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Dendritic cells (DCs) can develop from CD14+ peripheral blood monocytes cultured in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4). By 6 days in culture, the cells have the characteristics of immature DCs and can be further induced to mature by inflammatory stimuli or by monocyte-conditioned medium. After infection with macrophagetropic (M-tropic) human immunodeficiency virus type 1 (HIV-1), monocytes and mature DCs show a block in reverse transcription and only form early transcripts that can be amplified with primers for the R/U5 region. In contrast, immature DCs cultured for 6 or 11 days in GM-CSF and IL-4 complete reverse transcription and show a strong signal when LTR/gag primers are used. Blood monocytes and mature DCs do not replicate HIV-1, whereas immature DCs can be productively infected, but only with M-tropic HIV-1. The virus produced by immature DCs readily infects activated T cells. Although mature DCs do not produce virus, these cells transmit both M- and T-tropic virus to T cells. In the cocultures, both DCs and T cells must express functional chemokine coreceptors for viral replication to occur. Therefore, the developmental stage of DCs can influence the interaction of these cells with HIV-1 and influence the extent to which M-tropic and T-tropic virus can replicate.

Mature DCs provide a drug-resistant reservoir for HIV-1. This reservoir is activated within DCs by CD40L and upon interaction with T cells, and the virus then spreads rapidly to other T cells.

The findings that BF intersubtype recombinant human immunodeficiency type 1 viruses (HIV-1) with coincident breakpoints in pol are circulating widely in Argentina and that non-recombinant F subtype viruses have failed to be detected in this country were reported recently. To analyse the mosaic structures of these viruses and to determine their phylogenetic relationship, near fulllength proviral genomes of eight of these recombinant viruses were amplified by PCR and sequenced. Intersubtype breakpoints were analysed by bootscanning and examining the signature nucleotides. Phylogenetic relationships were determined with neighbour-joining trees. Five viruses, each with predominantly subtype F genomes, exhibited mosaic structures that were highly similar. Two intersubtype breakpoints were shared by all viruses and seven by the majority. Of the consensus breakpoints, all nine were present in two viruses, which exhibited identical recombinant structures, and four to eight breakpoints were present in the remaining viruses. Phylogenetic analysis of partial sequences supported both a common ancestry, at least in part of their genomes, for all recombinant viruses and the phylogenetic relationship of F subtype segments with F subtype viruses from Brazil. A common ancestry of the recombinants was supported also by the presence of shared signature amino acids and nucleotides, either unreported or highly unusual in F and B subtype viruses. These results indicate that HIV-1 BF recombinant viruses with diverse mosaic structures, including a circulating recombinant form (which are widespread in Argentina) derive from a common recombinant ancestor and that F subtype segments of these recombinants are related phylogenetically to the F subtype viruses from Brazil.

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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.

Highly diverse HIV-1 genetic forms are circulating in Cuba, including subtypes B and G and two recombinant forms of African origin (CRF18_cpx and CRF19_cpx). Here we phylogenetically analyze pol sequences from a large collection of recent samples from Cuba, corresponding to 425 individuals from all Cuban provinces, which represents approximately 12% of prevalent infections in the country. RNA from plasma was used to amplify a pol segment by reverse transcription-polymerase chain reaction; phylogenetic analyses were performed with neighbour-joining trees and bootscanning. The distribution of genetic forms was subtype B, 41.2%; CRF19_cpx, 18.4%; BG recombinants, 11.6%; CRF18_cpx, 7.1%; subtype C, 6.1%; subtype G, 3.8%; B/CRF18 recombinants, 2.6%; subtype H, 2.1%; B/CRF19 recombinants, 1.7%; and others, 5.4%. Seventy-five (17.6%) viruses were recombinant between genetic forms circulating in Cuba. In logistic regression analyses, adjusting by gender and region, subtype B was more prevalent (OR 5.0, 95% CI 2.0-12.3) and subtype G less prevalent (OR 0.1, 95% CI 0.0-0.5) among men who have sex with men (MSM) than among heterosexuals. Within the main genetic forms of Cuba there were phylogenetic subclusters, several of which correlated with risk exposure or region. BG recombinants formed three phylogenetically related subclusters, corresponding to three different mosaic structures; most of these recombinants were from MSM from Havana City, among whom they have expanded recently, reaching 31% HIV-1 infections diagnosed in 2003. This study confirms the high HIV-1 diversity and frequent recombination in Cuba and reveals the recent expansion of diverse related BG recombinant forms in this country.