We recently reported the finding of phylogenetically related HIV-1 BG intersubtype recombinant and G subtype nonrecombinant viruses circulating among injecting drug users in the region of Galicia in northwestern Spain. Here, we report the characterization of near full-length genome sequences of nine of these viruses (seven BG recombinant and two of nonrecombinant G subtype), obtained from epidemiologically unlinked individuals. Bootscan analysis reveals that six recombinant viruses share an identical mosaic structure, with two intersubtype breakpoints delimiting a B subtype segment comprising most of Env gp120 and the external portion of Env gp41, with the remaining portions of the genome being of subtype G, thus mimicking a pseudotype virion structure. The seventh BG recombinant virus exhibits breakpoints in env coincident with the other BG viruses but contains additional B subtype segments in gag and pol. In phylogenetic trees of complete genomes and of the B subtype segment of env, all seven BG viruses group in a monophyletic cluster. G subtype portions of the BG viruses group uniformly with the newly derived nonrecombinant G subtype viruses of Galicia in bootscan analysis, which points to the locally circulating G subtype strain as parental of the recombinants. These results allow us to define a new HIV-1 circulating recombinant form (CRF14_BG), the first reported to originate in Western Europe.

The aim of this study was to investigate the susceptibility to T20 and the dynamics of amino acid changes in HR1 and HR2 of gp41 of HIV-1 obtained from plasma, peripheral blood mononuclear cells (PBMC), and primary isolates (PI) in four highly antiretroviral-experienced patients. These patients received T20 plus an antiretroviral regimen and were followed-up over a period of 40-72 weeks. In one non-responder patient, N43D substitution was detected at 12 weeks of treatment, in association with a value of T20-IC50 of 10 microg/ml (10-fold increase). Double mutations N42T + N43D were observed in plasma RNA at 32 weeks and remained detectable up to 16 weeks after the withdrawal of the drug. The S138A substitution in HR2 was observed in plasma RNA at 32 weeks, and both in plasma RNA and in PI DNA at 40 weeks, associated with an increase of the T20-IC50 to 25 microg/ml (25-fold increase). Mutations V101G and E137K, not reported previously, were also observed in the HR2 region. Whether these new substitutions play a role in T20 resistance needs to be examined. In three temporary responders, coinciding with viral load rebound, G36D, and N42T substitutions were observed at 12, 24, and 40 weeks. G36D mutation was associated with a value of T20-IC50 of 5 microg/ml. The HR2 S138A mutation was detected after the detection of HR1 substitutions and was associated with an increase in the level of T20-IC50 to 125 microg/ml (125-fold increase) All these data reinforce the role of gp41 amino acids 36-45 and the potential influence of the HR2 S138A mutation in the genotypic/phenotypic resistance to T20.

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