Summary auto-generated
This study reports the first complete nucleotide sequence of an African human T-cell lymphotropic virus type II (HTLV-II) isolate, designated HTLV-II-Gab, obtained from an asymptomatic 44-year-old Gabonese man living in a remote rural area. Using nested PCR, researchers amplified 25 overlapping fragments spanning the entire proviral genome, which were cloned and sequenced. Sequence comparison and phylogenetic analysis revealed that HTLV-II-Gab belongs to subtype b, showing 98.2-99.3% nucleotide similarity to other subtype b isolates (G12, NRA, and Gu) compared to only 95.1% similarity to the subtype a prototype (Mo). Restriction fragment length polymorphism analysis identified a novel BanII site in the long terminal repeat region. The strain clusters phylogenetically with subtype b isolates and shows close relationship to a previously identified pygmy isolate from Cameroon (PYGCAM). Notably, the very low genetic divergence between this African strain and American strains raises questions about the evolutionary history and origins of HTLV-II, suggesting an ancient African presence of the virus despite the long period of independent evolution between continents.
Key findings
- HTLV-II-Gab is the first complete African HTLV-II sequence, identified in uncultured peripheral blood mononuclear cells from a healthy Gabonese male
- The isolate belongs to subtype b with 98.2-99.3% nucleotide identity to other subtype b strains (G12, NRA, Gu) versus 95.1% to subtype a
- HTLV-II-Gab displays a novel restriction profile with a newly identified BanII site and clusters in phylogroup BIII near the Cameroonian pygmy isolate PYGCAM
- Extended Tax protein characteristic of subtype b is present, with 25 additional amino acids compared to subtype a, potentially affecting viral transactivation
- The surprisingly close genetic relationship between African and American isolates suggests ancient African presence of HTLV-II despite estimated 50,000-100,000 years of independent evolution
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Abstract
We report the first complete nucleotide sequence of an African human T- cell lymphotropic virus type II. This new strain, called HTLV-II-Gab (Gab), was obtained from the uncultured peripheral blood mononuclear cells of a 44-year-old healthy Gabonese male who lived in a remote rural area, with neither history of blood transfusion nor sexual intercourse with non-Africans. Using nested PCR, 25 overlapping fragments, representing the entire proviral genome, were obtained, cloned and sequenced. The overall nucleotide sequence comparison with the four other available complete HTLV-II genomes indicated that Gab was more closely related to the HTLV-II subtype b prototypes (98.9, 99.3 and 98.2% nucleotide similarity with G12, NRA and GU respectively) than to the subtype a prototype (95.1% nucleotide similarity with Mo). Restriction profiles studies and phylogenetic analyses confirmed that Gab was a subtype b strain. However, this strain represents a newly described restriction fragment length polymorphism subtype, closely related to one of the rare partially sequenced African isolates originating from a pygmy living in Cameroon (PYGCAM). Nevertheless, the very low genetic divergence observed between this new African strain and the American strains raises several questions on the origins and level of genetic variability over time of this human retrovirus.