classifier, which was employed to predict the coreceptor tropism of all the full-length env gene sequences with information on coreceptor tropism currently available at the Los Alamos HIV Sequence Database. RESULTS: Employing 26 nucleotide positions in the TAN classifier, an accuracy of 95.6%, a specificity (identification of CCR5-tropic viruses) of 99.4% and a sensitivity (identification of CXCR4/dual-tropic viruses) of 80.5% were achieved for the in silico cross-validation. Compared with the phenotypic determination of coreceptor usage, the TAN algorithm achieved more accurate predictions than WebPSSM and Geno2pheno [coreceptor] (P<0.05). CONCLUSIONS: The use of the methodology presented in this work constitutes a robust strategy to identify genetic patterns throughout the HIV-1 env gene differently present in CCR5-tropic and CXCR4/dual-tropic viruses. Moreover, the TAN classifier can be used as a genotypic tool to predict the coreceptor usage of HIV-1 isolates reaching more accurate predictions than with other widely used genotypic tools. The use of this algorithm could improve the correct prescribing of CCR5 antagonist drugs to HIV-1-infected patients.

Identification of new splice sites used for generation of rev transcripts in human immunodeficiency virus type 1 subtype C primary isolates.

The HIV-1 primary transcript undergoes a complex splicing process by which more than 40 different spliced RNAs are generated. One of the factors contributing to HIV-1 splicing complexity is the multiplicity of 3' splice sites (3'ss) used for generation of rev RNAs, with two 3'ss, A4a and A4b, being most commonly used, a third site, A4c, used less frequently, and two additional sites, A4d and A4e, reported in only two and one isolates, respectively. HIV-1 splicing has been analyzed mostly in subtype B isolates, and data on other group M clades are lacking. Here we examine splice site usage in three primary isolates of subtype C, the most prevalent clade in the HIV-1 pandemic, by using an in vitro infection assay of peripheral blood mononuclear cells. Viral spliced RNAs were identified by RT-PCR amplification using a fluorescently-labeled primer and software analyses and by cloning and sequencing the amplified products. The results revealed that splice site usage for generation of rev transcripts in subtype C differs from that reported for subtype B, with most rev RNAs using two previously unreported 3'ss, one located 7 nucleotides upstream of 3'ss A4a, designated A4f, preferentially used by two isolates, and another located 14 nucleotides upstream of 3'ss A4c, designated A4g, preferentially used by the third isolate. A new 5' splice site, designated D2a, was also identified in one virus. Usage of the newly identified splice sites is consistent with sequence features commonly found in subtype C viruses. These results show that splice site usage may differ between HIV-1 subtypes.

Evaluation of genotypic tropism prediction tests compared with in vitro co-receptor usage in HIV-1 primary isolates of diverse subtypes.

OBJECTIVES: To evaluate the sensitivity and specificity of genotypic methods for predicting the co-receptor usage of subtypes B and non-B HIV-1 primary isolates, using as gold standard the infectivity of each primary isolate in GHOST cells stably expressing HIV-1 co-receptors. METHODS: Primary isolates were obtained by co-culturing either patient's peripheral blood mononuclear cells (PBMCs) or ultracentrifuged plasma with donor-activated PBMCs. In vitro co-receptor usage was determined by infecting GHOST cells. Tropism prediction, based on V3 sequences, was determined with simple rules and bioinformatic tools (Geno2pheno[coreceptor] and WebPSSM). RESULTS: This study includes 102 HIV-1 primary isolates; 23 (22.5%) subtype B and 79 (77.5%) non-B genetic forms. V3 sequences were classified into six subtypes (A-G), although 32 (31.4%) were circulating recombinant forms and 21 (20.6%) were unique recombinant forms. Sixty-nine isolates were R5, 27 R5X4 and 6 X4. The highest levels of sensitivity and specificity for the detection of X4 strains among V3 sequences, between 91% and 100%, were obtained by using PSSM(x4r5), PSSM(si/nsi) and the 11/25 rule for sequences of subtypes A, B and G, but not for subtype F. Establishing the recommended cut-off for clinical settings of a 10% false positive rate for Geno2pheno, we obtained 93% specificity and 97% sensitivity. CONCLUSIONS: Comparing genotypic assays for HIV-1 co-receptor use with a cell-culture phenotypic assay could provide more reliable results of sensitivity and specificity for the detection of X4 strains than comparing them with recombinant assays, considered as gold standard. In general, except for subtype F isolates, there is a good correlation for tropism prediction.

Identification of unusual and novel HIV type 1 spliced transcripts generated in vivo.

HIV-1 transcripts are generated through a complex alternative splicing mechanism, resulting in the production of multiple RNAs coding for each viral protein. HIV-1 RNA splicing has been analyzed mostly in in vitro assays, and in vivo data are scarce. Here we analyze HIV-1 transcripts generated in peripheral blood mononuclear cells of HIV-1-infected individuals by RT-PCR amplification and sequencing of RNA extracted from unstimulated cells. We identify several unusual or unreported transcripts, most of them splicing within the Nef coding sequence. The majority are predicted to code for a Nef C-terminal 34 amino acid peptide, but others code for Vpr, a truncated Tat, and a 41 amino acid peptide encoded in an antisense exon. We also identify nef and env transcripts splicing four nucleotides downstream of SA5. These results represent the first report on the in vivo generation of diverse novel HIV-1-spliced transcripts, frequently encoding a Nef C-terminal peptide.

Identification of a new HIV type 1 circulating BF intersubtype recombinant form (CRF47_BF) in Spain.

We report the identification of a new HIV-1 circulating recombinant form (CRF47_BF) derived from subtypes B and F. It was initially identified in protease-reverse transcriptase sequences from nine individuals from three separate regions of Spain who acquired HIV-1 infection via sexual contact. All nine sequences formed a strongly supported phylogenetic cluster, branching apart from all known CRFs, and in bootscan analyses were BF mosaics with two coincident breakpoints. Two epidemiologically unlinked viruses were sequenced in near full-length genomes, which exhibited identical mosaic structures, with 16 intersubtype breakpoints in a genome predominantly of subtype B. Subtype F segments of the new CRF failed to cluster with any of the near full-length genome subtype F sequences available in public databases. Recent dates of HIV-1 diagnoses and short genetic distances suggest a recent origin of this CRF. This is the tenth reported CRF_BF, the first apparently having originated outside of South America.

Molecular epidemiology of HIV-1 in St Petersburg, Russia: predominance of subtype A, former Soviet Union variant, and identification of intrasubtype subclusters.

OBJECTIVES: To examine HIV-1 genetic diversity in St. Petersburg. METHODS: Partial HIV-1 pol sequences from 102 plasma samples collected in 2006 were analyzed with a Bayesian phylogeny inference method. RESULTS: Subtype A, former Soviet Union (FSU) variant (AFSU), was the predominant clade (89.3%); other clades were subtypes B (9.7%) and F1 (1%). AFSU was predominant both among injecting drug users (98.2%) and heterosexually infected individuals (91.4%), whereas subtype B was more prevalent among homosexual men (75%). Within the AFSU variant, most sequences (93.5%) branched within 1 of 4 strongly supported subclusters. The largest comprised 63% AFSU viruses and was uncommon outside St Petersburg. A second subcluster (17.4% AFSU viruses) corresponds to the variant with the V77I substitution in protease, which is widely circulating in different FSU countries. Two minor subclusters comprised 8.7% and 6.5% AFSU viruses, respectively. There was no correlation between risk exposure and AFSU subclusters. Six of 8 subtype B sequences, 4 of them from homosexual men, grouped in a monophyletic subcluster. CONCLUSIONS: The results of this study show a great predominance of AFSU viruses in St Petersburg and point to a few phylogenetically identifiable introductions as the origin of most current HIV-1 AFSU infections in the city.

Oligonucleotide ligation assay for detection of mutations associated with reverse transcriptase and protease inhibitor resistance in non-B subtypes and recombinant forms of human immunodeficiency virus type 1.

The oligonucleotide ligation assay is a genotypic assay for the detection of resistance-associated mutations to reverse transcriptase and protease inhibitors in human immunodeficiency virus type 1 subtype B. This assay has been modified and developed for non-B subtypes and recombinant strains and has been evaluated with sequencing, resulting in a more sensitive assay than sequencing for non-B subtypes.